Common agricultural chemicals shown to impair honey bees' health

Common agricultural chemicals shown to impair honey bees' health
In a study of real-world conditions encountered by honey bees as they pollinate crops, researchers gathered pollen from commercial beehives placed in farm fields in the Northeastern US. Here the scientists take pollen samples from bees pollinating Maine blueberries. Credit: Michael Andree

Commercial honey bees used to pollinate crops are exposed to a wide variety of agricultural chemicals, including common fungicides which impair the bees' ability to fight off a potentially lethal parasite, according to a new study by researchers at the University of Maryland and the U.S. Department of Agriculture.

The study, published July 24 in the online journal PLoS ONE, is the first analysis of real-world conditions encountered by honey bees as their hives pollinate a wide range of crops, from apples to watermelons.

The researchers collected pollen from hives in fields from Delaware to Maine. They analyzed the samples to find out which flowering plants were the bees' main pollen sources and what agricultural chemicals were commingled with the pollen. The researchers fed the pesticide-laden pollen samples to healthy bees, which were then tested for their ability to resist infection with Nosema ceranae – a parasite of adult honey bees that has been linked to a lethal phenomenon known as colony collapse disorder.

On average, the pollen samples contained 9 different agricultural chemicals, including fungicides, insecticides, herbicides and miticides. Sublethal levels of multiple agricultural chemicals were present in every sample, with one sample containing 21 different pesticides. Pesticides found most frequently in the bees' pollen were the fungicide chlorothalonil, used on apples and other crops, and the insecticide fluvalinate, used by to control Varroa mites, common honey bee pests.

In the study's most surprising result, bees that were fed the collected pollen samples containing chlorothonatil were nearly three times more likely to be infected by Nosema than bees that were not exposed to these chemicals, said Jeff Pettis, research leader of the USDA's Bee Research Laboratory and the study's lead author. The miticides used to control Varroa mites also harmed the bees' ability to withstand .

Beekeepers know they are making a trade-off when they use miticides. The chemicals compromise bees' immune systems, but the damage is less than it would be if mites were left unchecked, said University of Maryland researcher Dennis vanEngelsdorp, the study's senior author. But the study's finding that common fungicides can be harmful at real world dosages is new, and points to a gap in existing regulations, he said.

"We don't think of fungicides as having a negative effect on bees, because they're not designed to kill insects," vanEngelsdorp said. Federal regulations restrict the use of insecticides while pollinating insects are foraging, he said, "but there are no such restrictions on , so you'll often see fungicide applications going on while bees are foraging on the crop. This finding suggests that we have to reconsider that policy."

In an unexpected finding, most of the crops that the bees were pollinating appeared to provide their hives with little nourishment. Honey bees gather pollen to take to their hives and feed their young. But when the researchers collected pollen from bees foraging on native North American crops such as blueberries and watermelon, they found the pollen came from other in the area, not from the crops. This is probably because honey , which evolved in the Old World, are not efficient at collecting pollen from New World crops, even though they can pollinate these crops.

The study's findings are not directly related to colony collapse disorder, the still-unexplained phenomenon in which entire honey bee colonies suddenly die. However, the researchers said the results shed light on the many factors that are interacting to stress honey bee populations.

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More information: "Crop pollination exposes honey bees to pesticides which alters their susceptibility to the gut pathogen Nosema ceranae," PLoS ONE July 24, 2013
Journal information: PLoS ONE

Citation: Common agricultural chemicals shown to impair honey bees' health (2013, July 24) retrieved 19 September 2019 from
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Jul 25, 2013
'The study's findings are not directly related to colony collapse disorder, the still-unexplained phenomenon in which entire honey bee colonies suddenly die.'

Let's get this straight shall we. CCD does not suddenly kill the bees. CCD causes, for unknown reasons, the entire colony to disappear. With the exception of a handful of stragglers. Not as inferred 'die' which would suggest the entire colony is found in a heap inside or outside the hive. These colonies subjected to CCD do not remain to be found. They simply disappear and no one knows why. That is what CCD is. The assumption is that they die. But as any detective will tell you for a murder to be investigated first you need a body. So find the colony or a substantial part of the colony and then we can discover what is really going on.
I suspect neonicotinoids and a raft of other impacts acting in concert to reduce the bees ability to do their job efficiently. Over time the colony size collapses and eventually disappears.

Jul 25, 2013
To add to the above point ask yourself why no one knows what has happened to these CCD colonies? Simple answer would be because we don't sit watching the colony behaviour 24/7. If we did we would probably notice the flow of bees seemingly to be normal because we have no way of distinguishing really effectively just how many bees leave a hive to forage and how many actually return. Try counting them if you don't believe me. Its impossible unless you resort to some fancy expensive gate counter system that can keep track.
So until we can actually set up some highly sophisticated systems to track bee movements we won't even spot the decline in numbers until its almost too late. And then we still won't know why its happened without more tests.

Jul 25, 2013
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