A new study has found that prolonged exposure to a commonly used pesticide not only significantly impaired the ability of bumblebees to forage, but also altered the preference for the type of flower that they visit. The results suggest that long-term pesticide exposure could negatively affect colony survival and the pollination services provided by these insects. The study has been published in Functional Ecology.
Bees, such as honey bees and bumblebees, are important pollinators of many of our crops. They’re used in modern agriculture to guarantee pollination of various vegetables, fruits and nuts. In fact, it has been estimated that approximately 1 mouthful in 3 of our diet benefits from bee pollination. Bees are therefore crucial to our food security, and given the fact that worker bees are likely exposed to pesticides during foraging activities, studies such as this are particularly important to assess the impact that this may have.
Bumblebees forage for both nectar and pollen and a food source. While pollen gets stuck on their furry coats whilst they suck up nectar, assisting the pollination process, they also deliberately vibrate their wings to release pollen from flowers. This forage is also returned to the nest to feed the colony; without it the colony quickly starves.
To investigate whether this foraging behavior is affected by pesticide exposure, researchers from Imperial College London and the University of Guelph monitored the activity of 259 bumblebees from 40 colonies for 4 weeks using radio tags. They followed the movement of the bees and also measured how much pollen was collected and from which flowers.
The researchers exposed the bees to either a neonicotinoid pesticide (imidacloprid) and/or a pyrethroid (lambda-cyhalothrin), alongside a control group not exposed to any pesticides. Neonicotinoids make up around 30% of the global pesticide market and it has been demonstrated that plants grown from neonicotinoid treated seeds possess the pesticide in their nectar and pollen.
They found that bees exposed to imidacloprid brought back significantly less pollen than the control bees, suggesting a decline in foraging performance. Furthermore, to compensate for this decrease in pollen, the colonies actually sent out more foragers.
Another important finding was that as control bees gained experience in foraging their performance increased; the opposite could be said for bees exposed to imidacloprid as they became worse over time. This suggests a chronic behavioral impairment. Finally, they also found that imidacloprid exposed bees collected pollen from different flowers to the controls.
Taken together, the results suggest that these behavioral effects could have serious knock-on consequences on colony growth and survival.
This is the first study to examine the impacts of long-term pesticide exposure on foraging behavior and adds to the growing body of evidence that imidacloprid is likely contributing to worldwide declines in honeybee colonies. The researchers therefore call for consideration of prolonged exposure to be taken when assessing the potential risks of pesticides to bees.