| A relatively new mosquitocidal strain of Bacillus thuringiensis, Bacillus thuringiensis jegathesan (Btj, strain 367), isolated from Malaysia was assayed for its larvicidal efficacy against field-derived early fourth-instar larvae of the southern house mosquito Culex quinquefasciatus (Cq), a major vector in the transmission of West Nile Virus from avian to incidental human hosts. The new bacterial strain was bioassayed in tandem with Bacillus thuringiensis subsp. israelensis, type H14 and the International Pasteur Standard (IPS) 82. Btj was shown to be only slightly more toxic than the more traditional formulation of Bt israelensis in wild-type Cq larvae obtained from natural wetland environments in the southeastern United States. The predicted LC50 of the Bt jegathesan formulation was determined to be .0095 mg/100ml, resulting in a potency of 22,156 ITU and a Btj:Bti activity ratio of 1.1. The Btj:IPS activity ratio was determined to be 1.4. The Wild-type, field-derived population of Cq was found to be less susceptible to the toxic effects of Btj than previously reported in trials against laboratory-cultured populations of Cq, which have reported Btj:Bti activity ratios of 6--40. |
