Micro-CT scans reveal the damage pesticide exposure can have on developing bee brains.

By Mike Pomranz
Updated March 09, 2020

Not that adults don’t deserve our empathy, but when something affects babies, our heartstrings are especially tugged. So while you are probably aware that our bee populations are struggling, and pesticides are a cause, but maybe this will get you to reevaluate just how dire the situation is: A new study suggests that pesticides are harming baby bees, too.

The study, conducted by researchers at Imperial College London and published in the journal Proceedings of the Royal Society B, explains that most studies have looked at the effect of pesticides on adult bees, but this kind of research can overlook the larger picture. “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,” Richard Gill, the lead researcher from the Department of Life Sciences, explained in announcing the findings.

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“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,” Gill continued. “These findings reveal how colonies can be impacted by pesticides weeks after exposure, as their young grow into adults that may not be able to forage for food properly. Our work highlights the need for guidelines on pesticide usage to consider this route of exposure.”

So how do you study tiny bumblebee brains? With micro-CT scanning technology, obviously. For this research, a bee colony was given “a nectar substitute spiked with a class of pesticides called neonicotinoids, some of which are restricted within the EU but used widely across the globe,” according to the Imperial College London news site. Through this method, the larvae were exposed to the pesticide, and then, after emerging from their pupa stage, these adults had their learning ability tested—by seeing if they could associate a smell with the reward of food—after three days and 12 days. (Yes, a 3-day-old bee is an “adult;” this species tends to have its lifespan measured in weeks.)

These results were then compared to both bees that were not exposed to pesticides at all and ones only exposed to pesticides as adults. Nearly 100 bees from all three groups also received micro-CT scans—which probably aren’t as cute as they sound. The result: Not only did the bees which were exposed to pesticides as babies perform worse on the tests, they also had less volume in an important section of their bee brains.

“There has been growing evidence that pesticides can build up inside bee colonies. Our study reveals the risks to individuals being reared in such an environment, and that a colony’s future workforce can be affected weeks after they are first exposed,” Dylan Smith, the lead author and part of the Science and Solutions for a Changing Planet Doctoral Training Partnership, added. “Bees’ direct exposure to pesticides through residues on flowers should not be the only consideration when determining potential harm to the colony. The amount of pesticide residue present inside colonies following exposure appears to be an important measure for assessing the impact on a colony’s health in the future.”

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