TOLERANCE OF DIFFERENT MAIZE VARIETIES AND WOOD SPECIES 
USED IN MAIZE STORAGE STRUCTURES IN THE VOLTA REGION, 
GHANA TO THE LARGER GRAIN BORER, PROSTEPHANUS TRUNCATUS 
(HORN) (COLEOPTERA: BOSTRICHIDAE)
BY
SAMUEL ADDO
DECEMBER, 1994
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(7-J46394
QLS^b'BSAAZ
~[Ue>£.s £crorO
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TOLERANCE OF DIFFERENT MAIZE VARIETIES AND WOOD SPECIES 
USED IN MAIZE STORAGE STRUCTURES IN THE VOLTA REGION, 
GHANA TO THE LARGER GRAIN BORER, PROSTEPHANUS TRUNCATUS 
(HORN) (COLEOPTERA: BOSTRICHIDAE)
BY
SAMUEL ADDO,
BSc.(Hons) Zoology, Dip. Ed.
SUBMITTED TO THE FACULTY OF SCIENCE IN PARTIAL FULFILMENT 
OF THE REQUIREMENT FOR THE AWARD OF 
MASTER OF PHILOSOPHY DEGREE IN ZOOLOGY
OF THE UNIVERSITY OF GHANA 
LEGON, GHANA
DECEMBER, 1994
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ABSTRACT
prostephanus truncatus (Horn) (Coleoptera: 
Bostrichidae), the Larger Grain Borer (LGB) has become a 
serious pest of stored maize and dried cassava chips 
since it was first seen in Ghana in 1989. Studies on the 
tolerance of maize varieties and wood species used in the 
construction of maize storage structures in the Volta 
Region of Ghana to P. truncatus were made under 
laboratory and field conditions.
Varietal resistance of maize to insects could be of 
great help to farmers, especially those who have not got 
money for chemical treatment. In field studies of 
farmers' barns, maize cobs with longer, tighter and 
stronger husks had much lower levels of LGB damage than 
others in the same barn. Selected cobs from farmers barn 
also showed that good husk is important in resisting 
penetration of LGB.
In no-choice laboratory trials, weight losses for 
local and improved maize varieties due to LGB were 
determined. The most susceptible improved variety had 6 
times the weight loss (19% in 40 days) of the most 
resistant local variety Hardness (that is seed coat) of 
grain showed no obvious relationship to resistance in 
dehusked cobs. Husk cover was significantly related to 
resistance (p= 0.005) in a laboratory trial on degree of 
husk penetration by LGB. This is likely due to physical
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qualities rather than biochemical factors as ground-up 
husks sent to the Natural Resources Institute (NRI), 
Chatham, England, showed no evidence of antifeedant 
properties.
A survey of maize storage facilities used in the 
Volta Region, showed that the platform, inverted cone and 
kitchen stores were the most widely used (51%, 18% and 
12% respectively of total stores surveyed). Other store 
types were the katchalla (grass mat store), room store 
and basket.
The survey identified 19 wood species used as 
components of these stores with bamboo (Bambusa vulgaris 
L.) and oilpalm (Elaeis guineensis Jacq.) fronds being 
the most widely used in all the agro-ecological zones.
The six most important woods (Bambusa vulgaris, Elaeis 
guineensis, Borassus aethiopium, Raphia hokerri, 
Azadirachta indica A. Juss., Chlorophora excelsa and 
Triplochiton sclerexylon K. Schum.) were chosen for 
further testing. None of these supported breeding of LGB 
in laboratory trials. However, adult LGB survived in all 
woods for 7 weeks. Farmers with LGB in their storage 
platforms may not be able to replace the wood before 
stacking the new maize. Two possible alternative 
strategies were explored: (a) leaving the platform long
enough for the adult LGB to die or (b) smoking the empty 
platform to disinfest it. Adult LGB survived in infested
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platform left in the open air for 3 months after removal 
of maize.
Smoking of LGB-infested bamboo platforms resulted in 
disinfestation of woods within 3 days with intense 
smoking and within a week when smoking was done to 
simulate farmer's cooking time of 7 hours a day alongside 
an oilpalm mat screened fireplace. However, without 
screen, smoking was ineffective: some live LGB were 
recorded even after 7 weeks.
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ACKNOWLEDGEMENTS
Much as the final work of this thesis remained to 
be mine, I wish to express my sincere and heartfelt 
gratitude to Dr. J. Allotey who supervised the various 
stages of this research, and whose pieces of advice and 
encouragement led to the successful completion of this 
thesis. My thanks also go to the other members of my 
supervisory committee, Professor W. Z. Coker and Ms. 
Millicent Cobblah for their advice on various aspects of 
the work.
I am also greatly indebted to my colleagues and 
workmates at the Ghana Larger Grain Borer Project 
(GLGBP), Ho and Accra, most of whom unknowingly were of 
immense help and were sources of inspiration during the 
period of this work. My thanks especially go to the 
following; Mr. Robin Boxall, Project leader, for his kind 
efforts in making sure laboratory equipment needed for my 
work was procured promptly anytime they were required;
Ms. J Compton, Ho Group leader, for her useful 
suggestions made on the experimental designs, reading 
through my manuscript and making useful and constructive 
criticisms; Mr Tony Ofosu for placing his great 
experience at my disposal and never tired of making 
useful suggestions; Ms P. Magrath for helping me with my 
computer work anytime I was at a loss and taking 
photographs of experimental lay-outs; the laboratory
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staff, especially Mr. Blaise Agbo who was present at all 
times to help with the laboratory analysis; Mr. Ken 
Acquaye, the Regional Post-harvest Officer for helping 
whenever necessary.
I wish also to thank, Dr. J. Compton who was on a 
short visit to Ghana for his invaluable help by looking 
through my script; Professor J. S. Djangmah, Head of 
Zoology Department, University of Ghana, Legon and Mr. K. 
Nicol, Head of Post-Harvest Development Unit, MoFA, who 
worked hard to get me a contract with the GLGBP to 
undertake the research through.
My special thanks also go to Messrs. E. K. Afari 
and V Afetorgbor, the two drivers who made my field work 
possible.
S . Addo
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December 30 1994
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DECLARATION
I declare that the work involved in this thesis for 
the degree of Master of Philosophy (Zoology) represents 
my original work and has not been previously submitted 
for any degree. All helps have been duly acknowledged.
