STUDIES ON THE SUITABILITY OF Parkia biglobosa 
(Jacq.) [AFRICAN LOCUST BEAN] FOR THE 
DEVELOPMENT OF Sitophilus zeamais Motschulsky 
(COLEOPTERA: CURCULIONIDAE).
BY
AUDU ABDULLAHI
B.Sc.(Hons), Agriculture, (Crop Protection).
University of Maiduguri, Nigeria.
A thesis submitted in partial fulfilment of the requirements for the award of 
the degree of Master of Philosophy in Entomology of the University of Ghana, 
Legon.
Insect Science Programme 
University of Ghana, Legon
August 2005
Joint interfaculty international Programme for the training of entomologists 
in West Africa. Collaborating departments: Zoology (Faculty of Science) & 
Crop Science (School of Agriculture, College of Agriculture and Consumer 
Sciences).
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SPf2_-
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DECLARATION
I do hereby declare that this thesis with the exception o f references to other people 
work which I have duly cited, this work is entirely my own research and has not 
been presented elsewhere for the award o f a degree.
Audu Abdullahi 
(Candidate)
Prof. J.'N. Ayertey 
(Principal Supervisor) (Co- Supervisor)
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This work is dedicated to my late Dad Alhaji Abdulrahman Mustapha Ali (May 
his gentle soul rest in perfect peace, Amen) and my Mum Hajia Abbo Mustapha 
whom through them I came to be.
DEDICATION
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ACKNOWLEDGEMENTS
First, I am grateful to the Almighty Allah who created me and gave me the 
strength to write this thesis. The completion o f this thesis was a mammoth and 
formidable task and was inspired by many remarkable personalities whom I wish 
to acknowledge.
The first bouquet o f appreciation goes to Prof. J. N. Ayertey. My Principal 
supervisor, and Former Coordinator o f the African Regional Postgraduate 
Programme in Insect Science (ARPPIS) and Mr. Bernard Boateng, my Co­
supervisor. Their suggestions were o f inestimable worth and their 
recommendations at various stages were gladly accepted.
I am grateful to my dear lecturers Profs.K, Afreh-Nuamah, D. Obeng-Ofori, (Late) 
Prof. W.Z. Coker, and Drs. D. Wilson, P. Attah, E. O. Owusu, R. Kyerematen, 
Ms. M. Cobblah and Mr. E. Cornelius. Not to be forgotten are : Prof. N. E .S. 
Lale, Drs D. M. Gwary, B. M. Sastawa, N. Gworgwor and Mall. M. Lawan all o f 
University o f Maiduguri for motivating me to higher achievements.
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I also want to thank Mr. Asante, for statistical advice and Mr. E. Addo, Mr. A. 
Appiah and Mr. K. Matey who all are technicians o f the Department o f Crop 
Science for their assistance. I also owe gratitude to Lydia Asiedu ARPPIS 
Secretary, Mr.Samuel Acquah ARPPIS driver and Mr. Boni Principal technician 
o f the Department o f Zoology for their valuable services.
My heartfelt gratitude goes to my parents and my entire family for their moral 
support, love, encouragement and prayers throughout the study. My gratitude also 
goes to'my friends at home: Muh’d S. Abubakar, Taiyu Muh’d, Usman, B. Shehu, 
Danladi S. Biu, Ali Garga and Ibrahim Musa. My special thanks go to Muh’d 
U.Watsada and Umar Labaran and all those that space does not permit me to 
mention.
I am also grateful to my fellow classmates Zakka Usman, Samuel, K. Charo, 
Badii, K. Benjamin, Olivia, A. Achonduh, Jacinta, A. O. Odhiambo including 
Nigerian colleagues, Utomiic Chukwuemeke, Fidelis Onykwere, Isaac Clement 
and Ngozi Angela, who deserve mention. Special thanks to Mike Osei, Miss 
Millicent, Daniel, A. Sackey, Stanley Dimpka and Sylvester Atijegbe and friends
v
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Poumo T. David, Thiam Amadou, Abdulrahman Jada, Sulyman, I. Olanrewaju and 
Abdulrahim S. Zakari, You all have touched my life in ways you cannot imagine.
Finally my gratitude to Deutscher Akademischer Austausch Dient (DAAD) for 
funding this study, to which I am eternally grateful.
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TABLE OF CONTENTS
PAGE
Declaration--------------------------------t------------------------------------------------------- ii
Dedication  --------------------------------------------------------------------------------  iii
Acknowledgements-----------------------------------------------------------------------------  iv
Table o f Contents--------------------------------------------------------------------------------  vii
List o f Figures------------------------------------------------------------------------------------- x
List o f Tables--------------------------------------------------------------------------------------  xi
List o f Plates---------------------------------------------------------------------------------------  xii
Abstract--------------------------------------------------------------------------------------------- xiii
CHAPTER ONE------------------------------------------------------------------------------  1
1.0.1.troduction .----------------------------------------------------------------------------------- 1
1.1. General Obj ective--------------------------------------------------------------------------  5
1.2. Specific objectives--------------------------------------------------------------------------- 5
CHAPTER TW O --------------------------------------------------------------------------------- 6
2.0.Literature Review------------------------------------------------------------------------------ 6
2.1.The Maize Zea mays (L.)---------------------------------------------------------------------6
2.1.1.Taxonomy, distribution and ecology------------------------------------------ 6
2.1.2.Economic Importance------------------------------------------------------------- 7
2.2.The African locust bean Parkia biglobosa{Jacq.)------------------------------------- 9
2.2.1.Taxonomy, distribution and ecology------------------------------------------ 9
2.2.2.Economic importance------------------------------------------------------------ 12
2.3 .Insect pests o f Parkia-------------------------------------------------------------------  15
2.4.Taxonomy of Sitophilus zeamais--------------------------------------------------------- 16
2.5. Biology o f S. zeamais------------------------------------------------------------------------ 19
2.5.1. Eggs------------------------------------------------------------------------------  20
2.5.2. Larvae------------------------------------------------------------------------------ 20
2.5.3. Pupae------------------------------------------------------------------------------- 21
2.5.4. A dults----------------------------------------------------------------------------  21
2.5.5. Reproduction--------------------------------------------------------------------- 22
2.6.Ecology and distribution---------------------------------------------------------------------23
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2.7.Feeding and breeding substrates----------------------------------------------------------  23
2.8.Economic importance--------------------------------------------------------------------------24
2.9.Managemen t -------------------------------------------------------------------------------------25
2.9.1. Cultural control--------------------------------------------------------------------25
2.9.2. Physical control--------------------------------------------------------------------26
2.9.3. Chemical control------------------------------------------------------------------ 28
2.9.4. Novel Approaches------------------------------------------------------------------ 30
CHAPTER THREE ------------------------------------------------------------------------------ 35
3.0. General Methodology.---------------------------------------------------------------------  35
3.1. Study a rea ------------------------------------------------------------------------------------  35
3.2. Test p lan ts-------------------------------------------------------------------------------------- 35
3.3. Culturing o f S. zeamais--------------------------------------------------------------------- 35
3.4. Experimental Design and Set U p ----------------------------------------------------- 38
3.5. Statistical analysis----------------------------------------------------------------------------42
CHAPTER FOUR---------------------------------------------------------------------------------44
4.0. Description o f experiments--------------------------------------------------------------- 44
4.1.Survival o f S. zeamais on Parkia and maize substrates-----------------------------44
4.1.1. Introduction--------------------------------------------------------------------------44
4.1.2. Materials and Methods----------------------------------------------------------- 44
4.1.3. Data collection-------------------------------------------------------------------  47
4.1.4. Data Analysis----------------------------------------------------------------------- 47
4.1.5. Results-------------------------------------------------------------------------------- 48
4.1.5.1. Survival o f .S', zeamais on Parkia and maize substrates 
under controlled environments------------------------------------------------ 48
4.1.5.2. Survival o f S. zeamais on Parkia and maize substrates 
under ambient environmental conditions--------------------------------- 49
4.1.6. Discussion----------------------------------------------------------------------------50
4.2.Preference for Parkia and maize substrates by S. zeamais-----------------------  53
4.2.1. Introduction--------------------------------------------------------------------------53
4.2.2. Materials and Methods----------------------------------------------------------- 54
4.2.3. Data collection--------------------------------------------------------------------  56
4.2.4. Data analysis------------------------------------------------------------------------ 56
4.2.5. Results-------------------------------------------------------------------------------- 57
4.2.5.1. Preference tests under controlled conditions-----------------------------57
4.2.5.2. Preference tests under ambient environmental conditions---------- 58
4.2.6. Discussion----------------------------------------------------------------------------59
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4.3,Oviposition o f S. zeamais on Parkia and maize substrates-------------------------60
4.3.1. Introduction--------------------------------------------------------------------- — 60
4.3.2. Materials and Methods----------------------------------------------------------- 61
4.3.3. Data collection--------------------------------------------------------------------  62
4.3 4. Data analysis--------------------------------------------------------------------  62
4.3.5. Results and Discussion--------------------------------------------------------- 62
4.4.Development o f S. zeamais on Parkia and maize substrates----------------------- 65
4.4.1. Introduction--------------------------------------------------------------------------65
4.4.2. Materials and Methods----------------------------------------------------------- 65
4.4.3. Data collection--------------------------------------------------------------------  66
4.4.4. Data analysis------------------------------------------------------------------------ 67
4.4.5. Results and Discussion----------------------------------------------------------- 67
4.4.6. Adult weight-------------------------------------------------------------------------68
CHAPTER F IV E --------------------------------------------------------------------------------- 69
5.0. Conclusion and Recommendations----------------------------------------------------  69
5.1. Conclusion--------------------------  69
5.2. Recommendations----------------------------------------------------------------------------70
REFERENCES----------------------------------------------------------------------------------  71
APPEND ICES----------------------------------- ----------- ------------------------------------101
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LIST OF FIGURES
PAGE
Figure l:M ean monthly temperature and relative humidity record from
December 2004-May,2005 obtained at Sinna Garden.----------------------- 39
Figure.. 2: Survival o f S. zeamais on Parkia and maize substrates under
controlled conditions April-May,2005--------------------------------------------52
Figure 3: Survival o f S. zeamais on Parkia and maize substrates under ambient
environmental conditions April~May,2005-------------------------------------52
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LIST OF TABLES
PAGE
Table l:M ean survival o f S. zeamais on Parkia and maize substrates
under controlled conditions from January-February,2005--------------------- 48
Table 2: Mean survival o f S. zeamais on Parkia and maize substrates
under ambient environmental conditions from Jan-Feb.,2005--------------- 49
Table 3:Mean number o f S. zeamais on maize and Parkia substrates
' under controlled conditions---------------------------------------------------------- 57
Table 4: Mean number o f S. zeamais on maize and Parkia substrates
under ambient environmental conditions----------------------------------------- 58
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PAGE
Plate 1 '.Parkia biglobosa tree in Mole National Park, Ghana (Shao,2002)--------------  12
Plate V.Parkia biglobosa fruit bunches, the form used for the experiments--------15
Plate 3 :S. zeamais adult..............................................................................-....................37
Plate 4:*S. zeamais cultures in the laboratory---------------------------------------------- 37
Plate 5:Experimental set-up in an environmental chamber in the laboratory------41
Plate 6:Experimental set-up under ambient environmental conditions
»in the Screen house--------------------------------------------------------------------- 41
Plate 7: Tray used for the preference test, showing different Parkia
substrates (pods, pulp and seeds) and m aize------------------------------------42
Plate 8:Experimental set up for the survival tests in an environmental
chamber in the laboratory------------------------------------------------------------- 46
Plate 9:Experimental set up for the survival tests under ambient environmental
conditions in the Screen house -------------------------------------------------------46
Plate 10:Preference test in an environmental chamber in the laboratory----------55
Plate 11 Preference test under ambient environmental conditions in the
Screen house----------------------------------------------------------------------------- 55
LIST OF PLATES
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ABSTRACT
Maize is an important staple food crop in Ghana and is cultivated throughout the 
country. The Guinea savanna zone in the Northern region, which is fast becoming 
a major production zone, is also the natural ecological zone o f Parkia plants. 
