ACTIVTIES OF DETOXIFYING ENZYMES IN Callosobruchus maculatus(Fabricius) and Araecerus fasciculatus (DeGeer) REARED ON DIFFERENT STORED FOOD TYPES

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.