Toxicity of Extract from Thai Neem, Azadiracta indica var. siamensis Valeton to Corn Stemborer, Ostrinia furnacalis (Guenee)

Abstract

Toxicity of solvent extract from seed kernels of Thai neem (Azadirachta indica var. siamensis Valeton) and synergism with piperonyl butoxide (PBO) 10 ppm were observed against corn stemborer, Ostrinia furnacalis (Guenee). The extracts contained different concentrations of the active substance, azadirachtin A. The LC50 of 2 nd – 3 rd instar lavae were 77.53 and 6.06 ppm at 3 and 5-day post exposure respectively. PBO at 10 ppm showed little synergism with neem extract at 3-day post exposure but at 5-day post exposure showed 2-fold synergism. The larval mortality at 5-day post exposure of aqueous neem seed kernel extract conc. 3-5% (w/v) (Aza A 28-46 ppm) was as high as that of the solvent extract containing Aza A 30-150 ppm (72.0-79.8 %), while that of chlorfluazuron 5% EC (rate of 25 ml/20 litre) was the highest (96.3%)