Impact of deltamethrin insecticide on Chironomidae (Diptera) of prairie ponds

Deltamethrin insecticide was applied by air, at recommended field application rates (7.5 g/ha), to two prairie ponds in June, 1986. Larval and emerging Chironomidae densities were monitored in the treated ponds and in two untreated ponds for 1 month prior to spraying, the remainder of the summer after spraying, and in the late part of the following spring. Following deltamethrin application, the density of chironomid larvae declined by two orders of magnitude in the treated ponds relative to the untreated ponds, with all genera being affected. Chironomid emergence declined in both the treated and untreated ponds. The pattern of recovery of the chironomid community was followed by multivariate analysis of larval genera abundances and qualitative comparisons of emerging species. The two treated ponds recovered at different rates: the community in one pond appeared to have recovered by 2 months after treatment, whereas that of the other treated pond showed little recovery until 1 year following treatment. In view of the high natural variation of chironomid communities and their habitats on the prairies, basic knowledge about these temporary pond ecosystems must be gathered in order to understand the long-term impact on such habitats of using deltamethrin and other insecticides.