The district operators spend a large portion of their time monitoring standing water for mosquito larva. When an operator checks a site for larva they will determine the mosquito species, stage of development and size of population present. In addition to gathering information about the mosquito larva they will assess the source and then determine the best control measures for the situation. When necessary, operators will use larvacides.

Larvacides are an important tool for the operators to help prevent larva from developing into widespread adults. We have 3 categories of products for the control of larva: insecticides, juvenile growth hormones, and larvicidal films and oils.

Microbial Insecticides

• The product known as Bti (Bacillus thuringiensis israeliensis) can be as effective as chemical insecticides. Bti is a bacteria that, when eaten by mosquito larvae, produces a protein crystal that destroys the larvae's intestinal lining. It has no effect on other aquatic organisms except midges in the same habitat.

Insect Growth Regulators

• Methoprene is an insect growth regulator widely used by mosquito control districts. Methoprene mimics a natural juvenile hormone, and when present in the larval habitat it keeps immature insects from maturing into adults. Unable to develop into adults, the mosquitoes die in the pupal stage. Vector control technicians sometimes use methoprene to reach larval sources that would otherwise be difficult to treat.

Larvicidal Films and Oils

• Larvicidal films are applied to the surface of standing water. The film reduces the surface tension of the water, making it difficult for mosquito larvae and pupae to attach to the surface and breathe. A significant advantage of using larvicidal films is that mosquitoes cannot develop a resistance, since control is through a physical mode of action.