Effective sustained release of microbial pesticides in aquatic environments can be achieved by the combination of buoyant particles with a particulate microbial active ingredient. The resulting materials in the form of a particulate have combined density of less than one. The materials are then dispersed into gypsum slurry that is poured into briquette molds, or made into granules or pellets of various sizes, to form a solid, sinking, pest control composition. Once applied in aquatic field sites, the surface of the matrix slowly dissolves, releasing many minute buoyant pesticide laden particles to the water surface over the life of the product. Once at the surface, the particulate microbial pesticide(s) release from the buoyant particles and are distributed throughout the water column to be ingested by susceptible immature filter feeding mosquitoes and pestiferous flies.
