Mosquito Management: Mosquito Management

Mosquito Management
An Integrated Approach

The Wetland Habitat and Mosquito Management (WHAMM) Program of the DEEP's Wildlife Division uses an integrated approach to manage mosquitoes that includes larval (immature) and adult mosquito population monitoring, public education, and cultural, biological and chemical control methods. Similar components are used in other Integrated Pest Management (IPM) strategies. However, the mosquito control profession has been practicing IPM concepts for over 100 years and has refined these practices to be specific to controlling mosquitoes. The American Mosquito Control Association and others recognize this specialized strategy as Integrated Mosquito Management or IMM.

Public education which promotes eliminating sources of mosquitoes around the home and minimizing exposure to mosquito bites by taking protective measures is critical to managing mosquitoes. Control measures can be initiated when immature (larval) mosquito levels reach certain threshold limits. Additional steps can be taken to reduce adult mosquito populations when viruses like Eastern Equine Encephalitis (EEE) or West Nile Virus (WNV) are detected in mosquitoes. If warranted, biological or chemical insecticides can be strategically applied by ground or aerial application equipment to control larvae or adults. Long-term control using water management, particularly in tidal wetlands, can be used for managing mosquitoes and can be further integrated into enhancing and restoring degraded wetland habitats. These various components of Connecticut's IMM strategy are discussed in further detail below.

Mosquito Management Around the Home
The Connecticut Public Health Code prohibits homeowners from creating or maintaining sources of mosquitoes on their property. Violators are subject to enforcement actions by their local health department. There are several ways homeowners can minimize the number of biting mosquitoes in their yards. One of the easiest and surest ways to manage mosquitoes around the home is to eliminate standing water where mosquitoes can lay eggs. Mosquitoes need at least 7-10 days in water to fully develop. Some common sources of mosquitoes around the home are:

  • Artificial containers that hold water (e.g., pails, paint cans, discarded tires)
  • Open cesspools or septic tanks
  • Boat or pool covers or tarps that collect rain water
  • Unmaintained bird baths or wading pools
  • Storm sewer catch basins, rain barrels and clogged roof gutters
  • Rot holes in trees and stumps

Practice good sanitation around the home. Homeowners should properly dispose of or recycle trash which can hold rainwater. Make it a practice to flush bird baths and wading pools weekly. Swimming pool filtering systems should be maintained and in good working order. Abandoned pools should be drained, filled or “shocked” with pool chemicals. Openings for standing water sources, such as septic tanks or rain barrels, can be sealed or covered with screening. Rotten stumps and tree holes can be filled with sand. Discarded tires should be disposed of properly, holes (0.5 inches or larger) can be drilled in the bottom of the tires to drain rainwater or the tires can be stacked and covered to prevent rainwater from entering. Lawns and gardens should be watered minimally to prevent puddling and to conserve water.

{Killifish} Ornamental pools and aquatic gardens can become sources of mosquitoes if the water is allowed to stagnate. Water should be changed frequently or an aerator can be installed. Homeowners can practice their own biological control by stocking minnows, such as Gambusia, koi or guppies, which will eat mosquito larvae. The fish will need to be brought indoors for the winter or restocked annually because they will not survive Connecticut winters. Large pond stocking with non-native fish or releasing fish into public waters is prohibited. Insecticides, such as those containing the bacteria Bacillus thurgiensis var. israelensis (Bti), are available at many nurseries and garden supply centers and can be used to treat mosquito breeding sites. In general, natural ponds and lakes are not sources of mosquito breeding, because permanent bodies of water usually contain fish and other predators that would consume mosquito larvae. 

There are also ways homeowners can minimize the annoyance caused by adult mosquitoes. Mosquitoes prefer to rest in shady, calm areas and will avoid more open sunny, breezy areas. Mowing tall grass will reduce places where mosquitoes can rest. Mosquitoes are most active around dawn and dusk although some, such as the common saltmarsh mosquito, may be active throughout the day or may be more active during cloudy, humid weather. Simply avoiding outdoor activity during these peak mosquito times can minimize contact with mosquitoes.

