Activity of rocaglamide, an insecticidal natural product, against the variegated cutworm,Peridroma saucia(lepidoptera: noctuidae)

Physiological and behavioural effects of rocaglamide, an insecticidal natural product, were determined for the variegated cutworm, Peridroma saucia, using different bioassays. Rocaglamide inhibited growth of neonate P. saucia in a dose-dependent manner when incorporated into an artificial diet. The dietary EC50 (effective concentration inhibiting growth by 50% relative to controls) was 1·37 mg kg−1. Lethal doses causing 50% mortality (LD50) of fourth-instar larvae were 0·32 and 0·34μg larva−1 for topical and oral administration, respectively, based on a 96-h observation period. Mortality did not become significant until at least 72 h following administration. Rocaglamide applied to cabbage leaf discs or incorporated into artificial diet had a moderate antifeedant effect towards larvae in choice tests. Nutritional experiments with fourth-instar larvae using dietary exposure or following topical application confirmed that rocaglamide possessed both antifeedant and toxic effects. Direct assays of feeding behaviour indicated that behavioural effects could not account for the complete bioactivity observed. Significant impairment of larval growth following topical administration, concomitant with reduced food consumption, suggests that rocaglamide may act partially through central inhibition of the feeding process, leading to anorexia.