Some insect pests, such as Sitophilus zeamais are a serious threat to maize 
production in Ghana. These insects appear to have adapted to and survive on some 
wild host plants. They may therefore emigrate from these alternative hosts to 
preferred hosts when the crops are planted in the field. The objective o f this study 
was to investigate the suitability o f Parkia biglobosa for the development o f S. 
zeamais and also to determine whether S. zeamais adults would exhibit any 
preference for Parkia substrates when given a choice. A comparative study o f the 
development o f S. zeamais on Parkia seeds, pulps, pods and maize showed that 
the weevil does not reproduce at all on Parkia substrates under both field and 
laboratory conditions. Mean developmental period on maize under controlled 
conditions was significantly (P < 0.05) shorter (41.2 days) than under ambient 
environmental conditions (47.0 days). The mean weight o f adults (3.4mg) under 
controlled conditions was, however, not significantly different (P > 0.05) from 
what was obtained under ambient environmental conditions (2.8mg). The mean
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number o f eggs laid on maize under controlled conditions was significantly (P < 
0.05) higher (114.5) than under ambient environmental conditions (94.75) and no 
eggs were laid on Parkia seeds, pulp and pods. In free-choice tests, significantly 
(P < 0.05) more weevils were recorded on maize than on Parkia substrates under 
both sets o f conditions. Comparative study on survival o f S. zeamais on Parkia 
seeds, pulp, pods and maize variety Volta local showed that survival o f  the 
weevils stabilized with time on maize but high mortality was recorded on Parkia 
seeds, pulp and pods under both sets o f conditions. More weevils survived on 
Parkia seeds, pulp and pods in an environmental chamber in the laboratory than 
under the field conditions. From this, no conclusion can be drawn that Parkia 
pods, pulp and seeds may act as alternate hosts for S. zeamais and investigation 
needed to be undertaken to determine the actual factors responsible for the 
unsuitability or unacceptability o f Parkia biglobosa as a host for S. zeamais. It is 
suggested that a better understanding o f the biology and behaviour o f S. zeamais in 
relation to Parkia pods, pulp and seeds will assist in the development o f improved 
management practices for the control o f this pest and so reduce heavy losses 
caused by this pest both in the field and storage.
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CHAPTER ONE
1.0. INTRODUCTION
A major shift in global cereal demand is underway and by the year 2020, the 
demand for maize in developing countries will surpass the demand for both wheat 
and rice (CIMMYT, 2004). This shift will be reflected in a 50 % increase in global 
maize demand from its 1995 level of 558 millions to 837 millions tonnes by 2020. 
Maize requirement in the developing world alone will increase from 282 million 
tonnes in 1995 to 504 million tonnes in 2020. An annual maize demand in sub- 
Saharan Africa is expected to double to 52 million tonnes by 2020 (CIMMYT, 
2004).
In Ghana about 400,000 hectares o f land is under cultivation o f maize (Zea mays 
L.). Maize production averaged around 375,000 tonnes per annum during 1970- 
1985 (Rouanet,1992) and has increased from 553,000 metric tonnes in 1990 to
961.000 metric tonnes in 1993 (Owusu-Akyaw, 1991; PPMED, 1994). Estimated 
production for 1995 was 1.4 million metric tonnes and currently estimated to be
1.800.000 metric tonnes (Morris et al., 1999 ; WFP, 2002 ; SRID, 2005).
Maize is a staple cereal crop in many parts of Africa and it has replaced many 
traditional starchy foodstuffs, such as sorghum and millets, particularly in South 
Africa, Malawi, Zimbabwe and Kenya, and in considerable sections o f Angola,
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Zambia, Tanzania, Mozambique, Cameroon, Benin, Togo, Ghana, Nigeria and 
Egypt (Purseglove, 1992). It is comparable in significance to rice in Asia and 
wheat in the Middle East (Kim, 1987). In Ghana, maize is one o f the most 
important cereal crops (Rouanet,1992) which is cultivated throughout the country, 
but yields are highest on well-drained, deep, fine soils. It is an important source o f 
carbohydrate and forms about 90 -  95 % o f  the total calorie intake o f the coastal 
savanna people (Baba, 1994; Dankyi et al., 1995). Insect pests are among the key 
factors contributing to low yield o f maize and they are central to many, if  not one 
o f the major problems facing maize production today (CIMMYT,2001). 
Worldwide more than 200 species o f insect pests have been recorded on maize 
(Purseglove, 1992). The most common among these are Sitophilus zeamais 
Motschulsky, Sitophilus oryzae (L.), Rhyzopertha dominica (F.), and 
Prostephanus truncatus Horn (NRI, 1996).
Post-harvest losses to storage insect pests, such as maize weevils, Sitophilus 
zeamais have been recognized as an increasingly important problem in Africa 
(Markham et al., 1994). S. zeamais is one of the most serious storage pests of 
maize in the tropics (Bosque-Perez and Buddenhagen,1992). The insect infests the 
ripening crop in the fields before harvest and multiplies further during storage 
(Caswell,1962 ; H ills,1983 ; Kim and Kossou, 2003). Current food losses during 
storage are estimated to be about 200 million tonnes and worth US$20 billion 
(Bengston,2005). In Africa, losses o f cereal crops have been estimated to be about
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10-80% (Youdeowei,2005). In Ghana, out o f the total annual harvest o f 250 -
300,000 tonnes o f maize, about 20 % were lost to insect pests and 15 % o f this 
was attributed to maize weevils (Prempeh,1971;Youdeowei,1989). In some cases 
total losses can occur (Obeng-Ofori and Amiteye,2005). Losses to food grains 
caused by storage insects are serious a threat to food security (Ayertey,2002). 
Therefore, post harvest production management is critical in ensuring food 
security (Sefa-Dedeh and Senanu,1995).
Parkia biglobosa (Jacq.) Benth, also called African locust bean, belongs to the 
family Leguminosae and the sub-family Mimosoideae (Hopkins, 1983). It is 
cultivated in areas with between 800 and 1500 mm of annual rainfall, 1400 and 
2100 mm of potential evapotranspiration, and is generally associated with a dry 
season-of five to seven months. It occurs on mid-toposequence position on deep 
soils and sometimes, through farmers protection, on well-drained soils in flood 
plains and riparian sites. It is absent from depressions where soil drainage is 
impeded (Hall et ah, 1997). The species naturally occurs in the dry forests o f the 
Sudano- Guinean savanna to the Southern border o f the Sahel ecozone on the 600 
mm isohyets (ICRAF,2004). In Ghana, P. biglobosa is found mainly in the 
Northern part o f the country and its distribution conforms to common 
environmental factors throughout its range (Shao, 2002).
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Parkia biglobosa is an important alternate host o f some insects. Setamou et 
al.(2000a) recorded several generations o f corn ear-borer, Mussidia nigrivenella 
Rogonots on P. biglobosa. Emerging M. nigrivenella populations from pods o f 
the natural host plant {P. biglobosa) constitute an important source o f infestation 
to nearby maize field (Setamou et al., 2000b). A weevil and pyralid moth were 
also observed on the pods; the moth eats both pulp and seeds (Hopkins,1983 ; 
ICRAF,2004). Sitophilus. zeamais has been observed on Parkia pods several times 
(Ayertey, personal communication).
The major difficulties associated with the management o f storage pests are the 
influence o f alternate hosts as important sources o f re-infestation to maize fields. 
Many species o f stored insect pests appear to have adapted to, and survive on 
some wild host plants. They may therefore emigrate from these alternative hosts to 
preferred hosts when the crops are planted in the field. In Northern Nigeria, the 
bruchid, Bruchidius atrolineatus (Pic) has been recorded from wild legumes, 
including Vigna triloba Walp, at different times during the dry season when 
cowpea, its principal host is not normally grown (Prevett,1961 ; Booker,1967). In 
Ghana, it was reported that larvae o f Eldana saccharina Walker remain in the 
stubble o f sugar-cane after harvest and re-infest new shoots. Thus, the stubble 
serves as a reservoir for re-infestation by stem-borers (Kumar, 1984). Sitophilus 
zeamais has also been recorded on several wild host plants such as chestnuts, 
acorns and sunflowers (William and Floyd, 1971 ; Delobel and Grenier, 1993).
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Therefore, the problems caused by alternate hosts as a reservoir o f insect pests 
cannot be overemphasized,as they promote infestation and reinfestation,thus 
making management o f insect pests difficult. Many studies have been done on the 
development o f S. zeamais on cereals but little or no work has been done on wild 
hosts, especially P biglobosa as an alternate host. This study is an attempt to 
investigate the suitability of P. biglobosa as an alternate host/breeding substrate 
for S. zeamais.
1.1. General Objectives
The general objective o f this work was therefore to investigate the suitability o f P. 
biglobosa pods, seeds and pulp as breeding substrates for S. zeamais.
1.2. Specific objectives
The specific objectives o f this study are therefore as follows:
(i)To evaluate the survival o f S. zeamais on Parkia and maize substrates.
(ii)To examine relative preference o f S. zeamais for Parkia and maize substrates.
(iii)To evaluate the oviposition of S. zeamais on Parkia and maize substrates.
(iv)To determine developmental period o f S. zeamais on Parkia and maize 
substrates.
(v)To determine mean weight of adults emerging from Parkia and maize 
substrates.
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CHAPTER TWO 
2.0.LITERATURE REVIEW
2.1. The Maize (Zea mays L.)
2.1.1. Taxonomy, distribution and ecology
Maize (Zea mays L.) is a monocotyledon of the Gramineae family adapted to both 
tropical and temperate agro-ecological zones and is the only species in the tribe 
Maydeae (Purseglove,1992). The tribe Maydeae consists o f annual or perennial 
herbs. There are eight genera, o f which five are in the old world, extending from 
India, through South eastern Asia to Australia. The name maize is derived from 
an Arawak-carib word “Mahiz”(Purseglove,1992). It is also known as ‘Indian 
com’ and in America it is simply called ‘com ’
Maize is one o f the most important staple crops in the world (CIMMYT,2004). It 
is the most widely distributed, and most important in the United States o f America 
which produces half the world’s total maize, occupying double the area than any 
other crop (Purseglove,1992). Maize was introduced into Africa from its native 
Mesoamerica in the 16th century (CIMMYT,2004). It has became an important 
source of carbohydrate in 16 African countries; a total o f 5,080,000 metric tonnes 
o f the crop were produced in these countries between 1986 and 1988, and the 
percentage increase in its use as food and feed 74.9 and 17% respectively 
(CIMMYT, 1990).
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A wide range o f environmental conditions affect maize growth. It is essentially a 
crop o f warm countries with adequate moisture. It requires about 450 -  600 mm 
of rainfall during its growing season (Purseglove, 1992). An optimum temperature 
of 32 -  35°C is ideal for its growth (Downey, 1971). Maize production in Ghana is 
affected by several factors of which moisture availability, high soil temperature 
and low soil nitrogen are important (Mintah,1998). Depending on agro-ecological 
location, there may be one or two cropping seasons o f maize in Ghana (Boateng, 
1996). There are two rainy seasons in the important production areas o f the forest 
and forest-savanna transition zones. These are the major and minor seasons. 
Rainfall in the major season begins in March/April and ends in August while the 
minor season begins in August/September and ends in November/December. With 
supplemental irrigation, three crops per year are obtainable (NARP,1993; 
Edwards, 1995). The dry spell in August allows for harvesting o f the major season 
crop and land preparation for the minor season. In Northern parts o f Ghana, 
covering the Guinea savanna areas, the unimodal rainfall pattern spanning over 
five month from May to September provide for only one crop (Boateng, 1996).
2.1.3. Economic Importance
Most o f the maize crop is used in the countries in which it is grown and only about 
10 percent enters the world trade and o f which the United States supplies about 60 
percent (Purseglove, 1992). Maize is used for three main purposes:(i)as a staple 
human food, particularly in the tropics.(ii) as feed for livestock, particularly in
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temperate and advanced countries, providing over two thirds o f the total trade in 
feed grains, (iii) as a raw material for many industrial products.
Maize is prepared and consumed in a multitude o f ways. It is usually ground and 
pounded, and the meal may be boiled, baked or fried (Purseglove,1992). The 
whole grain may be boiled or roasted and it may be fermented. Maize meal is 
cooked with water to provide a thick mush or dough, which is the commonest 
method of eating it in Africa. Com bread is made by mixing the meal with wheat 
flour. Mature cobs are roasted and eaten. Cornflakes made out o f maize are used 
as breakfast cereals (Purseglove, 1992). Maize constitutes an important part in the 
diet o f rural and urban Ghanaians, accounting for between 47 and 50% o f food 
intake (Edwards, 1995). Examples o f food prepared from maize are Kenkey, 
Banku, Koko,Fresh com (boiled or roasted) and maize drink (“alasa”) considered 
as fast food convenient for urban dwellers, much as hamburgers are enjoyed 
elsewhere. Infact, it is a politically sensitive crop to urban dwellers, such that the 
size of-a ball o f Kenkey was once shown in parliament as a reflection o f the state 
o f the economy (Edwards, 1995). It is a source o f protein in Ghana and thus 
features, prominently in infant foods such as ‘Weanimix’ and ‘Vitalmix’, and also 
in animal nutrition (Edwards, 1995). Maize ranks only after fish and legumes in 
terms o f annual protein production (Twumasi-Afriyie et al., 1992).
