<i>Bacillus sphaericus</i> 2362 larval activity against <i>Anopheles</i> sp. (Diptera, Culicidae) in the rivers from Amazon, Brazil

Abstract

Studies addressing vector control are important due to the high incidence of malaria in Amazonia. The present study aims to analyze the larvicidal activity of Bacillus sphaericus 2362 against anophelines in Amazonia. Laboratory assays testing B. sphaericus 2362 as lyophilised in waters collected from anopheline breeding sites in the Solimoes and Negro Rivers, were carried out on Anopheles nuneztovari larvae. A field test using a Bacillus sphaericus 2362 formulation, named Spherico, was applied on Anopheles species in the natural breeding sites in the Solimoes and Negro Rivers. Laboratory bioassay showed that, the B. sphaericus tested dosage are not efficient in the control of A. nuneztovari larvae in black water, with CL50= 0.563ppm, compared to the larvicide dosage found in white water presenting CL50= 0,859 ppm, in the 24 h reading, with a significance of p>0.05. Regression straight lines point out that in the highest B. sphaericus 2362 dosages (1 ppm, 0.5ppm), there was higher mortality rate against this target species in black water, than that found in white water. In the field assays the Anopheles predominant species, both in black and white water breeding sites, were A. triannulatus (74%) and A. albitarsis (22%). The present study showed a decrease in the man hour larval index (MHLI) values following the larvicide application, both, in Solimões and Negro River breeding sites, as compared to that found prior to the treatment. The Solimões River breeding site, presented a value of MHLI equal to 72% wherever the highest Spherico formulation (0.2mL/m2) was applied, and MHLI of 18% where the lowest larvicide dosage was applied (0.025mL/m2), both values were found in the 48 h evaluation. In the Negro River, the MHLI was 53 and, 11%, for the highest and lowest Spherico tested dosage. The activity of the B. sphaericus 2362 and Spherico formulation on anopheline larvae differed significantly between the two water types tested (Solimões and Negro Rivers).