PEST MANAGEMENT

Integrated Pest Management (IPM) programs are a sustainable approach to managing mosquitoes by combining biological, cultural, physical, and chemical tools in a way that minimizes economic, health, and environmental costs. IPM programs use current, comprehensive information on the biology of mosquitoes and their interactions with the environment. This information, in combination with available pest control methods, is used to manage mosquito populations by the most economical means and with the least possible hazard to people, property, and the environment. IPM programs for mosquito control are based upon principles of identifying mosquitoes through surveillance, initiating source reduction methods, applying direct control procedures such as adulticiding and larviciding (when necessary), and providing public education. These principles are described in more detail below. In addition, evaluation of IPM programs is important to ensure their efficacy in reducing mosquito populations and mitigating human health risks.

IPM was initiated to overcome the shortfalls associated with indiscriminate application of pesticides. Pesticide application alone is not effective in controlling mosquito populations because it is difficult to get the pesticide into the habitat of the mosquitoes due to weather conditions (ex. rain, wind) or changes in adult mosquito activity. In addition, most pesticides used for adult mosquitoes do not provide long term residual control. Mosquito larvae are left to continue their development, and will quickly replace adults. In fact, mosquitoes can build resistance if pesticides are overused. Aside from their ineffectiveness, pesticides can have long term ecological, environmental, and human/animal health impacts. The Environmental Protection Agency (EPA) encourages non-chemical mosquito control measures; therefore, in an IPM approach to mosquito control, pesticides play only a small part.

Mosquito surveillance identifies locations where mosquitoes are abundant, which allows targeted control measures to be implemented before a problem arises. Surveillance helps to determine the mosquito species in a given area, allowing us to recognize species that can carry disease. Nuisance mosquito calls from the public can serve as places to start mosquito surveillance.

Different techniques are used to monitor mosquito activity. Mosquito larvae can be actively collected from their aquatic habitats using mosquito dippers, suction as meat basters, tea strainers, and syringes. Traps for adult mosquitoes include light traps which may be baited with attractants like carbon dioxide, octenol or sweat derivatives, and gravid traps, which are frequently used to sample Culex mosquitoes ready to lay eggs. New traps are continually being modified and developed to mimic vertebrate hosts, such as using heat, carbon dioxide production, movement, and reflective surfaces.

Source reduction is the process of removing or modifying mosquito larval habitats to make them unsuitable for larval development. This is the most effective and economical long-term method for maintaining low mosquito populations. By eliminating discarded tires, emptying containers that can hold water and filling tree holes with sealants, the breeding places of several disease-carrying mosquito species can be reduced. In areas with a large accumulation of trash or tire dumps, it may take a combination of local, regional, and state cooperation to remove the problem source. Source reduction also involves habitat modification, such as re-grading drainage ditches, so water will drain away quickly and not leave pools of standing water.

Adulticiding is the process of spraying low rates (dosages) of pesticide to kill adult mosquitoes and uses special equipment, such as trucks, small aircrafts, and backpack sprayers. Appropriate application allows small droplets of pesticide to drift through areas where adult mosquitoes are flying or resting. Effective adulticide application requires correct equipment settings, specific weather conditions, and timely application, both during the time of day and time of year. Adulticiding is the least effective of all the control methods; however, it does play a small role in any IPM program. Adulticiding may be undertaken to assist in controlling an outbreak of a mosquito-borne disease.

Larviciding is more effective than adulticiding and involves placing a chemical or other product into a water source to kill mosquito larvae. Chemical control of larvae should only be carried out by trained personnel or at their instruction. Insect Growth Regulators (IGR) are a type of larvicide that prevent insects and related organisms from completing their development to adults. A potential negative effect of IGR use is the impact these chemicals may have on non-target insects and related organisms (ex. crustaceans). Other larvicides include several “biorational” larvicides (bacteria registered as pesticides), such as Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus. These bacterial agents are available commercially and are safe and easy to use since the active ingredient is only triggered when ingested by target insects. Although Bacillus thuringiensisvar. israelensis and Bacillus sphaericus are living organisms used to control mosquito populations and could therefore be classified as biological control agents (see below); these bacterial agents are stored and applied in the same way as conventional pesticides.

Other chemicals that can be used as larvicides can have adverse effects on the environment. For example, light mineral oils applied to ponds will suffocate the aquatic larvae and pupae. Unfortunately, these oils will also suffocate other organisms living in the water, such as fish and amphibians. Organophosphates can be used to control larvae in artificial water containers. However, due to the negative ecological impact and personal harm associated with these pesticides, their use is discouraged.

