Honeybees Suffer Severe Learning And Memory Problems When Exposed To Widely Used Pesticide

275 Honeybees Suffer Severe Learning And Memory Problems When Exposed To Widely Used Pesticide
Chlorpyrifos is used in over 100 countries worldwide, and could severely harm bees' ability to remember odors. Igor Podgorny/Shutterstock

There has been a lot discussion in recent years about the decline in honeybee populations around the world, and the role that pesticides have in threatening their survival. Much of the focus has been directed towards pesticides containing neonicotinoids, which in sub-lethal levels have been linked to negatively impacting the bees' ability to navigate, as well as making them more susceptible to other diseases. But a new study suggests that neonics aren’t the only pesticide that we should be worrying about.

The research, published in the Journal of Chemical Ecology, has shown that small doses of a pesticide known as chlorpyrifos can severely affect the learning ability and memory of honeybees, which could impact their ability to pollinate flowers and threaten their survival. They found that even at doses that were deemed “safe” for the bees, they were still compromised. The study goes to show that even if a pesticide is not lethal to pollinators, it can still have serious consequences.


The bees were collected from 51 hives across 17 locations in Southern New Zealand and then tested in a laboratory setting, in which they were placed into little harnesses and conditioned using a sugar reward. “What we do is a very simple learning assay, where we teach that an odor is predictive of a reward in the bees,” lead author Dr. Elodie Urlacher explained to Otago Daily Times. “What we do to condition the bee is to puff an odor just before, and then give the reward, and if we do that several times then the bee is going to extend her tongue, her proboscis, whenever she smells the odor.”

The bees in their little harnesses, ready to be conditioned by the researchers. Still from Otago Daily Times video/YouTube

When the researchers compared the bees that had been exposed to doses “thousands of times lower than the lethal dose of pure chlorpyrifos” to those that were clean, they found that the chlorpyrifos-fed bees didn’t just respond to the odors associated with reward, but to all smells they were exposed to. The pesticide-free bees, on the other hand, retained their memory specificity and only extended their tongue when exposed to the odor paired with the reward. If the pesticide is altering the bees' ability to learn and remember smells, it could ultimately be having an effect on pollination and honey production.  

Chlorpyrifos is a chemical that is widely used to control mites and other crop pests in nearly 100 countries worldwide. The pesticide is easily spread, with traces of it carrying on the wind and air, and it has even been detected in Arctic waters. It has also been found to harm prenatal development in humans, and is banned from households, however it is still widely used on farms. Its effect on biodiversity and wildlife is also significant, with just a few concentrated teaspoons of the stuff that's washed down a plughole apparently sufficient enough to poison insects and shrimp along a 15-kilometer (9-mile) stretch of river in England. In fact, starting in April 2016, it will be illegal to use pesticides containing chlorpyrifos in the U.K. 


But the new study proves that it is not just the lethal doses that we should be concerned about, but also those deemed “safe.” “Our findings raise some challenging questions about regulating this pesticide's use,” says Dr. Urlacher. “It's now clear that it is not just the lethal effects on bees that need to be taken into account, but also the serious sub-lethal ones at minute doses.”


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  • honey bee,

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  • New Zealand,

  • bee declines,

  • chlorpyrifos