Efficacy of neem limonoids on Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae) the rice leaffolder

In leaf cut choice assay and topical application experiments, the neem (Azadirachta indica) limonoids azadirachtin, salannin, deacetylgedunin, gedunin, 17-hydroxyazadiradione, and deacetylnimbin showed strong antifeedant and growth inhibitor activity against fifth instar larvae of Cnaphalocrocis medinalis, the rice leaffolder, a serious pest of rice in Asian countries. The parameters, used to evaluate the activity of the limonoids were larval food utilization, quantity of ingested and digested food; consumption index and feeding deterrence index. Azadirachtin, salannin, deacetylgedunin showed high bioactivity at all doses, while the other neem limonoids proved to be less active, and only at the higher doses did they display antifeedant activity. Azadirachtin was the most potent in all experiments. Gross dietary utilization (efficiency of conversion of ingested food) of C. medinalis was also decreased after treatment with limonoids. Our results suggest that neem limonoids may be used in IPM programs for rice leaffolder and should be evaluated for efficacy under field conditions.