Biological control is the use of a biological agent to control mosquito populations. Natural aerial predators, such as dragonflies, birds, and bats, usually do not specialize on eating adult mosquitoes only and will have limited impact on large mosquito populations. The most used biological agent is the Gambusia or mosquito fish, which eats the larvae.

Another major part of any mosquito control program is public education; schools are a good place to begin public education. The Centers for Disease Control and Prevention offer several educational mosquito programs targeted at school children. In addition, the general public should be informed of important mosquito bite prevention tips. This includes how to control mosquitoes around homes, making homes bug-tight (ex. window screens), and using appropriate personal protection when outdoors. Personal protection includes using insect repellant and wearing pants and long-sleeved shirts; interested individuals can also purchase head nets commercially. See http://www.cdc.gov/ncidod/dvbid/westnile/education.htm for more information.

To be successful, mosquito control programs should have the legal authority to perform mosquito surveillance and control activities, employ qualified staff, and have a stable and adequate source of revenue. Public health officials in West Virginia have the legal authority to reduce mosquito activity in an area. According to West Virginia code 16-3-6 (‘Nuisances affecting public health’), a public health officer “shall inquire into and investigate all nuisances affecting the public health within his jurisdiction” and is permitted (with judicial approval) to “restrain, prevent or abate the nuisance."

Mosquito control has proven successful in reducing human encephalitis cases in areas with arboviruses. For example, adulticide application has proven effective in reducing the number of mosquitoes that transmit West Nile virus1,2 and source reduction has also reduced the number of human cases of La Crosse encephalitis 3,4. These programs focused on removing mosquito breeding sites by searching throughout communities for artificial containers that hold water (old tires, buckets, childrens wading pools, upturned canoes) and applying larvicide in mosquito-breeding tires and other containers for short-term, seasonal mosquito control. Some programs have even taken legal action if residents did not dispose of tires or place artificial containers in storage after multiple warnings. Additional mosquito control activities include sealing tree holes with thermal insulation, making arrangements with retail tire dealers for proper tire disposal, and informing the community of mosquito control activities through television, radio, newspaper, and brochures.

In West Virginia, some county and regional efforts aimed at eliminating mosquito-borne disease cases have included reduction of mosquito breeding habitats (such as disposal or insecticide treatment of discarded tires and other artificial containers) and education about mosquito-borne disease prevention. Many insecticides are available in West Virginia for mosquito control, although some are considered to be “restricted use." For application of a “restricted use” insecticide, a person must have a license showing knowledge about pesticide application. Information about pesticides registered in West Virginia for general public use and professional application is available at http://www.kellysolutions.com/WV. Certification for restricted use pesticide application is completed through the West Virginia Department of Agriculture. Please see the following websites for more information: http://www.wvagriculture.org/Division_Webpages/READ-regulatory.htm and http://www.pestnetwork.com/continue/new%20state/westvirginia1.html.

1. Elnaiem, D. A., K. Kelley, S. Wright, R. Laffey, G. Yoshimura, M. Reed, G. Goodman, T. Thiemann, L. Reimer, W. K. Reisen, & D. Brown. 2008. Impact of aerial spraying of pyrethrin insecticide on Culex pipiens and Culex tarsalis (Diptera: Culicidae) abundance and West Nile infection rates in an urban/suburban area of Sacramento County, California. 2008. Journal of Medical Entomology 45 (4): 751-757.
2. Carney, R. M., S. Husted, C. Jean, C. Glaser, & V. Kramer. 2008. Efficacy of aerial spraying of mosquito adulticide in reducing incidence of West Nile virus, California, 2005. Emerging Infectious Diseases 14 (5): 747-754.
3. Parry, J. E. 1983. Control of Aedes triseriatus in La Crosse, Wisconsin. Pp. 355-364 in Calisher, C. H. & W. H. Thompson (eds.) California Serogroup Viruses. New York: A. R. Liss, Inc. xxiv + 400 pp.
4. Thompson, W. H. & C. B. Gundersen. 1983. La Crosse encephalitis: Occurrence of disease and control in a suburban area. Pp. 225-236 in Calisher, C. H. & W. H. Thompson (eds.) California Serogroup Viruses. New York: A. R. Liss, Inc. xxiv + 400 pp. Also based on CDC and EPA guidelines