Published time: July 25, 2013 20:24                                                                            

Reuters / Stephane Mahe

Honey bees are quickly disappearing from the US – a phenomenon that has left scientists baffled. But new research shows that bees exposed to common agricultural chemicals while pollinating US crops are less likely to resist a parasitic infection.

As a result of chemical exposure, honey bees are more likely to  succumb to the lethal Nosema ceranae parasite and die from  the resulting complications.

Scientists from the University of Maryland and the US Department  of Agriculture on Wednesday published a study that linked chemicals, including  fungicides, to the mass  die-offs. Scientists have long struggled to find the cause  behind the Colony Collapse Disorder (CCD), in which an estimated  10 million beehives at an average value of $200 each have been  lost since 2006.

Last winter, the honey bee population declined by 31.1 percent,  with some beekeepers reporting losses of 90 to 100 percent of  their bee populations. Scientists are concerned that   “Beemageddon” could cause the collapse of the $200 billion  agriculture industry, since more than 100 US crops rely on honey  bees to pollinate them.

The new findings are key in determining one of the causes of the  CCD, but they fail to explain why entire beehives sometimes die  at once.

UMD and DOA researchers found that pollen samples in fields  ranging from Delaware to Maine contained nine different  agricultural chemicals, including fungicides, herbicides,  insecticides and miticides. One particular sample even contained  21 different agricultural chemicals. To test their theory, they  fed pesticide-ridden pollen samples to healthy bees and then  infected them with the parasite. They found that the pesticides  hindered the bees’ abilities to resist the infection, thus  contributing to their deaths. The fungicide chlorothalonil was  particularly damaging, tripling the risks of parasitic  infection.

“We don’t think of fungicides as having a negative effect on  bees, because they’re not designed to kill insects,” Dennis  vanEngelsdorp, the study’s senior author, said in a news release.

He explained that federal regulations restrict the use of  insecticides while pollinators are foraging, but noted that   “there are no such restrictions on fungicides, so you’ll often  see fungicide applications going on while bees are foraging on  the crop. The finding suggests that we have to reconsider that  policy.”

Bees are declining at such a fast rate that one bad winter could  trigger an agricultural disaster. California’s almond crop would  be hit particularly hard, since the state supplies 80 percent of  the world’s almonds. Pollinating California’s 760,000 acres of  almond fields requires 1.5 million out-of-state bee colonies,  which makes up 60 percent of the country’s beehives. The CCD is a  major threat to this $4 billion industry.

Entomologists suspect that a number of other factors also  contribute to the CCD, including climate change, habitat  destructing and handling practices that expose bees to foreign  pathogens. But the effect of agricultural chemicals is  particularly alarming, especially since the US does not have laws  banning the use of the pesticides that are affecting bee health.

“The pesticide issue in itself is much more complex than we  have led to believe,” vanEngelsdorp said. “It’s a lot more  complicated than just one product, which means of course the  solution does not lie in just banning one class of product.”

Categories: Environmental

Tags: Agrochemical, Bee, Honey bee, Nosema ceranae, United States, United States Department of Agriculture, University of Maryland, University of Maryland College Park