Samuel Addo
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CERTIFICATION
I certify that this work was carried out by Mr 
Samuel Addo in the Department of Zoology, University of 
Ghana, Legon and the Ghana Larger Grain Borer Project, 
Volta Region, Ghana.
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iiv
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TABLE OF CONTENTS
ABSTRACT
ACKNOWLEDGEMENT
DECLARATION
CERTIFICATION
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF PLATES
LIST OF TABLES
GENERAL INTRODUCTION
Maize storage in the rural economy
Maize production in Ghana
Maize storage and its importance
Maize storage in the Volta Region
Insect pests and their importance in 
maize storage
LGB in Ghana
Objectives
LITERATURE REVIEW
Systematics of P. truncatus
Classification of P. truncatus
Recognition and identification of 
P. truncatus
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2.2 LGB: a review of its biology and
ecology 30
2.2.1 Distribution of LGB 30
2.2.2 Development of LGB 3 2
2.2.3 Sexual differences in development and
life span of LGB 35
2.2.4 Losses due to LGB 3 6
2.3 LGB as a wood borer 3 9
2.4 Maize varietal tolerance to post-harvest
insects 42
2.4.1 Variety and seed selection 42
2.4.2 Mechanism of varietal tolerance in
Sitophilus species 44
2.4.3 LGB and varietal tolerance 4 6
3. MATERIALS AND METHODS 4 7
3.1 Rearing 4 7
3.2 Maize variety studies 48
3.2.1 Laboratory studies 4 8
3.2. l.l Maize varietal resistance to LGB in
no-choice trials 48
3.2.1.2 Degree of penetration of husks by LGB
in no-choice trial 53
3.3 Field studies 55
3.3.1 Degree of penetration of husks by LGB
under free-choice 55
3.3.2 Free choice infestation of traditional
maize barns by LGB 55
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Page
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- X -
3.4 Maize storage woods
3.4.1 Survey of stores
3.4.2 Survival and development of LGB on 
common storage wood materials
3.4.3 LGB in storage platforms
3.4.3.1 Survival of LGB in empty storage 
platforms
3.4.3.2 Smoking of empty platforms to control 
LGB
4. RESULTS
4.1 Maize varietal studies
4.1.1 Maize varietal resistance to LGB
4.2 Free choice infestation of traditional 
maize barns by LGB
4.2.1 Relationship between infestation and 
husk factors
4.3 Maize storage structures and woods
4.3.1 Types of maize storage structures in
the Volta Region
4-3.2 Materials used in the storage structures
in the Volta Region
4.3.3 Survival and development of LGB in 
storage woods
4-3.4 Numbers of LGB in bamboo of storage
platforms
4-3.5 Survival of LGB in platforms after
removal of maize
4.3.6 Smoking storage platforms to reduce LGB
56
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Page
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Page
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DISCUSSION
Maize varietal resistance to LGB
Findings from maize varietal trials
Practical implications of the husk 
cover to the farmer
Maize storage structures and woods
Main findings on storage structures 
and woods
Practical implications of storage 
structures and wood studies
Suggestions for future research work
SUMMARY
REFERENCES
APPENDICES
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Page
LIST OF FIGURES
1. Map of Volta Region showing the position of
the Ghana Larger Grain Borer Project 3
2. Distribution of LGB in stores in the Volta
Region (1993) 20
3. Distribution of LGB in Ghana (1994) 22
4. The evolutionary tree of P. truncatus 28
5. Smoking empty platforms to control LGB :
Layout of trials 61
6. Maize storage structures in the Volta Region 77
Wood species used in the construction of
maize stores in the Volta Region 82
8. Live and dead LGB in bamboo storage wood
after removal of maize 87
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LIST OF PLATES
Experimental set-up for 40-day maize 
varietal resistance trials showing structure 
of box and tied maize cobs
Experimental set-up for 40-day maize 
varietal resistance trials: layout in the 
laboratory
Experimental set-up for degree of penetration 
of maize by LGB showing experimental cans 
with maize cobs
Experimental set-up for degree of penetration 
of maize by LGB: layout of cans in the 
laboratory
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Table Page
1. Production of maize in Ghana 9
2. Production of maize in the Volta Region 10
3. Average prices for maize in the Volta Region
(1986-1991) 13
4. Field and storage insect pests of maize 18
5. Ranking of farmers' solutions to LGB problem 23
6. Distribution of LGB in affected areas 31
7 Lower and upper limits of temperature for
the development of LGB 3 2
8. Developmental periods on different
development media 33
9. Oviposition rates for LGB on different
quantities of maize and cassava 34
10. Egg to adult development of LGB under
various environmental conditions 35
11. Weight losses in stored maize and cassava
due to LGB 3 7
12. Losses caused by Sitophilus spp.to maize in
one storage season 38
13. Survival and reproduction of LGB in woods 41
14 Characteristics of local maize varieties 48
15. Characteristics used in the classification
of husk and grains 4 9
16. Results from 7-day maize resistance trials 64
17 Results from 40-day maize resistance trials 65
18. Analysis of variance on the effect of maize
variety on weight loss inflicted by LGB in 
dehusked and undehusked cobs 6 7
LIST OF TABLES
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19. Analysis of variance on the effect of maize 
variety on weight loss inflicted by LGB in 
undehusked cobs
20. Analysis of variance on the effect of maize 
variety on weight loss inflicted by LGB in 
dehusked cobs
21. Penetration of husk of varieties of maize in
5-day no-choice condition
22. Free-choice penetration of cobs by LGB in 
traditional barn
23. Effect of husk characteristics on damage 
caused by LGB
24. Survival of LGB in storage woods
25. Numbers of LGB in infested wood after 
smoking empty platforms
Table
68
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84
Page
90
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CHAPTER ONE
GENERAL INTRODUCTION
Prostephanus truncatus (Horn) (Coleoptera: 
Bostrichidae) commonly called the larger grain borer 
(LGB) is a new and very serious pest of stored maize and 
dried cassava chips in Ghana. It originates from Central 
America and was first introduced into Africa in the early 
1980s. LGB was first noticed in the Tabora region of 
Tanzania (Dunstan and Magazini, 1981; Golob and Hodges, 
1982) and in West Africa, the outbreak of the pest was 
first recorded in 1984 (Krall, 1984; Harnisch and Krall, 
1984) It is probable that LGB was introduced into 
Africa through cereal shipments.
