Effects of Bacillus thuringiensis var. israelensis on the Black Fly Communities (Diptera, Simuliidae) in Tropical Streams.

Bacillus thuringiensis var. israelensis (Bti) Berliner, 1911 is widely used in the biological control of black fly and mosquito populations. The objective of this study was to evaluate the effects of Bti on the black fly communities in streams in the Atlantic Forest domain. The study was carried out in eight streams of Serra do Mar, in the municipality of Ubatuba, São Paulo. Some parts of the streams in this locality have received applications of Bti fortnightly for more than 25 years by the sanitary agency of the region. In each stream, two sections were sampled, with and without application of Bti (June 2015 and 2016). Black flies were collected and identified to the species level in the laboratory with 1382 larvae being identified, distributed in six species. Of this total, 73% of the individuals were found in sections where Bti was not applied. There was a difference in the abundance of simulids between the sections with and without Bti application, being more abundant in the latter. We measured the head capsule of individuals of the most abundant species, Simulium pertinax Kollar 1832, using a stereoscopic microscope with millimeter lens. These measurements demonstrated that there was a difference between the sections regarding the age structure of Simuliidae populations. In the sections without Bti application, there was a higher proportion of larvae in the last instar, while in the Bti-treated sections, smaller instars were predominant, possibly due to constant recolonization processes.