Bumblebees may develop a preference for pesticides in much the same way smokers develop an addiction to nicotine. That's the conclusion of a study recently published in Proceedings of the Royal Society B.
Researchers from Imperial College and Queen Mary University, both in London, tracked the foraging behavior of 10 bumblebee colonies for 10 days. The bees had several sucrose feeders to forage from. Each contained a solution with either 0, 2, or 11 parts per billion (ppb) of thiamethoxam, a neonicotinoid class of insecticide.
The experiment was set up in a way to mimic real-life foraging activity, offering the bees a variation of concentrations of thiamethoxam and multiple exposures to the pesticide. By using whole colonies, the researchers allowed the bees to preserve their usual social cues.
The team discovered that the so-called "naïve" bees appeared to prefer the "pure" solution (i.e. the one with no pesticide whatsoever). However, once an individual bee acquired a taste for the thiamethoxam, it kept going back for the pesticide-laced food. Apparently, it wanted another fix. Over time, they visited the pesticide-free solution less and the pesticide-laced food more – the 2 ppb appeared to be the favorite, seeing the biggest increase in feeding and the most feeding overall.
What's more, this behavior continued even after they tried to "trick" the bees by switching up the feeders, suggesting bees are able to detect the pesticide and then actively seek it out.
"Interestingly, neonicotinoids target nerve receptors in insects that are similar to receptors targeted by nicotine in mammals," Richard Gill from the Department of Life Sciences at Imperial explained in a statement.
"Our findings that bumblebees acquire a taste for neonicotinoids ticks certain symptoms of addictive behavior, which is intriguing given the addictive properties of nicotine on humans, although more research is needed to determine this in bees."
So, what exactly does this mean for wild bee populations?
Exposure to neonicotinoids can affect motor functions, learning, orientation, and navigation skills – and not in a good way. This may hurt foraging performance, which may threaten the health and numbers of the colony. The widespread use of pesticides like thiamethoxam in agriculture may even be one of the reasons city bees are surpassing country bees in reproductive terms (at least in the UK).
"This research expands on important previous work by groups at Newcastle and Dublin Universities," Richard Gill from the Department of Life Sciences at Imperial and lead author on the paper explained. "Here, we added a time dimension and allowed the bees to carry out more normal foraging behavior, to understand the dynamics of pesticide preference. Together these studies allow us to properly assess the risks of exposure and not just the hazard posed.
"Whilst neonicotinoids are controversial, if the effects of replacements on non-target insects are not understood, then I believe it is sensible that we take advantage of current knowledge and further studies to provide guidance for using neonicotinoids more responsibly, rather than necessarily an outright ban."