There has been a lot of buzz surrounding the risks of pesticide pollution to bees over the past decade, with many studies reporting that pesticide-contaminated pollen and nectar can have both lethal and non-lethal consequences for important pollinating insects. While most of the research in this area has focused on honeybees, the effects of pesticides on our vulnerable wild bees are commonly overlooked. Buff-tailed bumblebees (Bombus terrestris) are one such insect, responsible for pollinating a range of fruit and vegetable crops, as well as countless wild plant species. Despite their importance in providing ecosystem services to farmers and orchardists, bumblebees are under serious threat from agricultural practices, and a recent study from Imperial College London, UK, has revealed that pesticides are affecting these marvellous minibeasts in more subtle ways than previously understood.
As flight performance is such a crucial element to the survival and reproduction of bumblebees, lead author Daniel Kenna and his team were interested in investigating how agricultural pesticides interfere with the flight dynamics and endurance of wild bumblebees. To keep their experimental study as realistic as possible, the researchers chose to use the neonicotinoid pesticide imidacloprid because of its widespread use in farming around the world and only applied doses similar to those that have been found previously in the pollen and nectar stores of wild bees. Prior to the experimental flights, the team fed the bees either on imidacloprid-treated sucrose or untreated sucrose, and then assessed the insects’ flight performance using a circular flight mill comprising a revolving brass wire that ended in a small face-down magnet. The team then attached small metal tags to the backs of the bees which allowed them to fly continuously while remaining anchored to the mill. With this simple setup, the researchers were able measure the number and speed of circuits that the bees performed. As bumblebees do not fly continuously while foraging in the wild, the researchers allowed each bee a maximum of five brief rest breaks before ending the flight and, after 60 minutes, any bees still flying were brought to a stop.
Interestingly, the team discovered that the average circuit speed and average maximum speed achieved by the pesticide-treated bees was actually much higher than those of the control bees. The researchers explain that this hyperactivity is not entirely unexpected as neonicotinoids stimulate neurons in a similar way to nicotine, which could explain this burst of speed. However, in a plot twist torn straight from the pages of ‘The tortoise and the hare’, the researchers found that this frantic frenzy came at a big cost in the long run. The pesticide-treated bees covered much shorter distances (0.7 km) than the control bees (1.8 km) and the same was also true of flight duration, with flights of pesticide-treated bees (∼14 min) lasting nowhere near as long as control bee flights (∼48 min). In fact, while not a single pesticide-treated bee was able to fly for the full 60 minutes, 65% of the bees that had not received a neonicotinoid shot achieved this feat, effectively demonstrating the severe hampering of flight endurance brought about by exposure to the pernicious pesticide.
As well as underlining the serious consequences that a reduction in flight range and endurance can mean for a bumblebee's ability to forage and pollinate crops, the authors stress the importance of studying non-honeybee species, such as bumblebees, as one previous study found that honeybees actually increased flight endurance when treated with neonicotinoids, emphasising that what may be true for one pollinator species may not be true for all. Finally, by demonstrating how easily these patient pollinators can become doomed drag-racers when exposed to realistic neonicotinoid doses, this study adds to the growing body of evidence that pesticide pollution can be a real buzzkill.
