Physicochemical and Chemical Variation in Neem Oils and Some Bioactivity Leads against<i>Spodoptera litura</i>F.

Abstract

Forty-two neem ecotypes of India have been found to show a wide variation in the content of oil, and their physicochemical characteristics (color, specific gravity, refractive index, iodine value, acid value, and saponification value), total fatty acid, fatty acid composition (oleic, stearic, palmitic, linoleic, myristic, arachidic, and behenic acids), and the key meliacins (azadirachtin, nimbin, and salannin). The azadirachtin content did not correlate with any of the physicochemical and chemical parameters, but the nimbin and salannin contents correlated significantly with each other. The refractive index (+ve correlation) and iodine value (−ve correlation) showed weak but significant correlation with the contents of nimbin and salannin. Insect growth inhibition of Spodoptera litura revealed a wide variation in the EC50 of the oils. The salannin and azadirachtin contents of the oils correlated the most with bioactivity. The iodine and acid values correlated weakly but significantly with bioactivity. Keywords: Neem; neem oil; physicochemical variation in neem; chemical variation in neem; neem bioactivity