Field trials with Bacillus sphaericus and Bacillus thuringiensis serovar. israelensis commercial formulations against Culex quinquefasciatus larvae in suburban Dhaka, Bangladesh

A commercial corn-grit (CG) formulation of Bacillus sphaericus serotype H5a5b (strain 2362) (VectoLex^[○!R] CG) and a corncob granular (G) formulation of B. thuringiensis serovar. israelensis (B.t.i.) (VectoBac^[○!R] G) were evaluated at various treatment rates against Culex quinquefasciatus Say larvae in organically polluted roadside ditches and ponds in suburban Dhaka, Bangladesh. VectoBac G at rates of 11.2 and 22.4kg/ha gave short-lived larval reduction (76%) of all instars of Cx. quinquefasciatus for 3 days, declining rapidly to 3% at day 7 posttreatment with the lower rate, but up to 62-88% larval reductions for 7-10 days posttreatment at the higher rate of treatment which is the maximum allowable label use rate in the USA. In contrast, VectoLex CG was more effective and even at 5.6kg/ha gave 67-97% larval reductions of 3rd and 4th instar Cx. quinquefasciatus for at least 17 days posttreatment. At higher rates of 11.2 and 22.4kg/ha (maximum allowable label use rate in the USA), VectoLex CG gave control of higher magnitude and duration in the various habitats; specifically, at 22.4kg/ha, an excellent or complete control of 3rd and 4th instar Cx. quinquefasciatus larvae was achieved for nearly 5 weeks posttreatment. B. sphaericus and B.t.i., because of their effectiveness, environmental safety and other positive attributes, could be substituted to chemical control agents for larval control of Cx. quinquefasciatus in the Dhaka area, and in Bangladesh at large.