Centers for Disease Control and Prevention

Managing Rodents and Mosquitoes

Through Integrated Pest Management

MANAGING MOSQUITO INFESTATIONS Excerpt from 2002 Transcript CLICK HERE FOR full Transcript

“…Less than a hundred years ago there were an estimated 600 thousand cases a year of malaria.  But, in the 1940s, thanks to a variety of programs orchestrated by the Office of Malarial Control in Atlanta, malaria and other mosquito-borne diseases were effectively eliminated.  The Office of Malarial Control gave rise to what we know today as the Centers for Disease Control and Prevention.  CDC continues to work closely with state and local mosquito control or abatement programs, but is not directly involved in local mosquito control activities.  In the U.S., this is generally a local responsibility performed by city or county governments or public or private mosquito control programs.

Prior to the detection of West Nile virus in the United States in 1999, there were four important mosquito-borne zoonotic diseases transmitted in various parts of the country.  They are St. Louis encephalitis, eastern equine encephalitis, western equine encephalitis, and La Crosse encephalitis.

Is it fair to say though that in recent years the threat from mosquitoes has been increasing again?

Yes, especially in northern areas of the country.  However, areas with persistent, recurring zoonotic diseases have continued to maintain integrated mosquito management programs, especially since the 1975 epidemic of St. Louis encephalitis which caused around 21 hundred human cases and one hundred seventy deaths.

In many parts of the southern US, mosquito control programs have been maintained and enlarged due to an increased demand for fewer mosquitoes in expanding urban, suburban and recreational areas.  Fortunately, the programs that have the ability to manage nuisance mosquitoes also possess the ability to reduce the density of mosquitoes that transmit viral diseases.

The most effective way of controlling the mosquito population is to locate breeding sites and to actually control the mosquito larvae.  They’re most concentrated, they’re more accessible and they’re not as mobile as adults are.

… the cardinal rule is “manage the environment to manage the pest.”  We need to understand the relationship between mosquitoes and the environment.

In the mosquito life cycle, the adult female always looks for a habitat associated with water to lay her eggs.  Depending on the species, this could be a bucket with water, a storm drain, a salt marsh, the flood plain of a river, or a tree hole with water.  About 2 days after the eggs are laid, they are ready to hatch.  A small larva or wriggler comes out and begins to feed on bacteria and organic materials in the water.  At the end of four larval stages the mosquito transforms into a pupa and from an aquatic into a terrestrial creature.  After about 2 days in the pupal stage, the adult mosquito emerges onto the water’s surface and is soon able to fly.  The entire process from the egg hatching to the emergence of the adult mosquito can take as little as 7 days, under optimal conditions of food and temperature.

For Integrated Pest Management, applying interventions during the larval or aquatic stage of mosquito development has proved to be the most effective method of control.  To do this we employ various physical and chemical approaches to treat the unique aquatic habitats where different mosquitoes reproduce.  Pesticides used for larval control are known as larvacides.

There is always interest in biological interventions, namely the use of biological organisms or their byproducts to manage mosquitoes.  Fish that eat mosquito larvae are the most extensively used biocontrol agent.  Biocontrol has the potential of becoming a more important tool and playing a larger role in the future but more research is needed.

Adulticides are another method of chemical intervention that is used in aerosol form. Although less efficient than larvacides, they do sometimes represent an important part of any I-P-M program.  During epidemic periods or when mosquitoes are produced in adjacent jurisdictions, it may be the only option for mosquito control.  But the perceived ‘need’ for such spraying should be very carefully assessed in terms of public health and the environment.  They typically are applied as an Ultra-Low Volume spray dispersed either by truck-mounted equipment or from aircraft.  This is the common image that many people have of mosquito control but it is just one intervention of an I-P-M program.  Let's hear one caution about the use of pesticides.

(USE OF PESTICIDES TAPE)

Integrated pest management is an effort to reduce the use of pesticides in a mosquito controlled program because while pesticides are effective in mosquito control, they also can have long term harmful effects in the environment and to human health.  In our county we have been working with experts and citizen groups to reduce or eliminate any unnecessary use of pesticide, and to use other non-chemical measures where possible for reducing the mosquito problem.

You can’t be outside enjoying the evening air.  The children cannot play comfortably.  You have to buy sprays and whatever for your yard and for the air and for your children.  That can be expensive, too.

Clearly, public education about mosquitoes is another important component of I-P-M.  Residents can prevent the pots and other artificial containers in their backyards and patios from becoming prime mosquito habitats.  Any of these containers, ranging from buckets to tires to children’s toys to boat covers, if filled with water and left unattended for only a week, can produce mosquitoes, resulting in higher densities at the residence – the site where people are most commonly bitten by mosquitoes, including those that transmit West Nile virus.  Other habitats such as catch basins, discarded tires, roadside ditches, and intermittent streams in urban areas require local government management efforts. Let's hear what one local health officer has to say about public education.

(MOSQUITO BORNE DISEASE TAPE)

It’s very important for communities to be aware of pest controls, and safe ways to control pests including not using pesticide through preventive measures.  So the health department reaches out to communities through the internet on our website, through public service announcements, through appearances at community meetings, through flyers, through an informational hotline, and any way we can to get the word out about ways that people can prevent mosquito-borne diseases.  Mosquito control requires the cooperation of everyone in the community.  In order to get rid of standing water, homeowners need to do their part.  In order for catch basins to have larvacide applied, every municipality needs to make sure that the catch basins are cleaned.  Without the involvement of communities, homeowners, and everyone, it will be difficult to prevent mosquito-borne diseases.

In addition, residents need to be aware of the effectiveness and value of physical barriers or interventions.  Originally window screens were one of the important innovations which helped eradicate malaria in this country and they continue to be effective today. Using chemical repellents too is an important way in which people can prevent themselves being bitten by mosquitoes. “

Excerpt from EPA (Environmental Protection Agency) Website 10/2007: Resource Link is: http://www.epa.gov/pesticides/health/mosquitoes/larvicides4mosquitoes.htm#microbial

Microbial larvicides are bacteria that are registered as pesticides for control of mosquito larvae…. Microbial larvicides may be used along with other mosquito control measures in an IPM program. The microbial larvicides used for mosquito control are Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (B. sphaericus).

Bacillus thuringiensis israelensis is a naturally occurring soil bacterium registered for control of mosquito larvae. Bti was first registered by EPA as an insecticide in 1983. Mosquito larvae eat the Bti product that is made up of the dormant spore form of the bacterium and an associated pure toxin. The toxin disrupts the gut in the mosquito by binding to receptor cells present in insects, but not in mammals. There are 26 Bti products registered for use in the United States. Aquabac, Teknar, Vectobac, and LarvX are examples of common trade names for the mosquito control products.

Do Microbial Larvicides Pose Risks to Human Health?

The microbial pesticides have undergone extensive testing prior to registration. They are essentially nontoxic to humans, so there are no concerns for human health effects with Bti or B. sphaericus when they are used according to label directions.

Do Microbial Larvicides Pose Risks to Wildlife or the Environment?

Extensive testing shows that microbial larvicides do not pose risks to wildlife, nontarget species, or the environment, when used according to label directions.