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Bti
Bt are (Bacillus thuringiensis) naturally occurring bacteria found in soils around the world. Certain strains of this bacteria produce substances that kill insect larvae when ingested but don’t affect other animals. These strains have been developed into control tools to suppress pest insects, including mosquitoes, worldwide.
Different strains of the bacteria affect different groups of insects. One strain, Bacillus thuringiensis subsp. israelensis (Bti), is effective against mosquito larvae and certain other closely related aquatic insects. Unlike synthetic and chemical insecticides, Bti is only effective against mosquito larvae and other closely related aquatic insects.
How It Works:
Bti bacteria produce a protein crystal during fermentation. These microscopic crystals are ingested by mosquito larvae as they feed, and must be ingested by an insect to work. In the mosquito’s digestive system, the crystals are dissolved and converted into protein molecules that bind with unique receptor sites on the mosquito gut wall. This binding causes changes that destroy the walls of the mosquito larvae’s gut. The larvae stop feeding within hours and quickly die, never becoming flying adults.
PC: GDG Environment
How BNM uses Bti:
As a biopesticide, Bti is produced through fermentation, like making spirits or yogurt. The bacteria are fed nutrients and grow in large stainless-steel tanks. After several days, nutrients are cut off. The bacteria die, leaving dead cells, crystal proteins, and spores in the broth. Producers of BTi process the broth from such tanks to sell commercially including for home use.One of our partners, the Kaua‘i Forest Bird Recovery Project (KFBRP) has been treating mosquito pools by hand for the last six years. Liquid or granule forms of Bti are applied directly into the water where the mosquito larvae ingest the bacteria. In 2026, BNM will expand the use of Bti to critical forest bird habitat on Maui through aerial application. Distributing Bti by helicopter is a way to deliver the biopesticide to even the smallest mosquito pools and streams that are not feasible to hike to and treat by hand. The droplets from aerial liquid application are able to reach between vegetation in the forest as they fall to the ground, which means more pools and smaller habitats can be treated.
Aerial deployment of Bti in endangered honeycreeper habitat, Kaua'i
PC: DLNR
Is it Safe?
Bti selectively targets the larvae of mosquitoes and certain other flies, including black flies and some midges. It does not affect all insects indiscriminately, although some non-target aquatic invertebrates may be susceptible. It is non-toxic to humans, pets, and native wildlife.Bti has undergone nearly 40 years of lab and field research and over 30 years of large-scale operational use in a variety of public health programs around the world, primarily in urban areas. No studies to date have found any health effects in mammals or any health effects in communities where Bti spraying has been used. The World Health Organization has approved the use of Bti for drinking water. It breaks down rapidly under UV light and does not multiply in water.Additionally, it is commercially available in home improvement and hardware stores as ‘mosquito dunks’ for home use.
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