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Maize grain is at present the main energy source in non-ruminants (Edwards, 
1995). It is also an outstanding feed for livestock, high in energy, low in fibre and 
easily digestible. It is an important forage crop; being cut green, or dried for 
fodder or made into silage and over 500 important products and byproducts may 
be obtained from maize (Purseglove, 1992).
2.2. The African locust bean (Parkia biglobosa Jacq.)
2.2.1. Taxonomy, distribution and ecology
Parkia biglobosa (Jacq.) Benth was first described by Robert Brown in 1825 and 
he named it after Mungo Park, a Scot who had made remarkable journeys o f 
exploration into the interior of West Africa (ICRAF,2004). Parkia is a pan tropical 
genus comprising about 30-40 tree species which occur in Africa, Asia, and in 
South America (Hopkins, 1983 ; Luckow and Hopkins, 1995). Parkia. biglobosa is 
a perennial deciduous tree with a height ranging from 7-20 metres and can reach 
30 metres under exceptional conditions (Cobbina and Sabitti, 1992 ; Shao,2002 ; 
ICRAF, 2004) (See Plate 1). It is noted to be widely distributed in Africa (Cobbina 
and Sabitti, 1992), and the following are its synonyms: P. africana R. Br; P. 
clapperjoniana Keay; P. filicoidea  var. glauca Baker; P. oliveri J .F. Macbr; P. 
filicoidea  Oliver; Mimosa biglobosa Jacq.; Inga biglobosa (Jacq.) Wild.; Inga 
faeculifera Desv and P. intermedia Oliver (ICRAF,2004). A number of 
vernacular names appear in the literature: two ball nitta tree, fern leaf, monkey 
cutlass tree, arbre a farine, arbre a fauve, mimosa poupre, caroubier africain, nerre,
9
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neri, nete, nette, oul, ouli, se-ou, ulele, yif, mkunde,mnienze (Dalziel and 
Hutchinson, 1937; Burkill, 1995 ; ICRAF, 2004).
Hutchinson et al. (1958) recorded four indigenous species o f the genus Parkia in 
West Africa and these include P. biglobosa(Jacq.) Benth; P. clappertoniana Keay; 
P. bicolor A. chev; and P filicoidea Welw. Ex. Oliv. Burkill (1995) reported that 
recent monographic work has reduced the number o f species to two common ones: 
P. biglobosa which are known to be distributed from Senegal across the West 
African sub-region into Southern Sudan and are mainly savanna species and P 
bicolor, which overlaps with dispersal from Guinea to Eastern Zaire and is mainly 
a forest species. Parkia filicoidea  is a species o f Central to East Africa with 
restricted, disjointed and rare occurrence in the highlands o f Cote d ’ivoire, Ghana, 
Togo and Eastern Nigeria. It is probable, however, that species names are 
interchangeable and usages are applicable more or less, commonly to all. IAPT 
(1997) confirmed that P. biglobosa (Jacq.) R. Br ex G Don is the name in current 
use of the extant plant genera.
Parkia biglobosa occurs in a diversity o f agroecogical zones, ranging from 
tropical forest with high and well distributed rainfall to arid zones where mean 
annual rainfall may be less than 400 mm (ICRAF,2004). Mean annual rainfall for 
Parkia trees ranges from 500-1200 mm (Le Houerou,1986). Felker (1981) 
observed Parkia growing in areas with less than 400 mm but was dominant in
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areas with rainfall o f 600 -  700 mm. It thrives in Southwestern Nigeria in areas 
with rainfall o f  about 1500 mm. Parkia has a capacity to withstand drought 
conditions due to its deep tap root system and ability to restrict transpiration 
(Osunubi and Fasehun,1987 ; ICRAF,2004).
Parkia biglobosa has a wide distribution across the Sudan and Guinea savanna 
ecological zones (Cobbina and Sabitti, 1992 ;Burkill,1995). The range extends 
from the Western coast o f Africa in Senegal to Sudan (Shao,2002). Parkia 
biglobosa is found in nineteen African countries: Senegal, The Gambia, Ghana, 
Guinea Bissau, Sierra Leone, Mali, Cote d ’ivoire, Burkina Faso, Togo, Benin, 
Niger, Nigeria, Chad, Central African Republic, Zaire, Sudan and Uganda 
(Burkill, 1995 ; Hall et al., 1997 ; ICRAF, 2004). In Ghana P. biglobosa is found 
in appreciable numbers only in the North, and its distributions conform to 
common environmental factors throughout its range (Shao, 2002).
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Plate 1: Parkia biglobosa tree in Mole National Park, Ghana (Shao, 2002).
2.2.2. Economic importance
Parkia biglobosa has several functional uses and is very important because o f its 
products (Burkill, 1995). The most significant products are food. The food 
products collected from P. biglobosa are especially important due to the 
seasonality o f fruit maturation and food availability (Shao,2002). All parts o f the 
tree are useful in one-way or the other. In The Gambia, it is protected from felling 
by the native authority and it assumes such importance as a food-legume that 
native husbandry has developed special names for the various parts o f the tree and
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these are often without epithet e.g. “The tree” or “The seed” is understood to mean 
Parkia (Burkill, 1995).
The leaves were valuable famine food in Northern Nigeria in 1972 -  74 (Burkill, 
1995). In Ghana, powdered dried barks and roots when mixed with shea butter 
can be applied to the whole body o f children suffering from convulsion (Burkill,
1995). The whole pods is edible when fresh and is eaten throughout West Africa. 
Even when dried, a large proportion remains edible. Thus, pods were often taken 
on long journeys as a staple ration (See Plate 2). In Ghana, water is added to the 
pulps to produce a paste called “dozim” in Dagbani. In February or March, young 
green pods are roasted and eaten by men. In March and April, the beginning o f 
“hunger” season when other foods are scarce, mature pods are collected for food 
(Shao,2002).
The seeds are used in the preparation o f dawadawa, a protein and fat rich food 
(Shao,2002). Dawadawa is a traditional culinary product obtained from the 
fermentation o f African locust bean {P. biglobosa) by Bacillus spp.(Odunfa,
1986). It is considered the most important food condiment in the entire West/ 
Central African savanna region. Dawadawa is primarily used as a condiment or 
flavours intensifier for soups and to impart or enhance meatiness (Beaumont, 
2002). Dawadawa is the name designated by the Nigerian Hausa tribe for 
fermented locust beans. Similar fermentation has been characterized throughout
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Africa, with local adaptation in the form o f raw material selection. These regional 
versions are often given local names such as Kinda in Sierra Leone, lru in coastal 
Nigeria, Soumbara in The Gambia and Burkina Faso and Kpalugu in parts o f 
Ghana (Odunfa,1986).
Dawadawa is rich in protein, lipids and vitamin B2 and abundant in amino acids 
and in the Northern region o f Ghana, ten percent o f all meals contain dawadawa 
(Campbell-Platt, 1980). In Northern Nigeria, dawadawa constituted 1.4 percent o f 
the daily calorie intake and 5% o f the total protein intake (Odunfa,1985). The 
young seedlings are nutritious and heavily browsed by livestock. Seeds are rich in 
calcium, sodium, potassium and phosphorus; they are used as a coffee substitute 
(ICRAF, 2004).
Parkia biglobosa attracts bees and is a popular tree among beekeepers. Branches 
are sometimes loped for firewood. Pods and roots are used as sponges and as 
strings for musical instruments. Mucilage from part o f the fruit is used as gum or 
resin. Husk o f pods mixed with indigo improve the luster o f dye products; seeds 
and bark contain tanin and so the bark is used in tanning. Fresh pulp can be 
fermented into an alcoholic beverage. The bark and pods contain piscides; the 
alkaloid parkine occurs in pods. The bark is also used for traditional medicine 
(Burkill, 1995 ; ICRAF, 2004).
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Plate 2 : Parkia biglobosa fruit bunches, the form used for the experiments 
2.3.Insect pests o f Parkia
Parkia is an important tree, intercropped with guinea com or maize (Fagbemi, 
1989). Since it is grown in the same field with food crops; it may be an im p la n t  
alternate host o f some insect pests which constitute a source o f infestation^ %  
nearby crops. Setamou et a/.(2000a) recorded several generations o f  com ear 
borer, M  nigrivenella on pods o f P. biglobosa, which constitute an important 
source o f infestation to nearby maize fields.
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A weevil and pyralid moth were observed on the pods; the moth eats both pulp 
and seed. Four families o f Lepidoptera eat leaves o f P. biglobosa and timbers are 
readily attacked by insects such as termites and wood borers (ICRAF, 2004). Hall 
and Walker (1991) reported that storage structures, made from Parkia 
clappertoniana and shea butter woods, are susceptible to insect attacks.
2.4.Taxonomy of Sitophilus zeamais
The maize weevil, Sitophilus zeamais Motschulsky is a member o f a triumvirate 
o f species in the family Curculionidae, Subfamily Caladrinae, genus Sitophilus 
which is stored grain pest. Other species are the rice weevil, S. oryzae (L.) and the 
granary weevil, S. granarius (L.). It was first described by Linnaeus in 1763 as 
Curculio oryza, the first named species o f the group which was later revised by De 
Clairville and Scheltenburg in 1798 as Calandra oryzae: it uses the commonest 
generic synonym for Sitophilus. Many workers subsequently recognized that two 
distinct forms o f the species existed and were described as the 'large' and 'small' 
forms. In 1855, Motschulsky recognized the large form as a distinct species, which 
he named Sitophilus zeamais. Unfortunately, few workers recognized this revision 
and the name C. oryzae continued to be applied to all insects in this complex. 
Takahashi in 1928 and 1931 complicated matters by raising the small form to 
specific status as C. sasakii. This confused situation continued until 1959, when 
Floyd and Newsom (1959) revised the complex; this was followed by a further
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revision by Kuschel (1961). In these revisions it was shown that Linnaeus 
originally described the smaller species and that Motschulsky’s description o f the 
larger species was valid. Both species were therefore placed in the genus 
Sitophilus with the specific names proposed by Linnaeus and Motschulsky.
Unfortunately, the difference in size between S. oryzae and S. zeamais is not 
consistent, so it is not possible to be sure that references to the large and small 
forms o f C. oryzae refer to S. zeamais and S. oryzae, respectively. Therefore the 
only true and unconfused synonym of S. oryzae is C. sasakii; in pre-1960’s 
literature, C. oryzae 'small' and 'large' forms could refer to either S. zeamais or S. 
oryzae, and it is also possible that some references to 'S. oryzae' in the 1960’s and 
early 1970’s literature actually relate to S. zeamais misidentified by use o f old 
keys. The genus Sitophilus and its species may be identified using the keys of 
Gorham (1987) or Haines (1991).
Sitophilus oryzae and S. zeamais are almost indistinguishable from each other 
externally (Haines, 1991). Body sizes o f adult range from 2.5 to 4mm and the 
thorax is large and conspicuous (Hill, 1983). The body colour varies from light 
brown to black. Both species usually have four pale reddish-brown or orange- 
brown oval markings on the elytra. Both have the characteristic rostrum and 
elbowed antennae o f the family Curculionidae which are carried in an extended 
position when the insect is walking. Separation o f S. oryzae and S. zeamais
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requires examination o f the genitalia. The aedeagus o f S. zeamais has two parallel 
grooves on its dorsal surface; these are absent in S. oryzae making this structure in 
the latter smooth and convex (Halstead, 1963 ;Proctor,1971). In female S. zeamais, 
the prongs o f the Y -  shaped sclerite are pointed at the ends and the gap between 
is wider than the combined width. However in S. oryzae, the prongs are rounded 
and the gap between them is narrower than their width (Vowotor,1992). 
Arrangements made by pronotal pits on the prothorax can also be used to 
differentiate the two species. Halstead (1963) and Fisher (1987) reported that the 
rostrum o f the male S. zeamais and S. oryzae are distinctly shorter and wider than 
that o f the female. Furthermore, the rostrum o f the female in both species are 
comparatively longer and narrower than those o f the males; the rostrum o f the 
female is smooth and shinning while that o f the male is rough. It is sometimes 
difficult to distinguish between S. zeamais and S. oryzae based on morphological 
characteristics (Lale and Ofuya, 2001 ; Adedire, 2001). However, in S. zeamais, 
the adult weevil is larger and the patches on the elytra are more easily discernible 
than in S. oryzae (Appert, 1987). It is a better flier and prefers larger grain than the 
rice weevil. The granary weevil, S. granarius on the other hand is seldom found in 
the hot tropical regions except on grains imported from the temperate countries 
(Appert,1987). It is easily distinguishable from the other two species by the 
absence o f dark patches on the elytra and its inability to fly. Nardon and Nardon 
(2002) reported that S. zeamais and S. oryzae can be distinguished by the 
following new characters:(1) In the larvae, there exists a small difference exists in
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mandible structure with the apical zone more depressed in S. oryzae than in S. 
zeamais. (2) In adults, four new distinctive features which occur are:(i) The 
structure o f the metathoracic epistemum with two rows o f punctures in S. oryzae 
and three in S. zeamais. (ii) The frontal groove much more depressed in S. zeamais 
than in S. oryzae. (iii) The complex setae bordering the frontal groove bigger in S. 
oryzae than in S. zeamais and (iv) The presence o f a little structure called "rosette 
", at the base o f the rostrum, easy to see in S. zeamais but less visible in S. oryzae. 
