Effect of Margosan-O on the development ofEarias insulana

The effect of Margosan-O, a formulation of a natural insecticide obtained from the neem tree (Azadirachta indica A. Juss), on the development of and the penetration rate of larvae of the spiny bollworm,Earias insulana (Boisd.), into cotton bolls was investigated by (i) incorporating Margosan-O into a semisynthetic diet and recording mortality until the adult stage; and (ii) spraying leaves and bolls with, or standing cotton seedlings or twigs of cotton with one boll per twig in aqueous dilutions of Margosan-O in an attempt to protect leaves or cotton bolls from feeding or penetration, respectively, by the larvae. Margosan-O was found to be effective when incorporated into the semisynthetic diet, even at low concentrations, especially when it was offered throughout the larval life span. Survival rate and average weight of the larvae were much lower on leaves treated with 0.5% or 0.2% Margosan-O, or exposed to its systemic effect at 0.5% or 0.25%, than on control leaves. Larval penetration into Margosan-O-sprayed bolls at concentrations of 0.01– 0.5% wasca 30–45% of that into control bolls. Margosan-O was active also as systemic treatment: onlyca 35% of the larvae penetrated the 0.25%-treated bolls compared with the untreated ones.