Commonly used agricultural chemicals — including many commonly used fungicides — damage and impair the abilities of commercial honey bees to fight off dangerous potentially lethal parasites, according to new research from the University of Maryland and the US Department of Agriculture.
Commercial honey bees are regularly exposed to these chemicals during the corse of their pollination activities — many of the most productive agricultural crops in the world are entirely dependent upon honey bees for pollination, but their numbers have been rapidly falling in recent years for “unknown” reasons.
This new research 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 University of Maryland has details:
The researchers collected pollen from honey bee 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 beekeepers 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 parasitic infection.
Beekeepers know they are making a trade-off when they use miticides, said University of Maryland researcher Dennis vanEngelsdorp, the study’s senior author. The chemicals compromise bees’ immune systems, but the damage is less than it would be if mites were left unchecked. 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 stated. Current federal regulations limit the use of insecticides during the time periods when pollinating insects are foraging, “but there are no such restrictions on fungicides, 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.”
One of the more interesting findings of the new research is that the majority 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 flowering plants in the area, not from the crops. This is probably because honey bees, which evolved in the Old World, are not efficient at collecting pollen from New World crops, even though they can pollinate these crops.”
The researchers make the distinction that these new findings aren’t “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.”
The new research was just published July 24th in the online journal PLOS ONE.