Both species can also be separated from S. granarius by the presence o f 
metathoracic flight wings, and oval-shaped punctures on the prothorax o f the 
former JHaines, 1991).
2.5. Biology of S. zeamais
Sitophilus zeamais undergoes holometabolous metamorphosis; they have four life 
stages- egg, larva, pupa and the adult. Total developmental periods from egg to 
adult range from 30-35 days under optimal conditions to over 110 days at sub- 
optimal conditions o f temperature and relative humidity (Richards, 1947 ; Haines,
1991). The actual length o f the life cycle also depends upon the type and quality o f 
grain being infested; for example, in different varieties o f maize, mean 
development periods o f S. zeamais at 27°C and 70% r.h. have been shown to vary 
from 31 to 37 days (Birch,1944 ; Howe, 1952 ; Longstaff ,1981 ; Haines,1991). 
Sitophilus zeamais is a multivoltine insect pest, producing up to 7 generations in
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one year (Hill, 1983 ; NRI, 1996). The longevity o f the adult weevil is from a few 
months to one year (Longstaff, 1981 ; Lale, 2002).
2.5.1. Eggs
Eggs are laid throughout most o f the female adult life, although 50% may be laid 
in the first 4-5 weeks; each female may lay about 300 to 400 eggs in its lifespan 
(Adedire, 2001). Each female lays 2 to 3 eggs per day during her life (NRI, 1996). 
The eggs are laid individually in small cavities chewed into cereal grains by the 
female; each cavity is sealed, thus protecting the egg by a waxy secretion (usually 
referred to as an 'egg-plug') produced by the female. The incubation period o f the 
egg is about 6 days at 25°C (Howe, 1952). Eggs are laid at temperatures between 
15 and 35°C (with an optimum around 25°C) and at grain moisture content o f over 
10%. However, rates o f oviposition are very low below 20°C or above 32°C, and 
below about 12% moisture content (Birch, 1944).
2.5.2. Larvae
Eggs hatch after about 8 days into legless,4 mm long larvae (NRI, 1996). The 
larvae are plump creamy white in appearance and apodous, hence they are 
immobile; the larvae commonly called grubs which feed exclusively on the grain 
(Adedire, 2001). The larval stage is the most destructive stage o f the weevil and 
accounts for most o f the damage to the grains. The larva chews through the grain 
kernel leaving a characteristic tunnel and develops through 4 instars (Sharifi and 
Mills, 197la  ; Shade et al., 1990 ; Vowotor, 1992 ; NRI, 1996 ; Adedire, 2001).
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The chewing activity o f the larva is responsible for loss in quality and quantity o f 
the stored crops (Urrelo et a l, 1990). At the next larval moult; the larva increases 
in size, thereby widening the tunnel. The duration o f the larval stage is about 21 
days at 25° to 27°C and 70% r.h.(Sharifi and Mills,1971b). The first and fourth 
instars have been found to be longer than the second and third instars (Urrelo and 
Wright, 1989).
2.5.3. Pupae
The fourth instar larva lives within the chamber and moults into a prepupa. The 
duration o f this prepupal stage is about one day (Sharifi and Mills,1971b ; Baker 
and Mabie,1973), after which it moults into a pupa for about 6 days (Vowotor,
1992). After emerging from the puparium, the newly developed adult remains 
inside the kernel for several days before emerging. The extent o f this period varies 
with temperature among other factors (Vowotor, 1992). Duration o f pupal period 
lasts from 5 to 16 days (NRI, 1996).
2.5.4. Adults
The adults emerge after a further 5-16 days and will live for about 9 month. The 
adult emerges through a circular hole which it has cut out o f the grains (NRI,
1996). The holes are characteristic of this insect pest. Adults reach a length o f 3 - 
3.5mm long (average 3 mm); dark brown, nearly black with four clearly defined 
reddish spots on the elytra; 8-segmented antennae; prothorax with round or
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irregular punctures; hindwings present (NRI, 1996). Sitophilus zeamais has a 
greater ability and tendency to fly (Giles, 1969). Where grain is stored on small 
farms, S. zeamais is thus more likely than S. oryzae to fly to the ripening crop in 
the field and establish an infestation in the grain before harvest.
2.5.5. Reproduction
In S. zeamais, reproduction occurs with mating. Mating may take place many 
times and sperms are stored for many days (Vowotor,1992). Virgin males are 
often found on the grain surface. Surtees (1964) reported that virgin females spend 
more time on the surface o f a grain mass, as compared to mated female which 
spend most o f their time feeding and ovipositing. Ayertey (1981) reported that 
virgin males were more active than virgin females. Walgenbach and Burkholder 
(1987) further explained that virgin females began copulation sooner and are 
more likely to mate than previously mated females. Mated males were 
reported to be more successful at mating than virgins. Copulation lasts for 
an average o f 4.8 hours and does not usually occur before the age o f 3 
days (Vowotor,1992). The duration o f copulation is neither affected by the 
age o f mating status o f the female nor by the period o f time since first 
copulation. Aggregation pheromones are reportedly produced by males before 
mating. Mated females are significantly less responsive to it than virgins. Mated 
males are also less responsive although less so than mated females (Walgenbach 
and Burhholder, 1986). Aggregation pheromone systems are highly tied to food
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resources, as studies indicate that feeding is required by males to produce 
pheromone and optimum response by females and males is achieved when the 
aggregation pheromone is released together with food odours (Phillips, 1997).
2.6. Ecology and distribution
Sitophilus zeamais and S. oryzae are found in all warm and tropical parts o f the 
world but S. oryzae may also be found in temperate regions o f the world (Hill, 
1983 ; Appert, 1987 ; Adedire, 2001). The maize weevil is one o f the most serious 
cosmopolitan pests o f stored cereal grain, especially o f maize in tropical and sub­
tropical regions (Throne, 1994). Food preference o f the two species are variable; 
S. zeamais is a serious primary pest o f maize while S. oryzae is a principal pest o f 
rice in the tropics and other warm regions o f the world (TDRI,1984 ; 
Adedire,2001). Sitophilus granarius on the other hand is seldom found in the 
hot tropical regions except in grains imported from the temperate countries 
(Appert, 1987).
2.7. Feeding and breeding substrates
Sitophilus zeamais is a serious primary pest o f maize while 5. oryzae is a principal 
pest o f rice in the tropics and other warm regions o f the world (Haines, 1991 ; Lale 
and 0fuya,2001). Sitophilus zeamais is secondarily found attacking other crops 
such as rice, sorghum, yam products, groundnut, cowpea, millet, dried cassava, 
cassava flour, cocoyam, beniseed, triticale, processed cereal products such as pasta
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(Haines, 1991 ; Nwanna,1993 ; NRI, 1996). Sitophilus oryzae is also a secondary 
pest o f all these stored produce except rice which happens to be its major host 
(Lale and 0fuya,2001). Sitophilus oryzae strains have been found which can 
develop on legumes, peas (Coombs et a/., 1977 ; Haines,1991). Sitophilus 
granarius is known to attack smaller cereal grains such as wheat, millet, sorghum, 
barley etc, but they are occasionally found on larger grains (Lale and Ofuya, 
2001). „ Delobel and Grenier (1993) reported the development o f S. zeamais, S. 
oryzae and S. linearis on non-cereal foods and it shows the adaptability o f cereal 
weevils to different seeds and high performance on chestnuts and acorns. William 
and Floyd (1971) also reported that S. zeamais were found on several wild host 
plants such as sunflowers.
2.8. Economic importance
Sitophilus zeamais is an important pest o f maize but it was also associated with 
other cereals and processed food. Adult and larvae feed on undamaged grains and 
reduce them into powdery form. Infestation may commence from the field just 
before harvest and continues to reproduce and destroy the grains in the store. The 
larvae develop and pupate within grains. The developmental activities o f the 
weevil often lead to severe powdering and tainting o f the grains with excrement. 
The infested grains are often rendered susceptible to caking and mould infection 
thereby reducing their market value (NRI, 1996 ; Adedire, 2001 ; Lale and Ofuya,
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2001). In stored maize, heavy infestation o f this pest may cause weight losses o f as 
much as 30-40%, although losses are commonly 4-5% (Lale and Ofuya, 2001).
2.9. Management
There are a number o f control strategies employed to control maize weevil both in 
the field and in storage. These may be grouped into four broad methods: cultural, 
physical, chemical, biological. The three principal approaches to the protection o f 
stored grain: physical, biological and chemical are collectively known as 
integrated pest management (Proctor, 1994).
2.9.1. Cultural control
Cultural control methods include the burning o f cobs and sheath from which the 
maize was shelled, storage o f the crop in improved ventilated cribs, early 
harvesting to eliminate or reduce field infestation (FAO,1985). Cleaning o f bins 
or granaries, avoidance o f mixing infested grains with healthy ones, burning crop 
residues after-harvest, sealing cracks and crevices in muddy structures and any 
other practices that ensure that the crop is stored in a clean and uncontaminated 
environment (Proctor, 1994). Sanitation is a simple practice that can save the 
product from losses due to infestation. Good sanitation involves the removal o f old 
grain and dust in and around the grain bin, removal o f old grain from comers, 
floors, and walls and grain that may have spilled on the exterior o f the bin, 
removal o f any unnecessary objects from the store, cleanliness o f the store through
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sweeping, removal o f left over and prompt burning o f the trash is essential before 
receiving in a new lot. Sanitation in stores is a key factor for preserving products 
in good condition (Suss and Locatelli, 1993 ; Vinuela et ah, 1993 ; Rotundo et al., 
1995).
2.9.2. Physical control
The physical methods o f controlling pests in storage includes the following: 
Physical disturbance o f grain, by turning it from one elevator bin to another, can 
reduce live grain weevil infestation to a considerable extent due to physical stress 
and damage due to handling and processing of the grain (Joffe,1963). Hygiene and 
physical removal o f infestation nuclei, including commodity residues, secondary 
or unproductive primary hosts for field pests, cleaning, hand-picking, sun drying 
to drive away insects; cleaning should involve brushing and washing and disposal 
o f all residues containing or supporting live insects (Hall,1970 ; Proctor, 1994). 
Physical control also include all methods which reduce the moisture content o f the 
crop for safe storage (Dobie,1984). Infestation o f stored maize can be reduced by 
storing it as unhusked cobs; a long tight husk cover on maize cobs will physically 
prevent infestation in some instances (NRI, 1996). Inclusion of silica-containing dusts 
and ashr with stored grain has been found to control effectively storage insects (Proctor, 
1994). They may be used at rates above 30 percent o f the weight o f the grain. 
Dusts made o f silica aerogels, various clays, diatomaceous earth, activated carbon, 
pyrophylite and a number of other silicates kill insects by absorbing or abrading
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the waxy layer from their cuticle, causing desiccation and death (Proctor, 1994). 
Ajayi et a/.(1987) reported the control o f S. oryzae with wood ash and refined 
palm oil. Seed treatment with wood ash or dung ash at 1.5% was effective in 
controlling S. oryzae and ash from the plant o f Tamarindus indica was shown to 
protect stored grains for 7 weeks (NRI, 1996). Hall (1970) reported on an 
expirement in Kenya using a diatomite dust o f local origin, this mineral dust, when 
applied to stored maize in bags was believed to scratch the waterproofing layer o f 
the wax surfaces o f insect cuticle and led to the death o f the insects. 
Diatomaceous earth preparations and mixtures with silica aerogel showed some 
effects on the reproduction rate o f S. granarius (Flachsbarth et al., 2000). The 
powders derived from various diatomaceous fossil deposits were effective as an 
insecticide against Rhyzopertha dominica, Triholium. castaneum, and S. oryzae 
(Baldassari et al., 2002). Experiments showed that washed ash from burnt cow 
dung worked faster than unwashed ash; on average washing shortened the 
mortality period by 30% and the knock-down period by 45% and was effective 
against S. granarius, Cryptolestes ferrugineus, T. castaneum , and larvae o f 
Tenebrio molitor and Calliphora vomitoria (Hakbijl, 2002). A lower dose of 
3g/kg diatomaceous earth (DE) as a top-dressing for prophylactic control reduced 
the numbers o f Oryzaephilus surinamensis and S. granarius by greater than 90%. 
The use o f DEs as part of an IPM strategy was emphasized and lower doses could 
be commercially effective (Cook et al., 2002). Mortality o f adult S. zeamais, in
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wheat treated with diatomaceous earth was always greater than controls, and 
ranged.from 56 to 90% at 22°C and was >90% at 32°C (Arthur and Throne, 2003).
