Pesticides Affecting Population and Behavior of Bumblebees

Exposure to pesticides affects the colonies of bumblebees and its foraging behavior, finds a new study.

Bees contribute to 80 percent of pollination by insects. Significant decline in the population of bees may have serious consequences for the ecosystem and agricultural production. It is very important to understand the causes behind population decline in bees.

Researchers from the University of London, UK, monitored 40 early stage bumblebee colonies to analyze the impact of two pesticides - the neonicotinoid 'imidacloprid' and the pyrethroid 'λ-cyhalothrin' - on the foraging behavior of the bees in realistic field conditions.

"The novelty of this study is that we show how the sublethal effects of pesticide exposure affects individual bee behavior with serious knock-on consequences for the performance of the colony as a whole," researcher Richard Gill, from the University of London, said in a statement.

Some bumblebees were exposed to imidacloprid pesticide, while the second group was exposed to pyrethroid crop spray. The third group was exposed to both the pesticides and the fourth group of bees was not exposed to either of the chemicals.

The bees were observed for four weeks while they foraged on flowering crops. Researchers tracked the amount of time the bees spent outside their colony using radio frequency identification (RFID) tagging technology.

They found that the pesticides affected the foraging activity of the bees and also increased the mortality rate causing a harmful impact on colony success.  Bees that were exposed to imidacloprid pesticide were less effective in collecting pollen and foraged more. Their colonies did not have enough food available, and could not raise as many new workers.

Researchers noticed that the percentage of bees getting lost after exposed to pesticide imidacloprid was 55 percent more than those bees that were not exposed to pesticides.

The bees that died after exposure to pyrethroid crop spray were four times more than those bees that were not exposed to any chemical. Bumblebee colonies that were exposed to both the pesticides were the worst affected, said a report in Daily Mail.

"There is an urgent need to understand the reasons behind current bee declines as they are essential pollinators of many agricultural crops and wild flowers. We rely on these insects to produce most of the food we eat and maintain the landscapes we enjoy," Nigel Raine from the university said.

Raine suggested that policy makers need to consider the evidence and work on better ways to reduce the risk of pesticides to all bees.

The findings of the study, "Combined pesticide exposure severely affects individual- and colony-level traits in bees," are published in the journal Nature.