Field and laboratory trials in Mali to determine the effects of neem extracts on three millet pests: Heliocheilus albipunctella de Joannis (Lepidoptera: Noctuidae), Coniesta ignefusalis Hampson (Lepidoptera: Pyralidae) and Kraussaria angulifera Krauss (Orthoptera: Acrididae).

摘要

Formulations of aqueous neem extracts were sprayed in field experiments. Results showed that a 0.5% and 1% concentrations were effective in reducing grasshopper feeding and diminishing damage caused by the millet stemborer, C. ignefusalis. In 1988, neem diminished egg-laying and mine damage by the headminer, H. albipunctella, but no data were available for 1989 because of the low infestation levels of this pest.;Experiments to test the residual activity of neem showed that this botanical insecticide can effectively protect millet against K. angulifera for at least seven days, and possibly longer if ultra-violet rays and rainfall are not prevalent. Analysis of plant selection behavior of K. angulifera showed that neem is an antifeedant rather than a repellent. On first to third instar nymphs, growth regulating activity expressed as a difficulty in molting or an absence of sclerotization may occur. Topical applications of neem to the stemborer, C. ignefusalis, also caused growth abnormalities, mostly molting disturbances. Treated larvae that reached the adult stage were malformed.;This research indicates that neem based insecticides offer considerable promise for Sahelian farmers for protecting millet crops. It is effective against K. angulifera, but less effective against the stemborer, C. ignefusalis. Although the data obtained for H. albipunctella in 1988 was promising, it was insufficient to reach any conclusions regarding neem's efficacy with respect to this pest. (Abstract shortened by UMI.);Neem exhibited some systemic activity. Soil applied neem kernel powder partially protected millet against K. angulifera and C. ignefusalis. Neem treated plots yielded more grain and suffered less damage by insect pests than four different cultural practices. Only the addition of fertilizer was superior to neem in reducing yield losses but it was inferior in limiting pest losses.