Ecological Monitoring in the New River Gorge National River: Analysis of Environmental Impacts from the Black Fly Pest Management Program

Voshell, J; Orth, Donald

Examines the environmental impact of a black fly pest management program at NERI.... Executive Summary A pest management program for the black fly, Simulium jenningsi Malloch (Diptera: Simuliidae) was implemented by the state of West Virginia in the New River in 1986. The West Virginia Department of Natural Resources (WVDNR) made extensive and frequent applications of the bacterial pesticide, Bacillus thuringiensis var. israelensis (sti), from late-spring to early autumn to kill black fly larvae before they emerged as adults. The purpose of this study was to determine if the black fly pest management program caused adverse environmental effects to the New River. There were two major components of the overall project: (1) intensive studies of aquatic insect productiion and fish growth and condition at two sites on the New River (immediately below Bluestone Dam and immediately above Sandstone Falls) and (2) extensive studies of macroinvertebrate and fish community structure at selected sites throughout the New River from Bluestone Dam to the downstream boundaries of New river Gorge National River at Fayette Station. Potential direct and indirect effects of black fly pest management on the benthic macroinvertebrates in the New River included changes in community structure and reduced productivity. Data from treatment years were compared with pretreatment data to test for effects of black fly pest management. The benthic macroinvertebrate community was sampled quantitatively immediately below Bluestone Dam, immediately above Sandstone Falls, Prince, Thurmond, and Fayette Station in summer. Productivity of doinant taxa was estimated immediately below Bluestone Dam and immediately above Sandstone Falls by sampling every 2 weeks when flows were low enough for wading (usually June 1 to November 30) and applying the size frequency method. Total benthic macroinvertebrate production immediately below Bluestone Dam in 1990 was the highest in the 4 years of the study and was 3% higher than 1983, the reference year with no Bti treatment. Results of secondary production measurements of aquatic insects immediately below Bluestone Dam provide evidence that factors other than Bti treatments are responsible for the different levels of production that have been observed during this study. in 1990 as compared to 1983 was the mayfly H. curiosum, which was practically nonexistent at this study site after 1986. It is unlikely that the demise of H. curiosum was caused by Bti treatments because another mayfly in the same family, B. intercalaris, achieved higher production in three of the four treatment years as compared to the reference year without treatment. Both of the major taxa accounting for most of the aquatic insect production, the caddisfly C. campyla and chironomids in the subfamilies Chironominae/Orthcladiinae, achieved higher levels of production in 1990 as compared to 1983. Bti treatments do not appear to have caused either direct (toxicity) or indirect (food chain) adverse effects to nontarget organisms.