There is something wrong with bees, the pollinators responsible for adding billions of dollars of value to the world’s crops. An unusually large number of bee colonies are not surviving the winter, but it is not clear why.
Some scientists believe the problem is linked to familiar pests and diseases.
There is also new evidence that sub-lethal effects of pesticides play a role, but there is also evidence to the contrary.
Brandon reporter Robert Arnason spoke with bee scientists and discovered the problems plaguing bees appear as complex as bee colonies themselves.
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It doesn’t rank with the 9-11 bombings or the “faked” Apollo moon landings, but the mystery surrounding bee deaths and Colony Collapse Disorder has generated multiple conspiracy theories over the last few years.
While certain folks believe cell phones are destroying the world’s pollinators and others think global warming is to blame, most conspiracy theorists claim that pesticides are killing the bees of North America, Europe and other parts of the planet.
Typically, respected scientists dismiss the rantings on the internet, but leading entomologists are now declaring that the conspiracy theorists may be right: pesticides may be the masked villain in this story.
“There is this growing body of evidence that it is one of the things that have changed in the last few years, which could be involved in pollinator decline,” said Jeff Pettis, who heads the U.S. Department of Agriculture’s bee research laboratory in Beltsville, Maryland.
Since the winter of 2006-07, when U.S. beekeepers began reporting bee losses of 30 to 90 percent in their hives, USDA entomologists and university researchers have attempted to determine the causes of the phenomenon known as Colony Collapse Disorder (CCD). As described on a USDA website, the symptoms of CCD include a bee colony with a live queen, a large number of immature bees, but few adult bees and no dead honey bees in the hive.
During the same period, Canadian beekeepers reported losses similar to American apiarists, as about 33 to 35 percent of bees died over the winter in Canada from 2007 to 2010, based on a study conducted by University of Manitoba entomologist Rob Currie. Before 2007, normal over-wintering losses in Canada were 15 percent.
Yet bee colonies in Canada haven’t demonstrated the symptoms associated with CCD, widely seen across the U.S. As a result, bee experts have attributed the Canadian winter colony losses to varroa mites developing resistance to miticides, viruses transmitted by mites, the nosema parasite that attacks bees’ intestines and poor bee nutrition going into the winter.
Initial investigations into CCD in the U.S. also suggested a combination of factors behind the bee deaths.
But recent research indicates that pesticides have a larger impact on bee health than scientists initially suspected, said James Frazier, an entomologist who specializes in chemical ecology at Penn State University.
“In the next year, we’re going to see a lot of publications about the sub-lethal impacts of pesticides on bees.”
As an example of a sub-lethal effect on bee health, Steve Sheppard, University of Washington State entomologist, referred to an experiment conducted by scientists in Taiwan.
The scientists behind the study, published in theJournal of Economic Entomologyin 2008, placed a dish of sugar water a distance from a hive and measured how long it took bees to make the round trip from the dish and back to the hive.
“Something like 98 percent of time, the bees came back within five minutes,” Sheppard said
But when the researchers added a small dose of imidacloprid, an insecticide produced by Bayer, to the sugar water, the bees lost their navigation skills and memory.
“At pretty amazingly low levels, well below the level considered harmful to the bees… the bees started taking a lot longer,” Sheppard said. ” They would come back after a half-hour, or they would come back the next day, or they wouldn’t come back.”
These types of sub-lethal effects aren’t taken into account when the U.S. Environmental Protection Agency or its Canadian counterpart, the Pest Management Regulatory Agency, approve or reject a pesticide for agricultural use.
Instead the chemical is evaluated based on its toxicity to bees, Sheppard noted, not on overall impacts to bee health.
“They (regulators)… apply it to the bee and if the bee isn’t dead, it’s OK.”
In another study on sub-lethal effects, Judy Wu, a former master’s student in entomology at Washington State, gathered samples of bee combs from apiaries in the Pacific Northwest. She wanted to know what pesticides were in the combs and if the chemicals were harmful to bee health.
“In this study, we wanted to look at what is going on with beekeepers in real life,” said Wu, who is now working on her PhD., at the University of Minnesota.
Wu separated the combs into two groups, based on the amount of pesticide on the beeswax. She had a queen bee lay eggs on the combs and raised the bees in a common environment.
“So the only difference (for the bee) was you were raised in wax with high residue or low residue (of pesticides),” Sheppard said.
Wu’s paper, published inPLoS One,determined that bees reared on the high residue died four days earlier than bees reared on the low pesticide wax.
“So what? What does that mean?” Sheppard asked. “As a forager, (bees) live from two to 19 days… with an average of about 8.8 days…. If it reduces your lifespan by four days, then it might be half of your foraging life.”
For Wu, the interesting part of her longevity experiment is the potential consequence on the colony. Within a hive, bees take on specific roles at different stages of their life. Basically, labour in the colony is divided according to age.
Jobs include providing food for bee larvae (a nurse bee), cleaning out cells, receiving nectar from foragers and guarding the entrance to the hive. At the end of its career and life, a bee becomes a forager that collects pollen and nectar.
If a forager dies prematurely or can’t find its way back to the hive because it gathered pollen from a plant treated with imidacloprid, the loss has a “cascading” effect on the hive, Sheppard said.
Guard bees that aren’t physically ready to forage must go out and collect pollen, because the hive requires food. And the domino effect rolls on, because another bee has to assume the role vacated by the guard bee.
“It’s a cascade. It goes all the way back. It’s almost like having child labour…. Through this hypothesis, this could have an amplified effect on colony health,” Wu said.
If it becomes an accepted fact that pesticides have sub-lethal effects on bees, it could affect North American agricultural policy, said Pettis, whose research has shown that bees exposed to imidacloprid are more susceptible to the nosema parasite.
“None of those things (sub-lethal effects) are lethal by themselves,” he said. “(But) when do sub-lethal effects rise to the level that there are concerns to the beekeeper? That’s really the big question that a number of labs are trying to work on to understand.”
Several European countries, including Germany, France and Italy have already changed agricultural policy because of concerns about bees and pesticides.
They have restricted the use of neonicotinoids, a class of insecticides, in response to incidents that caused the poisoning of honeybees. But, according to the U.S. Environmental Protection Agency, those restrictions are not related to bee losses associated with CCD.
Nonetheless, James Frazier, a Penn State entomologist, believes policy makers need to revamp guidelines for pesticide application to protect bee colonies.
At the moment, American and Canadian labels on pesticides tell growers not to spray when bees are active.
But that label is useless, Frazier said, because spraying when the sun goes down does little to protect bees.
“The next morning, when the sun comes up, the residue is going to be on those flowers… at full concentration. Every bee that comes on there is going to get a toxic dose.”
Instead, the label on pesticides should be simple and direct, Frazier said.
“The warning that should be there is ‘Do not spray during bloom’-period. If that was followed we’d have a huge step forward for pollinator safety.”
Getting such a label on pesticides won’t be easy, Pettis said, because agricultural policy makers can’t jeopardize crops for the sake of bees.
“If canola (for example) is putting out an amount of a systemic (pesticide)… is that a danger to the beekeeper? How do we balance that with the canola growers?” he asked.
“It’s a big farming policy debate…. It’s the demand to feed the world and how do we accomplish that?”
