Avaliação da susceptibilidade e do controle de borrachudos (Diptera: simuliidae) pelo emprego dos larvicidas à base de Bacillus thuringiensis var. israelensis (Bti) e Temephos em Caarapó-MS

Abstract

The species of hematofagous blackfly generate trouble due to the intensity of bites which interfering with quality of life of people or animals. Economic activities such as agriculture and tourism, which are located near lotic environment are harmed by the action of female blackflies. This study aims to raise subsidies for management of blackflies (Diptera: Simuliidae) in the town of Caarapó-MS. The evaluation of the stress caused by the presence of black flies was conducted among population by questionnaires in the cities of Dourados and Caarapó-MS. The analysis of the questionnaires defined the study area as Caarapó and then we proceeded to the mapping of streams Caarapó, Gloria and its affluent to identify blackfly breeding. We collected larvae, pupae and adults for species identification, seeking anthropophilic species. It was also evaluated the activity of esterase by biochemical test of filter paper, which served as the subsidy for indication of resistant populations of the blackfly to Temephos. For confirmation of resistance to the organophosphate insecticide two bioassays with Temephos (Fersol 500 CE) were made using the operating concentrations: 0.5 ppm ia/10min. and 2.5 ppm i.a./10min. on Caarapó stream. In a stretch of Caarapó setrem and the affluent of Gloria stream we evaluated the drift of the product based on Bacillus thuringiensis var. israelenses (Bti) Vectobac 12 AS. Biochemical tests were performed to assess the relationship between the density of black flies with fecal coliform in areas of high concentration of blackfly larvae in streams and sparsely populated stretches of black flies in streams in Dourados for comparisons. We also conducted microbiological analyses next to places where it was recorded low and high level of nuisance caused by these insects in Dourados and Caarapó-MS. The identified species were: Simulium subpallidum, Simulium perflavum, Simulium subnigrum, Simulium inaequale, Simulium nigrimanum. Based on the results obtained by the analysis of filter paper we observed indicative of resistance to temephos by blackfly species. Through bioassay of toxicity in the operational concentrations of 0.5 ppm ia./10 min. and 2.5 ppm i.a./10min. the mean mortality and standard deviation were 5.67% (3.40) and 44.63% (18.76), confirming the resistance of the blackfly to larvicide. Entrainment of Bti in the two areas was low, so we can infer that higher concentrations of the product, a longer exposure or a strategy for continuous release of insecticide should be tested for better transportation. The results of microbiological analysis did not allow relating the areas with a high density of blackfly larvae in Caarapó with low density of larvae in Dourados, as the streams of both cities had high concentrations of fecal coliform. Thus, we conclude that the concentration of fecal coliform is not the only determining factor for the high population density of black flies in the city of Caarapó. This study showed that there is need for the establishment of a control program of blackfly in Caarapó-MS in order to reduce the population density of the insect.