THE EFFECT OF PHORATE ON WETLAND MACROINVERTEBRATES

The effects of phorate, an organophosphorus insecticide, on aquatic ma croinvertebrates was studied in littoral mesocosms in South Dakota wet lands. In 1991 and 1992, four mesocosms were constructed in each of th ree wetlands. In each wetland, one mesocosm was a reference and phorat e concentrations of 1.2, 2.4, and 4.8 kg/ha were applied to treatment mesocosms. Phorate caused mortality to amphipods and chironomids throu ghout the study. Leeches and snails were resistant to phorate. Few liv ing macroinvertebrates were present in mesocosms after phorate treatme nt and populations recovered only slightly after 1 month. Macroinverte brate taxa that were sensitive to phorate included: Odonata, Hemiptera , Culicidae, Heliidae, Ephemeroptera, Acarina, Coleoptera, Stratiomyid ae, and Hydracarina. Taxa that were tolerant to phorate included: Hiru dinea, Gastropoda, Oligochaeta, and Ostracoda.