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 (Bspft) serotype H5a5b (Vectolex®CG, 670 Bs ITU/mg) agunst 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 applicationrate and duration ofeffect for Bti and Bsphin representative larval habitats as compared with the organophosphatetemephos. The biolarvicides were tested at 100% (high) and 50% (low) of the maximum recommendedapplication rate. Temephos was applied at a rate of 100 ml/ha. At least 4 replicate experiments with VectobacG (5.6 and 11.2kg/ha), Vectolex CG (11.2 and 22.4 kg/ha) were conducted in each study site. All 3 larvicidescaused 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 Bsphwas variable depending upon breeding habitat, mosquito species, and general ecology of the area. Both biopesticideshad a similar duration of activity (2-3 wk) and were generally as effective as temephos for these timeperiods. In some cases, the high and low application rates for Bti and Bsph produced equivalent control over2-3 wk. The 2 Bacillus biopesticides were less effective in habitats with high algal content and in fast flowingstreams primarily because of the inability to penetrate algal mats and dilution effect, respectively. The resultsshow that application of the 2 biolarvicides bimonthly to streambed pools, rain pools, and similar habitats wouldmaintain control of the anopheline mosquito population.