Zooplankton community responses to a novel forest insecticide, tebufenozide (RH-5992), in littoral lake enclosures

The effects of tebufenozide (RH-5992), a potential forest insecticide, on zooplankton communities were determined in 16 littoral enclosures in a small forest lake of northern Ontario. Community structure in enclosures treated with 9, 36, or 157 mu g tebufenozide/L (0.2, 0.7, and 3 times the expected environmental concentration) was compared with natural zooplankton communities in control enclosures. No significant treatment effects on zooplankton communities were detected, even at 3 times the expected environmental concentration. While some changes in community structure of crustacean zooplankton in enclosures occurred through the season, these did not appear to be related to the tebufenozide treatments. Tebufenozide residues in water dissipated following exponential decline kinetics with time to 50% dissipation (DT50) ranging from 32 to 35 days irrespective of initial concentration. There were no differences in pH, dissolved oxygen, conductivity, and phytoplankton abundance among treatment levels (repeated-measures ANOVA, p > 0.07).