In Ghana, LGB was first recorded in eastern Volta 
Region using pheromone traps in January 1989 (Ofosu, 
pers. comm.) LGB is carried to uninfested areas via 
maize and dried cassava chips ("kokonte") bought at rural 
and urban markets, and via sacks which have previously 
carried these commodities. LGB may spread from one 
country to another by a similar process, especially on 
the Ghana-Togo border where there is much local movement 
of small amounts of grains across the border as head­
loads. Passengers travelling long distances by buses or 
lorries also carry small quantities of maize and cassava 
chips for gifts or personal consumption; and these 
commodities may sometimes be infested. LGB may have
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2entered Ghana from Togo either through trade or by 
flight.
The LGB problem has assumed a very serious 
dimension in Ghana. In 1992 the Ministry of Food and 
Agriculture (MoFA), in collaboration with the U.K. 
Overseas Development Administration (ODA) set up a 
project known as the Ghana Larger Grain Borer Project 
(hereafter referred to as GLGBP) to research into the LGB 
problem in Ghana and come out with appropriate 
recommendations. The GLGBP research group is based in 
the Volta region, Eastern Ghana (Figure 1) where the work 
in this thesis was carried out.
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Pigure 1: Map of Volta Region showing the location of
Ghana Larger Grain Borer Project (GLGBP) and district 
boundaries.
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4Ghanaian farmers (especially those in the Volta 
Region) see LGB as a real threat to stored maize which is 
the backbone of the economy of the small scale farmer In 
many areas, infestation in farmers' stores is getting 
worse, with the resultant change in farmers' attitude 
towards the production and storage of maize. Many 
farmers who previously cultivated maize as a cash crop 
before suffering serious LGB infestation declare that 
they will switch to other crops (Farmers meetings in the 
Volta region, pers. comm.).
The subject matter presented in this thesis 
includes:
(i) Maize storage in the rural economy
The importance of maize production and consumption 
in Ghana with particular reference to farmers in the 
Volta region. Maize in the economic and social set­
up of farmers in the northern, central and southern 
sectors of the Volta region and the forms in which 
it is stored have been treated in this section.
(ii) Insect pests and their importance in maize storage
A brief account of pests of maize before and after
storage have been documented. Other pests of maize 
including stem borers in West Africa are also looked 
at.
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5(iii)LGB in Ghana
The records of the incidence of LGB in Ghana and 
data showing trap catches and infestation in the 
Volta region. Farmer group assessments of LGB and 
of possible solutions to the LGB problem have been 
discussed.
(iv) Objectives of research
The objectives of this research have been discussed 
as; wider or long-term, short-term and specific 
objectives to meet the expectations of various 
groups which will benefit from the research 
f indings.
Chapter 2: Literature review
(i) Classification, recognition and identification of 
LGB
This section summarizes the evolutionary tree of 
LGB, characteristics and features used in the 
recognition and identification of LGB.
(ii) Biology and ecology of LGB
The distribution of LGB in various countries, 
development and losses due to LGB have been reviewed 
with current observations by GLGBP.
(iii)LGB as a wood borer
The role of LGB in infesting wood is reviewed.
(iv) Maize varietal tolerance to post-harvest pests 
In this section, maize varieties and their 
selection, varietal tolerance to LGB and Sitophilus 
zeamais Motschulsky (Col: Curculionidae) have been 
tackled.
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6Chapters 3 (Methods) and 4 (Results) form the main body 
of the thesis. These are sub-divided as follows:
(a)Laboratory studies
(i) Laboratory studies of maize varietal tolerance to 
LGB
This part of the work looked at the laboratory tests 
involving local and high-yielding varieties. Tests 
were done on their susceptibility to LGB both in 
dehusked and undehusked form over 40-day period. 
Penetration of different varieties of maize by LGB 
over a 5-day period were also investigated.
(ii) Development of LGB on common woods
Some woods used in the construction of stores in the 
Volta Region were infested with LGB under 
laboratory conditions to determine their potential 
as hosts for survival and development.
Laboratory studies to determine the survival and 
development of LGB in some selected woods.
(b) Field studies
(i) Survey of materials used in traditional storage 
structures
Various types of storage structures for maize in the 
Volta Region of Ghana were documented. In each of 
the districts covered, wood species used in the 
construction of the stores were recorded.
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7(ii) Maize storage studies
Ewe raised platform type stores were investigated by 
looking at the pattern of infestation by LGB under 
free-choice condition and the influence of husk and 
grain type on damage levels.
(iii)LGB in storage platforms
The survival of LGB in empty infested maize storage 
platforms was recorded over a period of time to 
assess the period of survival in platforms.
Materials and methods used in smoking of LGB- 
infested platforms under different experimental 
conditions as a way of disinfesting the storage 
woods were reported in this section.
Chapter 5
This deals with the discussion of results, 
recommendations from work done and suggestions for 
future work.
1.1. Maize storage in the rural economy
1.1.1 Maize production in Ghana
Maize is an important crop in the domestic economy 
of the Ghanaian. The production of maize cuts across all 
the regions of Ghana. Two crops a year ("major" and 
"minor" season maize) are produced in most areas, but in 
some areas there is only one season which may be 
variously attributed to a unimodal rainfall pattern, 
incidence of stem borers or farmers involved in other
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lucrative crops. Maize and cassava are the major staples 
of Ghana and are grown almost everywhere in the country, 
but the bulk of the maize is grown in Brong Ahafo,
Ashanti and Eastern Regions. Of the total area of 3 
million hectares under cultivation, maize covers 400,000 
ha. and accounts for 50-60% of total production of 
cereals. The average annual yield estimate for the 
period 1986-90 is 605,000t. Root and tubers (cassava, 
yams, sweet potato, cocoyam, etc.) are cultivated over an 
area of about 60% of the total area under cultivation 
(Dixon and Ocansey, 19 88)
Maize production figures in 1993 have increased by 
six times since 1990 according to the estimates of the 
Policy Planning Monitoring and Evaluation Department 
(PPMED) of the Ministry of Food and Agriculture.
National maize production figures are shown in Table 1.
