Study Links Pesticides Exposure to Reduced Size of Worker Bumblebees

A latest study says that prolonged use of pesticides on flowering crops has resulted in hatching of smaller-sized bumblebees.

The study done by a team of researchers at the Royal Holloway University of London claims that prolonged exposure to a widely used pesticide called pyrethroid pesticide-used on flowering crops to arrest insect damage, is responsible for the reduced size of individual worker bumblebees produced by a colony.

Previously conducted studies focusing on the pesticide pyrethroid,  designed to get rid of roaches, carpenters ant, boll weevils and other undesirable critters, have revealed that the chemicals presents in the pesticide impair the reproduction of the bees. Another study uncovered the effect of this common pesticide on the foraging abilities of the worker bumblebees. Exposure to the pesticide affects the bees' ability to trace their home successfully and even reduces the numbers of queens in a colony.

In the current study, researchers Gemma Baron, Dr Nigel Raine and Professor Mark Brown worked with colonies of bumblebees in the laboratory. As part of the experiment, the researchers exposed half of the bumblebees to pesticides. After exposure to the pesticide, the growth of the bees in the colonies was monitored over a four-year period. They recorded the size and weight of the bees.  Apart from this, the researchers kept a check on the number of queen and male bees produced by the colony.

"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," study researcher Gemma Baron, said.

This is the first study to observe the impact of the pyrethroid pesticide on the entire lifecycle of the bumblebee.

According to Mark Brown, bumblebees are vital to the food chain hence, it is important to understand the impact of such commonly used chemicals on wild bees. Simultaneously, it is important to protect plants from the damage caused by insects. Scientists say a balance needs to be established.

The European Union recently imposed a freeze on the use of three neonicotinoid pesticides, which in turn has increased the use of other classes of pesticide, including pyrethroids.

Dr Nigel Raine, said, "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."

Last year, nearly 25,000 bumblebees were spotted dead in a parking lot of a shopping center in Wilsonville, Oregon. The conservationists claimed that insecticides sprayed on the trees were responsible for the deaths of the black and yellow bumblebees.

The study was documented in the Journal of Applied Ecology.