Mosquito Control and the Environment

Mosquito graphic

Fighting Mosquitos around the world is a difficult and unending task. For the summer months to be enjoyable in some places, extreme measures are sometimes taken. The intense use of pesticides applied directly to wetlands and other stagnant water bodies can have severe environmental repercussions.

In the Minneapolis Star Tribune on April 20th, an article was published inaugurating the beginning of the 48th mosquito-fighting season (link may require login) for the Twin Cities Metropolitan Mosquito Control District. Many other areas around the US and other mosquito-afflicted regions are also now beginning their mosquito control seasons. The methods used for this vary widely - and some of them are pretty scary.

As it happens, the Twin Cities are using Bti, or Bacillus thuringiensis israelensis. This bacterial insecticide is considered one of the most environmentally sensitive tools available. The pesticide is highly targeted, effecting only mosquitos, blackflies, and midges. It is a spore composed of insecticidal proteins created by the Bti soil bacterium in unfavorable conditions - when mosquito larvae consume these spores, it kills them. As an insecticide, Bti uses dead bacteria to avoid releasing live organisms into the environment. The root bacterium, Bacillus thuringiensis has many strains - others are used to control a wide variety of insect pests.

Other common pesticides, unfortunately, are not so nearly harmless. Bti is only effective for controlling mosiquitos in the larval stages of growth - pesticides used to control adult mosquitos can be quite dangerous. One common pesticide for this purpose is Resmethrin. Although considerd to be "slightly toxic to practically non-toxic", this is only true of most organisms. Resmethrin is highly toxic to fish. Fortunately, the chemical is more likely to be applied in places where adult mosquitos congregate - spraying trees and lawns with a mist applicator. Still, any chemical that reaches the earth has the potential to reach water sources. The most significant danger in the use of Resmethrin is in run-off patterns to surface water, where the chemical can potentially be consumed by fish.

Although much of the United States has converted to relatively safe and non-human or animal toxic pesticides, many developing countries continue to use DDT, the first modern pesticide developed. Although DDT gained a violently negative public opinion in the 1970's following the publication of the book Silent Spring, the scientific basis of her book has been questioned. It is unclear to date whether DDT is as serious a problem as she stated, however there is no question that it has some significant environmental consequences. DDT is highly toxic to aquatic invertebrates, can affect the human nervous system, liver and kidney, and has potential for chronic problems. DDT has a very long half-life of 2-15 years in soil.

Why do Mosquitos need to be controlled?

Although the primary reason for mosquito control in the United States has long been pure annoyance, there are dangers associated with diseases carried by mosquito. Malaria has been wiped out in the United States, but still is of great concern in many other parts of the world. In the US, the recent development of the West Nile Virus has been a cause of concern, having killed 9 people in Minnesota alone in the last 3 years. Disease control continues to be a major motivating factor in controlling mosquitos and other biting flies.

More information:

Updated by Joe Dolson on 24 August, 2009

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