Laboratory and semi-field evaluation of the efficacy of var. (Bactivec®) and (Griselesf®) for control of mosquito vectors in northeastern Tanzania.

Bacterial larvicides var. () and () have been used extensively for mosquito control. However, their efficacy varies greatly mainly due to factors related to target mosquitoes, larval habitat conditions, and inherent larvicide properties. We evaluated the efficacy of (Bactivec®) and (Griselesf®) for control of complex, and larvae under laboratory and semi-field conditions in northeastern Tanzania. Laboratory bioassays were conducted with five to six different concentrations of and , replicated four times and the experiment repeated on three different days. Larvae mortality was recorded at 24 or 48 h after the application of larvicide and subjected to Probit analysis. Laboratory bioassays were followed by semi-field trials to establish initial and residual activity of and . Semi-field trials were conducted in artificial larval habitats in the open sunlit ground and in "mosquito spheres". These artificial larval habitats were colonized with mosquito larvae, treated with and , and the impact of treatments on mosquito larvae was monitored daily. Lethal concentration values that caused 50% and 95% mortalities of test larvae (LC and LC) showed that complex and tested were highly susceptible to and under laboratory conditions. Likewise, larvae of were highly susceptible to , with LC value as low as 0.052 mg/l. However, larvae were not susceptible to under practical doses of laboratory settings. In semi-field trials, all treatment dosages for provided 91.0-100% larval mortality within 24 h whereas resulted in 96.8-100% larval mortality within the same time-frame. had a more prolonged residual activity, with pupal reductions range of 55.7-100% for 9 days at all application rates while the corresponding pupal reduction with was 15.4-100% for 5 days. Due to the low residual activity of and tested, weekly application at a maximum label rate would be appropriate to reduce mosquito larvae in natural larval habitats. Based on laboratory findings, product tested would not be recommended for use in the control of .