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Wetland Symposium

Direct and Indirect Impacts of Esfenvalerate on Wetland Biota


WILLIAM F. McCARTHY AND MARY G. HENRY

U.S. Fish and Wildlife Service, Minnesota Cooperative Fish and Wildlife Research Unit, University of Minnesota, Department of Fisheries and Wildlife, St. Paul, MN 55107

A two-year study was conducted to investigate the direct impacts of the pyrethroid esfenvalerate on aquatic invertebrates and the indirect effects of a reduced invertebrate forage base on ducklings. Results from 1991 showed a correlation between the reduction of invertebrate numbers and short-term weight change of mallard (Anas platyrhynchos) ducklings per controlled forage bout. We found duckling mortality was significantly higher at 15 days post-treatment for birds reared on treated wetlands in 1992. The use of imprinted ducklings facilitated the study of the indirect impacts and enabled the control of forage bouts and regular measures of short-term weight change and growth. In addition to physical measures, behavioral observations were collected.

The aquatic invertebrate community was monitored to study the direct effects of esfenvalerate; invertebrates were sampled using benthic cores, artificial substrates, activity traps, and emergence traps. We found that amphipods were more sensitive to esfenvalerate than chironomids and treated sites were still void of amphipods one-year post-treatment. The sensitivity of cultured Hyalella azteca and Chironomus tentans to esfenvalerate was demonstrated by in-situ bioassays.

This research was conducted in semipermanent wetlands in western Minnesota, where the primary land use is agricultural. Accidental introduction of chemicals into wetlands has occurred in the past and is still of concern. Preliminary results indicate that when esfenvalerate enters wetlands it has both direct and indirect impacts on associated biota.


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