INSECTICIDAL AND ANTIFEEDANT BIOACTIVITIES OF NEEM OILS AND THEIR RELATIONSHIP TO AZADIRACHTIN CONTENT

Neem seed oil, a possible precursor to new botanical insecticides, varies widely with respect to concentrations of the limonoid azadirachtin, the putative active ingredient. Among 12 samples of neem oil analyzed by liquid chromatography, azadirachtin concentrations ranged from <50 (limit of detection) to over 4000 ppm. Oils were bioassayed for larval growth inhibition and antifeedant activity against the variegated cutworm (Peridroma saucia) and for molt disrupting activity against the milkweed bug (Oncopeltus fasciatus). For each of the three bioassays, bioactivity of the oils, as measured by EC50values, is highly correlated with azadirachtin content of the oils. From 72% to 90% of the variation in bioactivity of the oils can be accounted for by variation in azadirachtin content. As azadirachtin content of neem oil varies widely and is highly correlated to bioactivity against these bioassay species, azadirachtin content may be a useful quality-control criterion for neem oil as a precursor for insecticide production. © 1990, American Chemical Society. All rights reserved.