Low Levels of Pesticide Exposure Can Stress Bees Causing Colony Failure

A new research says that bees around the world are succumbing to stress, which is causing their colonies to collapse.

The latest study, conducted by researchers at the Royal Holloway University of London, discovered that even low levels of pesticides can trigger a stress response in bees. Due to pesticide exposure they undergo a behavioral change that affects their work.

"One in three mouthfuls of our food depends on bee pollination," lead author, Dr John Bryden from the School of Biological Sciences at Royal Holloway said in a statement. "By understanding the complex way in which colonies fail and die, we've made a crucial step in being able to link bee declines to pesticides and other factors, such as habitat loss and disease which can all contribute to colony failure."

Bees are an important part of the food chain. In the year 2012, the U.S. lost nearly one-third of its honeybee colonies. Reduction in bee-population dramatically affects the entire ecosystem. Since 2006, several beekeepers across the country have reported noticing a bizarre phenomenon called the 'Colony Collapse Disorder' (CCD) where the adult bees just disappear from the colony hives.

In the present study, the researchers have highlighted a strong correlation between a pesticide called neonicotinoid and falling numbers of honeybees. Continuous exposure to pesticides at levels the bees encounter in fields has a subtle impact on the individual insect, which eventually leads to the collapse of the entire colony.

"Exposing bees to pesticides is a bit like adding more and more weight on someone's shoulders. A person can keep walking normally under a bit of weight, but when it gets too much - they collapse. Similarly, bee colonies can keep growing when bees aren't too stressed, but if stress levels get too high the colony will eventually fail," added Dr Bryden.

The impact of insecticides on bees was very evident in a recent case, where over 25,000 bumble bees were found dead under the European linden trees in a parking lot of a shopping center in Wilsonville, Oregon. This was the largest mass-death of bumble bees reported in the region's history. The cause for such a massive die-off was not immediately known but conservationists say that it was the insecticides sprayed on the trees that killed the bees.

Every day, honeybee populations around the world battle with another threat - diesel exhaust. A recent study uncovered the impact of air pollutants emitted from diesel exhausts on the bees' sense of smell. The study claimed that diesel exhausts hamper the bee's foraging activity.

"Exposing bees to pesticides is a bit like adding more and more weight on someone's shoulders. A person can keep walking normally under a bit of weight, but when it gets too much - they collapse. Similarly, bee colonies can keep growing when bees aren't too stressed, but if stress levels get too high the colony will eventually fail," added Dr Bryden.

With this finding, the researchers offer strong evidence for the policymakers. They say that the way pesticides are tested and the way their impact on bees is assessed needs to be improved.

The findings were published in the journal Ecology Letters.