A Basic Mosquito Primer

Editor’s note: This article is modified from the upcoming Fly Field Guide, 2nd Edition.

Mosquitoes are the most important group of flies in terms of human health as they carry and transmit disease organisms to humans and animals and are responsible for more death and misery than any other factor in human history. Mosquitoes by themselves have changed history by decimating invading armies or causing groups of humans to abandon certain areas due to the presence of mosquito-borne disease.

In the United States, citizens generally are well protected from mosquito-borne diseases thanks to the hard work of health officials and pest professionals. Today, the occasional mosquito-borne disease outbreak involves some form of encephalitis. Newly emerging diseases including dengue fever and Zika virus recently have been in the news.

About 166 different species of mosquitoes are found within the United States, and many of these species have specific habitat requirements. Of these, 139 species in this country belong to four genera — Anopheles, Aedes, Culex and Psorophora.

KEY INSPECTION TIPS. Most pest control companies rarely get involved in widespread mosquito control, but some companies are equipped and licensed to perform mosquito ULV applications or to apply larvacides to mosquito breeding sites. Occasionally, mosquitoes will cause a problem in a particular home or commercial building and the owners or residents look to a pest professional for relief from their mosquito issues.

In most situations involving structures, adult mosquitoes are entering from outside or are disrupting outdoor activities by their presence on vegetation surrounding the building. Adult mosquitoes will be breeding on or very near the property in sources of standing water which include small ponds, drainage ditches, drainage ponds, culverts and manholes with standing water. Other, usually overlooked locations, are old tires, bird baths, tree holes, trays under potted plants, clogged rain gutters, and any item on the ground that can collect and hold water for seven days or longer (see photo below). Mosquitoes also can breed in standing water in a crawlspace, basement or sump pumps. In coastal areas of the South, plants called bromeliads collect rainwater and may serve as breeding sites for mosquitoes.

Whenever inspecting outside during any pest or termite service, keep an eye out for likely larval breeding sites so these can be identified to the customer. Checking larger bodies of water like a pond or drainage ditch requires a long-handled scoop to sample the water along the edges for larvae.

Adult mosquitoes will be attracted to a building for various reasons with the presence of people being the primary factor. During the day, mosquitoes will rest within vegetation — typically under leaves in more shaded areas — around or near the building. Using an insect net is the quickest way to sample vegetation for adult mosquitoes. Darkened or shaded walls inside and out also should be inspected for resting mosquitoes.

CONTROL TIPS. Unless properly equipped, trained and licensed in area- wide mosquito control, a pest professional should avoid becoming involved in situations where treatment of large areas or entire neighborhoods are involved. This article will examine only those limited situations involving mosquitoes in and around urban structures.

Identify Breeding Sites. Before a control program can be designed to control mosquitoes in or around a particular building, the mosquito resting sites and breeding sites on the property must be identified. If the building is located right next to a river, pond, marsh or in a wooded area, any significant, long-term relief from mosquitoes may not be possible. Consult with the appropriate local county or city authorities for help in these situations.

Eliminate Breeding Sources. The best long-term control of mosquitoes is to identify, empty or treat breeding sites. Any containers holding water should be drained and stored upside down, where possible, to keep from collecting water. Customers should be advised to empty items (such as bird baths) that fill with water and refill them weekly. Tree holes can be filled with sand to eliminate them as a breeding source. Gutters need to be checked regularly for clogs and standing water.

Controlling Mosquito Larvae. Ponds, drainage ditches and other bodies of water can be treated with larvicides to control mosquito larvae that 1) use an IGR mosquito product or 2) contain the bacteria B.t.i. These products are specific only to mosquito larvae and have minimal effect on the surrounding environment or other types of aquatic life. Methoprene (an IGR)is formulated as briquets, pellets, granules and liquid. The photo at right shows an Altosid briquet placed on dry ground in a low area known to collect water and breed mosquitoes near a rural home. Consult with manufacturer representatives for advice in the most effective use of their product(s).

Controlling Adult Mosquitoes. The best way to control adult mosquitoes indoors is by excluding them from the building using screens and keeping doors closed except while in use. Large industrial buildings such as warehouses, however, often keep open for ventilation purposes during the summer and should equip such doorways with tight-fitting screens.

Vegetation should be kept to a minimum near buildings located in prime mosquito habitats, especially next to entryways. Less vegetation provides less shelter for adult mosquitoes. Outside vegetation may be treated to kill mosquitoes where they land to rest using one of a number of residual insecticides labeled for mosquitoes. Follow label directions and any state regulations regarding such applications.

Residual applications should be applied lightly as mist or fine spray, directed to the underside of leaves of vegetation where adult mosquitoes are known or suspected to harbor during the day. Typically, affected vegetation will be near the ground and not tree limbs overhead. Care must be taken to avoid treating flowering plants where bees and other pollinators may visit. Applications in areas where bees are active should be avoided.

Outside and inside surfaces where mosquitoes alight to rest can be spot treated with a labeled residual CS or SC insecticide. Direct treatments to surfaces behind vegetation, under decks, under soffits and similar sites where adult mosquitoes are likely to harbor during the day.

Traps. A number of commercially available mosquito traps that use heat and/or carbon dioxide to attract and capture mosquitoes may be purchased. Some PMPs sell and service these traps. The Catchmaster AGO Trap is a bucket-style trap designed to attract and remove female mosquitoes looking to deposit eggs (oviposit). Other mosquito traps include the Biogents mosquito trap (Nixalite) and the In2Care Mosquito Trap (sold by Veseris). I urge you to contact your supplier reps for more details.

Mosquito traps designed for interior use may be useful in attracting and reducing numbers inside large warehouses and similar areas where mosquitoes may be entering in significant numbers. Large commercial operations may be located at the periphery of towns and cities or in rural areas next to wooded areas, marshes, or rivers and be subject to greater mosquito pressure.

ULV Treatments. On occasion, a customer may request quick reduction of mosquitoes seen indoors. A space (ULV) treatment using a non-residual insecticide may be applied to kill mosquitoes. Follow the ULV product’s label carefully and take necessary safety precautions (e.g., turn off HVAC, temporarily cover or shut off smoke detectors, extinguish all pilot lights). Keep in mind that after treatment, new mosquitoes can enter the building if steps are not taken to reduce outside numbers near the building and to exclude them from entering.

Final Feed Mosquito Bait. A novel bait product called Final Feed recently was introduced by Catchmaster. Final Feed is applied to vegetation and surfaces where mosquitoes are likely to hang out. The bait contains a specialized sugar formulation with microencapsulated garlic as the toxicant. Final Feed takes advantage of the male and female mosquitoes’ desire to feed on nectar to obtain sugars used for energy. Males only feed on nectar while females also require a blood meal to produce eggs. Both sexes readily seek out a sugar meal soon after molting into adults and blood feeding by females is suppressed after feeding on this bait. Final Feed controls Aedes, Anopheles and Culex mosquitoes.

SUMMARY. Mosquitoes occur most everywhere in the U.S. so pest professionals will encounter many situations where services can be offered. Remember some states may require a firm to have an additional public health category license in addition to a GHP license in order to treat for mosquitoes. Those providing mosquito management services should not offer just one method of control. PMPs need to provide prevention services by removing and managing breeding sources.