2.9.3. Chemical control
Use of fumigants and insecticidal dusts can be employed for chemical control of 
the maize weevils. Chemical control methods have the advantage o f effectiveness, 
simplicity, versatility, low cost and immediate availability (Appert,1987 ; Proctor, 
1994). Dusting and fumigation o f grains are the most commonly used chemical 
methods among small-scale farmers (Rai et ah, 1987). The most commonly used 
insecticide dusts belong to two main groups o f chemicals rorganophosphorus 
compounds (such as chlorpyrifos-methyl, fenitrothion, etrimfos, malathion, 
methacrifos and pirimiphos-methyl) and pyrethroids (such as cyfluthrin, 
deltamethrin, fenvalerate and permethrin). Fumigation is a widely used method all 
over the world on small-as well as large scale storage. The method can be applied 
at the farm level in gas-tight granaries or silos, under gas-tight sheets carefully 
covering the product or at large scale storage as in large warehouses. Fumigants 
are commercially available in a solid, liquid or gaseous state. There are various 
gases which can be used and these are: Methyl bromide (a possible ozone depleter, 
scheduled for deregistration in 2005), nitrogen, phosphine and carbon dioxide 
(Krall, 1984 ; Auger et al., 2002).
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Moreno et al.(2002) reported on the control o f S. oryzae and O. surinamensis 
using carbon dioxide under increased pressure (1, 25, 60 and 100 bar) at 
temperatures o f 20, 40 and 60°C, and durations o f 5, 30 and 60 minutes, where 
stored pests were effectively controlled at 60°C, 1 bar and 60 minutes, as well as 
at 25 bar and 5 minutes. At 20 and 40°C, 25 bar and 30 minutes, mortality was 
100%. Studies have also shown that organophosphorus insecticides, such as 
pirimiphos-methyl, tetrachlorvinphos and malathion effectively control grain 
weevils, keeping grains protected for 8 months (McFarlane, 1975 ; Golob et al 
1985). Pyrethroids like permethrin, deltamethrin or fenvalerate plus fenitrothion in 
powder formulation o f 0.5 % w/w, applied at 2.5-3.0 ppm on shelled maize or 
cobs, have been shown to give protection for 10 months or more and do not 
present any residual problems for human consumption (Golob et al., 1985 ; 
Makundi,19S6). It was therefore recommended that on mixed infestations by P. 
truncatus and Sitophilus spp. a combination o f organophosphate and pyrethroids, 
such as pirimiphos-methyl and deltamethrin, will give an excellent control o f both 
pests. Aburto and Garza (1986) reported the control o f Sitophilus spp. in stored 
grain with pirimiphos-methyl and trimethacarb; trimethacarb gave good control 
and had no residual effect after one month.
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2.9.4. Novel Approaches
The novel methods for possible application in stored-grain pest control include 
control by the use o f predators, parasites, insect diseases and sterile males, the use 
of pheromones for pest monitoring, mating disruption or enhanced mass trapping, 
and the use o f insect growth regulators (IGRs)
Biological control may provide a useful and safe alternative for the control o f crop 
pests (Proctor, 1994). Both S. zeamais and S. oryzae are commonly parasitized by 
pteromalids (and occasionally other Hymenoptera). Common pteromalid parasites 
include Anisopteromalus calandrae, Lariophagus distinguendus and Theocolax 
elegans (Dobie,1984). The parasitoid, a predator or a pathogen manipulate the 
reproductive processes, behaviour, feeding and other biotic aspects o f the p e s t . A 
parasitoid resides and feeds on the host pest itself which eventually dies (Proctor, 
1994). Suppression o f S. zeamais populations in drums o f com by single and 
multiple releases o f the parasitoid A. calandrae reached over 90 %  (Wen and 
Brower, 1994). The use o f insect pathogens such as Bacillus thuringiensis is 
considered as an alternative to synthetic insecticides; B. thuringiensis subsp. 
Morrison and B. thuringiensis subsp. Tenebrionis were effective for the protection 
of stored grains from pest infestation. (Abdel-Razek, 2002).
Entomopathogenic fungi (e.g. Beauveria spp.) used as mycopesticides may also 
provide an environmentally safe and cheap alternative for controlling storage
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insects: Metarhizium anisopliae and Beauveria bassiana were virulent to S. 
zeamais and 92-100% mortality was recorded (Kassa et al.,2002).
The use o f pheromones provide an alternative mechanism, being non -  neurotoxic, 
and is one o f the most promising techniques aimed at the control o f stored product 
insects that may lead to a drastic reduction o f chemical treatments against crop 
pests (Trematerra, 1997). Pheromone traps can be used to monitor the dynamics 
and occurrence o f different stored product pests, such as male aggregation 
pheromones known as “Sitophilure” for monitoring pest population and lures to 
attract maize weevils (Hodges et al., 1998 ; Ronaldo and Valeria, 1999). Allium’s 
allelochemicals (thiosulfinates) has repellent and antifeedant activity (Auger et al.,
2002).
Insect growth regulators (IGRs). These compounds have been found highly 
effective against various stored-product and other insect pests, including pest 
strains-that are resistant to organic insecticides. Generally IGRs have very low 
toxicity to mammals and other non-target organisms and, rapidly degrade in the 
environment (Kostyukovsky et al.,2000). These characteristics make IGRs 
potential alternatives to conventional insect pests control measures. According to 
their modes o f action, IGRs are divided into three main groups: juvenoid, which 
mainly affect larval metamorphosis by mimicking juvenile hormone; ecdysteroid, 
which affect moulting; and chitin synthesis inhibitors (CSIs) which interfere with
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cuticle formation (Post et a/., 1974 ; Bengstonl987 ; Gwinner et a/., 1990), though 
the mode o f action remains elusive (Ishaaya and Horowitz, 1998; Oberlander and 
Silhacek,1998). Among the diverse in vivo actions o f CSIs on the life cycle of 
insect pests o f various orders are ovicidal and larvicidal effects (Ascher et al.,
1987). Impairment o f cuticle secretion in affected embryos may be the cause of 
the hatchability reduction that results from treatment with CSIs (Elek, 1998). The 
larvicidal effects o f CSIs are most likely achieved through interference with the 
formation o f a new cuticle (Oberlander and Silhacek, 1998 ; Kostyukovsky and 
Trostanetsky,2005). Chitin synthesis inhibitors (teflubenzuron, benzamide, 
chlorfluazuron, and diflubenzuron) decreased the fecundity o f S. granarius and 
Acanthoscelides obtectus while juvenile hormone analogue (fenoxycarb) and 
chlorpyrifos-methyl could give good protection for at least 12 months against T. 
castaneum, O. surinamensis, R.. dominica and S. granarius (Nawrot et al., 1987 ; 
Edwards et al., 1987). Fenoxycarb controlled populations o f O. surinamensis, R.. 
dominica and T. castaneum for 2 years, but was not completely effective at 
controlling populations o f S. granarius (Mkhize,1988 ; Edwards et al., 1991). 
Silica aerogels used alone and in combination with IGRs were effective against S. 
oryzae and S. zeamais adults and afforded 91-98% control o f the weevils (Ammar, 
1988;Casaco et al., 2002 ; Conceicao et al., 2002). Diflubenzuron and methoprene 
were effective in protecting stored sorghum from S. oryzae and R. dominica under 
commercial storage conditions. (Daglish and Wallbank, 2005)
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Botanical insect deterrents or seed protectants may be applied to some products 
with varied degrees o f success. Plant products such as neem powder, neem 
extracts, leaves o f hoary basil (Ocimum spp.), mint (Mentha spp.) or black pepper 
(Piper spp.), Chinaberry tree (Melia azedarach) extracts, Alligator pepper 
(Aframomum melegueta) seed powder and oil extract, seed extracts o f Castor bean 
(Ricinus communis) showed some positive results in limiting insect 
infestation.(Kossou,1989 ; Haubruge et a/.,1989;Cobbinah and Appiah-Kwarteng , 
1989). Leaves and stems of maize and sorghum, powder from dry ground leaves 
of Mexican tea (Chenopodium ambrosioides), leaves o f post-harvest grain maize, 
sorghum, seed powder and oil o f black pepper, Piper nigrum, P. guineese, P. 
umbellatum and Capsicum frutescens showed good results in reducing damage by 
certain pests and also caused high adult mortality (Ojo,1991 ; Lale.1992 ; Risha, 
1993 ; Ishrat et al., 1994 ; Jembere et al., 1995). Other extracted oils, such as palm 
kernel oil, copra seed oil, citrus peel oil, maize oil, soyabean oil, groundnut oil, 
have been recognized as toxicants or growth inhibitors (Mahgoub and 
Ahmed, 1996 ; Okonkwo and Okoye,1996 ; Adedire, 2001 ; Wongtong et al., 2001 
; Tapondjou et al., 2002 ; Bekele, 2002 ; Obeng-Ofori and Amiteye, 2005). Oils o f 
groundnut, soyabean, castor, coconut, sesame, Lippia adoensis oil and olive have 
been reported to effectively control S. zeamais infestation and caused 100% 
mortality o f adult S. oryzae (Ivbijaro,1984 ; Salas, 1985 ; Odeyemi, 1993). Oils 
from. Xylopia aethiopica Dunal, Ocimum gratissimum, P. nigrum killed 97%, 
74%, 96% of S. zeamais (Ngamo et a l ,  2001).
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Plant extracts o f  the following: Azadirachta indica, Chromolaena odorata, 
Cissampelos owariensis, Datura metel, D. stramonium, Ricinus communis, 
Erythrophleum suaveolens, Grewia carpinifolia, Sida acuta, Solanum nigra, 
Strophantus hispidus and pulverized seeds o f Uvaria afzelli, P. umbellatum, 
Eugenia aromatica and the bark o f Erythrophleum guineese were highly toxic to 
S. zeamais, S. oryzae, A. obtectus and P. truncatus (Niber et al., 1992 ; Ladije et 
al., 1998). Leaves from  Eucalyptus globulus, Schinese molle, Datura stramonium, 
Phytolacca dodecandra, and Lycopersicum esculentum cause high adult weevil 
mortality for S. zeamais (Firdissa and Abraham, 1999).
Eugenol, isoeugenol and methyleugenol were effective against S. granarius, S. 
zeamais, T. castaneum and P. truncatus with overall repellency in the range o f 80- 
100%, and development o f eggs and immature stages inside grain kernels was 
completely inhibited (Obeng-ofori and Reichmuth, 1997 ; Huan et al., 2002).
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CHAPTER THREE 
3.0. GENERAL METHODOLOGY
3.1. Study area
The studies were carried out in the Entomology Laboratory and in the Screen 
house at Sinna Garden both at the Crop Science Department, University o f Ghana, 
Legon from July 2004 to June 2005.
3.2. Test plants
Parkia seeds, pods and pulps (about 10kg) and maize grains (about 10kg) were 
obtained from markets in Northern Ghana and Southern Ghana, respectively, and 
kept under cold storage at a temperature o f 10 °C.
3.3. Culturing of Sitophilus zeamais
Sitophilus zeamais adults (See Plate 3) were obtained from a stock culture 
maintained on maize at the Ghana Atomic Energy Commission and cultured in the 
Entomology laboratory o f the Crop Science Department. This provided a source o f 
supply of insects for the studies. Sub-samples o f maize grains (about 2500g) were 
withdrawn from the lot purchased from market and frozen in a deep freezer at 
about 1°C for two weeks to disinfest the grains (TDRI, 1984 ; Valerie et al., 1989 ; 
Hodges and Dobsona, 1998). The maize grains were then sterilized in a 
Gallenkamp Oven at 60°C for 3 hours, to kill off insects that may have survived the 
freezing temperatures. 1000 ml glass jars were also sterilized at 60 °C for 3 hours
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(Allotey and Azalekor, 2000). After cooling, about 500g o f the maize grains were 
put into each glass jar. One hundred, 7-14 day old unsexed adults S. zeamais were 
introduced into each glass jar with an aspirator and five o f such cultures in jars 
were prepared. Each glass jar was covered with a lid which is cut in the middle 
but sealed with a mesh (4cm in diameter) to facilitate ventilation o f the culture but 
keeps in the desired insects while it kept out mites and other unwanted insects. All 
the cultures in glass jars were held in trays with supports immersed in engine oil to 
prevent insects from crawling into them. After 7 days o f oviposition, the adult insects 
were sieved out with (6-mesh/in) (John Laing International Ltd, U.K.). This was 
repeated daily for three consecutive days to ensure thorough removal o f all adult 
insects. The cultures were kept for four weeks until adult emergence. Adults (7- 
14-day old) that emerged from these cultures were used to set up the experimental 
cultures. Re-culturing o f the insects was carried out at regular intervals to ensure 
availability o f experimental insects (See Plate 4).
