Nowadays, we understand the importance of biological diversity and the value of all species occupying the ecosystem. However, for thousands of years past, humankind has been battling the mosquito. It seems an uneven battle. We're big, strong, smart, adept at technology. They're small and fragile, with no tools and not much in the way of intelligence. So why are they still around?

In the old days in the Yukon, First Nations people sometimes burned an area where they planned to settle. It was a relatively harmless practice that reduced the mosquito population, at least for a while, and increased the local moose population by providing more of their favourite plants.

In the early 1920s, technology entered the battlefield. The first systematic attempts to limit the mosquito population involved spreading oil on the surface of mosquito-producing ponds to kill mosquito larvae.

The method works because mosquito larvae breathe air, explains Benoit Godin, head of Environment Canada's Environmental Contaminants section in Whitehorse. The larva pokes its abdomen through the surface of the water and breathes through an opening at the tip, hanging suspended by tiny hairs caught in the surface tension. Oil spread on the water forms a thin layer on the surface and blocks the breathing apparatus, suffocating the larva.

"It's effective, but it's messy," says Godin. The oil affected the entire ecosystem, killing organisms besides mosquitoes. As the ponds dried, it settled on the ground, leaving a sticky mess that inhibited revegetation and sometimes seeped into streams and groundwater.

In the 1940s, mosquito control methods shifted to toxic chemicals called organochlorines, the best-known of which is DDT. For a while, organochlorines looked like the solution to all insect problems. They were extremely toxic and persistent, so one application kept on killing insects for a long time.

Organochlorines did the job, says Godin, but they had unexpected side-effects. Because they persisted, they accumulated in the environment. As predators ate victims and contaminated survivors, organochlorines moved up the food chain with disastrous effects. For some vertebrates, such as fish, these chemicals were fatal. In birds of prey, organochlorines thinned eggshells, so that eggs didn't hatch and the birds did not reproduce. Peregrine falcons almost disappeared as a result. The Yukon discontinued DDT use in 1969 and the product was banned in Canada shortly thereafter.

DDT is still used in some countries because it's cheap, but its effectiveness is decreasing. Mosquitoes, it appears, are talented survivors and they are adapting to organochlorines.

"Now there are some species that can live in substantially high concentrations of DDT," says Godin.

In the 1970s a new group of chemicals hit the mosquito ponds: organophosphates. They were less toxic than organochlorines and less persistent, Godin says, but they also had unfortunate side-effects.

Like organochlorines, organophosphates are not selective. They kill all insects, not just the pests they are directed at. And, although they don't kill birds directly, they attack the birds' nervous systems, affecting balance and co-ordination.

In the 1980s, scientists shifted toward biological controls. The idea was to produce something that would attack only specific insects, while remaining harmless to everything else. What they produced was a mosquito disease.

The bacterium, which goes by the grand name of Bacillus thuringiensis var. israeliensis (better known as B.t.i.), is introduced into the mosquito pond in the form of spores. The larvae eat the spores, get sick, and die.

"There's no vertebrate toxicity at all," says Godin. Unfortunately, the spores also have no effect on mosquitoes in the pupal or adult stages. If they don't reach the larvae, they are harmless.

The latest approach, Godin says, is called integrated pest management. That means using a variety of approaches, including draining small areas of standing water where mosquitoes breed and encouraging natural predators like dragonflies and birds.

"Society has learned much from tinkering with the ecosystem with chemicals, so we're going more toward a biological approach," says Godin. "In the end our dependency on intensive mosquito control may be greatly reduced. We must not forget that they are important food sources for a multitude of other species in the ecosystem."

"There will always be a level of annoyance," he says. "After all, we are living in a boreal forest. But there are alternatives to intensive control programs, such as putting up bird boxes to encourage mosquito-eating birds to nest."

For more information about mosquitoes and mosquito control, contact Environment Canada, Whitehorse, or the Yukon Department of Community and Transportation Services.