Bti

Bacillus thuringiensis israelensis (Bti) is a bacterium used as a biological larvicide to control populations of mosquitoes and black flies. It is a subspecies of Bacillus thuringiensis that produces crystal proteins, including Cry toxins (such as Cry4Aa, Cry4Ba, Cry11Aa) and Cyt toxins (notably Cyt1Aa), which are activated in the guts of certain insect larvae.

Mechanism and formulation products: When mosquito or black fly larvae ingest Bti crystals, the toxins are activated in the alkaline larval gut. The activated proteins bind to gut receptors and form pores, causing cell lysis and larval death. This specificity largely limits effects to Diptera larvae, making Bti available in several formulations, such as granules, briquets, and liquids, for application to standing water, wetlands, ponds, and drainage ditches. Treatments are typically repeated as long as larvae are present and environmental conditions permit.

Applications and use: Bti is widely used in public health and vector control programs to reduce disease risk by lowering mosquito populations, especially in water bodies where chemical insecticides are impractical or undesirable. It is also used in some agricultural and wastewater contexts to target pest larvae without broad-spectrum toxicity.

Safety and environmental impact: Bti is generally considered to have low risk to humans, vertebrates, and many non-target aquatic organisms when used as directed. Its toxins are specific to certain Diptera larvae and do not persist long in the environment. Nevertheless, regulatory assessments emphasize following product labels and local guidelines, and considerations should be given to potential impacts on non-target aquatic invertebrates in sensitive habitats.

Limitations: Effectiveness depends on the presence of target larvae and suitable water conditions. High organic load, clumped larval habitats, or rapid dilution can reduce impact. Some mosquito species can exhibit reduced susceptibility, and resistance management strategies are advised in long-term programs.