THE EFFECT OF NEEM ALLELOCHEMICALS ON NUTRITIONAL PHYSIOLOGY OF LARVAL SPODOPTERA-LITURA

Neem allelochemicals azadirachtin, salannin, nimbinene and nimbin were administered to different larval instars of the tobacco armyworm, Spo doptera litura orally in artificial diet, topically or via injection. Nutritional analyses revealed strong antifeedant and growth regulatory effects of azadirachtin which were independent of each other. While s alannin and nimbinene induced concentration dependent feeding deterren ce only; nimbin was inactive to the 1000 ppm level against this insect species. One of the causes of the reduced growth rate of azadirachtin treated insects was due to an increase in the costs associated with g rowth. This was relative to a drastic reduction in the activity of gut trypsin. Salannin and nimbinene, however, did not interfere with the trypsin activity of the gut. These results and those from nutritional studies suggest that salannin and nimbinene have no toxicity mediated effects on S. litura larvae and antifeedant activity is a result of th e effects on deterrent and other chemoreceptors. The fact that azadira chtin directly or indirectly inhibits the secretion of trypsin by the enzyme-secreting cells of the gut is discussed.