Beekeepers in Ontario have launched a lawsuit against two big chemical companies, alleging their pesticides have caused widespread bee deaths that have driven up costs and reduced honey production.

The honey makers allege Syngenta AG and Bayer CropScience were "negligent" in the "design, sale manufacture and distribution" of neonicotinoid pesticides, which are used to grow corn, soybeans and many other crops.

The lawsuit, which seeks $450-million in damages, alleges beekeepers experienced damaged or lost bee colonies, lost profits and unrecoverable costs as a result of neonic use on plants and crops. None of the allegations have been proven.

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The case marks an escalation in the battle between Ontario beekeepers and chemical companies, two groups farmers rely on for pollination and crop protection.

The lead plaintiffs in the suit are Sun Parlor Honey Ltd. and Munro Honey, both of which are family-owned business in southwestern Ontario, the heart of the province's agriculture sector.

In the statement of claim filed Wednesday, both companies allege they respectively lost more than $2-million in bees and honey production because of neonics between 2013 and 2006, when the pesticides became widely used in Canada.

Tom Congdon, whose grandfather started Sun Parlor Honey 89 years ago, said Health Canada has confirmed dead and dying honeybees at some of his 1,950 hives. In an interview, he said his business has sustained widespread bee losses all summer, and he has no doubt the neonic pesticides are to blame.

In the statement of claim, Sun Parlor Honey alleges neonic-related bee deaths have cost the company 139,000 pounds of honey over the past seven years worth more than $700,000. Replacing dead bees and hives has cost more than $2-million, Sun Parlor alleges.

Mr. Congdon, whose bees feed on a variety of crops, said bee deaths have worsened in recent years as corn and soybeans have become more widely grown due to rising demand for biofuels.

Syngenta and Bayer did not respond to interview requests on Wednesday about the lawsuit. The chemical companies have said that honeybees do not absorb enough neonics in the field to suffer ill effects, and the pesticides are safe if used as directed.

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A spokesman for Bayer Cropscience said the company has not been served with the lawsuit and had no comment on it.

"We believe the products we develop, market and steward represent the latest innovations in crop protection that have helped make Canadian agriculture productive and sustainable," Derrick Rozdeba said.

Dimitri Lascaris, a lawyer with the firm representing the plaintiffs, said he has been retained by many large Ontario beekeepers that represent the majority of the country's honeybee industry. He said he plans to seek Canada-wide certification for the class action, which can take more than a year.

Neonics are systemic pesticides that farmers use to protect their crops against insects. The pesticides are temporarily banned in Europe and their approval is being reassessed by Health Canada. The Ontario government says it plans to regulate the use of neonics, which have been cited as contributing to the 58-per-cent bee mortality rate in Ontario over the past winter.

Health Canada has blamed the planting of corn in Ontario for honeybee deaths, and directed farmers and chemical companies take steps to reduce the amount of pesticide-laden dust that is kicked up during seeding.

Honeybees are important pollinators, responsible for helping produce about one-third of the food we eat. This amounts to $1.5-billion worth of food in Canada every year, and $150-billion globally, said Ernesto Guzman, a scientist who studies honeybees at Ontario's University of Guelph.

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Over the past six years, honeybee losses in Canada have averaged 30 per cent annually. Causes for the decline include pesticides, parasitic mites, viruses, cold winters and the stresses placed on colonies when they are moved among farms. Scientists and bee experts believe neonics weaken the bees and make them more vulnerable to the pathogens.

"Neonic poisoning is, of course, a factor, but it is not the only factor," Mr. Guzman said.

The Canadian Association of Professional Apiculturists, which tracks bee mortality rates, says normal winter losses are 15 per cent.

Mr. Congdon said the virus-bearing mites are under control in his hives, and are not to blame for the piles of dead bees he sees near hives, nor for the many that never return home.

"The mites have contributed to winter loss, there's no debate about that," Mr. Congdon said in an interview. "But it's nothing compared to what we've been seeing. All summer long we're fighting to keep the colonies in shape. [Neonics] just weaken them down and make them susceptible to other pathogens."

A group of European scientists known as the Task Force on Systemic pesticides reviewed 800 scientific papers that studied neonics and found clear evidence they pose serious risks to bees and other pollinators. They found the use of the pesticide is unsustainable.

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Neonics are applied to the seed or sprayed on fields. They become present in all parts of the plant and are 20 times stronger than DDT, a pesticide that was banned decades ago, Mr. Guzman said.

Editor's note: An earlier version of this story spelled Mr. Lascaris's name incorrectly.