The allelochemical azadirachtin given to the nymphs of S. gregaria inhibits
growth without reducing food intake.The growth reducing effect of azadirachtin is
independent of antifeedant effect. A decrease in the efficiency of utilization ,of dietary nitrogen was associated with a drastic reduction In the activity of midgut trypsin. It is suggested that this is the cause of the increased costs associated with the reduced rate of growth. This plant defense strategy and that of direct inhibition of herbivore proteinases by allelochemical proteinase inhibitors is discussed.