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Pesticides and Mosquito Control
If you have questions about neighborhood ponds and mosquito treatments, please contact Sylvia Heaton, DEQ Water Division at 517-373-1320.
Control of Culex Larvae and Pupae is a Priority
Although WNV has been detected in several species of mosquitoes, about 70% of the positive samples have been from Culex pipiens (the house mosquito) and related species of Culex. The house mosquito breeds most prolifically in stagnant water that has a heavy organic content. In urban areas, catch basins, artificial water-filled containers like used tires and poorly draining ditches are common production sites for Culex mosquitoes. Additionally, most of the house mosquitoes present in a community are produced locally because the house mosquito does not fly more than 1 to 2 miles from its larval development site. In contrast, the inland floodwater mosquito (Aedes vexans) can fly 10 or more miles from where they hatch, particularly along prevailing winds. Although floodwater mosquitoes can be a nuisance to the public when they are abundant, they have not been significant disease carriers in Michigan and are currently believed to be minor carriers of WNV.
Integrated Pest Management (IPM) is the most appropriate approach to controlling mosquito populations for reducing the risk of infections by the WNV. An IPM approach includes a variety of techniques including: education and outreach, surveillance of mosquito populations, source reduction to reduce the opportunity for mosquito breeding, larviciding breeding sites to kill the preadult stages of mosquitoes, and adulticiding to kill remaining adults in order to further reduce the breeding populations.
"Larviciding" or the treatment of locations where mosquito larvae are present such as the water impounded in the bottom of "catch basins" (storm drains) is an effective measure. Catch basins may be found along streets, in parking lots and sometimes in backyards. Because catch basins are a major source of the house mosquito in urban areas, catch basins should be treated at least twice during the summer (June and July) to control Culex mosquitoes. Ideally, municipalities would use larvicides to treat catch basins and other locations that produce Culex mosquitoes as often as determined by inspection, according to insecticide label directions (See Mosquito Larvicides Commonly Used in Michigan) and as authorized by the Michigan Department of Environmental Quality (MDEQ) - See MDEQ Approval Process of Mosquito Control Projects . This would reduce numbers of vector mosquitoes during late summer, the period of greatest risk to humans.
We recommend that local officials review the references about mosquito control found in the On-line Mosquito Control References, particularly the CDC /USEPA Joint Statement on Mosquito Control and Integrated Methods of Mosquito Control. All applications of pesticides to surface waters of the state and wastewater treatment facilities must be approved by the MDEQ. The alteration of wetlands (draining and filling) is not an acceptable recommended method for mosquito control. The alteration of wetland habitats will have serious long-term impacts on fish and wildlife habitat. Wetland alteration may require state and federal permits (See Wetland Permits).
Spraying for Adult Mosquitoes
Adult mosquito control (also called "fogging," "spraying" or "adulticiding") is the method of mosquito control that is most familiar to the public and should be part of a comprehensive integrated mosquito control program. Adulticiding kills only mosquitoes that contact insecticide droplets; the fog soon dissipates. Although the local mosquito population is reduced for a few days, fogging does not prevent mosquitoes from re-entering the area. Because only a part of the local adult mosquito population is reduced only for a few days by adulticiding, municipalities should give priority to larval mosquito control of Culex mosquitoes. Nonetheless, when the risk of human disease is present, the only method that will reduce the population of WNV-infected mosquitoes is knowing where mosquito density poses a risk to humans and focused adulticiding to reduce the mosquito population. Treatment for control of WNV-infected adult mosquitoes is a valid and legal option for local officials to employ as a supplement to larviciding.*
Be advised, community wide spray programs are regulated by MDA and require notification and communication with the public when treatment for adult mosquitoes is planned. An informed public will better understand the measures being taken and will be able to take precautions to limit their exposure to pesticides.
In summary, local agencies that conduct mosquito control should give highest priority to eliminating breeding sites (source reduction) and larviciding. Elimination and treatment of Culex mosquito production sites will help municipalities protect Michigan citizens from mosquito-borne West Nile virus.
*Adulticiding for adult mosquitoes should ONLY be conducted at the proper time (evening or early morning) and under appropriate environmental conditions (such as temperatures from 60 to 85 degrees Fahrenheit and low wind speeds). For ultra-low volume (ULV) spraying units to control mosquitoes, they MUST be serviced so they produce a proper droplet size spectrum. Please consult the pesticide label and manufacturer's recommendations for further information. Communities are advised that direct or incidental application of adulticides to surface waters is prohibited by both the pesticide use labels and by state regulation. In Prep: Water Division Site
See the Homeowner Mosquito Control section for simple, non-chemical mosquito control methods that can be used to eliminate mosquitoes around your home.
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