Efficacy of Bacillus thuringiensis israelensis, Bacillus sphaericus and temephos for managing Anopheles larvae in Eritrea

Abstract

We evaluated the larvicidal activity of the granular formulation of Bacillus thuringiensis israelensis (Bti) serotype H-14 (Vectobac G, 200 ITU/mg) and Bacillus sphaericus (Bsph) serotype H5a5b (Vectolex CG, 670 Bs ITU/mg) against Anopheles arabiensis and other mosquitoes in breeding habitats in 3 sites, Gash-Barka, Anseba, and Debub zones, in Eritrea. The primary objective was to determine the optimal application rate and duration of effect for Bti and Bsph in representative larval habitats as compared with the organophosphate temephos. The biolarvicides were tested at 100% (high) and 50% (low) of the maximum recommended application rate. Temephos was applied at a rate of 100 ml/ha. At least 4 replicate experiments with Vectobac G (5.6 and 11.2 kg/ha), Vectolex CG (11.2 and 22.4 kg/ha) were conducted in each study site. All 3 larvicides caused significant mortality of the main malaria vector species, An. arabiensis, and other mosquito species (Anopheles cinereus, Anopheles pretoriensis, Culex quinquefasciatus). The larvicidal activity for Bti and Bsph was variable depending upon breeding habitat, mosquito species, and general ecology of the area. Both biopesticides had a similar duration of activity (2-3 wk) and were generally as effective as temephos for these time periods. In some cases, the high and low application rates for Bti and Bsph produced equivalent control over 2-3 wk. The 2 Bacillus biopesticides were less effective in habitats with high algal content and in fast flowing streams primarily because of the inability to penetrate algal mats and dilution effect, respectively. The results show that application of the 2 biolarvicides bimonthly to streambed pools, rain pools, and similar habitats would maintain control of the anopheline mosquito population.