AZADIRACHTIN INDUCED CHANGES IN FEEDING, DIETARY UTILIZATION AND MIDGUT CARBOXYLESTERASE ACTIVITY OF THE FINAL INSTAR LARVAE OF SPODOPTERA-LITURA (FABRICIUS) (LEPIDOPTERA, NOCTUIDAE)

Final (sixth) instar larvae of Spodoptera litura were fed in increasin g amounts of azadirachtin and the effects on feeding activity, dietary utilization and mid-gut carboxylesterase activity were determined. Th e antifeedant activity of azadirachtin did not increase in a dose-depe ndent manner as reflected by the decline in antifeedant effect at high er doses of 30 and 50 ppm. Dietary concentrations of azadirachtin alth ough significantly lowered the efficiencies of conversion of both inge sted (ECl) and digested (ECD) food, it failed to lower the approximate digestibility (AD). The latter however, increased significantly with increasing concentrations of azadirachtin. Feeding of higher doses (30 and 50 ppm) resulted in significant increase in midgut carboxylestera se activity. Thus insensitivity to antifeedant effects and induction o f midgut carboxyesterase activity in the older larvae of S.litura in r esponse to high doses of azadirachtin observed in this study can have adverse consequences unless particular attention is paid in developing application strategies for azadirachtin based biopesticides for use i n pest control protocols.