Use of Outdoor Freshwater Pond Microcosms: Ii. Responses of Biota to Pyridaben

The effects of pyridaben, an insecticide–miticide on zooplankton, macroinvertebrates, and fish were studied in outdoor freshwater microcosms using an analysis of variance design with three chemical concentrations (0.34, 3.4, 34.0 mg/L) and one untreated control randomized among 24 tanks. Each treatment was replicated six times. Monitoring was conducted during an 11month baseline phase followed by a total of three months for treatment and posttreatment phases. Two applications of a wettable powder formulation were sprayed directly below the water surface with a 30-d interval between treatments. Copepoda adult abundance was significantly reduced at 34.0 mg/L but recovery occurred within 6 weeks after application. Abundance of copepoda nauplii was significantly reduced at 3.4 and 34.0 mg/L, after applications one and two; effects were more severe at 34.0 mg/L and recovery was more rapid at 3.4 mg/L. Abundance of Rotifera was reduced at 34.0 mg/L, after applications one and two, and recovery occurred within 8 weeks for all groups except Polyarthra and Keratella. Of the most abundant Cladocera, abundance of Alona was not significantly affected and abundance of Latonopsis was significantly reduced at 34.0 mg/L, after applications one and two, but recovery occurred within 6 weeks. Abundance of Latonopsis also was significantly reduced at 3.4 mg/L, after applications one and two, but recovery occurred within 2 weeks. A significant decrease occurred in the abundances of Cnidaria, Insecta, and Hydracarina at 34.0 mg/L, only after application one. Pyridaben was toxic to bluegill at 34.0 mg/L, but was not acutely toxic at the laboratory 96-h LC50 concentration (;3.4 mg/L). Keywords—Aquatic microcosms Pyridaben Insecticide Pesticides