The present work aimed at assessing the temporal and spatial effect of applying the insecticide imidacloprid on the arthropod community associated with the canopy of common beans (Phaseolus vulgaris). About 2 ha of bean field was divided into two adjacent fields subjected to the same crop management practices except for insecticide application. Imidacloprid 700 GrDA (147 g a.i./ha) was applied to 20-day old plants. Three transects were extended from the mid-part of the sprayed area to the mid-part of the non-sprayed area. Nine sampling points 10 m apart were established in each transect. Arthropods were sampled from the plant canopy before and 3, 8, 14, 22, 29 37 and 44 days after insecticide application. There was a strong temporal effect of the insecticide on some arthropod guilds, but the spatial effect of the insecticide application was only noticeable in Empoasca kraemeri Roos & Moore whose dispersion from the non-sprayed area masked the insecticide effect on the treated area. The insecticide decreased the Thrips tabaci (Lind.), Caliothrips brasiliensis (Morgan), and E. kraemeri populations until 22 days after its application. Imidacloprid also prevented population increase of springtails (Collembola), but it did not significantly affect plant-chewing insects nor Frankliniella sp., Liriomyza spp. and Bemisia (Genn.). Imidacloprid was selective in favor of the most common bean pest predators and parasitoids.
Insecta; neonicotinoid; environmental impact; Phaseolus vulgaris
