Towards integrated pest management of Thrips tabaci in onions

Populations of onion thrips, Thrips tabaci, and their natural enemies were monitored in small field plots of onions to which standard insecticide (methamidophos, endosulfan and chlorpyrophos), selective insecticide (imidacloprid and spinosad), organic (YR015) insecticide or no insecticide treatments were applied. The mean number of thrips per plant was kept below 12 in the standard and selective treatments. The numbers of thrips in the organic and no insecticide treatments were comparable, reaching over 60 thrips per plant. This resulted in increased plant damage and shorter leaves. High rainfall in 2001-02 coincided with a reduction in thrips numbers in untreated plots, which peaked at 70 thrips per plant, compared with nearly 500 thrips per plant in the drier 2000-01 season. Natural enemies observed in the unsprayed and organic treatments included Ceranisius menes, Aeolothrips fosciatum. Buchananiella whitei, syphids and entomogenous fungi. None of these natural enemies increased sufficiently to provide effective thrips control. No natural enemies were found in the standard or selective insecticide treated plots.