Ontario’s bee die-off last year raised the question of how bees were coming into contact with this pesticide, if indeed the seeds were buried. That spurred investigators to look at the planting process, which was when most of the recorded bee deaths occurred.
When corn planters sow their fields, a lot of dust is kicked up as the large tractor and planter, followed by a fertilizer container, move up and down the fields. As the insecticide-coated corn seed moves through the hopper, it leaves behind residue that is carried up into dust clouds that can stay airborne and carry across the fields.
The irregular shape of the corn seed may further accentuate the problem. A talcum powder is sprinkled over the irregular shaped seed to help it flow smoothly through the hopper.
The powder itself is benign, but Health Canada and CropLife Canada now acknowledge that the talc actually helps disseminate the dust off the seeds.
This “fugitive dust” is now considered by Health Canada and others as one likely route of exposure to neonicotinoids for honeybees and other pollinators.
Bees can come into contact with the insecticides through “direct contact caused from planter dust, in which case bees are probably doomed almost instantly. It contaminates nearby flowers in a typical wash like any pesticide,” says University of California apiarist Eric Mussen.
Evidence is mounting
Some scientists think the acute deaths that seem to coincide with planting are just the tip of the iceberg.
Jeff Pettis is the research leader at the U.S. Department of Agriculture bee lab in Maryland. Last September, around the time Health Canada reported the insecticide residues on 70 per cent of the dead and dying bees, Pettis told CBC News, “I am almost more concerned about the possible residues in corn pollen as the plants mature than the temporary exposure that occurred this spring with planting and dust.”
A farmer pours neonicotinoid-covered corn seeds into a barrel. (Janet Thomson/CBC)
Eric Mussen at the University of California agrees. Because of the systemic nature of the insecticide, he says, “any time the plant is in bloom you’re going to have a long-term exposure, and now it becomes incorporated into the bee hive.”
Laval University entomologist Val Fournier suggests another potential source of exposure. When she sampled surface water from puddles in fields two to three weeks after they were planted with neonicotinoid-treated corn, she found levels of neonicotinoids 10 times higher than what is known to cause death.
“This water would be very, very toxic for bees,” she says.
In April, the European Union issued a moratorium on neonicotinoids as it assesses the ongoing global decline in bee populations. But Canada’s pesticide regulatory agency does not want to take that step.