Pesticides Hamper Bumblebee Growth and Pollination

Bees are exposed to numerous pesticides during the process of collecting pollen and nectar from crops. But not much is known about the effects of such exposure.

A study conducted at the University of London, is the first study that examines the potential effects of exposure to a combination of pesticides under realistic field conditions.

According to the researchers, individual worker behaviour and colony success are both affected when bees are exposed to a combination of pesticides.

For this study, the researchers focused on the bumblebee colonies that rely heavily on the collective performance of numerous individual worker bees.

They study depicted how the chronic exposure to two commonly-used pesticides namely neonicotinoid and pyrethroid, at concentrations approximating field-level exposure, impaired natural foraging behaviour and increased worker mortality.

This is the prime reason for the significant drop in the colony success and increased rates of colony failure.

There were studies done, the worked on the role of pesticides on either individual bee behaviours, or the impact on whole colonies. But how changes to individual behaviour could have incidental effects for the colony has not previously been shown.

"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," said Raine.

"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," added Dr Gill.

This study presented the realistic scenarios in which 40 early stage bumblebee colonies received four-week exposure to two pesticides that are frequently encountered when foraging on flowering crops namely the neonicotinoid and the pyrethroid.

Neonicotinoid was provided in a sucrose solution at levels that could be found in nectar. Pyrethroid was administered following label guidance for field spray applications.

The researchers witnessed how the bees were able to forage in the field providing a realistic behavioral setting. With the help of the radio frequency identification (RFID) tagging technology, the foraging behaviour of individual workers was recorded.

The bees that were exposed to neonicotinoid were less able to forage effectively, particularly when it came to collecting pollen. Indicating, treated colonies had less food available to them, so could not raise as many new workers. On average, the percentage of workers leaving the colony and then getting lost was 55 percent higher in those receiving neonicotinoid when compared to those who were not exposed to pesticides.

The study clearly indicates that combinatorial exposure to pesticides increases the tendency of bee colonies to fail.

"Policymakers need to consider the evidence and work together with regulatory bodies to minimize 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," said Raine

Professor Douglas Kell, Chief Executive of BBSRC, said: "Bumblebees play an important role in pollination, working earlier in the morning and later into the evening than many bees. Understanding the threats to all insect pollinators is vital if we are to ensure we mitigate the impact of their decline on the production of agricultural and horticultural crops. The results of this study contribute to a wider initiative to help inform strategies for securing the futures of all insect pollinators."

The study details was published in the journal Nature.