Meisner, J., Dept. of Entomology, ARO, The Volcani Center, Bet Dagan, 50250, Israel
Klein, M., Dept. of Entomology, ARO, The Volcani Center, Bet Dagan, 50250, Israel
Ben-moshe, E., Dept. of Plant Introduction, ARO, The Volcani Center, Bet Dagan, 50250, Israel

The effect of Margosan-O, a formulation of a natural insecticide obtained from the neem (Azadirachta indica A. Juss) tree, on the development of the leafhopper Asymmetrasca decedens (Paoli), was investigated by testing insect performance (i) on cotyledons of Gossypium hirsutum cotton seedlings treated with different concentrations; (ii) on cotton seedlings stood with their petioles in different aqueous dilutions of Margosan-O and recording mortality until the adult stage; and (iii) determining the repellent effect on adults by recording their location on treated vs untreated cotyledons in choice and no-choice situations. In foliar and in systemic treatments with 2% Margosan-O, practically none of the leafhoppers reached the adult stage. As the concentrations were lowered there was a gradual rise in the percentage of adults emerging; on untreated cotyledons 60-80% of the adults emerged. Feeding was zero or very low at high Margosan-O concentrations. Adult leafhoppers settled in significantly higher numbers on untreated than on treated cotyledons in both choice and no-choice experiments. © 1992 Springer Science + Business Media B.V.