The federal government is being taken to court for approving the use of neonicotinoid pesticides that have been blamed for the "catastrophic" decline of some bee populations in Canada.

In two linked applications filed Wednesday in Federal Court, environmental groups argue Health Canada's Pest Management Regulatory Agency (PMRA) acted unlawfully when it registered a group of pesticides for use without fully considering its impact on public health and the environment.

"Wherever neonicotinoids are used you have massive poisoning of bees," said Gwen Barlee, a director of the Wilderness Committee, which brought the action along with the David Suzuki Foundation, Friends of the Earth Canada and Ontario Nature.

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Ms. Barlee said the groups have been campaigning for years to have the pesticides banned, but because of a lack of action by Ottawa they have now decided to go to court.

"This isn't something we want to do," she said of the applications. "But it is so serious we really don't have much choice."

Ms. Barlee said bee populations in some areas have declined dramatically and she believes the widespread use of neonicotinoid pesticides is to blame.

"Neonicotinoids are catastrophic to bees," she said.

Statistics Canada reports that the number of honeybee colonies across Canada has been generally increasing, but there have been some significant regional die-offs, including about half of Ontario's bees in 2013. That collapse prompted the Ontario government to promise restrictions on neonicotinoids by 2017. Harsh winters and "colony collapse disorder," which is caused by invasive mites, have also been blamed for the die-offs.

In an e-mail, Eric Morrissette, a Health Canada spokesman, defended the government's registration of the pesticides.

"The registration decisions made by Health Canada's PMRA pertaining to thiamethoxam and clothianidin were made based on sound science and evidence. Health Canada is currently reviewing the judicial review applications and cannot comment further at this time," he stated.

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Also named in the applications are Sumitomo Chemical Company Ltd., Bayer Cropscience Inc., Valent Canada Inc., Syngenta Canada Inc. and Elanco Canada Ltd.

Most companies were unable to respond immediately or declined comment.

But Derrick Rozdeba, vice-president of communications for Bayer, defended use of the pesticides.

"Canadian farmers have come to depend on neonicotinoid insecticides due to their efficacy, their safety to applicators and their favourable environmental profile, when used according to label instructions," he stated in an e-mail. "These insecticides have helped farmers and homeowners manage destructive insect pests and extensive research has shown that these products are not responsible for declines in honey bee colony health."

Chris Davison, head of corporate affairs Canada for Syngenta, said in an e-mail his company hadn't yet seen the application and it would be inappropriate to comment on it.

"That said, we do take concerns about pollinator health very seriously and the scientific evidence demonstrates that bees and other pollinators can co-exist safely with modern agricultural technologies, including neonicotinoids," Mr. Davison stated.

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Charles Hatt, a lawyer with Ecojustice, a non-profit law organization representing the environmental groups, said the applications ask the court to declare that the PMRA "acted unlawfully" when it registered several pesticides containing chemical ingredients known as cloathianidin and thiamethoxam.

Those products belong to the neonicotinoid family of pesticides, which use a nicotine-like chemical to kill a wide range of insects.

Mr. Hatt said the pesticides are doing unacceptable damage to the environment because they are so lethal to bees.

"When the PMRA decides to register or continue the registration of a pesticide, they are supposed to determine whether its risks … are acceptable … to human health and the environment," he said.

Mr. Hatt said that the government failed to do so.

"When you look at the registration histories for these pesticide products, what you see is that for years now the PMRA has been concerned about the … risks to pollinators, to bees, and has requested scientific studies from the registrants of these products," he said. "They have either not gotten any information on the type of risks they are worried about, or have gotten studies that they have deemed unacceptable and yet they have been registering and continuing the registration of these products."