Studies on Damage by Prostephanus Truncatus (Horn) (Coleoptera: Bostrichidae) And Araecerus Fasciculatus (Degeer) (Coleoptera: Anthribidae) to Dried Yam Chips
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Date
2002-11
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University of Ghana
Abstract
In West Africa, especially Nigeria, Benin Republic, Togo and Ghana, dried yam chips
constitute an important food material. The recent introduction of the larger grain borer into
Africa and its devastating effect on cassava chips necessitated a study of the biology and
damage caused by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidea) and Araecerus
fasciculatus (Degeer) (Coleoptera: Anthribidea) on dried yam chips in Ghana. Three yam
varieties were investigated in the studies; these were: “Asaana” and “Pona” (Dioscorea
rotundata Poir) and “Afasie” (Dioscorea alata L.). The dried yam chips were obtained
following different treatments as follows: Parboiled oven-dried, Non-parboiled oven-dried,
Parboiled sun-dried and Non-parboiled sun-dried. Two hundred grammes of each treatment
of dried yam chips were placed in a glass jar and ten insects of P. truncatus and A.
fasciculatus were placed in each separately as single cultures. Mixed cultures with a starting
population of twenty insects: ten insects from each species of P truncatus and A.
fasciculatus and a control were also set up. The studies were carried out for three durations:
one month, two months and three months at 30 } 3°c and 70 - 92% R.H. The proximate
compositions of dried yam chips were also investigated before and after infestation by P
truncatus and A. fasciculatus.
P. truncatus survived and established on all the treatments processed from the three varieties
of yams. However, A. fasciculatus did not survive on oven-dried yam chips, but survived
and established on sun-dried yam chips. Ten adults of P. truncatus (age 0-7days) produced
578 progeny and ten adults of A. fasciculatus (age 0-14 days) produced 328 progeny after
three months of storage. The mixed culture with a starting population of twenty insects
produced 501 progeny (322 of P. trucatus and 179 of A. fasciculatus) after three months of
storage. Based on varietal differences, “Afasie” dried yam chips supported the highest
progeny of P. truncatus and A, fasciculatus which was significantly more than that
supported by “Asaana” and “Pona”. There was no significant difference between the number
of progeny supported by “Asaana” and “Pona”. Therefore, “Afasie” dried yam chips were
the most susceptible to infestation by P. truncatus and A. fasciculatus.
P truncatus survived and established more significantly on dried yam chips processed from
the three varieties than A. fasciculatus. Consequently, the percentage damage and weight
loss produced by P. truncatus was high. The highest percentage weight loss produced by P.
truncatus was 94.91% while A. fasciculatus produced 91.51% after three months of storage.
Parboiled sun-dried yam chips and non-parboiled sun-dried yam chips in all the varieties
used recorded the highest weight loss by P. truncatus and A fasciculatus. P truncatus
produced significant weight loss on parboiled oven-dried yam chips and non-parboiled
oven-dried yam chips for all the varieties of yam used for the studies, while A. fasciculatus
did not, as it was unable to survive and breed on these chips. Based on varietal differences,
P. truncatus and A. fasciculatus produced the highest weight loss on Afasie dried yam chips
which was significantly more than those produced on “Asaana” and “Pona”. There was no
significant difference in weight loss produced between “Asaana” and “Pona”.
The proximate composition of the varieties of yam used for the studies showed slight
differences after infestation by P. truncatus and A. fasciculatus. moisture increased
significantly, while fat, ash, protein and fibre show no significant difference after
infestation, carbohydrate, decreased significantly. Reducing and non-reducing sugars
decreases drastically after infestation. Decreases in proximate compositions may be due to
degradation and use by the insects for their biological activities.
Based on these studies, P. truncatus was found to multiply rapidly and was more destructive
than A. fasciculatus. Parboiled oven-dried yam chips and non-parboiled oven-dried yam
chips were less damaged by P. truncatus but were not damaged by A. fasciculatus. P.
truncatus and A. fasciculatus significantly damaged the parboiled sun-dried yam chips and
non-parboiled sun-dried yam chips. Also the presence of insects on dried yam chips leds to
increases or decreases in some proximate compositions. It can be concluded therefore that,
“Asaana” and “Pona” are significantly better than “Afasie” for the production of yam chips
that can be stored for longer periods.
Description
Thesis, ( MPhil) - University of Ghana, 2002