To reduce the chance of being bitten when outside, wear protective clothing such as long sleeves, long pants and head cover. Light-colored, loose-fitting clothing is preferable because dark clothing radiates more heat and attracts more mosquitoes. Insect repellents containing DEET, picaridin, IR3535 or oil of lemon eucalyptus can be used by most people and are often effective for varying lengths of time. Permethrin, a synthetic pyrethroid that is widely available for repelling and killing ticks, also repels and kills mosquitoes. It is applied to clothing and provides longer-lasting protection. Do not apply permethrin products directly to skin. Although not marketed as repellents, there are several cosmetic liquids and creams that claim some level of mosquito repellency. These products may effectively repel when mosquito pressure is light, but need to be reapplied frequently. The U.S. Environmental Protection Agency (EPA) provides further information on the use and effective use of repellants.

Homeowners may also consider spraying pesticides labeled for mosquito control to shade trees, hedges and shrubs adjacent to foundations, fences and stone walls where adult mosquitoes are most likely to light. There are several over-the-counter aerosol sprays that homeowners can use to control mosquitoes. Always read and follow the label. Private, CT-certified applicators can also be hired to treat yards and neighborhoods. Make sure the applicator is certified in the "Mosquito and Biting Fly" category (cat. 7f) by the CT DEEP Pesticide Management Program. (Businesses Registered to Perform Mosquito Control in Connecticut)

To reduce mosquito infestations in the house, maintain screens over doors and windows. A porch or deck also can be enclosed with screening. Outside light use should be reduced and yellow light bulbs used when possible.

EEE and WNV can be fatal to horses. Horse owners are strongly encouraged to protect their horses from EEE and WNV by inoculation. Canine heartworm (filariasis) is a fatal disease circulated in dogs by biting mosquitoes. The DEEP, CAES or DPH do not monitor for heartworm in mosquitoes. Dog owners are encouraged to protect their pets from canine heartworm by administering preventative medications obtained through their veterinarian.

Managing Mosquitoes Using Insecticides
Insecticides used for mosquito management are grouped into two categories. Larvicides/pupacides are used to control immature (larval or pupal) mosquitoes in aquatic habitats. Adulticides are used to control adult mosquitoes. The insecticides used are registered by the EPA and the CT DEEP Pesticide Management Program and do not pose any health hazards to humans or the environment when used in accordance with the label. 

Larvicides are applied by hand-, backpack or aerial application equipment to mosquito-breeding habitats when there is an abundance of larvae. Larviciding is more efficient and effective for managing mosquitoes than adulticiding because the larvae are concentrated in relatively small, well-defined, aquatic habitats. If larval control methods are successful, the need for adult mosquito management is greatly reduced or eliminated. 

Currently, the primary larvicides used by the WHAMM Program are the microbial compounds Bti (Bacillus thuringiensis var. israelensis) and Bs (B. sphaericus) and insect growth regulators containing methoprene. The microbial products release toxins when ingested by the filter-feeding mosquito larvae. Bti and Bs target mosquitoes and Bti is also labeled to control black flies and some midges. Bti has a short effective life (two to three days) and must be reapplied to each new generation of mosquitoes. The bacterial spores in Bs recycle in the larval mosquito population and can provide 4-6 weeks of larval control. Since these products must be ingested by mosquito larvae to be effective, they do not control the non-feeding pupae or adult mosquitoes. 

Methoprene is a compound that mimics the action of an insect growth-regulating hormone and prevents the normal maturation of mosquito larvae. The active ingredient, S-methoprene, breaks down rapidly in ultraviolet light. Methoprene does not persist in the environment but encapsulated formulations allow a slow release of minute amounts of methoprene and can provide several weeks of control. Methoprene is also used in flea and tick control in pets.

Pupacides in the form of monomolecular films (MMF’s) or oils create a thin film on the water surface which drowns the larvae, pupae or emerging adult. MMF’s break down in about 10-14 days.