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Plate 3: S. zeamais  adult (mag. x  100)
Plate 4: S. zeamais cultures in the laboratory
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3.4. Experimental Design and Set Up
The experimental design used for both controlled and ambient conditions was 
completely randomized design (CRD). Four treatments: Parkia seeds, Parkia 
pods, Parkia pulp and maize variety Volta local which were replicated four times 
were randomly selected and held in trays with supports immersed in industrial oil 
under controlled conditions in the laboratory at 25°C, 70 ±5% r.h. Similar four 
treatments were also replicated four times and maintained in wooden cages under 
ambient conditions at the Screen house.
The experiments were conducted in an environmental chamber (model Rumed- 
Rubarth Apparate GmbH. Germany) at 25°C, 70 ±5% r.h. Relative humidity was 
maintained in the chamber with a saturated sodium chloride salt solution 
(Solomon, 1951). This was held in a vessel which was placed below the three 
shelves in the chamber on which the experimental glass jars were arranged. 
Temperature and r.h. in the chamber were monitored with a tiny tag data logger 
(Gemini Data Loggers Company, U.K.). Similar records were taken o f the ambient 
temperature and relative humidity conditions using a thermohygrograph (See 
Figure 1).
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Figure 1 : Mean monthly temperature and relative humidity record from 
December 20Q4 ■ May 2005 obtained at Sinna Garden.
90 
80 
70 
60
Mean monthly 5° 
record 40
30
20
10
0
The Parkia and maize substrates (experimental treatments) that were used for the 
experiments were set up as follows: one hundred grammes o f each treatment was 
put into 1000 ml glass jars, and one hundred,7-14 day old unsexed adult S. 
zeamais were introduced into each glass jar with an aspirator. Each glass ja r was 
covered with a metal lid which is cut in the middle but sealed with a mesh (4cm in
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diameter) to facilitate ventilation into the culture. Four replicates o f each treatment 
were set up and held in trays with supports immersed in industrial oil to prevent 
insects from crawling into them; all trays were put into an environmental chamber 
(25°C,-70±5% r.h.) in the laboratory (See Plate 5). Another set o f treatments was 
prepared similar to the previous set up and maintained in wooden cages (each cage 
measuring 61cm x 45cm x 41cm) under ambient conditions. The cages were 
mounted on shallow trays with oil to prevent insects from crawling into them (See 
Plate 6).
Preference test that were also conducted under controlled and ambient conditions 
and were set up as follows: ten grammes o f four treatments (Parkia seeds, Parkia 
pods, Parkia pulp and maize variety Volta local) (See Plate 7), replicated four 
times, were placed on a filter paper inside Petri dishes (9cm diameter). The Petri 
dishes were randomly arranged in a circular form in a plastic tray (104cm x 7cm x 
5cm). The trays were covered with muslin cloth. Four replicates o f such trays were 
set up. Forty, 7-14 day old unsexed adults S. zeamais were introduced in the centre 
o f the trays. The set up was observed at 24 hour intervals for a total o f 72 hours
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Plate 5:Experimental set-up in an environmental chamber in the laboratory.
Plate 6‘.Experimental set-up under ambient environmental conditions in the 
Screen house.
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Maize variety 
Volta local Parkia pulp
Parkia pods * * Parkia seeds
Plate 7: T ray used  for the preference test, show ing different 
Parkia  substrates (pods, pulp  and seeds) and maize.
3.5. Statistical analysis
Data generated from the study were analysed using Genstat Software Version 5 
Release 3.2 (Lawes Agricultural Trust, 1995). Data collected on relative preference 
tests were transformed using square root o f (x + 1), and data on survival tests were 
transformed using arcsine o f sin-1 (Vx+1) to meet analysis o f variance assumptions 
o f normality and homogeneity o f variances and subjected to analysis o f variance at 
95% level o f significance. Mfewis were separated using least significant difference 
(LSD). Graphs were drawn using Microsoft Excel and tables were used to 
summarize the results. As no adult weevils emerged from Parkia substrates, data 
on developmental period and mean weight o f adults as well as data on oviposition 
were not included in the statistical analysis.
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on developmental period and mean weight o f adults as well as data on oviposition 
were not included in the statistical analysis.
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CHAPTER FOUR 
4.0. DESCRIPTION OF EXPIREMENTS
4.1. Survival of S. zeamais on Parkia and maize substrates.
4.1.1. Introduction
The establishment o f an insect on a host is not determined only by its ability to 
survive and grow on this host but also by its ability to breed on the host (Krishna 
and Mishra, 1985). A significant increase in the numbers o f an insect on a specific 
food is an indication o f the suitability o f such product as a host for the insect. 
Insects are therefore known to cause considerable damage to products that are 
suitable to them as food (Williams, 1999). Some plants species are best for 
survival, others are suited for egg production (Costa et al., 1991). In this study, 
survival tests were also conducted to determine the survival o f S. zeamais on 
Parkia and maize substrates.
4.1.2. Materials and Methods
Survival tests were conducted both at the Entomology Laboratory and in the 
Screen house at Sinna garden, Department o f Crop Science. Before infestation, the 
moisture content o f the Parkia and maize substrates were determined using a 
Digital Grain master (Protimeter PLC., England). The moisture content o f the 
substrates under both set o f conditions were: Parkia seeds (18.00%), Parkia pulp 
(16.10%), Parkia pods (19.70%) and maize variety Volta local (13.00%). One 
hundred grammes o f each treatment (Parkia seeds, Parkia pulp, Parkia pods and
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maize Variety Volta local) were put into each o f four glass jars, which were 
replicated four times and one hundred,7-14 day old unsexed adults S. zeamais 
were introduced into each glass jar to oviposit for 7 days. The experimental 
treatments were randomly arranged in a completely randomized design and 
maintained in an environmental chamber in the laboratory (See Plate 8). Live 
insects were counted weekly and put back into the jars while dead insects were 
removed, live insects were counted for five weeks. Another set o f treatments 
similar, to the previous experimental set up were prepared and maintained in 
wooden cages under ambient conditions (See Plate 9).
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Plate 8: Experimental set up for the survival tests in an 
environmental chamber in the laboratory.
'3™ #ass®® r a ® !aa^ ®
Plate 9: Experimental set up for the survival tests under 
ambient conditions in the Screen house.
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4.1.3. Data collection
The numbers o f both dead as well as live insects were counted weekly. An insects 
was considered dead if  it did not respond to probes with a pin; dead insects were 
sieved out with an Impact Test Sieve with mesh size o f 710 microns and the live 
insects were put back. The experiment was terminated when all adults on Parkia 
substrates had died. The experiments were repeated twice.
4.1.4. Data analysis
Data collected on survival tests were converted to percentage and then 
transformed using arcsine o f sin-1 (Vx+1) and subjected to analysis o f variance. 
The mean values were separated using LSD.
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4.1.5. Results.
4.1.5.1. Survival of S. zeamais on Parkia and maize substrates under 
controlled environments.
There were significant differences (P < 0.05) between the substrates in relation to 
percentage survival in the controlled environment (Table 1). The percentage 
survival o f S. zeamais decreased over time on Parkia substrates while the survival 
stabilized with time on maize variety Volta local. The percentage survival 
recorded on maize variety Volta local in week 1 was not significantly different (P 
>0.05) from the survival recorded on Parkia pods. It was during week 2 that 
differences in the rate o f survival became quite clear with highest percentage 
survival o f the weevils was on maize (94.0±1.35) and the lowest percentage survival 
was on Parkia seeds (16.2± 9.3) (Table 1).
Table 1: Mean survival of S. zeamais on Parkia and maize substrates 
under controlled conditions from January- February, 2005.
Substrates
Percentage survival ± S.E* 
Week 1 Week 2 Week 3 Week 4 Week5
Maize 95.5±0.65a 94.0± 1.35a 93.0± 1.35a 92.2±1.44a 92.2 ± 1.44a
P. Pulp- 71.2± 3.54 b 31.2± 7.3°
l_
12.2± 4.19
1_
3.7±3.12 2.7 ±2.43b
P. Pods 86.0±2.3a 38,0± 6.49 17.7± 9.06 9.7± 8.47b 0.2 ± 0.25b
P. Seeds 54.5 ± 6.74° 16.2+ 9.3d 2.2± 2.25b 1.0 ± 1.00b 0.2±0.25b
Different Parkia substrates designated as P. Pulp, P. Pods and P. Seeds 
* Values are means o f four replicates ± standard error.
Means followed by same letter(s) in a column are not significantly different 
from each other at 5 % LSD.
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4.I.5.2. Survival of S. zeamais on Parkia and maize substrates under ambient 
environmental conditions
The study on the survival of S. zeamais on Parkia and maize substrates under 
ambient environmental conditions revealed significant differences (P < 0.05) 
among' the percentage survival o f maize weevils on the various substrates. 
Survival o f S. zeamais on Parkia substrates decreased over time while the survival 
stabilized with time on maize variety Volta local. The highest percentage survival 
recorded (94.5 ±1.55) was on maize during the first week while P. Pods recorded 
the lowest percentage survival of weevils (0.7± 0.75) during week 2 (Table 2).
Table 2.Mean survival of S. zeamais on Parkia and maize substrates 
under ambient environmental condition from Jan.-Feb., 2005.
Percentage survival ± S.E*
Substrates Week 1 Week 2 Week 3
Maize 94.5±1.55a 91.5±2.87a 90.2 ±3.30:
P. Pulp 78.2 ±3.9b 3.0± 1.0b 0.0± 00 b
P. Pods 69.0±2.42C 0.7± 0.75b o .o ± o ob
P Seeds 46.7± 6.45d o .o± .oob o .o ± o o b
Different Parkia substrates designated as P. Pulp, P. Pods and P. .Seeds 
*'Values are means o f four replicates ± standard error.
Means followed by same letter(s) in a column are not significantly different 
from each other at 5 % LSD.
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4.1.6. Discussion.
The present study showed that there were significant difference (P < 0.05) in the 
percentage survival o f S. zeamais under both field and laboratory conditions. 
Comparison o f the two experimental environments showed that higher percentage 
o f survival o f S. zeamais was on maize, the survival o f S. zeamais was decreasing 
at a fast rate till observations were terminated at the end o f week three under 
ambient environmental conditions and week five under controlled conditions. 
These differences in the survival may not be attributed to environmental 
conditions and the reason are not clear. These were confirmed when the 
experiment was repeated for controlled environment (Figure 2) and ambient 
conditions (Figure 3); the differences in the survival followed similar trends to the 
previous experiments. On the other hand considerable level o f mortality was 
recorded on Parkia substrates under both sets o f conditions, with few S. zeamais 
adults surviving beyond second week under ambient environmental conditions and 
week five under controlled conditions. A possible reason for the observed 
mortality on Parkia substrates may be due to the presence o f potentially toxic 
substances in the seeds and parkine in the pods. Hopkins (1983) reported the 
presence o f parkine from pods o f P. biglobosa which has similar physiological 
action to that o f the alkaloids mimosine and physostigmine. It could also be due 
djenkolic acid and lectins present in the seeds. It may also be that Parkia 
substrates are nutritionally inferior for weevil survival and development. Cobbina
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and Sabitti (1992) reported that raw Parkia seeds appear inferior in nutrient 
content than Parkia pods
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Figure 2 : Survival of S.zoamals on Parkia and maize substrates in an 
envlromental chamber In the laboratory (April- May, 2006)
Time (Weeks)
- Maize 
~P. Pulps
P. Pods
- P. Seeds
Figure 3 : Survival of S. zeamais on Parkia and maize substrates under 
ambient enviromental conditions (April-May, 2005).
100 1 2
Time ( Weeks)
—♦—Maize 
~m— p. pulps 
P. Pods 
™— P. Seeds
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4.2. Preference for Parkia and maize substrates by S.zeamais.
4.2.1. Introduction
Preference for a particular produce by an insect could be attributed to factors such 
as quality, texture and other physical or chemical characteristics o f the produce. 
This is also related to the suitability o f the produce for oviposition and 
development (Chijindu,2002). The use o f preference test for studying choice 
between two or more plant species had been studied by different authors 
(Jermy,1966 ; Jenny et al., 1968 ; Jermy and Szentesi,1978 ; Reddy et al.,2002). 
They all reported that substrates selection for oviposition and other behavioural 
activities, such as orientation and colonization are governed by two factors:(i) 
Feeding stimulant such as certain plant substances which include saccharide, 
amino acids, ascorbic acid etc, which evoke biting or feeding responses;(ii) 
Inhibitory factors such as the presence o f feeding deterrents. Sitophilus zeamais 
adults show definite preference for grains on sections o f maize cobs for egg 
deposition (Vowotor, 1992). Genetics or physical factors may be responsible for 
weevil preference. Schoonhoven et al. (1976) reported that the physical factors that 
may cause maize kernel infestations include the presence o f damaged kernels 
where the endosperm is exposed, and presence o f seed-borne fungi on kernels 
which may create moisture differentials along the cobs and results in conditions 
that are conducive for insect infestations. In this study, tests for preference was 
conducted under controlled and ambient conditions to evaluate the relative 
preference o f adults S. zeamais for Parkia and maize substrates.
