To help control mosquito populations, the Standing Water Initiative uses an Integrated Pest Management (IPM) approach which includes surveillance, source reduction and larviciding.  Mosquitoes can be prevented by eliminating standing water (source reduction) or by treating aquatic sites with environmentally friendly larvicides (insecticides designed to kill mosquito larvae).  Larviciding is the process of controlling mosquitoes when they are in the larval stage.  If standing water cannot be eliminated, controlling mosquitoes when they are in the water is an effective approach because the mosquito is somewhat isolated and known breeding sites can be recorded and routinely monitored.

Standing Water Initiative employees inspect and treat standing water on county property to control mosquito larvae throughout the spring, summer and fall.  Our control efforts are focused on eliminating mosquitoes in the larval stage.  We do not conduct adulticide operations.  We use a truck-mounted liquid larvicide applicator to treat county-owned mosquito breeding sites, such as roadside drainage ditches, flooded wetland areas, and underground storm water pipes.  Smaller areas are usually treated by hand with a granular form of larvicide.  Our larvicide treatments are based on field surveillance to ensure we are targeting areas in need of control and not applying larvicides where it is not necessary.

Treatment

There are a number of different products available for mosquito larval control and often times, one product will be better suited for a particular mosquito breeding site than another product.  Listed below are the common larvicides (active ingredients) we use:

Bti  – Bacillus thuringiensis israelensis (Bti) is a naturally occurring soil bacterium. Susceptible mosquito larvae species eat the Bti product and the toxin disrupts the gut in the mosquito.  Larvae become sluggish and die within 24 hours.

B. sphaericusBacillus sphaericus is a naturally occurring soil bacterium very similar to Bti. Mosquito larvae of susceptible species ingest a lethal dose of B. sphaericus crystals and spores. Toxins are released in the larva’s gut, paralyzing and damaging the digestive system. The larvae become sluggish and die within 48 hours

Spinosad – Spinosad is also a naturally occurring soil microorganism.  It is ingested by the susceptible mosquito larvae species, resulting in rapid excitation of the insect nervous system.

Methoprene – Methoprene is an insect growth regulator (IGR) that interferes with normal mosquito development.  Methoprene is absorbed through the skin of the larvae and disrupts the normal development cycle resulting in the inability to complete their metamorphosis.

Monomolecular Film – A Monomolecular Film (MMF) has the tendency to spread a thin film on the water surface.  It acts as a surfactant, reducing the surface tension of the water and making it difficult for the larvae and pupae to attach. Since larvae and pupae need to be able to attach to the water’s surface in order to breathe, this process slowly fatigues them until they drown.

Additional information about pesticides used for mosquito control may be found on USEPA’s Larvicides for Mosquito Control Web page.