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9Table 1. Production of maize in Ghana
Year Production figures 
('000 metric tonnes)
1983 141
1984 575
1985 411
1986 559
1987 553
1988 600
1989 715
1990 553
1993 961
Source: PPMED (MoFA), 1993 .
In the Volta region production of maize is high 
compared to national output. Figures of maize production 
in the Volta region between 1986 and 1991 and the 
proportion to national production levels are given in 
Table 2.
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10
Table 2: Production of maize in the Volta region
Year Total production 
( ' 000 metric t .)
% Share in terms of 
national production
1985 54 . 0 10
1987 53 .4 9
1988 42.0 7
1989 80 . 4 11
1990 91 . 5 17
1991 116 . 3 13
Source: PPMED (MoFA), 1991.
Maize is very important in the diet of the Ghanaian
especially in the southern part of the Volta region where 
foods such as 'akple' (thick maize porridge), and kenkey 
(steamed, fermented maize dough) are taken every day As 
maize can be stored longer than root crops, it is 
important during the lean season.
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11
Nyanteng and van Apeldoorn (1971) have identified 
some factors which influence the storage of maize in 
Ghana. These factors come under two main categories; 
positive and negative. On the positive side the reasons 
given are:
(i) storing for consumption by the farmer and his 
family;
(ii) storing as seed for the next planting season;
(iii)storing to await higher prices; and
(iv) storing as a means of saving.
The negative factors include:
(i) infrequent visits by buyers, or no buyers at all;
(ii) infrequent marketing opportunities elsewhere;
(iii)lack of transport or poor roads;
(iv) credit arrangements which in some cases force 
farmers to store.
In areas where prices increase throughout the year, 
farmers tend to hold back substantial quantity of their 
grain in order to take advantage of price rises 
(Southworth et al., 1980). This trend in price hikes is 
seen in some maize markets in Ghana especially maize 
deficit areas where maize prices can increase by over 
200-300% from the main harvest to the lean season.
1.1.2 Maize storage and its importance
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12
A rapid survey of representative villages in the 
Volta Region (Ghana Larger Grain Borer Project (GLGBP) 
1993a) showed that maize is the most important cash crop 
for many farmers, especially in the former cocoa-growing 
areas of the Jasikan, Kadjebi and Hohoe districts. The 
cocoa and coffee trees have become overgrown and 
financial returns from cocoa farms are very low, trees 
had been cut down and replaced with maize as a cash crop. 
In some areas of the region, maize is a major staple and 
is depended on throughout the year.
A crop budget for the production of maize under the 
traditional and partially mechanised technologies showed 
that it is profitable to produce maize and Volta region 
ranks first in terms of profitability of cereals 
including maize (FAO, 1986) .
Average retail prices (in cedis) for a unit bowl 
(2.5 kg.) of maize in the Volta region are given in Table 
3 .
1.1.3. Maize storage in the Volta region
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1 J
Table 3: Average prices for maize in the Volta region 
(1986-1991)
Year Average price 
(cedis/2.5 kg bowl)
1986 82
1987 124
1988 175
1989 146
1990 260
1991 298
Source: Kartey, 1992
Maize storage by farmers in the Volta region is 
becoming more lucrative every year. PPMED analysis on 
average maize prices for Volta region show seasonal price 
spreads ranging from 73% to 293% for the period 1986- 
1991. These price increases are significant even when 
one takes into account the rate of inflation which was 
usually 13-40% per annum over the same period (Magrath, 
1994)
A GLGBP survey of four markets: Ho, Kpeve,
Brewaniase and Dodo Amanfrom from September 1993 to July 
1994, also showed seasonal price spreads from 210% to as 
high as 320-s with an average of 236% for the four markets 
(Magrath and Compton, 1 9 9 4)
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14
In the northern parts of the Volta Region, which 
include the Kete Krachi and Nkwanta districts (see Figure 
1), the major staple is yam fufu, consumption of maize is 
low and small quantities are mixed with kokonte. Maize 
however plays an important role since it is one of the 
main cash crops of farmers in this area. In certain 
parts of the Kete Krachi district, around Dormabin, maize 
is a second staple and a major cash crop.
In the Kpando and Ho districts (see Figure 1) maize 
is harvested twice a year, so most farmers dispose of 
major season maize early when they expect the minor 
season maize to be good. The major season crop is 
harvested between July-September and the minor season 
harvest occurs from December to January Most farmers 
store maize up to 10 months in order to get higher market 
prices during the lean season. Although cassava fufu is 
the main staple of the people in this area, maize is 
gradually becoming more important in the diet in the 
southern part of Ho district.
The southernmost part of the Volta Region takes 
into account the coastal savannah zone (see Appendix 7) 
This includes Ketu, Akatsi, and North and South Tongu 
districts (see Figure 1) where maize is the major staple 
(except for those along the Volta lake who eat a lot of 
kokonte) The greater part of this zone is a maize 
deficit area.
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15
Maize is stored in different traditional ways. In 
Northern Ghana, maize is stored in mud silos and in 
Ashanti and Brong Ahafo regions most of the maize is 
stored in bags (Ofosu, 1987). In much of the northern 
part of the Volta Region, maize is stored as dehusked 
cobs in a 'katchalla', which is a large basket made from 
' zana grass' (Andropogon gayanus) (see Appendix 5) .
In central and southern Volta region, maize in the husk 
is stored in the "Ewe barn" (raised platform or inverted 
cone) type (see Appendix 5). In the forest zones of the 
Volta region where the rainfall is quite heavy during the 
harvest time kitchen stores where maize is packed in the 
loft above the fireplace are very common. The idea is 
that the fire lit beneath the platform should accelerate 
the drying process.
Most farmers aim to store major season maize for 
almost 9 months (August to May) to serve as a food 
reserve during the lean period of February to June.
Farmers with substantial surplus also store for this long 
period so as to fetch higher market price for the 
commodity (Magrath, 1993) .
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16
The revenue from storage is very vital since it 
helps in the preparation of new maize fields, pay fees of 
dependants and as a savings to meet other family and 
social commitments. In some areas very large barns 
standing in the compound is a source of pride and 
portrays the wealth status of the farmer, and in some 
cases it determines the potential of a farmer to get a 
new spouse (personal communication with maize farmers in 
Hohoe, Ketu and Kpando districts).
