| The effect of neem oil, a product from the neem tree, Azadirachta indica A. Juss, on the biology of the maize weevil, Sitophilus zeamais Motsch., was investigated. Corn kernels treated with 100, 1,000, and 10,000 ppm of neem oil in acetone did not affect the survival of adult weevils. However, their oviposition rate was greatly reduced when they were held with corn kernels treated with 1,000 and 10,000 ppm of neem oil. The detrimental effect of the 1,000 ppm neem oil treatment was lost by 30 days after treatment, but the 10,000 ppm retained its effect for 60 days. The threshold concentration of neem oil affecting oviposition was 500 ppm. Weevils held for 7 days on corn kernels treated with 1,000 and 10,000 ppm laid fewer eggs than controls, but when the period of exposure was increased to 15 and 21 days, weevils oviposited normally. When given a choice, fewer weevils were found in treated than in untreated kernels. In all tests, the emergence of the F1 progeny was not affected by any concentration of neem oil. Similarly, 100 ppm neem oil and 10,000 ppm mineral oil affected neither weevil distribution nor oviposition.; Doses of 1,000 and 10,000 ppm of neem oil repelled weevils from corn kernels 24 h before the test; however, repellency disappeared after 15 days in the 1,000 ppm, but not the 10,000 ppm treatments.; Neem oil, at all doses tested (100-10,000 ppm), did not show any detectable effect on the biology of Anisopteromalus calandrae (Howard), a parasitoid of the maize weevil. However, at 10,000 ppm, neem oil showed a significant effect on the reproductive potential of the parasitoid, as measured by adult emergence and normal reproduction of the F1 progeny.; Neem oil has a potential for protecting stored grains from the attack of some major stored grain insect pests. In developing countries, where synthetic insecticides are expensive, the application of neem oil would offer a cheaper and suitable control strategy, specially in small scale storages. |
