Mosquito Control Around the Home

— Written By Deborah Hunter
en Español

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Mosquitoes are important pests because their biting activity often interferes with outdoor activities. They may transmit disease organisms to people and domestic animals, although the incidence of such diseases in NC is relatively low. Most mosquitoes are active during twilight hours and at night; however, around the home, mosquitoes produced in discarded containers are active during the day.

Although mosquito species differ in their biology and behavior, they share one common requirement: they need water to complete their life cycle. We traditionally associate mosquitoes with marshy areas. Although many species do breed in such areas, there are other species that deposit their eggs in areas that flood during rainfall, e.g., tree holes, discarded man-made containers, or depressions in the ground. These eggs can actually lay dormant for several years.

When water is present, mosquito eggs usually hatch in 24-48 hours, releasing larvae that are commonly called “wrigglers.”  Generally, the larvae feed on microorganisms and organic material in the water, but some mosquitoes prey on larvae of other mosquito species and are regarded to be beneficial. About 7-10 days after eggs hatch, larvae change to the pupal or “tumbler” stage in preparation for adult life. Female mosquitoes begin seeking animals to feed on several days after emerging from water. Males do not bite; they feed on plant juices.

Mosquito control based solely on using pesticides will likely fail. An effective mosquito control program requires a true IPM approach aimed at disrupting the mosquito’s life cycle through habitat modification and insecticides where appropriate. It is important to remember that mosquitoes need water to complete their life cycle. Therefore, bird baths, discarded tires, plant pots and other man-made containers can serve as breeding sites for mosquitoes around the home. Removal of discarded containers will help reduce (but not eliminate) mosquitoes populations by eliminating some of their breeding sites. Because some mosquito species can fly some distance from their breeding sites, efforts to reduce mosquito populations must be community-wide. If extensive natural breeding sites exist, then local residents should consider the need to form a local mosquito control program. These programs may include treatments of breeding sites and/or the application of insecticidal sprays to control adults. However, mosquito control programs can be costly and controversial, since some insecticides, if used improperly, have negative off-target effects. Communities should determine the source of their mosquito problems and explore community cleanup projects as a means of controlling mosquitoes before they consider the development of an insecticide based program.

Chemical control programs can target larvae and/or adults. Concern over the impact of common insecticides on non-target organisms in natural mosquito breeding areas has led to greater use of a biological insecticide “Bti” which contains a bacterium *Bacillus thuringiensis israelensis*. This insecticide is somewhat similar to the “Bt” products used for controlling caterpillars on plants; however, “Bti” only affects the larvae of mosquitoes and a few related insect species, such as black flies. A popular form of Bti is the “Bactimos” brickette that can be placed into the water. The insecticide essentially leaches from the brickette over a period of several hours and can reduce larval populations within 24 48 hours. There is now a Bti product available to homeowners, sold under the name “Mosquito Dunks”. These products tend to be expensive compared to regular insecticides and they are probably most effective in small mosquito breeding sites. However, one key point to convey to your callers: just because an area floods periodically does *not* automatically make it a mosquito breeding area. Larvicidal treatments should be based on observations, not assumptions, of pest activity.

Control of adults usually relies on fogging an area, primarily in the evening when most mosquitoes are active. Spraying shrubs around property that may serve as adult resting areas is probably most effective when you have large hedgerows adjacent to flood plains. For most homeowners, spraying the azaleas, hollies and other shrubs in the yard will have little impact on mosquito populations; their effort is better spent on personal protection and identifying the real source of the mosquitoes.

Some personal protection from mosquitoes can be achieved through the use of insect repellents. The formulation containing the highest percent of active ingredient as stated on the product label should be chosen and applied to exposed skin. HOWEVER, repeated use of repellents over a short period of time should be discouraged, especially for children and pregnant women.

Most non-chemical control methods are more “show” than actually aids in reducing mosquito populations. Electrocutor traps (“bug zappers”) placed out of doors has not been found to reduce or eliminate mosquito populations. Similarly, those electronic mosquito repellers that emit high-frequency sound to “repel” mosquitoes are not effective. On the biological front, it is true that Purple Martins and bats do consume mosquitoes; however, the feeding activity of insect-eating birds and bats has not been found to be sufficiently selective to cause noticeable reductions in mosquito populations. Also, claims that certain plants will repel mosquitoes are not supported by test results. These plants are most effective as decorations on the deck, not for reducing the invasion of mosquitoes.

Prevention is the best overall strategy. Aside from protecting themselves outdoors, homeowners would be better off spending the time and money making sure that their window and doors fit tightly and are kept in good repair.

(Charles Apperson and Mike Waldvogel, N.C. Cooperative Extension Entomology)