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17
Food commodities in tropical Africa are usually 
infested with insect pests either from the field before 
harvest or through poor post-harvest storage systems.
The activities of these pests which the peasant farmer 
has to cope with, lead to substantial losses of food 
commodities especially in the sub-Saharan regions of 
Africa (Hall, 1970; Adams, 1977, Allotey, 1991, 1993) .
Insect pests in stored food commodities belong to two 
major groups; the Coleoptera and Lepidoptera, with the 
beetles being the dominant group. These insects are the 
most important agents of storage losses in the tropics 
where they play a dominant role in the biodeterioration 
of stored grains. The storage environment in the tropics 
is often highly favourable for insect growth and 
development all the year round (Semple, 1982). Maize 
storage insect pests, earworms and other stem borers in 
tropical Africa are shown in Table 4.
1.2. Insect pests and their importance in maize storage
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Table 4: Most important field and storage insect pests of 
maize in West Africa
Insect species Order Family
Pre-harvest Dests
Sitophilus zeamais Motschulsky Coleoptera Curculionidae
Sitophilus oryzae (Linnaeus) Coleoptera Curculionidae
Sitotroga cerealella (01.) Lepidoptera Gelechiidae
Sesamia calamistis Hampson Lepidoptera Noctuidae
Eldana saccharina (Wlk.) Lepidoptera Pyralidae
Mussidia nigrivenella Rag. Lepidoptera Pyralidae
Cryptophlebia leucotreta (M.) Lepidoptera Tortricidae
Tribolium castaneum (Herbst) Coleoptera Tenebrionidae
Ephestia cautella (Wlk.) Lepidoptera Phycitidae
Post-harvest orimarv Dests
Rhizopertha dominica (Fab.) Coleoptera Bostrichidae
Dinoderus minutus (Fabricius) Coleoptera Bostrichidae
Prostephanus truncatus (Horn) Coleoptera Bostrichidae
Sitophilus zeamais Motschulsky Coleoptera Curculionidae
Secondarv Dost-harvest Dests
Oryzaephilus spp. Coleoptera Silvanidae
Carpophi1 us spp. Coleoptera Nitidulidae
Cryptolestes ferrugineus (S.) Coleoptera Cucuj idae
Cathartus quadricollis G-Men. Coleoptera Silvanidae
Ref: Mould, 1973; Hodges, 1984; Allotey, 1991; Schultess 
et al., 19 91; Gounou et al. , 19 9 4 ;
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Maize in the field in some parts of Ghana (for 
example around Dodi Papase in the Kadjebi district of the 
Volta Region) has also been observed to be infested with 
bamboo borers such as Dinoderus spp. before harvest 
(personal communication with District Post Harvest 
Officer in charge of Kadjebi district). Maize coming in 
from the field sometimes has high levels of Sitophilus 
spp. infestation, and appreciable numbers of Cathartus 
quadricollis, Tribolium spp., Carpophilus spp. and 
Cryptolestes spp. Usually cobs from the field have high 
earworm (Lepidoptera) attack especially for major season 
harvests (personal observation of cobs and laboratory 
cultures)
1.3. LGB in Ghana
LGB was first recorded in eastern Volta region 
using pheromone traps. A 1989 survey showed that LGB was 
present in villages along a 150km stretch of border with 
Togo from Kpetoe in the south to Ameyoe in the north 
(Dick et al., 1989). By 1993, a GLGBP survey showed that 
LGB was present in all the districts of the Volta Region 
(GLGBP, 1993a) (refer to Figure 2) .
LGB is also spreading to other regions of Ghana.
Its presence in Greater Accra was first confirmed by 
Allotey (1993)
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Figure 2: Oistributior of LGB in ".tore
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National monitoring of LGB in which every district 
had at least one trap set every fortnight revealed how 
serious the LGB situation is in Ghana. By September 
1994, LGB had been trapped in all the regions of Ghana 
(Boxall, 1994) (refer to Figure 3). The most affected 
part of the country apart from the Volta Region are the 
Saboba district of the Northern region, the Dangbe West 
district of Greater Accra and the areas of the Eastern 
Region bordering Volta Region. LGB has also been found 
in maize and dried cassava chips in the Upper West 
Region, south of Wa (Robin Boxall, pers. comm.).
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r i gut 6 3 O i s t r  i  b u t  i o n  o f  1. G {• i n  G l'i 3 1 )«ft.
Sou rce , ;  B o x u l l ,  jc jq^  i'•-ip ii'te* Lu-fi prate* fc #
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A group of small-scale farmers was interviewed 
during a participatory training workshop of staff of 
GLGBP (1993b). One group of farmers ranked perceived 
solutions to the LGB as shown in Table 5.
Table 5: Ranking of farmers' solutions to LGB problem
Rank Solution Criteria used
1 Use Actellic Super 
dust to treat maize
Very effective, easy 
to apply.
2 Use of 'Phostoxin' 
(Phostoxin tablets)
Very effective, easy 
to apply.
3 Using Actellic 25EC Effective for all 
other insects except 
LGB, costly and not 
easy to formulate
4 Shell maize early 
and bag untreated
Quite effective for 
some insects but not 
LGB
5 Use of neem leaves No cash cost but not 
effective against LGB
6 Frequent sun drying Has some effect on 
fast-moving insects 
like weevils
7 Smoking of barns Effective for other 
insect pests but not 
LGB
* Note: Farmers were unaware of chemical hazards.
Source: 
data.
S. Addo, P Magrath and P Ahiable, unpublished
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The current recommendation by the Postharvest Unit 
of Ministry of Food and Agriculture (MoFA) is to shell 
the maize and treat with the chemical protectant called 
"Actellic Super" which is a dust containing 1.6% 
pirimiphos-methyl and 0.3% permethrin. Although Actellic 
Super is very effective, it is hardly used by most 
farmers because of its cost. Some farmers complain of 
lack of sacks and storage space. Farmers who readily 
accept the use of Actellic Super are mostly those who 
have already experienced severe LGB attacks to their 
stored maize.
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1.4 Objectives
The long-term objective of this research is to help 
in understanding maize storage problems in Ghana, 
establish the missing but important facts about the 
larger grain borer, thus enabling better pest management 
tactics against this destructive insect pest in Ghana.
