Susceptibility of Simuliidae larvae (Diptera) to a new solid formulation based on Bacillus thuringiensis var. israelensis (Bti), and bioecological aspects of the breeding sites in Cascavel - Parana, Brazil

Abstract

Due to the hematophagous habits of females, some species of black fly (Diptera, Simuliidae) are known to be responsible for economic losses and can cause significant damage to the health of human and livestock populations. To control populations of these insects, several bioinsecticides based on the bacterium Bacillus thuringiensis var. israelensis (Bti) are widely used. The objective of the current study was to evaluate the susceptibility of black fly larvae to a new Bti solid effervescent formulation, comparing it with a commercial standard formulation, Vectobac(R) liquid formulation, under laboratory conditions. The study was carried out in the municipality of Cascavel, Parana, Brazil. Eighteen hours after application of the formulations, larval mortality was evaluated. The control group did not exceed 20% mortality, for concentrations of 50 and 60 mg/L, the mean mortality rates were 50.6% and 64.2%, respectively, and neither differed significantly from the Vectobac(R). The stream sampled showed external fecal contamination during the eight weeks of monitoring and water quality parameters that could interfere with the efficiency of the control with Bti at the site. The following species of black flies were collected and identified in the two watersheds sampled: Simulium pertinax, S. subpallidum, S. nigrimanum, S. rubrithorax, S. perflavum, and S. inaequale. Bioecological aspects of the breeding site were addressed and presented here, this being the first report of black fly species for the municipality of Cascavel. The potential of the solid effervescent formulation was proven under laboratory conditions and the bioecological evaluations demonstrated the relevance of environmental diagnosis and monitoring in the optimization of control protocols for Simuliidae.