Scientists know pesticides are killing the world’s bee populations, putting prolific pollinators in jeopardy, but a new study sheds light on exactly how the insects change their behaviour when exposed to neonicotinoids, a common form of pesticide that disrupts the central nervous system.

A bumblebee assisting with pesticide research. Credit: Crall, et al.

Using tiny robots, researchers led by James Crall of Harvard University in the US find that under exposure to imidacloprid, a type of neonicotinoid, worker bumblebees (Bombus impatiens) stop nursing the colony’s larvae, become less social, and stop constructing hive insulation – behaviours that can lead to colony collapse.

“In addition to foraging, workers in social insect colonies perform critical tasks within the nest … that are vital for colony development,” write the scientists in a paper published in the journal Science.

“We find that exposure to field-realistic levels of imidacloprid impairs nursing and alters social and spatial dynamics within nests.”

Using a robotic platform to continuously monitor bees, Crall and his colleagues find that workers in colonies that had been exposed to imidacloprid “spent significantly less time active”. The exposed colonies were also less adept at regulating hive temperature and showed reduced foraging and social interactions.

Testing different levels of exposure, Crall and his colleagues see that “acute imidacloprid exposure altered nest behaviour within 24 hours, with effects qualitatively similar to those of chronic exposure”.

The researchers conclude that “neonicotinoids induce widespread disruption of within-nest worker behaviour that may contribute to impaired growth, highlighting the potential of automated techniques for characterising the multifaceted, dynamic impacts of stressors on behaviour in bee colonies”.

Bees have been declining worldwide for the last 50 years. A 2015 review, also published in Science, blamed the decline on loss of habitat, climate change, infectious disease, and chemical pollution. The loss of pollinators, overall, the scientists warned, could lead to a “pollination crisis” and loss of crops.

Earlier this year, a group of more than 200 scientists wrote an open letter calling for the urgent restrictions on neonicotinoids, saying the neurotoxins are “contributing to the current massive loss of global biodiversity”.

They cited one study that found neonicotinoids are present in 75% of honey samples taken from around the world. Another found that less than 5% of the chemicals’ active ingredients are taken up by target plants. The rest migrate into the greater environment.

“Failure to respond urgently to this issue risks not only the continued decline in abundance and diversity of many beneficial insects, but also the loss of the services they provide and a substantial fraction of the biodiversity heritage of future generations,” wrote the authors, led by Davie Goulson from the University of Sussex in the UK.