Cowlitz County Mosquito Control District (CCMCD) is designed to keep mosquito populations below levels where they become a nuisance or a threat to public health throughout Cowlitz County. The Integrated Mosquito Management (IMM) is used by Cowlitz County Mosquito Control District
The District utilizes Integrated Pest Management (IPM) to formulate operation strategies and response to threats from mosquito borne disease. IPM is an effective integrated strategy endorsed by Washington State’s Department of Ecology and the Centers for Disease Control (CDC). IPM emphasizes a strategy of multiple methods to achieve long-term control of mosquito populations in order to prevent adults that are able to spread disease. Prevention is achieved through public education, surveillance, monitoring of treatment threshold levels, and control activities that use the least toxic and most environmentally friendly methods available.
Source Reduction and Habitat Modification:
Whenever possible CCMCD will reduce mosquito breeding sites through the elimination of standing water. As part of our public education, we urge residents to eliminate breeding sites around their homes and commercial properties and to report potential standing water in their neighborhoods. Additionally, CCMCD will collaborate with local, state, federal, and private agencies to identify water sources that create mosquito breeding problems and reasonable efforts will be made to reduce mosquito development in these zones.
If surveillance indicators meet established thresholds, the district will reduce development of larvae and pupae by selective use of larvicides in areas that cannot be emptied or drained. CCMCD will consider the toxicity and environmental impact when selecting pesticides and will make efforts to choose the least toxic and environmentally friendly pesticide that meets treatment requirements. The accuracy, quality and efficacy of the larvicide application will be closely monitored to ensure compliance with Federal and State guidelines.
Larviciding is the process of controlling mosquitoes when they are in the larval or pupal form. Controlling mosquitoes when they are in the water is an effective approach because the mosquitoes are concentrated, relatively immobile and mosquito specific larvicides can be used. For many Districts, including Cowlitz County MCD, this is the bulk of their operations.
Larvicides We Use:
Bacillus thuringiensis israelensis (Bti) is a microbe used in controlling mosquito larvae. Mosquito larvae of susceptible species ingest a lethal dose of Bti crystals and spores. Toxins are activated in the larval midgut, paralyzing and damaging the digestive system. Larvae become sluggish and die within 24 hours.
Bacillus sphaericus works very similar to Bti. Mosquito larvae of susceptible species ingest a lethal dose of B. sphaericus crystals and spores. Toxins are released in the larval midgut, paralyzing and damaging the digestive system. The larvae undergo tremors, become sluggish and die with 48 hours.
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 metamorphosis.
Spinosad is a natural substance made by a soil bacterium that can be toxic to insects. It is a mixture of two chemicals called spinosyn A and spinosyn D. It is used to control a wide variety of pests. Discovered in an abandoned Caribbean rum distillery in 1982, the parent bacterium was later fermented and found to have insecticidal qualities.
Larviciding oils are petroleum hydrocarbons that act as surfactants to prevent larvae and pupae from breaking through the water’s surface tension and blocks their breathing tubes so that they eventually drown. It can also make surface attachment more difficult.
If surveillance indicators meet established thresholds, adult mosquitoes will be controlled through the use of adulticides. Mosquito density and distribution, mosquito species, persistence of WNV activity, weather, time of year, and the proximity to human populations will be carefully considered in determining the necessity for adult mosquito control. The accuracy, quality and efficacy of the adulticide application will be closely monitored to ensure compliance with Federal and State guidelines. When adulticiding is required, the least toxic products possible will be applied using truck-mounted Ultra Low Volume (ULV) sprayers
Adulticiding is the process of controlling mosquitoes when they are mature, flying mosquitoes. Adult female mosquitoes are the ones that bite, so ultimately they provide the largest threat to public health. Adulticiding is necessary because larviciding is not 100% effective, some sites may be unknown, and mosquitoes can migrate into the District from surrounding areas. Also, there are areas that we cannot treat, and the mosquitoes have the opportunity to develop without intervention from us. Adulticiding can provide temporary control of mosquitoes in a given area, but is not practical as the only method of control.
Adulticide We Use in Trucks:
A pyrethroid is a synthetic version of pyrethrin, which is a natural chemical found in chrysanthemum flowers. Pyrethroids are the most common active ingredient in commercially available insect sprays. The pyrethroids permethrin, resmethrin, and sumithrin are registered for mosquito-control programs. Cowlitz County Mosquito Control District currently uses a adulticide product with Permethrin called Permanone RTU (4% Permethrin).
This is the EPA’s statement on Permethrin for mosquito control: Permethrin
Truck Application Example
The usual application rate of Permanone RTU is 1.98 fluid ounces per acre. Permanone RTU contains 4% Permethrin (a pyrethroid) . So, only 0.079 fluid ounces of Permethrin is applied per acre, which works out to 1 fluid ounce for every 12 acres. This incredibly small amount can be used because (1) mosquitoes have a low body mass and don’t require much insecticide to kill them and (2) we use ultra-low volume (ULV) technology in our truck foggers, which allows very small droplets to be formed