A group of doctors and nurses is urging the Ontario government to ban an agricultural pesticide blamed for the deaths of bees and other insect pollinators.

The Canadian Association of Physicians for the Environment and the Registered Nurses' Association of Ontario are placing advertisements in Toronto's subway system, warning "neonic pesticides hurt our bees and us." In the ads, a young boy is gazing sadly upon a dead bee.

Gideon Forman, executive director of the Canadian Association of Physicians for the Environment, said the neonicotinoid insecticides used to grow corn, canola and other crops are a "major threat to both nature and people."

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"For the first time, we've got doctors and nurses standing together and saying we've got to ban these substances. I think it's unprecedented, this level of health professionals' concern," Mr. Forman said.

The doctors' group is the campaign's main funder, with contributions from David Suzuki Foundation and Ontario Nature.

Neonics, which are temporarily banned in Europe, make the crops toxic to field pests such as worms and grubs, but also bees, butterflies and other beneficial pollinators. Farmers say neonics, which have become widely used in the past decade, are safer for people and the environment than older chemicals. The chemical companies that sell seeds coated with neonics say they are safe when used as directed.

But neonics are said to be partly to blame for the rise in bee mortality rates in several countries, worsening the effects of viruses, mites and long winters.

The Ontario government is about to unveil regulations or a permit system for the use of neonics that will go into effect next year.

Mr. Forman said the Ontario government should go further and ban the pesticides.

"Minimally there should be a moratorium for a couple years," Mr. Forman said. "But ultimately we think we need to be banning them. All the science that we've looked at … really strongly suggest that these are very toxic to a range of pollinators."

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As Ontario gets set to outline the new restrictions on neonics, a coalition of agriculture groups is mounting a campaign of its own, warning new regulations on farming practices will drive farmers out of the province and reduce food production.

"An unpredictable regulatory system that responds to emotion and activist pressure is going to create an environment in this province that's going to restrict agriculture investment and growth for the industry," said Henry van Ankum, chairman of the Grain Farmers of Ontario, which is one of the groups in the coalition that includes Ontario Pork and Ontario Fruit & Vegetable Growers Association.

Ontario's Environmental Commissioner Gord Miller last month said neonics are a serious threat to bees and other pollinators, and likened the chemicals to DDT, a pesticide that was phased out in the 1970s for its devastating environmental impact.

The European Food Safety Authority said last year two neonics, acetamiprid and imidacloprid, may adversely affect the development of the human brain, and acceptable exposure levels for the chemicals should be reduced.

"Neonics are neurotoxins, so it's not surprising there could be some adverse effects for human brain development," Mr. Forman said.

But the report that caused the greatest stir was published in July of this year. A team of researchers known as the Task Force on Systemic Pesticides looked at 800 peer-reviewed studies published over 20 years and concluded the negative effects of neonics are turning up in everything from ground water to worms and birds.

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"We are witnessing a threat to the productivity of our natural and farmed environment equivalent to that posed by organophosphates or DDT," said Dr. Jean-Marc Bonmatin, one of the lead authors of the report. "Far from protecting food production, the use of neonics is threatening the very infrastructure which enables it, imperilling the pollinators, habitat engineers and natural pest controllers at the heart of a functioning ecosystem."