Evaluation of neem Azadirachta indica seed extracts and oils as oviposition deterrents to noctuid moths

Abstract

AbstractApplications of three concentrations of oil‐free neem seed extracts (Azadirachta indica A. Juss; Meliaceae) to cabbage plants in cages did not deter oviposition by individuals of three species of noctuid moths, Trichoplusia ni, Peridroma saucia, and Spodoptera litura. The concentrations used corresponded to 10, 50, and 100 ppm of the main active ingredient, azadirachtin. The total number of eggs laid per female, female longevity, and median day of oviposition were not affected. Sprays of the neem oil‐based insecticide Margosan‐OR, and a 1% aqueous emulsion of a refined neem seed oil similarly had no effect on any of the parameters studied. However, a 1% crude oil emulsion significantly reduced the proportion of eggs laid by S. litura on treated plants. Our results suggest that literature reports of significant neem‐based oviposition deterrence to S. litura are the result of compounds that are removed by higher levels of processing and thus not likely to be found in most commercial neem seed formulations. Sprays consisting of highly processed neem seed extracts, used at concentrations that provide larval control, are unlikely to be generally effective as oviposition deterrents to noctuid pests.