Adulticides are considered for use by the WHAMM Program for reducing the adult mosquito population when a public health threat from mosquito-borne diseases like EEE or WNV exists. Adulticiding provides an immediate but short-term reduction in adult mosquito numbers. Backpack or truck-mounted equipment is used to create tiny, ultra-low volume (ULV) droplets of insecticide that drift through the swarm of mosquitoes or impinge on vegetation on which the mosquitoes will land. Truck-mounted applications are used in relatively small, localized areas where road access allows adequate coverage. If, however, the public health threat exists in a larger geographic area, where truck-mounted spraying would be ineffective, aircraft can be used to aerially-apply adulticides. The primary adulticides used by the WHAMM Program contain synthetic pyrethroids, such as resmethrin, sumithrin, or bifenthrin. These products contain the same active ingredients as several over-the-counter yard, garden and pet sprays. They do not pose unreasonable risks to humans or the environment when applied according to the label. Adulticiding is more costly than larviciding because adulticides are usually applied over larger areas.

The WHAMM Program is actively evaluating new mosquito control products as they become available. New products must provide consistent mosquito control, be nonhazardous to humans and the environment and be cost-effective. If new products meet these requirements, they are considered for possible use.

Low ground pressure equipment is used to excavate shallow ponds and channels on the marsh surface. These ponds provide habitat for larvae-eating killifish and other wildlife.

Resmethrin Fact Sheet  |  Scourge Fact Sheet

{Equipment excavating ponds and channels}
Low ground pressure equipment is used to excavate shallow pools and channels on the marsh surface to control mosquitoes and provide wildlife habitat.
 
{Aerial view of a marsh}
Shallow pools and plugged ditches restore wildlife habitat and control mosquitoes.
 
{Shorebirds in a marsh.}
Open marsh water management creates and restores habitat for fish, invertebrates, shorebirds, wading birds and waterfowl.

Mosquito Control Using Water Management
Where environmentally feasible, the WHAMM Program uses water management for source reduction and biological control of mosquitoes by making the sites 1) unsuitable for mosquito egg and larval development and 2) enhancing the area to provide open water habitat for natural mosquito predators such as fish and birds. This method provides more permanent control of mosquitoes than insecticides, resulting in a substantial reduction in insecticide applications and costs.

In tidal saltmarshes, a technique known as Open Marsh Water Management (OMWM) is the preferred method for controlling mosquitoes and enhancing or restoring wetland habitat (more about OMWM pdf). Unlike the parallel grid-ditch method used in the 1930’s which had adverse affects on tidal wetland hydrology and habitat, OMWM involves the selective excavation of shallow pools and ditches in mosquito-breeding areas. These pool and ditch networks are not connected directly to tidal channels and, therefore, do not drain at low tide. A higher water level is maintained in the pools which provides habitat for fish and other wildlife and encourages revegetation of the surrounding marsh by native grasses. Mosquito management is achieved by modifying egg-laying sites and by creating open water habitat for small naturally-abundant killifish, which prey on mosquito larvae and pupae. OMWM systems provide long-term control of mosquitoes, thus reducing the need to apply insecticides.

Mosquito Myths
A number of products on the market claim to have mosquito control capabilities. In most cases, these products have not been rigorously tested and do not perform as advertised. Mechanical traps, such as ultraviolet “bug zappers” or devices that repel using ultrasonic sound waves, do not meet advertiser’s claims. In fact, bug zappers attract few mosquitoes and may actually kill beneficial insect predators. The Connecticut MMP as well as other states and the American Mosquito Control Association do not endorse the use of these products to reduce mosquito infestations. Natural products, such as citronella-scented candles and plants, clove oil, peppermint, or diet supplements like garlic or vitamins that claim to repel mosquitoes are not supported by scientific evidence. There are many individuals who feel these products are effective; however, each person has a unique metabolism and body chemistry and these products may not be equally effective for everyone.

Natural predators, such as bats and some birds, will eat adult mosquitoes as do other types of insects such as dragonflies. However, studies have shown that mosquitoes make up a very small percentage of a bat or bird's diet. Bats and insectivorous birds are opportunistic feeders and may consume a large quantity of mosquitoes if mosquito populations are very high. However, if adult mosquitoes are at moderate or low levels (but yet are at pestiferous levels or in numbers that could still effectively transmit disease) bats or birds will not expend the energy to chase enough mosquitoes to obtain the equivalent amount of food as say a moth or large beetle. The CT Mosquito Management Program encourages the placement of bat and bird houses for the conservation of these species but does not endorse the use of them solely for the control of mosquitoes. For further information on mosquito myths read the Rutgers Cooperative Research and Extension Fact Sheet (pdf) or visit the University of Florida's Mosquito Information Website.