The peasant farmer is the target, having to take a new 
look at his present way of maize storage in order to 
avoid high losses from larger grain borer attack. The 
research is also intended to assist the Post Harvest 
Development Unit and Plant Protection and Regulatory 
Services, and research institutions on what policies to 
implement in the control of LGB. The outcome of this 
project will also assist the government and the Ministry 
of Food and Agriculture to save our major maize producing 
areas of Brong Ahafo, Ashanti, Northern and Eastern 
Regions from the LGB menace.
The short-term objectives are to:
(i) look for alternative non-chemical methods for 
protecting maize and storage woods against LGB.
These methods should be accessible to the low-income 
farmer and on the national level, save foreign 
exchange,
(ii) identify maize varieties and maize storage woods 
which are resistant to LGB infestation and can be 
used by the farmer
45
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For this purpose, the investigation was designed 
with the following specific objectives in mind:
(i) to investigate the susceptibility of selected maize 
varieties to the larger grain borer under no-choice 
laboratory conditions including:
(a) effect of maize husk type,
(b) effect of grain type,
(c) rate of penetration of husk.
(ii) to investigate the susceptibility of maize varieties 
held under 'free choice1 conditions in traditional 
stores in the Volta Region.
(iii)to identify the main maize storage structures and 
wood/plant species used as components in store 
construction in the Volta Region of Ghana.
(iv) to undertake laboratory studies to assess the
survival and development of larger grain borer in
woods and other materials commonly used in storage 
structures.
(v) to undertake a scientific study of smoking of LGB-
infested storage platforms as a traditional method
of disinfestation.
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CHAPTER TWO
LITERATURE REVIEW
2.1. Svstematics of P. truncatus
2.1.1. Classification of P. truncatus
A full account of the systematics of P. truncatus 
and other bostrichids was given by Potter (1935). The 
evolutionary tree of LGB is shown in Figure 4.
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Figure 4: The evolutionary tree of P. truncatus
Coleoptera
Polyp laga j
Bostrichoidea
Ptinidae Anobiidae Bostrichidae Lycticidae Psoidae~|
Dysidinae Psoinae
Dinoderitae Bostrichitae Lyctitae J
Bostrichinae Endecatominae
Dinoderinae
1= Boving and Craighead, 1930; CSIRO, 1970; Arnett, 1971 
2= Lesne, 1924 (not currently accepted)
3= Lesne, 1924
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2.1.2. Recognition and identification of P. truncatus
Keys relating to the identification of P. truncatus 
and other bostrichids are that of Fisher (1950) and, to a 
lesser extent, those of Kingsolver (1971) and Hodges 
(1986) Detailed descriptions of adults (Horn, 1878; 
Lesne, 1897) and the larva and pupa (Spilman, 1984) have 
been used extensively in works involving P. truncatus. 
Adults may be sexed using clypeal tubercles (Shires and 
McCarthy, 1976) and pupae according to the size and 
shapes of the genital papillae (Bell and Watters, 1982) .
The adults of LGB can be distinguished by the 
following features (Haines, 1991):
typical bostrichid shape, the body cylindrical and dark 
brown to black in colour
the head is ventral to the prothorax.
the pronotum bears rows of teeth on the anterior part. 
the antennae are 10-segmented and have a loose three- 
segmented club.
the funicle is slender and clothed with long hairs, 
posteriorly, the elytra are flattened and quite steeply 
inclined.
the tarsi are all five-segmented.
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Larvae of bostrichidae can be distinguished by the
following features:
body C-shaped (grub-like or scarabaeiform) 
head retracted into prothorax.
mesotergum, metatergum, or abdominal terga are all 
divided into 2 or 3 folds.
-abdominal spiracle VIII smaller or larger than other 
abdominal spiracles
spiracles oval or circular
setae simple, hairlike, not flat not dense.
2.2. LGB: a review of its biology and ecology
2.2.1. Distribution of LGB
LGB was first noted in Central America including 
Mexico, tropical South America and the southern region of 
the United States of America (U.S.A.) (Chittenden, 1911). 
Quite recently LGB has spread to a number of African 
countries and there is evidence of the pest in the Middle 
East. Various reports of this beetle have been 
summarized in the reviews of Howard (1983); Krall,
(1984); Hodges (1986); Dick, (1988); Golob, (1988); Dick
et al., (1989) and Markham et al., (1991).
Records of the pest in various areas have been
documented as shown in Table 6 below:
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Table 6 : Distribution of LGB in affected areas.
Country Reference
The Americas
U.S.A. Chittenden, 1911*
Back and Cotton, 1922*
Guatemala Cotton and Good, 1937*
Peru Wright, 1984
Honduras, El Salvador McGuire and Crandall, 1967*
and Panama
Nicaragua Giles and Leon, 1975
Costa Rica Fisher, 1950*
Brazil Cotton and Good, 1937*
Colombia Posada et al., 1976*
Mexico Chittenden, 1911;*
Delgado and Hernandez Luna, 
19 51*;
Quintana et al., 1960*
Middle and Far East
Israel Calderon and Donahaye, 1962*
Iraq Al-Sousi et al., 1970*
China Lesne, 1939*
Hong Kong Zimmerman, 1990
India Verma and Lai, 1987;* 
Verma et al., 1988*
Africa
Tanzania Dunstan and Magazini, 1981; 
Golob and Hodges, 1982
Togo Krall, 1984; Harnisch and Krall, 
1984
Kenya Kega and Warui, 1983
Burundi Golob, 1988
Ghana Dick et al., 1989
Burkina Faso Bosque-Perez et al., 1991
Nigeria Pike et al., 1992
* Cited in Markham et al. , 1991
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LGB is becoming a major pest problem, especially in 
the last decade in tropical Africa Dunstan and Magazini, 
(1981); Dick et al., (1989); Pike et al., (1992). The
mechanism of arrival of LGB in a previously uninfested 
area is not thoroughly understood, but it is believed 
that most of the spread is through trade. Most major 
market centres in the Volta Region, with high influx of 
traders have been among the first areas in the region to 
become infested with LGB (personal observation of 
markets)
2.2.2. Development of LGB
The optimum conditions for LGB development on maize 
are 32°C and 70-80% relative humidity (r.h.) (Shires,
1979, 1980; Bell and Watters, 1982; Hodges and Meik,
1984) The life cycle of LGB can be completed within a 
fairly wide range of temperature and r.h. as shown in 
Table 7.
