Efficacité d'un insecticide à base de neem dans la lutte contre quelques ravageurs du cotonnier au Bénin

Efficacy of a Botanical Insecticide Based on Neem Extract in the Management of Cotton Pests in Benin. The effect of an insecticide based on neem , Azadirachta indica A. Juss (Meliaceae), has been evaluated in a comparative trial with synthetic insecticides on cotton caterpillars: Haritalodes derogata, Helicoverpa armigera, Pectinophora gossypiella and Thaumatotibia leucotreta. The experiment was conducted in two localities Kandi and Savè, species distribution areas. Those areas are located in the northern and central Benin. The neem formulation contained 0.5% of Azadirachtin and was used at the doses of 2, 3 and 4 l/ha. The synthetic insecticides contained emamectin 24 g/l + acetamiprid 32 g/l; cypermethrin 35 g/l + 300 g/l chlorpyrifos and beta-cyfluthrin 45 g/l + imidacloprid 100 g/l. The different applications were performed according to the calendar program of cotton protection recommended in each of the two regions. In total, ten treatments were carried out with the neem based insecticide and six treatments with the three synthetic insecticides. The results showed that the neem based insecticide was as effective as the synthetic insecticide (cypermethrin 35g/l+chlorpyrifos 300 g/l) in the control of endocarpic caterpillars, P. gossypiella and T. leucotreta. The neem based insecticide reduced the percentage of damaged plants by the leaf-cutting ants ( Haritalodes derogata), by 25% against 100% reduction by the chemical synthetic insecticide. A dose effect of the neem based insecticide was observed with 36.1%, 29.8% and 6.1% of the damaged plants, for doses of 2, 3 and 4 l/ha respectively. Cotton yields of plot treated with aqueous extract of neem were higher than those of the untreated plots. In endocarpic area, yields obtained from the plots treated with neem extract insecticide were not statistically different from those of the chemical insecticides. This study indicates the neem based insecticide could be used in an integrated management system for endocarpic caterpillars.