EVALUATION OF A BRIQUET FORMULATION OF BACILLUS-THURINGIENSIS VAR ISRAELENSIS (H-14) AGAINST AEDES SPP AND CULEX SPP LARVAE IN DAMBOS IN KENYA

Bacillus thuringiensis Berliner var. israelensis serotype H-14 (Bti) in briquet formulation (Bactimos(R)) was tested in a field trial against ground-pool breeding mosquitoes in a dambo located in a Rift Valley fever virus-enzootic/epizootic area in central Kenya. Bactimos(R) (10% Bti; 7000 AA International Toxic Units/mg) was tested for 30 days in 3 separate treatment areas at the rate of 1 briquet/9 m2, later increased to 1 briquet/1.5 m2 on day 13 postflood; 1 briquet/9 m2; and 1 briquet(4.6 m2). An estimate of the daily survival rate of larvae at different periods during the study revealed that mosquitoes in the area treated with 1 briquet/9 m2 had a significantly lower (64%) survival rate than those in the control site (92%) against Aedes spp. and was not significantly different from the site treated with 1 briquet/4.6 m2. Mosquitoes in the site treated with 1 briquet/1.5 m2 on day 13 postflood had a much-reduced survival rate (25%) when compared to those in the control site (67%) during the 3rd Culex spp. generation (22 - 26 days postflood). This five-fold increase above standard label dosage still failed to prevent Culex spp. emergence. There was no significant difference in survival rates between the control and any of the three treatment sites during the first or second Culex generation (9 - 20 days postflood). Emerged adults collected as pupae from control and treatment sites indicated that Aedes mcintoshi Huang and Culex antennatus (Becker) were the most predominant Aedes and Culex species.