Table 7- Lower and upper limits of temperature for the 
development of LGB
R.h. Lower Upper Source
(%) (°C) ( C)
40 25 32 Bell and Watters, 1982
70 18 37
Under optimum conditions of temperature and r.h., 
the medium on which LGB is reared influences the 
developmental period, as shown in Table 8.
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Table 8: Developmental periods of LGB on different 
development media
Development
media
Life cycle 
(days)
Source
Whole grain 24-25 Bell and Watters, 1982
Packed flour 24-25 Bell and Watters, 1982
Loosely packed flour 35 . 4 Shires, 1979, 1980
Differences in the developmental period were 
attributed to the degree of packing of the development 
medium. Bell and Watters (1982) observed that in firmly 
packed flour the larvae made narrow tunnels against which 
they could brace themselves and hence were able to force 
their mandibles into the forward end of the tunnel for 
effective chewing. In low density media, the tunnels 
were wider and larvae often twisted back and forth 
without moving their heads, and this useless expenditure 
of energy may have retarded their growth rate.
Oviposition in LGB has been reviewed by many 
authors (Hodges, 1982; Howard, 1983; Markham et al.,
1991) Neat round holes are made as a result of adults 
boring into maize grains and large quantities of maize 
dust are produced. Adult females lay most fertilized eggs 
within the grain, in blind-end chambers bored at right 
angles to the main tunnel (Hodges, 1982; Howard, 1983) 
Oviposition on stabilized grain and maize cob is more 
productive than on loose grain as oviposition periods
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become longer (sometimes equal in length to the life of 
the female) on loose grains (Cowley et al. , 1980) .
Howard (1983), studying this in more detail, worked 
with adult pairs confined to damaged grains embedded in 
maize flour and maintained at 25°C and 70% r.h. Under 
these conditions, pre-oviposition was about 5 days, 
average length of oviposition period 14 weeks and mean 
life-time fecund period as high as 114 days. Even higher 
figures were reported for LGB confined to simulated cobs 
at 30°C and 70% r.h., when the life-time egg production 
averaged 430 and two individuals each laid over 600 eggs 
(Howard,1983)
The quantity of food provided for LGB may influence 
the rate of oviposition, as shown in Table 9.
Table 9: Oviposition rates for LGB on different 
quantities of maize and cassava
R.h. Temp. Quantity of Number of
(%) (°C) food (g/LGB) eggs laid/day
Maize
70 27 l
6
Cassava
70 27 i
6
1 . 4
3 . 9
1 . 1
2 . 3
Source: Nyakunga, 1982
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Larvae hatch from eggs after about three days at 
27°C and 70% r.h. and seem to thrive on the dust produced 
by boring adults. The egg to adult development time of 
LGB is influenced by environmental conditions as shown in 
Table 10.
Table 10: Egg to adult development of LGB under various 
environmental conditions.
Food
media
R.h.
(%)
Temp. 
(°C)
Period
(days)
Source
Maize flour 70 32 25 - 4 Bell and Watters, 
1982
Cassava 70 27 43 .1 Nyakunga, 1982
Maize grain 
(America No.3)
70 27 39.2
2.2.3 Sexual differences in development and life span of 
LGB
Hodges et al. (1985) found some differences in
emergence time between the sexes developing on dried 
cassava. At 70% r.h., the females emerged at an average 
of one half day after the males, while at 50% r.h., the 
difference was more substantial, females emerging on 
average 1-2 days after the males.
Shires (1980) found that on maize flour at 32°C and 
80% r.h., females generally out-lived males, the mean 
life expectancies being 61.S days and 44.7 days for 
female and male respectively. In contrast at 25°C and
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70% r .h ., on maize flour and grains, males were found to 
outlive females (Howard, 1983) These differences in 
female longevity may be due to different oviposition 
rates; the females in Howard's studies having a much 
higher rate, hence a shorter longevity
2.2.4. Losses due to LGB
Larger grain borer appears to cause very high 
weight losses within a few months of maize storage. The 
average weight losses in stores for maize and cassava are 
shown in Table 11
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Table 11: Weight losses in stored maize and cassava due 
to LGB
Country Storage 
period 
(months)
Storage
form
% wt. 
loss
Reference
Weiaht losses due to LGB in maize
Nicaragua 6 cob 40 Giles and Leon, 
1975
Honduras 3-6 cob 30 Hoppe, 1986
Tanzania 3-6 cob 34 Hodges et al. , 
1983
6 cob 17 . 9 Keil, 1988
8 cob 41.2
Togo 8 cob 44 . 8 Pantenius and 
Schulz, 1986
Ghana 6 cob 14-20 Golob, Addo and 
Harding,
unpublished data
Weiaht losses due to LGB in cassava chips
Tanzania 4 dried
tubers
70 Hodges et al. , 
1985
Togo 3 dried
tubers
9 7 Wright et al., 
1993
7 dried
tubers
19 . 5
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By comparison, damage in traditional storage 
systems (on the cob) caused by more common storage pests 
such as Sitophilus spp. is typically much lower, as shown 
in Table 12.
Table 12: Losses caused by Sitophilus spp. to maize in 
one storage season
Country Species % wt. 
loss
Reference
Zambia S. oryzae 2-6 Adams, 19 77
Kenya S. zeamais 3-5 De Lima, 1979
Malawi S. cereallela 2-5 Golob, 1981
The most obvious cause of loss in LGB attack is the 
conversion of maize grain into flour by adult boring 
rather than consumption by the larvae during the course 
of development. Large quantities of dust are associated 
with infested maize cobs (Hodges et al., 1983). The 
production of dust and frass by LGB is much higher than 
with S. zeamais. Farmers in Ghana as in Togo (Compton, 
1991) reject for human consumption the large amounts of 
flour' produced by LGB. LGB is less efficient at 
utilization of its diet than S. zeamais and may produce a 
lot of dust from maize grains when feeding (Demianyk and 
Sinha,1987) and this may explain the higher weight 
losses.
