OTTAWA — Environmentalists worry that anxiety about West Nile virus will lead to the use of mosquito-killing chemicals more dangerous than the virus itself.

They argue the virus has no harmful effect on most people and that Canadians will become resistant to it in time, while the proposed chemical combatant, malathion, has many harmful effects. Ontario says it will allow municipalities to decide whether to use malathion to kill mosquitoes that spread the virus. There has been talk of spraying in other provinces as well, and Manitoba has been using the pesticide for years.

"To respond in this kind of sledgehammer way, I think it's still probably way out of proportion," scientist and broadcaster David Suzuki said in an interview Monday.

Last summer there were more than 300 confirmed or probable human cases of West Nile virus in Canada. Nine people who were known to have the virus died, although not all those deaths were attributed to West Nile.

Ecologist David Schindler of the University of Alberta said there are well documented scientific concerns about malathion.

"While it is advertised as one of the most harmless of organophosphate pesticides, it has caused birth defects, mutagenic and teratogenic effects, brain damage, childhood leukemia, disruption of endocrine functions."

Chris Krepski, a spokesman for the Pest Management Regulatory Agency, part of Health Canada, said malathion is safe if used according to instructions.

"It's got a good record of safe use for these sort of programs," he said.

Krepski said the concentrations of malathion used in mosquito control would be much lower than those commonly used in agriculture.

But Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, said he was surprised malathion is being used for mosquito control in Canada.

"I am totally shocked. The ecological impacts of malathion is something we do know something about, bees being the first casualty."

After the first North American outbreak of West Nile disease in New York City the authorities used malathion against mosquitoes, but stopped the practice after a public outcry in favour of more innocuous chemicals.

Krepski said many chemicals used in the United States are not available in Canada because the manufacturers don't find it worthwhile to sell them in such a small market.

Winnipeg environmentalist Dan Moroz, who has been fighting malathion spray programs in that city for years, says fogging kills only about 85 per cent of mosquitoes.

"Malathion is more toxic to honey bees than mosquitoes," said Moroz. "In Winnipeg after they fog you look at street lights and there's no moths flying around them.

"You should be able to see those things, you should be able to see butterflies on your lawn and honey bees on clover."

And Moroz argues that West Nile virus doesn't pose a health emergency.

"More people died of the flu already this year in Canada by far than will perish from West Nile in all of North America."

Canadian Alliance MP Carol Skelton, who has been following the West Nile issue, said spraying will be ineffective if it is done on a patchwork basis.

"They blow in and they hatch and everything, so if one municipality is spraying and the next one isn't, there's no visible boundary out there that will tell mosquitoes, 'Don't go there.'

"You'd need a combined effort by everybody and then they're still not going to kill them all."