Antifeedant activity of Jatropha gossypifolia and Melia azedarach senescent leaf extracts on Spodoptera frugiperda (Lepidoptera: Noctuidae) and their potential use as synergists.

BACKGROUND: To reduce rates of synthetic insecticide applications, natural product alternatives and synergists are needed. A study has been made of the toxicity of ethanolic senescent leaf extracts (SLEs) of Jatropha gossypifolia and Melia azedarach on larvae of the noctuid pest Spodoptera frugiperda. Their effects as syngergists and inhibitors of several enzyme activities are also reported. RESULTS: When added to the diet, M. azedarach SLE showed lower toxicity than J. gossypifolia SLE. However, after 2 weeks on the diet, the M. azedarach SLE proved to be lethal to 100% of the larval population. Artificial diets with both SLEs have an antifeedant effect on armyworm larvae. Acute toxicity after topical application in a dipping assay was relatively low for both J. gossypifolia and M. azedarach SLEs (LC(50) of 2.6 and 1.4 g L(-1), respectively, after 24 h). However, mixtures of the SLEs of M. azedarach and J. gossypifolia had a strong synergistic effect with cypermethrin. Synergism was higher with the J. gossypifolia SLE, perhaps because it contains several natural products with a methylenedioxyphenyl moiety. Both extracts inhibited P450, general esterase and acetylcholinesterase activities in vitro and in vivo. CONCLUSION: Both J. gossypifolia and M. azedarach SLEs are antifeedants to armyworm larvae when present in the food, and also have a synergistic effect with cypermethrin in topical assays. Although the synergistic effect is less than with piperonyl butoxide, both SLEs have some inhibitor activity against detoxification enzymes and acetylcholinesterase. Thus J. gossypifolia and M. azedarach SLEs may be considered as ecofriendly approaches for the control of S. frugiperda in order to reduce cypermethrin usage.