RP10 Aquatic Ecotoxicology
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(GRU-1117-920996) West Nile virus, mosquito control, and aquatic invertebrates: implications for Pacific Northwest wetlands.

Tamayo, Mariana¹, grue, christian¹, ¹ University of Washington, seattle, WA, USA

ABSTRACT- Loss of human life due to the rapid spread of West Nile virus across North America has generated increasing pressure to aggressively control mosquitoes, including on national wildlife refuges. Mosquito control using Bacillus thuringiensis israelensis (Bti) had been proposed on Franz Lake National Wildlife Refuge (Washington) to reduce the threat that mosquitoes pose to adjacent landowners. However, there is concern that Bti may adversely affect a variety of fish (e.g., salmonids) and wildlife that feed on non-target invertebrates. We assessed the short-term effects of Bti on the invertebrate communities present in Franz Lake by establishing eight plots (40 m x 6 m separated by a 50 m buffer) along the southern shore of the lake in 2003. We used a spot treatment regime that consisted of three Bti applications (VectoBac-G®) at 9-10 d intervals using a rate of 7.8 kg ha-1 in four of the plots. Benthic and water column samples were collected from all eight plots before and 7 d after treatment. The southern shore of Franz Lake supported a fairly diverse macroinvertebrate community consisting of >40 taxa. Although insect families represented most of the taxa (>50%) found within the lake's shoreline, Oligochaeta and Cyclopoida were the most common taxa. There were no significant differences between the control and treatment plots, both had similar physical variables (water temperature, water depth) and macroinvertebrate communities across the spray events. Our study suggests that using a Bti spot treatment regime of 1-3 applications for one season may be a suitable management tool for some wetlands present on national wildlife refuges to control mosquitoes without having any significant short-term effects on the macroinvertebrate communities. However, the potential for cumulative effects on these wetland communities when exposed to multi-year applications of Bti remains to be determined and warrants further research.

Key words: Bti, wetlands, invertebrates, non-targets