Abstract:
In order to adapt to the toxic compounds of plant origin which they constantly encounter
during their feeding activities, insects have enzymes which facilitate detoxification. Such
enzymes include glutathione-S-transferase (GST) and acetylcholinesterase (AChE). In this
study, the activities of these two detoxifying enzymes, in two storage insect
pests,Callosobruchus maculatus (Fabricius) (Bruchidae) (cowpea weevil)and Araecerus
fasciculatus(Anthribidae) (De Geer) (coffee bean weevil)were assessed by rearing these
insects on different foods. C. maculatus was reared on four varieties of cowpea; Vigna
ungniculata, namely, Oloyin, Ife brown (IFBV), Kanannado (KDV) and Sokoto. A.
fasciculatus was reared on yam chips, cassava chips, cocoa beans and maize. The adult insects
emerging from each food item were subjected to enzyme assays using standard methods. The
Results show that the sex of the insects and the food type on which the insects were raised
greatly affect enzyme activities. AChE and GST activities in C.maculatus and A.
fasciculatusvary significantly among the sexes of the insects and food types. Female bruchids
reared in KDV had the highest AChE activity (0.00896mmol/minmg) and those reared in
Sokoto variety had the least AChE activity of 0.000908mmol/minmg; among males, IFBV
bruchids had the least AChE activity (0.00605mmol/minmg) while bruchids from Oloyin had
the highest AChE activity (0.0103mmol/minmg). Female C.maculatus reared in KDV had the
least GST activity (12.210mmol/minmg) and those reared in IFBV had the highest GST
activity (52.696mmol/minmg). For males, bruchids from Oloyin had the least GST activity
(15.739mmol/minmg) while those from Sokoto had the highest GST activity
(54.979mmol/minmg). Among food types, maize caused the highest AChE and GST activity
in A. fasciculatus. In C.maculatus, the highest AChE activity was observed when reared
inIFBV while the highest GST activity was observed in insects reared in Sokoto. These have
implications on the control of these storage pests. The knowledge of the detoxification of
toxic and anti-nutritional compounds in foods is important in developing integrated pest
management techniques because this will helpto combat resistance in insects.
