Does synergized pyrethrin applied over wetlands for mosquito control affect Daphnia magna zooplankton or Callibaetis californicus mayflies?

Abstract

BACKGROUND: Public health agencies may apply aerosolized synergized pyrethrin over wetlands repeatedly to control mosquitoes. This concerns wildlife managers because studies have shown the accumulation of pyrethroids, which are chemically similar to pyrethrin, in sediments in amounts that can be toxic to invertebrates. The authors tested whether repeated applications of synergized pyrethrin over wetlands caused mortality of two aquatic invertebrates: the zooplankton Daphnia magna Straus and a mayfly, Callibaetis californicus Banks. Fifteen wetland mesocosms were either exposed to repeated pyrethrin sprays or were protected by lids. Invertebrates in screened cages were placed in mesocosms before the fifth and eleventh spray, and directly into wetlands before spray 11. Six mesocosms were exposed to spray deposition. Caged adult mosquitoes were used to verify that sprays drifted over mesocosms. Sediments were analyzed for insecticide residues.

RESULTS: There were no detectable effects of synergized pyrethrin on 36 h survival of Daphnia or mayflies, but most exposed adult mosquitoes died. Some exposed sediments yielded pyrethrin (≤34.5 ng g⁻¹); most showed piperonyl butoxide (PBO) (≤14.9 ng g⁻¹).

CONCLUSIONS: Deposition of aerosolized 25% pyrethrin + 5% PBO may contaminate wetlands, but its application at rates used for mosquito control did not produce detectable effects on indicator species. Copyright © 2008 Society of Chemical Industry