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4.2.2. Materials and Methods
Ten grammes o f the four treatment {Parkia seeds, Parkia pulp, Parkia pods and 
maize variety Volta local) were placed on a filter paper inside separate Petri dishes 
(9cm diameter). The Petri dishes were randomly arranged in a circular form on a 
plastic tray (104cm x 7cm x 5cm). The trays were covered with muslin cloth. Four 
replicates o f such trays were set up with the experiment being repeated twice. 
Forty, 7-14 day old unsexed adults S. zeamais were introduced in the centre o f the 
trays. The set up was observed for a total o f 72 hours (Calvitti and Remotti,1998 ; 
Reddy et al., 2002). Preferences were assessed based on the number o f weevils 
found during each 24-hour interval on each substrate. The whole set up was 
maintained in an environmental chamber in the laboratory (See Plate 10). Another 
set-up, similar to the previous one, was prepared and maintained in wooden cages 
(each cage, measuring 61cm x 45cm x 41cm) under ambient conditions (See Plate 
11).
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Plate 10: Experimental set up for preference tests in  an 
environmental chamber in  the laboratory.
Plate 11: Experimental set up for preference tests under 
ambient conditions in  the Screen house
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4.2.3. Data collection
The number of weevils found on each experimental unit after every 24-hours was 
recorded and the data were collected for 72 hours.
4.2.4. Data analysis
Data on tests for preference were transformed using square root o f  (x + 1) and 
subjected to analysis o f variance, and the mean values were separated by LSD.
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4.2.5. Results:
4.2.5.1. Preference test under controlled conditions
The orientation and colonization responses o f maize weevils in free choice tests 
shown in (Table 3) revealed that, significantly more (P < 0.05) weevils were 
recorded on maize variety Volta local than on Parkia substrates under the 
controlled conditions. Some 24-72 hours after introduction, higher numbers o f 
weevils were recorded on maize than on Parkia substrates (Table 3). Statistically, 
the number initially recorded on maize was not different (P > 0.05) from the 
number recorded on P. Pulp. Also, observations made at both 48 and 72 hours 
intervals revealed that the number o f weevils recorded followed a similar trend to 
the previous observation with significantly (P < 0.05) more weevils recorded on 
maize compared to Parkia substrates (Table 3).
Table 3. Mean number of S.zeamais on maize and Parkia
substrates under controlled conditions.
Mean number of S.zeamais ±S.E*
Substrates 24 hours 48 hours 72 hours
Maize 9.0± 2.00 a 25.2± 9.99a 38.5± 9.003
P. Pulp „ „ . ab 4.7 ±1.49 7.2± 2.36b 10.5± 4.56b
P. Pods 3.2±0.75b 3.2± 1.65 4.2± 1.38b
P. Seeds 3.5±1.71b
1_
5.2±1.93 6.2± 1.44b
Different Parkia substrates designated as P. Pulp, P. Pods and P. Seeds 
* Values are means o f four replicates ±standard error 
Means followed by same letter(s) in a column are not significantly 
different from each other at 5 % LSD.
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4.2.5.2. Preference test under ambient environmental conditions
In free-choice tests, there were significantly more (P < 0.05) weevils recorded on 
maize variety Volta local than on Parkia substrates under ambient environmental 
conditions (Table 4). When data were examined 24 hours after the introduction, 
significant differences (P < 0.05) were observed in the mean number o f weevils 
recorded on some o f the substrates used. P. Pods had the least mean number o f 
insects'(4.5 ±1.66) recorded, while the highest mean number o f (18.5 ±1.76) was 
recorded on maize variety Volta local. After 48 hours, it was observed that the 
mean number o f weevils recorded followed a similar trend as that o f 72 hours. 
Significantly (P < 0.05) more weevils were recorded on maize variety Volta local 
than on Parkia substrates (Table 4).
Table 4. Mean number of S.zeamais on maize and Parkia
substrates under ambient environmental conditions.
Mean number o f S.zeamais ±S.E*
Substrates 24 hours 48 hours 72 hours
Maize 18.5± 1.76a 38,50±0.65a 39.50± 0.29a
P. Pulp
o K
12.5± 3.48 7.2± 2.84b 8.5 ± 2.02b
P. Pods 4.5 ± 1.66b 3.0 ± 0.82b 3.5± 1.15b
P. Seeds 6.2± 1.55b 6.0 ± 1.58b 4.0± 0.58b
Different Parkia substrates designated as P. Pulp, P  . Pods and P. Seeds.
* Values are means o f four replicates ± standard error 
Means followed by same letter(s) in a column are not significantly different 
from each other at 5 % LSD
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4.2.6. Discussion
A comparison o f the orientation and colonization responses o f the S. zeamais 
under ambient and controlled conditions showed that initially there was significant 
difference in the number o f weevils recorded on both Parkia and maize variety 
Volta local substrates, and with time significantly (P < 0.05) more weevils were 
recorded on the maize variety Volta local compared to the Parkia substrates. The 
test for feeding preference lasted for 72 hours, which conforms to observation by 
Calvitti and Remotti (1998) that polyphagous insects need at least 72 hours to 
make final choice. Therefore, quick recognition to morphological and olfactory 
cues are important determinants o f host choice than exploratory feeding 
assessment o f hosts. Accordingly, greater feeding and oviposition would be 
expected on hosts that are more attractive for initial feeding than those suitable for 
long time survival. Another explanation o f the choice appears to be related to a 
predominant reaction to odour and taste o f the food item or that o f both the odour 
and taste o f the food item and make it easier for an individual to make a choice. 
High degree o f colonization exhibited by the adult weevils for maize may be 
attributed to that. Niewiada et al.(2005) reported that weevils can recognize a 
food by the qualitative and quantitative chemical composition o f the grain testa 
and may be one possible reason for the high colonization o f the maize kernels.
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4. 3. Oviposition of S. zeamais on Parkia and maize substrates 
4. 3.1. Introduction
The oviposition behaviour o f Sitophilus spp. has been studied under different 
conditions o f relative humidity and temperature on different varieties o f maize and 
other cereals such as rice, sorghum and wheat. Many studies on the biology and 
behaviour o f Sitophilus spp. are mostly on S. granarius and S. oryzae (Richards, 
1947 ; Segrove,1951 ; Longstaff,1981 ; Danho et al., 2002;). Insect oviposition 
behaviour is an important contributor to the fitness o f insects because o f the 
consequent effect on the number and quality o f offspring (Smith, 1986 ; 
Honek,1993 ; Stejskal and Kucerova,1996). In holometabolous insects, where the 
immature have restricted movements, the oviposition behaviour o f adults and 
larval development in the host are decisive factors in terms o f host range 
(Wasserman and Futuyma,1981 ; Jansen and Nylin,1997; Carriere,1998). There 
are many factors that may influence the oviposition o f insects on a specific host, 
such as morphology (Johnson and Kistler, 1987), nutritional quality, host 
abundance (Jansen and Nylin,1997 ; Barros and Zucoloto, 1999), places free o f 
predators (Bemays and Graham,1988) and competition (Siemens et al., 1991). 
Oviposition behaviour therefore varies according to the insect species and strain, 
population density, environmental conditions, food, age and size o f the individual 
(Stejskal and Kucerova, 1996). This study was undertaken with a view of 
understanding the oviposition behaviour o f S. zeamais on Parkia and maize 
substrates.
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4. 3. 2. Materials and Methods
Tests for oviposition were conducted both at the Entomology laboratory and in the 
Screen.house at Sinna Garden. Before introduction o f test insects, the moisture 
content o f the Parkia and maize substrates were determined using a Digital Grain 
master (Protimeter PLC., England). The moisture content o f substrates under the 
controlled conditions were: Parkia seeds (15.71%), Parkia pods (16.21%), Parkia 
pulp (18.10%) and maize variety Volta local (12.10%). The moisture content o f 
substrates under ambient conditions were Parkia seeds (16.00%), Parkia pods 
(17.70%), Parkia pulp (17.50%) and maize variety Volta local (11.80%). One 
hundred grammes o f each treatment (Parkia seeds, Parkia pulp, Parkia pods and 
maize variety Volta local) were put into each o f four glass jars, which were 
replicated four times and one hundred,7-14 day old unsexed adults S. zeamais 
were introduced into each glass jar to oviposit for 7 days. The experimental 
treatments were randomly arranged on shelves in a completely randomized design 
and maintained under controlled conditions. Another set o f treatments similar to 
the previous experiment was also set up and maintained in wooden cages under 
ambient environmental conditions. At the end o f the oviposition period (7 days) all 
the adult insects were sieved out with an Impact Test Sieve mesh size o f 710 
microns.
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4.3.3.Data collection
Egg counts were based on the assumption that each egg-plug covered only one egg 
and each egg was covered by one plug (Sharifi,1972 ; Vowotor,1992). After 
oviposition, the shelled kernels were stained with acid fuschin, using procedure 
described by Sharifi (1972). Excess water was removed from the stained grains by 
spreading and drying them in a layer o f tissue paper for 1-day in the laboratory 
and the number o f eggs laid were examined under illuminated stereo microscope. 
Eggs plugs stained deep cherry red, differently from mechanical injuries which 
stained lighter. Counting o f the eggs started 1-day after the termination o f the egg 
laying period and continued everyday thereafter until all eggs were counted. 
Where counting could not be completed on kernels in a day, the uncounted kernels 
were put into glass jar and deep frozen to arrest further development. No eggs- 
plug was seen on the Parkia substrates, so it was assumed that no egg was laid on 
the Parkia substrates.
4.3.4. Data analysis
Data collected on the number o f eggs laid on maize were analysed using 
descriptive statistics.
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4.3.5. Results and Discussion
The study on oviposition showed that the mean number o f eggs laid on maize 
under controlled conditions was significantly (P < 0.05) higher (114.5) than the 
number under ambient conditions (94.75). However, no eggs were laid on the 
Parkia substrates under both set o f conditions. The results o f this investigation 
have demonstrated that oviposition was significantly affected by temperature and 
relative humidity. Optimum temperature favours the large number o f eggs 
recorded under controlled conditions than ambient conditions. This agrees with 
Birch (1944), Richards (1947) and Howe (1952) that optimum temperature for 
eggs laying was around 25°C. It was observed from the study that S. zeamais 
tended to cluster eggs on kernels, leaving many kernels untouched. Legg et 
a/.(1987) reported that the distribution o f maize weevil eggs on maize kernels was 
aggregated and that eggs aggregation generally increased with increasing maize 
weevil density and duration o f oviposition/feeding period although the specific 
response depended on grain density. Reasons for clustering o f eggs on kernels are 
not clear. However, it was reported by Urrelo and Wright (1989) that egg 
aggregation behaviour o f the female weevils enhances the fitness o f larvae and 
emerged FI progeny. This behaviour o f the female weevil is, however, mal­
adaptive where multiple oviposition occurred in the maize or wheat kernel. Maize 
weevils may be guided by chemosensory factors, in addition to physical factors in 
selecting a favourable oviposition site on the maize kernel (Vowotor, 1992). The 
choice o f a favourable oviposition site would enhance faster development by the
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larvae that hatch, because they would have easier access to more nutritious 
materials within the kernel. The reason why oviposition and/or feeding were 
inhibited on Parkia substrates is not clear. It could be due to either physical 
properties o f the substrates such as pericarp characteristics (testa) or hardness o f 
seeds. Locatelli and Limonta (1998) reported that the presence o f pericarp obstruct 
both the egg laying and emergence o f grain weevils {Sitophilus spp.). Therefore, 
the maize weevils may find it difficult to gain a grip on the seeds, pulp or the 
pods, and thus have inadequate leverage for feeding and/or oviposition. From the 
foregoing, it is evident the strain o f S. zeamais used in the present studies was 
unableto lay eggs on Parkia substrates under both set o f conditions, which may be 
due to antixenosis or antibiosis.
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4.4. Development of S.zeamais on Parkia and maize substrates
4.4.1. In troduction
Development o f any insect from egg to adult depends on a number o f factors such 
as temperature, humidity, the nature o f substrate, and the type and quality o f grain 
being infested, which may be related and known to affect the development of 
insects (Haines, 1991 ; Chijindu,2002). The development o f S. zeamais on maize 
ranges from about 35 days under optimal to over 110 days at sub-optimal 
conditions o f temperature and relative humidity (Richards, 1947 ; Haines, 1991). 
