Bioefficacy, residual activity and sublethal effects of Bacillus thuringiensis H-14 (water dispersible granules, WDG) against

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Date
2006-11
Authors
Lee, Yean Wang
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Abstract
The efficacy, residual activity and effect on sublethal exposure of Bacillus fhuringiensis H-14 against dengue vectors, Aedes aegypti and Ae a/bopictus have been studied. Breeding/infestation of Aedes species in targeted dengue endemic area was carried out before the field evaluation of Bti. Three types of water containers (earthen jars, 50L; big glass jars, 3L; and milk can, 300ml) were used, milk can and big glass jar are successfully attracted highest numbers of Aedes species based on number of larvae per volume or per surface area collected. Both Ae. aegypti and Ae. albopictus were found in the test site. Dose response study showed a decrease in the sensitivity level of Bti with storage. Bti still performed effectively against laboratory-cultured susceptible Ae. aegypti and Ae. albopictus strains after being in storage for 40 months. Study against field collected Ae. aegypti and Ae. a/bopictus strains from dengue endemic area showed the effectiveness of Bti after up to a storage age of two years (18-24 months). Laboratory-cultured Ae. aegypti and Ae. a/bopictus strains are more susceptible compared to all the field strains. The Diagnostic Dose of Bti against Ae. aegypti and Ae. a/bopictus are 1500 and 3000 ITU/L, respectively. Laboratory study indicated that Bti at the tested dosages (3000 ITUIL, 6000 ITU/L and 15000 ITU/L), performed effectively against both Ae. aegypti and Ae a/bopictus for a minimum of 28 days. The Bti provided better larvicidal activity with replenishment of water compared to without replenishment of water especially for the higher dosage (15000 ITU/L). In the field study, Bti water dispersible granules formulation showed more than 80% reduction of Aedes mosquito larvae breeding up to 40 days. Aedes aegypti and Ae. a/bopictus larvae exposed to a sublethal dose (Le50) of Bti, showed that the pupal and adult survival rate, blood engorgement rate and egg production (fecundity) were significantly reduced (p<0.05), either at parental stage or at the offspring stage, after being treated with Bti at the dosage of compared to the control. Both Ae. aegypti and Ae. a/bopictus required longer life developmental period (number of days) for the offspring to emerge to become an adult from egg for after Bti treatment. Bacillus thuringiensis H-14 significantly decreased the Ae. aegypti offspring sex ratio, but not Ae. a/bopictus.
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The efficacy, residual activity and effect on sublethal exposure , of Bacillus fhuringiensis H-14 against dengue vectors
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