Jan 20, 2014 09:06 AM EST By Staff Reporter, UniversityHerald Reporter

Pyrethroid pesticide, a widely used insect repellent on flowering crops, shrinks bee size, according to a new study by Royal Holloway University of London. Researchers said that exposure to the pesticide hinders growth of worker bumblebees.

For the study, the researchers - Gemma Baron, Dr Nigel Raine and Professor Mark Brown from the School of Biological Sciences - exposed half of the colonies of bumblebees in their laboratory to the pesticide.

They observed the bees' growth over a four month period including the number of queens and male bees produced, recorded their size and weighed them on micro-scales.

"We already know that larger bumblebees are more effective at foraging. Our result, revealing that this pesticide causes bees to hatch out at a smaller size, is of concern as the size of workers produced in the field is likely to be a key component of colony success, with smaller bees being less efficient at collecting nectar and pollen from flowers," Baron said in a press release.

This is the first study to look at the impact of pyrethroid pesticides on the lifecycle of bumblebees.

"Bumblebees are essential to our food chain so it's critical we understand how wild bees might be impacted by the chemicals we are putting into the environment. We know we have to protect plants from insect damage but we need to find a balance and ensure we are not harming our bees in the process," Brown said.

Since the EU has slapped a two-year ban on three key neonicotinoid pesticides, the use of other pesticides, including pyrethroids, is likely to increase.

"Our work provides a significant step forward in understanding the detrimental impact of pesticides other than neonicotinoids on wild bees. Further studies using colonies placed in the field are essential to understand the full impacts, and conducting such studies needs to be a priority for scientists and governments," Dr Nigel Raine, who is an Invited Speaker at the national Bee Health Conference (22-24 January), said.

The finding has been published in the Journal of Applied Ecology.

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