Sustained release pellets for control of Culex larvae with Bacillus sphaericus

Area of Science:

• Environmental science
• Microbial pest control
• Entomology

Background:

• Bacillus sphaericus is a bacterium used for mosquito larval control.
• Traditional formulations can be susceptible to environmental inactivation.
• Developing stable, long-lasting formulations is crucial for effective mosquito management.

Purpose of the Study:

• To evaluate a novel pellet formulation of Bacillus sphaericus for enhanced residual activity against mosquito larvae.
• To assess the efficacy of preflood application of these pellets in artificial habitats.
• To compare the performance of pellet formulation with primary powder suspension.

Main Methods:

• Bacillus sphaericus was formulated into pellets using partially hydrogenated vegetable oil, talc, and a starch-based superabsorbent polymer.
• Pellets were applied to dry artificial larval habitats 5 days before flooding.
• Larval control efficacy was assessed against Culex spp. and Psorophora columbiae.
• Residual bacterial activity was measured after drying and reflooding cycles.

Main Results:

• The pellet formulation significantly increased residual activity against Culex spp. larvae in various plot sizes and water conditions.
• Preflood application of pellets eliminated Psorophora columbiae hatched upon flooding.
• Bacillus sphaericus persisted at 611 colony-forming units/ml after drying and reflooding.
• Primary powder suspension was ineffective as a preflood treatment due to solar inactivation.

Conclusions:

• Pellet formulation enhances the residual efficacy and persistence of Bacillus sphaericus.
• Preflood application of Bacillus sphaericus pellets offers a promising strategy for mosquito larval control.
• This formulation overcomes limitations of primary powder suspensions, particularly regarding solar inactivation.