The mean developmental periods o f S. zeamais at 27°C and 70% r.h. have been 
shown to vary from 31 to 37 days, on different maize varieties (Birch,1944 ; 
Howe, 1952 ; Longstaff,1981 ; Haines, 1991). Vowotor et a/.(1994) reported that 
the developmental period o f S. zeamais on shelled grains was 42 days and on ears 
with or without husks was 52 days. This study was conducted under field and 
laboratory conditions with a view to compare development o f S. zeamais on 
Parkia and maize substrates.
4.4.2. M aterials and Methods
The development o f insects were conducted both at the Entomology Laboratory 
and in the Screen house at Sinna garden. Before infestation, the moisture content 
of the substrates was determined using a Digital Grain master (Protimeter PLC., 
England). The moisture contents under both set of conditions were: Parkia seeds 
(18.25%), Parkia pulp (20.10%), Parkia pods (14.70%) and maize variety Volta
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local (13.50). One hundred grammes o f each treatment (Parkia seeds, Parkia pulp, 
Parkia pods and maize variety Volta local) were put into each o f four glass jars 
which were replicated four times and one hundred,7-14-day old unsexed adults S. 
zeamais were introduced into each glass jar to oviposit for 7 days. The 
experimental treatments were randomly arranged in a completely randomized 
design and maintained in an environmental chamber in the laboratory. Another set 
of treatments similar to the previous experimental set-up was prepared and 
maintained in wooden cages under ambient environmental conditions. After 7 
days o f oviposition, all the adult insects were sieved out with an Impact Test Sieve 
with mesh size o f 710 microns, after which all jars were left undisturbed until 
adult emergence o f the Fi generation.
4.4.3, Data collection
Emerged adults from maize were removed on a daily basis and their numbers 
counted and recorded until all o f the Fj generation had emerged. The weight o f 
adults emerging from the substrate was also taken using a sensitive Mettler 
balance Model 870 KERN. As for Parkia substrates, nothing emerged from them, 
so developmental period and mean weight could not be collected.
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4.4.4. Data analysis
Data on developmental period and mean weight o f adults emerging from Parkia 
substrates were not included in the statistical analysis. Only the developmental 
period and mean weight o f adults emerging from maize were determined.
4.4.5. Results and Discussion
The mean developmental period on maize under controlled conditions was 
significantly (P<0.05) shorter (41.2 days) than the period under ambient conditions 
(47.0 days). Comparison o f the developmental period under controlled and 
ambient conditions showed that more weevils developed in the culture placed in 
controlled conditions than those kept under ambient condition, although no 
significant differences were observed in the monthly records o f temperature and 
relative humidity under both set o f conditions during these periods. These 
differences in the development period may be due to more satisfactory 
temperature and relative humidity in the controlled conditions that favoured more 
weevil development than under ambient condition. The development period 
observed in this study fell within the range reported by several authors. 
Schoonhoven et a/.(1974) showed that the development period for weevils reared 
on maize kernels and pellets made from maize kernel fractions at 27°C and 
68%r.h. varied from 42.9-48.9 days. Similarly, Kossou et a/.(1993) and Vowotor 
et al.( 1994) found that development o f S. zeamais was 31.5 days- 52.0 days from 
egg hatch to adult emergence at 25°C and 70—75% r.h. depending on whether it is
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shelled grains or unshelled; husked or dehusked cobs, respectively. Sitophilus. 
zeamais did not reproduce at all on Parkia substrates under both sets o f conditions. 
It is clear from the present investigations that S. zeamais does not lay eggs on 
Parkia substrates, eggs were not hatched nor were larvae able to survive (no dead 
larvae were found in any o f the expiremental units). It was clear from this 
investigation that Parkia substrates is not a suitable host for the strain o f S. 
zeamais used in these studies.
4.4.6. Adult weight
The mean weight o f S. zeamais FI adults that emerged from maize variety Volta 
local under the controlled conditions (3.4mg) was not different (P > 0.05) from 
what was obtained under ambient environmental conditions (2.8mg). The mean 
weight in controlled conditions was slightly heavier than those under ambient 
conditions. The results o f this study are similar to that observed by Adams (1976) 
who reported the mean weight o f 3.1 mg for S. zeamais adults developing in 13.5% 
moisture content maize at 27°C and 70% r.h. Similarly, Vowotor (1992) recorded 
adult weights o f 3.07-3.41 mg from different varieties o f maize and 3.10-3.26 mg 
for unshelled and shelled kernels in different storage forms in a laboratory at 
25±2°C and 70± 2% r.h. Danho et al.(2002) reported the mean weight o f 3.16 and 
3.05 mg for female and male weevils developing in a laboratory at 30°C and 70%
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CHAPTER  F IVE
5.0.CONCLUSION AND RECOMMENDATIONS
5.1. Conclusion
Suitability studies on Parkia pods, pulp and seeds as alternative breeding medium 
for the survival, oviposition and development o f S. zeamais were conducted under 
two sets o f conditions, namely an environmental chamber in the laboratory and 
ambient conditions in the Screen house. The results revealed that Parkia pods, 
pulp and seeds are not suitable host for the strain o f S. zeamais used in the present 
studies. Since host suitability is an ability to survive, reproduce and grow after 
feeding on a host (Teixeira and Zucoloto, 2003) and only survival were observed 
on the Parkia pods, pulp and seeds, the results o f these studies indicate that Parkia 
pods, pulp and seeds may not act as an alternate hosts to S. zeamais. During the 
course o f the study, it was observed that some substances in the seeds (such as 
djenkolic acid and lectins) and pods (such as parkine) could be repelling the 
weevils and preventing them from settling on the them.
From this, no conclusion can be drawn that Parkia pods, pulp and seeds may act 
as alternate hosts for S. zeamais and investigation needed to be undertaken to 
determine the actual factors responsible for the unsuitability or unacceptability o f 
Parkia biglobosa as a host for S. zeamais.
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5.2. Recommendations
From this study, it is suggested that a better understanding o f the biology and 
behaviour o f S. zeamais in relation to Parkia pods, pulp and seeds will assist in the 
development o f improved management practices for the control o f this pest and so 
reduce heavy losses caused by this pest both in the field and storage. Further work 
needs to be done to investigate oviposition deterrents/inhibitors and even the 
potential o f Parkia substrates as botanical insecticides because o f the repellent 
effects that were observed during the course o f the study.
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APPENDICES 
APPENDIX 1 : Analysis of variance for relative preference of 
Sitophilus zeamais for Parkia and maize substrates.
(ambient conditions)
APPENDIX 1.1(a): Analysis of variance for twenty-four hours
Source o f variation d.f. s.s. m.s. F.cal. F. pr.
Treatments 3 488.19 162.73 8.01 0.003
Residual 12 243.75 20.31
Total 15 731.94
APPENDIX 1.2(b): Analysis o f variance for forty-eight hours
Source o f variation d.f. s.s. m.s. F. cal. F. pr.
Treatments 3 3321.69 1107.23 95.08 <.001
Residual 12 139.75 11.65
Total 15 3461.44
APPENDIX 1.3(c): Analysis o f  variance for seventy-two hours
Source of variation d.f. s.s. • m.s. F. cal. F. pr.
Treatments 3 3562.750 1187.583 212.70 <.001
Residual 12 67.000 5.583
Total 15 3629.750
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(Controlled conditions)
APPENDIX 1.4: Analysis o f variance for twenty-four hours
Source o f  variation d.f. s.s. m .s. F. c a l . F pr.
Treatments 3 85.250 28.417 2.93 0.077
Residual 12 116.500 9.708
Total 15 201.750
APPENDIX 1.5: Analysis o f variance for forty-eight hours
Source o f  variation d.f. s.s. m .s. F. cal. F pr.
Treatments 3 1226.2, 408.7 3.66 0.044
Residual 12 1341.2 111.8
Total 15 2567.4
APPENDIX 1.6: Analysis o f  variance for seventy-two hours 
Source o f  variation d.f. s.s. m .s. F. cal. F. pr.
Treatments 3 3058.3 1019.4 9.65 0.002
Residual 12 1267.5 105.6
Total 15 4325.8
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APPENDIX 2: Analysis of variance for the survival of Sitophilus 
zeamais on Parkia and maize substrates from Jan.-Feb., 2005 .
(C on tro lled  cond itions)
APPENDIX 2.1: A nalysis o f  v a rian ce  fo r w eek  one
Source  o f  v a ria tio n d.f. s.s. m .s. F .cal. F  pr,
Treatments 3 3849.69 1283.23 20.08 <.001
Residual 12 766.75 63.90
To ta l 15 4616.44
APPENDIX 2.2: A nalysis o f  v a rian ce  fo r w eek  two
Source  o f  v a ria tio n  d.f. s.s. m .s. F .cal. F  p r .
Treatments 3 13862.2 4620.8 24.80 <.001
Residual 12 2235.5 186.3
T o ta l 15 16097.7
APPENDIX 2.3: A nalysis o f v a rian ce  fo r  w eek  th re e
Source o f  v a ria tio n  d.f. s.s. m .s. F .ca l. F  p r .
Treatments 3 20789.2 6929.7 65.06 <.001
Residual 12 1278.2 106.5
To ta l 15 22067.4
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APPENDIX 2.4: Analysis of variance for week four
Source  o f  v a ria tio n  d.f. s.s. m .s. F .cal F  p r .
Treatments 3 23085.19 7695.06 91.04 <.001
Residual 12 1014.25 84.52
T o ta l 15 24099.44
APPENDIX 2.5: A nalysis o f  v a rian ce  fo r  w eek  five
Sou rce  o f  v a ria tio n  d.f. s.s. m .s. F .ca l F  p r .
Treatments 3 24950.750 8316.917 1028.90 <.001
Residual 12 97.000 8.083
T o ta l 15 25047.750
(Am bien t cond itions)
APPENDIX 2.6: A nalysis o f  v a rian ce  fo r  w eek  one
Source  o f  v a ria tio n  d.f. s.s. m .s. F .cal. F . p r .
Treatments 3 4767.25. 1589.08 24.37 <.001
Residual 12 782.50 65.21
T o ta l 15 5549.75
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APPENDIX 2.7: Analysis o f variance for week two
Source o f variation d.f. s.s. m.s. F.cal. F. pr.
Treatments 3 24454.687 8151.563 830.73 <.001
Residual 12 117.750 9.813
Total 15 24572.437
APPENDIX 2.8: Analysis o f variance for week three
Source o f variation d.f. s.s. m.s. F.cal. F. pr.
Treatments 3 24435.19 8145.06 747.54 <.001
Residual 12 130.75 10.90
Total 15 24565.94
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APPENDIX 3 : Analysis of variance for the survival of Sitophilus 
zeamais on Parkia and maize substrates from April- May, 2005 . 
(Controlled conditions)
APPENDIX 3.1: Analysis o f  variance for week one 
Source o f  variation d.f. s.s. m .s. F.cal. F pr.
Treatments 3 3757.19 1252.40 20.40 <.001
Residual 12 736.75 61.40
Total 15 4493.94
APPENDIX 3.2: Analysis o f  variance for week two
Source o f  variation d.f. s.s. m .s. F.cal. F pr.
Treatments 3 12079.2 4026.4 22.94 <.001
Residual 12 2106.3 175.5
Total 15 14185.4
APPENDIX 3.3 : Analysis o f  variance for w eek  three
Source o f  variation d.f. s.s. m .s. F.cal. F pr.
Treatments 3 19098.7 6366.2 58.00 <.001
Residual 12 1317.2 109.8
Total 15 20415.9
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APPENDIX 3.4: Analysis of variance for week four
Source of variation d.f. s.s. m.s. F.cal. F pr.
Treatments 3 19771.5 6590.5 64.43 <.001
Residual 12 1227.5 102.3
Total 15 20999.0
APPENDIX 3.5: Analysis o f variance for week five
Source o f variation d.f. s.s. m.s. F.cal. F pr.
Treatments 3 20682.69 6894.23 271.92 <.001
Residual 12 304.25 25.35
Total 15 20986.94
(Ambient conditions) 
APPENDIX 3.6: Analysis o f variance for week one
Source o f variation d.f. s.s. m.s. F.cal. F pr.
Treatments 3 6394.3 2131.4 11.78 <.001
Residual 12 2171.5 181.0
Total 15 8565.7
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APPENDIX 3.7: Analysis of variance for week two
Source  o f  v a ria tio n  d.f. s.s. m .s. F .cal.
T reatments 3 26280.69 8760.23 681.51
Residual 12 154.25 12.85
T o ta l 15 26434.94
APPENDIX 3.8: A nalysis o f  v a rian ce  fo r  w eek  th re e
Source  o f  v a r ia tio n  d.f. s.s. m .s. F .cal.
Treatments 3 25346.19 8448.73 730.70
Residual 12 138.75 11.56
T o ta l 15 25484.94
F  p r.
<001
F  p r .
<.001
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