Bumblebees exposed to pesticides are slower to learn foraging behaviour: study

A new study finds that bumblebees exposed to pesticides have different foraging behaviour.

The joint study produced by researchers at the University of London, England, the National University of Ireland in Galway, Ireland, and the School of Environmental Sciences at the University of Guelph in Guelph, Ontario, shows that sub-lethal exposure to neonicotinoid pesticides changes the interaction between bumblebees and wildflowers in a number of ways, a result which the study’s authors say should be factored into future pesticide risk assessments.

Concern over the health and vitality of the world’s bee colonies has been climbing over the past two decades, just as the number of bees keeps declining. Last year saw reported losses of 40 per cent of bee populations in North America for reasons not yet fully understood. Experts place the blame on a number of factors, including a deadly pest known as the varroa mite, the loss of bees’ native habitat, the use of insecticides and other factors. An estimated 35 per cent of the food we eat is pollinated by bees.

And while the honeybee gets much of the attention due to its larger role in agriculture and food production, the bumblebee also serves the role of pollinator for both crops and wild plants. Bumblebees get exposed to pesticides when they forage on treated crops and typically the level of exposure is non-lethal, hence the need for research into how chronic exposure to pesticides can affect bee activity and the long term health of bee colonies.
Studies have shown that neonicotinoids -commonly used nicotine-based pesticides- can affect the honeybee’s learning and memory as well as their navigation, foraging and reproduction.

Researchers for the current study created field-realistic exposures to a widely used variety of neonicotinoid called thiamethoxam for ten colonies of bumblebees, averaging 109 worker bees each. The results showed that in comparison to a group of control colonies who were not exposed to the pesticide, the exposed bees showed increased activity, in that they visited more flowers than the control group and had a higher proportion of bees from each exposed colony released to become foragers. Yet the control bees learned to manipulate the wildflowers (i.e., get access to nectar and pollen) after fewer visits than did the pesticide-exposed bees, effectively making the control group faster than the exposed bees at learning how to collect pollen (it can take up to 30 foraging trips for an individual bee to become efficient at foraging.)

“Our research confirms that changes in foraging behaviour on wildflowers represent another sublethal impact of pesticide use, which may have implications for the delivery of pollination services to wild plants,” say the study’s authors.

The authors argue that their results as well as other conclusions on the non-lethal effects of pesticides should figure into pesticide risk assessment. Current practices for pesticide risk assessment factor in a pesticide’s impact only on bee mortality and reproduction.

So far, Europe has banned the use of three types of neonicotinoid pesticides on bee-attracting crops, while the pesticides are still available for agricultural use throughout Canada and the United States. The province of Ontario has restricted the use of seeds treated with neonicotinoids and is moving towards an 80 per cent reduction in neonicotinoid use by 2017.

The study was published in the journal Functional Ecology.

More Cantech Science