Teeny brain scans have shown how pesticides have a damaging effect on the development of baby bumblebee brains.
The research found that exposure to pesticides during the larval stage of bumblebees can mangle their brain development, causing specific parts of the brain to grow less, or abnormally, leaving them with smaller or functionally impaired brains when older. The research also strongly hints that this could help to explain why pesticides have such a dramatic effect on the behavior of bee populations, often impairing foraging bumblebees' ability to navigate and recognize flowers.
Reported in the journal Proceedings of the Royal Society B this week, Imperial College London researchers carried out detailed micro-CT scans on the brains of almost 100 bees – which, for context, are just 0.0002 percent the size of a human brain. Some of the bees were part of a colony that was fed a diet of nectar spiked with neonicotinoids, a controversial pesticide that is banned in parts of Europe but still widely used across the USA.
The team scanned the brains of bees three days and 12 days after emerging from the papal, then compared these results to the young from colonies that were fed no pesticides and others that were fed pesticides only once they had emerged as an adult.
More specifically, the bees that were exposed to pesticides appeared to have a smaller volume of the “mushroom body,” a pair of structures in the brain of insects that play a role in learning and memory (shown above). This makes sense, given the known effect of some pesticides on bees' ability to navigate and forage for food.
The research then went a step further and tested the bees’ cognitive abilities by seeing if they associate a smell with a food reward. As anticipated, the pesticide-spiked bees were poorer at performing the task later in life.
“Bee colonies act as superorganisms, so when any toxins enter the colony, these have the potential to cause problems with the development of the baby bees within it,” lead researcher Dr Richard Gill, from the Department of Life Sciences at Imperial, said in a statement.
“Worryingly in this case, when young bees are fed on pesticide-contaminated food, this caused parts of the brain to grow less, leading to older adult bees possessing smaller and functionally impaired brains; an effect that appeared to be permanent and irreversible.”
The declines of bees and other pollinating insects around the world remains one of the most concerning (and underestimated) challenges of our time. There are many factors behind this, from the destruction of habitat to disease, but the use of pesticides consistently stands out as a major factor. Considering about 35 percent of the world’s food crops depend on animal pollinators to reproduce, that's extremely worrying.