As might be expected, insect damage to maize is 
reflected in economic loss. A study of the relationship 
between maize retail price and the degree of insect
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infestation was carried out by GLGBP In this study, 
groups of maize traders were presented with a range of 
bowls containing previously-prepared maize samples of 
known damage levels. Four markets in the Volta Region 
were used. The percentage of damaged grains in the 
sample due to damage by LGB and Sitophilus spp. had a 
consistent relationship to retail price. The 
relationship appeared almost linear, with about a 0.75% 
drop in retail price for every 1% increase in damaged 
grains (Compton, 1993, 1994)
2.3. LGB as a wood borer
The presence and behaviour of LGB in various woody 
materials have been of interest to many workers on the 
biology of the LGB because of the idea that these 
materials might be potential alternative hosts and thus 
sources of infestation. A considerable amount of work on 
LGB in woody materials has been performed and has shown 
that while some wood species only allow for survival of 
adults, others actually support reproduction.
Earlier works on the survival and reproduction of 
LGB in wood were undertaken in Mexico, Honduras, Togo and 
Benin. Recent studies using pheromone traps show that 
the larger grain borer is widespread in natural 
vegetation in Tsavo National Park, Kenya. Laboratory and 
field experiments to determine alternative hosts of LGB
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have shown it capable of feeding and breeding in tree 
species in the families Leguminoceae, Sterculiaceae, 
Euphorbiaceae, Burseraceae and Anacardiaceae (Nang'ayo 
al. , 1993 ; Nang'ayo and Hill, 1994) These works have 
been summarised in Table 13 below.
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Table 13: Survival and reproduction of LGB in woods.
Country Wood species Reference
Woods suDDortina survival
Mexico Schinus molle 
Prosopis spp
Rios Ibarra, 1991
Honduras Spondias purpurea Wright and 
Novillo1, 
unpublished 
observat ion
Mexico Bursera fagaroides 
Spondias purpurea
Ramirez et al., 
1991
Woods suDDortinq reproduction
Togo & Benin Manihot esculenta 
Poincinia regia
Helbig et al. , 
1990
Benin Tectona grandis 
Fagara xanthoxyloides 
Azadirachta indica 
Mallotus oppositifolius
Kossou, 1992
Kenya Commiphora campestri 
Commiphora riparia 
Commiphora spp. 
Euphorbia tirucalli 
Delonix regia 
Cajanus cajan 
Acacia mellifera 
Cassia abbreviata 
Cassia siamea 
Prosopis spp. 
Leucaena spp. 
Calliandra spp. 
Lannea spp.
Sterculia africana
Nang'ayo et al., 
1993.
1= Cited in: Markham et al. , 1991
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The breeding success of LGB is dependent upon the 
wood's age, and its moisture content (Nang'ayo et al. , 
1993). LGB breeding in wood under different constant 
humidity regimes confirms that breeding occurs within a 
relatively narrow range of wood moisture content, with an 
optimal range at around 10-12% (Nang'ayo and Hill, 1994) 
Nang'ayo and Hill (1994) also observed that the 
proportion of immatures and adults in LGB populations of 
susceptible wood species is quite different, suggesting 
that LGB has different growth characteristics on 
different host plants.
2.4. Maize varietal tolerance to postharvest insects.
2.4.1 Variety and seed selection
Farmers in the Volta Region tend to use local maize 
varieties for storage and planting . A major problem 
with the adoption of high-yielding maize varieties has 
been the high level of damage due to S. zeamais sustained 
by high-yielding varieties in storage (Kossou et al., 
1993a) Some improved varieties grown in Africa, for 
example, SR52 selected in Zimbabwe, also suffer severe 
damage from larger grain borer (Keil, 1988) .
In some Southern African countries, where marketing 
boards until recently offered good prices for maize, 
farmers are growing both the local and high-yielding
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varieties. The high-yielding varieties are grown for 
immediate sale to the marketing boards while the 
traditional, low-yielding but storage durable varieties 
are grown for home consumption (Adams and Harman, 1977; 
Hindmarsh and Macdonald, 1980; Giga and Katerere, 1986; 
cited in Coulter and Compton, 1991) .
Improving resistance of maize to storage insects, 
especially LGB, could be of immense value in rural 
storage system and it will serve as an additional weapon 
in pest control strategies. Farmers already take storage 
pest resistance into account when selecting their 
planting materials. In Mexico and Central America, 
farmers are happy with the local "criollo" varieties, 
which they feel are somehow resistant to LGB (In: Markham 
et al. , 1991) . This may possibly have influenced the 
lower damage levels experienced in the region. In the 
Ashanti Region of Ghana, Nyanteng (1972) observed that a 
local maize variety (called 1Mampong maize') is preferred 
to other maize types because the grains have a hard testa 
which most storage insect pests find difficult to 
penetrate. Surveys on farmer practices in the Moroceli 
and Jamastran provinces of Honduras have similarly shown 
that the criteria for cob selection include: tightness of 
husk, coverage, freedom from damage, cob size and weight 
of cob (Espinal, pers. comm.)
In the Volta Region of Ghana there are two basic 
strategies tor seed selection. Some farmers select cobs 
(with good husk cover) at harvest and store this
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Similarly, Appiah (1980) who looked at the 
susceptibility to attack by rice weevils (Sitophilus 
oryzae) of four maize varieties, 'Composite 4 , La 
Posta1, 'Golden Crystal' and a local, in a laboratory 
experiment reported that La Posta was the most resistant 
variety in terms of percentage of damaged kernels, 
viability of grains, least population increase of 
weevils, grain weight loss, fat acidity production and 
moisture after a 12-week infestation period.
In maize, the value of a complete, well fitting set 
of husks for reducing pre-shelling infestation by 
Sitophilus spp. has been recognised by post-harvest 
scientists for many years (see e.g. Giles and Ashman,
1971; Dobie, 1977) However, the detailed effects of 
husk cover have only been examined recently (Kossou et 
al., 1993a)
The effect of husk cover has also been examined in 
a lot of experiments. In one of these trials, the 
susceptibility of cob maize to maize weevil, S. zeamais, 
in field and traditional storage systems between two 
international improved maize varieties introduced into 
the Republic of Benin, one partially improved local 
variety and a local variety obtained from farmers were 
looked at. Results showed that the international 
improved varieties had significantly higher yield but had 
significantly poorer husk cover. Due to their superior 
husk cover, local varieties were significantly more 
resistant to weevils when infested in the traditional,
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