Bee colonies suffer when exposed to a combination of pesticides

October 22nd, 2012 by Royal Holloway University of London

A bee rests in a Hydrangea flower in St Peter Port on 16 June 2011 (click image to expand - ©RLLord)

The behaviour of bees and the success of their colonies are significantly affected when exposed to a combination of pesticides, according to research from the School of Biological Sciences at Royal Holloway, University of London published in the paper ‘Combined pesticide exposure severely affects individual-and colony-level traits in bees‘ in Nature.

The researchers, Dr Richard Gill, Oscar Ramos-Rodriguez and Dr Nigel Raine, found that exposure to two commonly-used pesticides (a neonicotinoid and a pyrethroid) at levels normally seen in the field, affected the foraging behaviour of individual bumblebees and increased mortality leading to a detrimental impact on colony success.

Bees are typically exposed to numerous pesticides when collecting pollen and nectar from crops.

This is the first study to examine the potential effects of exposure to a combination of pesticides under realistic field conditions.

Dr Richard Gill said “the novelty of this study is that we show how the sublethal effects of pesticide exposure affects individual bee behaviour with serious knock-on consequences for the performance of the colony as a whole”.

Forty early stage bumblebee colonies received four-week exposure to two pesticides that are frequently encountered when foraging on flowering crops: the neonicotinoid ‘imidacloprid’ and the pyrethroid ‘λ-cyhalothrin’.

Bees were then able to forage naturally in the field, with researchers keeping track of how long they spent outside the colony using radio frequency identification (RFID) tagging technology.

A bee visiting Scabiosa sp in a garden in St Peter Port, Guernsey on 9 June 2012 (click image to expand - ©RLLord)

The results showed that the bees exposed to imidacloprid were less effective when foraging, particularly when it came to collecting pollen.

This meant treated colonies had less food available to them, and could not raise as many new workers. On average, the percentage of workers leaving the colony and then getting lost was 55% higher in those receiving imidacloprid than those that were not exposed to pesticides.

“Previous studies investigating the possible role of pesticides in current bee declines have focused on honeybees, but it is also crucial that we understand how pesticides affect other bee species,” Dr Richard Gill said.

While recent studies have investigated the role of pesticides on either individual bees, or the impact on whole colonies, how changes to individual behaviour could have knock-on effects for the colony has not previously been shown.

Dr Nigel Raine said “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.”

“Policymakers need to consider the evidence and work together with regulatory bodies to minimise the risk to all bees caused by pesticides, not just honeybees. Currently pesticide usage is approved based on tests looking at single pesticides. However, our evidence shows that the risk of exposure to multiple pesticides needs to be considered, as this can seriously affect colony success.”


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