Comparative Larvicidal and Residual Activity of Bacillus Thuringiensis var. Israelensis and Temephos (1.0 % Sg) in Granules against Culex Pipiens Pallens (Diptera: Culicidae) in Semi-Field Tests

Abstract

The study looked at comparative larvicidal activity and residual effects of granular formulations of Bacillus thuringiensis var. Israelensis (Bti); a bio pesticide and temephos (Abate); phosphorus based non-systemic pesticide. The study was carried out in semi-field station and used rainwater to simulate natural conditions. Mosquitoes of; Culex pipiens pallens Coquillett; a member of the Culex pipiens complex were used. The third instar larvae were used to allow observations before pupation and adult emergence. The methods used were a modification of those used by Thavara et al [24] and Laws et al [20]. Abate applied at concentrations; 1.0mg/l, 2.0mg/l and 4.0mg/l of 1% SG showed that the residual activity of abate is dependent on the concentration used in the treatment. Bti was applied at 0.4g/l, 0.8g/l and 1.6g/l. The study found that both formulations were effective, with Bti offering a short residual activity period of seven days to two weeks, while temephos gave prolonged residual period of up to two months. Between day one and day twenty five of the tests, there were no significant differences at p > 0.05 in the residual activity of the three concentration; 1.0 mg/l, 2.0 mg/l and 4.0 mg/l of Abate. After the day 25, however, there were significant differences between the residual activities of Abate at 1.0 mg/l and those of the 2.0 mg/l and 4.0 mg/l (p < 0.05) (Table 1). In Bti (Aquabac), the residual activity period of the three concentrations used in the tests differed significantly at p < 0.05 (Table 2). The findings about the larvicides can help choose the right larvicide to apply depending on the habitat, the population density, cost and length of the mosquito breeding season.