When a mosquito slips in to your home through a broken window screen, a
high-pitched buzzing in the ear and a couple of itching welts are
probably the only immediate consequences. But the mosquito is a
deceptively minor irritation, because contained within that tiny
insect--light as a feather, almost transparent--is a tangle of issues,
where infectious disease, chemical toxins, ecological damage, and local
politics all intersect.
Mosquitoes transmit some of the most devastating diseases on earth:
malaria, dengue fever, yellow fever, filariasis (which causes
elephantiasis of the limbs), and encephalitis viruses, including West
Nile fever, which first appeared in the Western hemisphere in New York
City in 1999. The female insect, which needs blood so she can lay her
eggs, picks up parasites and viruses from the mammals on which she
feeds. (Males never bite animals; they feed on flower nectar.) When she
goes for another meal, these pathogens travel from her mouth into the
blood of her victim.
The diseases transmitted by mosquitoes kill millions--malaria alone is
responsible for close to a million deaths every year--but the U.S. is
relatively safe from mosquito-borne illness. Here, mosquitoes carry
encephalitis viruses and, very rarely, dengue fever. Immigrants and
travelers sometimes bring yellow fever and malaria with them to these
shores, but these diseases are almost never transmitted within the U.S.
But while the U.S. offers little risk of malaria-borne disease to its
inhabitants, the emergence of West Nile virus raised public concern to
new heights about the importance of reducing mosquito populations and
limiting mosquito bites, not only because they are a nuisance but also
because they are a health threat. At the same time, concerns about the
health and ecological effects of reducing mosquito populations have also
There are about 2,500 species of mosquito, only some of which transmit
diseases. Local mosquito populations are monitored and controlled by
Mosquito Control Districts or Departments of Health on a state-by-state
basis. These mosquito brigades use a range of strategies, from setting
up hotlines for nuisance complaints to spraying chemicals over entire
communities. In those places where sprays are used, different kinds of
sprays may have different health and ecological impacts.
Organophosphates are a class of chemicals that act against mosquitoes by
interfering with the nervous systems of insects--and sometimes other
species, including humans. Malathion is one of the least toxic of the
organophosphates. Nevertheless, it has been linked to eye disorders,
immune system disruptions, and genetic damage. It also can cause
headaches, dizziness, nausea, and respiratory distress. Malathion is
highly toxic to fish and to some beneficial insects such as honeybees,
and it may cause ecosystem damage if used improperly.
Another organophosphate (OP) used for mosquito control is naled, which also causes dizziness and nausea. At very high doses, naled, like all
OPs, can cause convulsions and death. Naled is highly toxic
to all insects, including honeybees, whose pollinating skills are vital
Fenthion, or Baytex, is an OP used for mosquito control in
some parts of Florida. Exposure to even tiny amounts of fenthion can
kill birds, and it is also harmful to shrimp, crabs, and other aquatic
species if sprayed near water. Due to Florida's importance as a stopover
point for migrating birds, use of fenthion there is particularly
Another OP found in sprays, pest strips and pet collars is Dichlorvos or DDVP, a known carcinogen and developmental toxicant which can cause headaches, nausea and vomiting. Despite an EPA health assessment indicating risks, the EPA has not banned DDVP for residential use. Because pest strips can result in chronic expsoure, it is best to avoid the chemical in products such as Alco No-Pest Strip, Amvac Insect Strip, and Swat Pest Strip and check labels of other products.
Another class of anti-mosquito chemicals is the pyrethroids. Like
organophosphates, pyrethroids kill insects by interfering with their
nervous system. Insecticides that fall into this category include
permethrin, resmethrin and d-phenothrin. Experts have relatively few
concerns over the acute toxicity of pyrethroids, but this class of
chemicals may over the long term interfere with the immune system and
disrupt hormone functions. In one study, pyrethroid insecticides caused
estrogen-sensitive breast cancer cells to multiply in a test tube, for
example. Pyrethroids may also damage the liver and thyroid.
Spraying is a tactic used to kill adult mosquitoes. Some Mosquito
Control Districts focus instead on the larval stage of mosquito
development, adding chemicals to water bodies in which mosquitoes breed.
One such chemical, the insect growth regulator methoprene, is applied to
water to prevent larvae from developing into adults. The Northwest
Coalition for Alternatives to Pesticides reports that methoprene, while
posing little harm to humans and other mammals, nevertheless delays the
development of other invertebrates and is toxic to some fish. Methoprene
also interferes with the maturation of several non-target insects,
including beneficial ones.
The Solutions >
Last Updated: March 30, 2002
| Readers' Ratings|
The Green Guide surveyed users of the eco-friendly products recommended in this Product Report. Click here to learn what they say about the products' effectiveness.