Larvicides are products that are used to control mosquitoes in their larval stage. The Florida Keys Mosquito Control District uses several larvicides, depending on the situation.
Bacillus thuringiensis israelensis, or Bti, is a naturally-occurring soil bacterium. The bacterium produces proteins in a crystalline form. When the mosquito larvae eat these crystals, the proteins attack their gut wall, killing the larvae. Bti has a highly specific mode of action, and is of minimal environmental concern. Bti is quickly biodegraded and leaves no residue. The Florida Keys Mosquito Control District applies Bti either by hand or by helicopter. The field inspectors apply Bti in liquid form by hand. Applications of Bti in granular form (attached to ground corncob) are made by helicopter. Bti is applied for control of mosquito larvae in large areas of water.
Bacillus sphaericus (Bs) is a common soil-inhabiting bacterium. The bacterium produces a protein toxin that may be used to control mosquito larvae. The Florida Keys Mosquito Control District applies Bs as a granular formulation (attached to ground corncob) to control mosquito larvae in highly polluted water, such as sewage treatment plants. Bs is nontoxic to nontarget organisms.
Methoprene is a synthetic mimic of juvenile hormone, a hormone found in insects. When methoprene is present, the development of the mosquito larvae is disrupted, and they do not proceed to the adult stage. The Florida Keys Mosquito Control District uses methoprene in situations like cisterns and abandoned swimming pools. The breeding site needs to be treated only once every 30 days.
Temephos is used very sparingly and infrequently by the Florida Keys Mosquito Control District. It is applied only to temporary pools that contain mosquito larvae but do not support nontarget organisms.
Spinosad is used in a tablet form in long-standing water sources like cisterns and abandoned swimming pools. The breeding site needs to be treated once every 2 months through 6 months, depending on the water quality and form of spinosad used.
Chlorpyrifos is used to treat ornamental bromeliads (water-holding plants). The water that accumulates in these plants is a favored breeding site for some mosquito species. These mosquitoes account for many complaints in some neighborhoods.
Oils and monomolecular surface films are used to control pupae and late-fourth instar larvae by interfering with their ability to breathe. These products are used only when an adult emergence will occur without treatment.
Gambusia are species of mosquito-eating fish. The Florida Keys Mosquito Control District raises these fish and stocks them in permanent freshwater bodies. These fish will reproduce and continue to eat mosquito larvae.