Honeybees that consume pollen containing commonly used fungicides may be more susceptible to infection by the gut parasite Nosema, research carried out by USDA and the University of Maryland has found.
The study was prepared by collecting pollen samples from honey bees that pollinated apples, watermelons, pumpkins, cucumbers, blueberries or cranberries. The scientists then analyzed the pollen to determine how much fungicide, insecticide, miticide and/or herbicide the bees were exposed to while pollinating each of the six crops.
In many cases, the pollen that bees brought back came primarily from plants other than the targeted crop, but the average number of pesticides present on the pollen – including herbicides, miticides and fungicides – was nine.
Fungicides were the most frequently found chemical substances in the pollen samples, USDA said. The most common was the fungicide chlorothalonil, which is used on apples and other crops. The most common miticide was fluvalinate, which beekeepers use to control varroa mites. Neonicotinoid insecticides were only found in pollen from bees foraging on apples.
"Honey bees that were fed pollen that contained the fungicide chlorothalonil and was collected at the hive entrance were almost three times more likely to become infected when exposed to the parasite Nosema, compared with control bees," explained study author Jeff Pettis, research leader of the Bee Research Laboratory in Beltsville, Md. The lab is part of ARS, USDA's chief intramural scientific research agency.
The fungicide pyraclostrobin, which was found less frequently in the pollen samples, also increased bees' susceptibility to Nosema infection.
The study is complementary to a larger report prepared and released by the USDA in May. That report said that multiple factors play a role in honey bee colony declines, including parasites and disease, genetics, poor nutrition and pesticide exposure.
The May report specifically highlighted the need for additional research to determine if there are any risks presented by pesticides, along with the need for improved collaboration and information sharing.
Study co-author Dennis vanEngelsdorp with the University of Maryland said the study reinforces the need to study bees further, and better understand how pesticides can enter the hive.
The issue dwindling bee populations has garnered its fair share of attention earlier this year both in the U.S. and the European Union. The EU voted in April to temporarily prohibit the sale and use of seeds treated with three nicotinoid pesticides on concerns that they were to leading cause of bee deaths.
However, not all countries initially agreed to the ban, citing incomplete evidence. The European Commission, which approved the ban, agreed to revisit the issue as soon as new information is available, within no longer than two years.
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