CBC Manitoba

Mosquitoes vs Malathion

Every summer, the city of Winnipeg's insect control branch uses a variety of insecticides – both biological and chemical – to control the population of harmful and nuisance insects, such as mosquitoes, cankerworms, elm bark beetles and other bugs.

The city uses malathion to control adult mosquitos. Malathion is an organophosphate insecticide that has been registered for use in Canada since the 1950s.

For mosquito control, malathion is applied by fogging, using ultra-low volume equipment on trucks. The equipment creates a very fine mist of about 60 grams of malathion per hectare.

Besides mosquito control, malathion is also used to control other insects in agricultural settings, such as food or ornamental crops.

Is it dangerous?

Malathion is toxic to all insects, including those considered beneficial to humans, such as honeybees. It is also toxic to fish and other aquatic animals. Health Canada's Pest Management Regulatory Agency says the insecticide "displays low toxicity" to birds and mammals.

The chemical degrades rapidly in the environment; officials say it has a half-life of less than one day in soil, which means it takes less than a day for half of a dose to disappear. In the air, its half-life is 1.5 days, on plants about 5.5 days, and in water half a day to 19 days.

Opponents to malathion say the chemical can weaken the immune system and cause cancer, birth defects, intestinal disorders, kidney problems and other health problems.

However, the Pest Management Regulatory Agency (PMRA) recently completed a re-evaluation of public health uses of malathion. It determined the insecticide is still "acceptable for use in controlling adult mosquitoes."

Even for someone who is outside during fogging, the PMRA says, exposure levels would be much lower than those that caused problems in animal tests.

Young animals were more sensitive to the toxic effects of malathion, and the chemical appeared to have adverse effects on the offspring of test animals.

However, the PMRA says the amount of malathion ingested by those animals is far greater than the amount people would be exposed to in fogging situations.