Larvicides

A larvicide (alternatively larvacide) is an insecticide that is specifically targeted against the larval life stage of an insect. Their most common use is against mosquitoes. Larvicides may be contact poisons, stomach poisons, growth regulators, or (increasingly) biological control agents.

The biological control agent Bacillus thuringiensis, also known as Bt, is a bacterial disease specific to Lepidopteran caterpillars. Bacillus thuringiensis israelensis, also known as Bti, and Bacillus sphaericus, which affect larval mosquitoes and some midges, have come into increasing use in recent times.

Bti and B. sphaericus are both naturally occurring soil bacterium registered as larvicides under the names Aquabac, Teknar, Vectobac, LarvX, and VectoLex CG. Typically in granular form, pellets are distributed on the surface of stagnant water locations. When the mosquito larvae ingest the bacteria, crystallized toxins are produced that destroy the digestive tract, resulting in death. These larvicides will last only a few weeks in water and pose no danger to humans, non-targeted animal species, or the environment when used according to directions.

Methoprene is an insect growth regulator agent that interrupts the growth cycle of insect larvae, preventing them from development beyond the pupa stage. MetaLarv and Altosid are products containing S-methoprene as the active ingredient. They are usually applied to larger bodies of water in the form of time-release formulations that can last from one to five months. Use of this larvicide does not pose an unreasonable health risks to humans or other wildlife and it will not leach into the ground water supply. Methoprene is moderately toxic to some fish, shrimp, lobster, and crayfish, and highly toxic to some fish and freshwater invertebrates; it bioaccumulates in fish tissues.

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