Kennen, J.G. 1989. Effects of a larvicide, Bacillus
thuringiensis var. israelensis, on
community structure of macroinvertebrates in streams of the
central Adirondacks. M.S. Thesis, SUNY-ESF, Syracuse, 140 pp.
Abstract: This study investigated the influence of biological disturbance using Bacillus thuringiensis var. israelensis (Bti) on benthic community structure in Adirondack streams. Macroinvertebrate communities were compared to determine if manipulation resulted in a shift in ecological organization of these communities. Differences in community characteristics including diversity, richness, similarity, and equitability were analyzed to determine if these indices were modified as the result of a field application of Bti. Shifts in the relative proportion of functional feeding groups, modes of existence, and taxa were examined.
Larval black flies comprised less than 4% of the community abundance in the study streams. The genus (Simulium) comprised more than 97% of the black fly larvae collected. Yet in other New York streams black flies may represent as much as 50% of the community composition. The greatest density of black fly larvae was 486/m2. During the primary period of treatment with Bti (May 20 to July 25), the reduction in black fly larvae ranged from 30% to 70%. The majority of the macroinvertebrates collected in the study streams were Chironomidae, Baetis, Habrophleboides, Leuctra, Simulium, Hydropsyche, Dolophilodes, Promoresia, Oulimnius, and Oligochaeta (Branchiobdeliidae: Xironogiton). Chironomids consistently dominated the samples, comprising from 40% to 60% of the community abundance in both streams.
Collector-gatherers were the most abundant functional feeding group, comprising 40% of all samples taken. Predators made up greater than 25% of the benthic community. In an analysis of modes of existence, clingers comprised greater than 44% of the community abundance throughout all dates sampled. This finding reflected the sampling design, in which the majority of samples were taken within riffle sections where organisms must adhere tightly to the substrate. Sprawlers and burrowers contributed between 20 and 30% of the community abundance. The "mode of existence" analysis contributed to an understanding of community organization in relation to the role of Bti. However, no major modifications in either functional components (functional feeding groups) or structural components (modes of existence and taxonomic composition) of the stream communities were seen in response to Bti. No major difference in macroinvertebrate diversity was evident between control and treated sections in the study streams. Diversity within Big Sucker and Little Sucker Brooks fluctuated inversely with dominance and in proportion to evenness. The similarity between control and treated sections of the study streams was greater than 80%.