July 25, 2013
Bee Colony Collapse Influenced By Cocktail Of Agricultural Chemicals
Brett Smith for redOrbit.com - Your Universe Online
Colony collapse disorder (CCD), the mysterious and increasingly rampant die-off of a honey bee colony, isn't just a problem for bees, it's also a problem for farmers who rely on those bees to pollinate their crops.According to researchers from the University of Maryland and the US Department of Agriculture, commercial bees are regularly exposed to a cocktail of agricultural chemicals that could be playing a role in CCD.
In a study recently published in the open access journal PLOS ONE, the team of researchers looked at which chemicals bees are exposed to and how these chemicals affect bees resistance to the parasite Nosema ceranae, which has been known to decimate honey bee colonies.
The researchers began by collecting pollen samples from honey bee hives that pollinated cranberry, watermelon and other crops throughout northeastern coastal US states. The samples were analyzed to see which plants were the bees' main sources of pollen and what chemicals they were being exposed to.
After finding a host of chemicals in the pollen samples, the samples were then fed to healthy bees to see whether the chemicals impacted their ability to resist infection with Nosema.
Pollen samples were found to contain an average of nine different fungicides, herbicides, insecticides and miticides. One sample was found containing 21 different pesticides. The fungicide chlorothalonil and the insecticide fluvalinate were the two most common chemicals found in pollen.
Most alarmingly, bees that had ingested pollen samples containing chlorothonatil were almost three times more likely to be infected by Nosema than other bees in the study, researchers said.
The chemical used to control Varroa mites also reduced bees' ability to resist parasites. Miticides are used judiciously by most farmers because they are known to compromise bees' immune systems. However, unchecked mite infestations can cause severe damage to a farmer's crops, according to study co-author Dennis vanEngelsdorp, a University of Maryland researcher. He added regulations need to be strengthened if common fungicides can be harmful at real world dosages, as his study found.
"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, 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."
Many pesticides are labeled with instructions that say they are not to be used while bees are nearby, but this warning doesn't always apply to fungicides.
The study also unexpectedly found crop pollination did not benefit bees very much with respect to providing nourishment. Instead of getting food from watermelon plants or other crops, the study bees got most of their pollen from weeds and wildflowers, researchers said. They speculated that because US bees are descended from European bees, they probably haven't evolved to effectively feed on North American crops. And even the wild plants the bees seemed to prefer as nectar sources showed traces of pesticides despite not being explicitly targeted by farmers.