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Scientists Say They’ve Found the “Missing Link” on Bees and Pesticides

New research may give greater insight into the connection between insecticides and our declining pollinator numbers.

New research may give greater insight into the connection between insecticides and our declining pollinator numbers. (Photo: Bee on Flower via Shutterstock)

Scientists believe that they’ve cracked the seeming conflict between their research that shows pesticides can harm honeybees and the fact that in field tests larger colonies of bees seem to be able to survive pesticide exposure.

The pesticide industry has long used this as a reason why governments shouldn’t ban the pesticide family called neonicotinoids because, they say, the discrepancy shows that the lab tests are unreliable and have toxicity rates that are not reproduced in the wild. However, the lab results have been fairly consistent so clearly neonicotinoids were having an effect on bees, it just wasn’t translating into a real world setting the way that scientists had expected. Now, scientists think they have the answer as to why.

Writing in the journal Royal Society journal Proceedings B French researchers say their tests prove that honeybees foraging around neonicotinoid areas do indeed die off faster than their counterparts who haven’t been exposed to these pesticides. Lab tests have shown that neonicotinoids appear to alter the bees’ ability to navigate, weakens their immune system and, through cumulative effects, may lead to early death.

To find evidence of this the researchers monitored 18 bee colonies that had been exposed to oilseed rape that had been treated with the neonicotinoid thiamethoxam.

The researchers found that the colonies were able to compensate for die-off by producing more female workers at the expense of male drones. This serves to keep the bee colony fed and may ensure its survival despite what the researchers called “significant excess mortality.”

Researcher Dr. Mickael Henry of the French National Institute for Agricultural Research, INRA, told the BBC: “We could find evidence of troubles at the individual scale in the field but these troubles were compensated for by the colonies. The population inside the hive was able to compensate for the increased loss of worker honeybees by increasing brood production.”

The researchers saw no major effects at the colony level, but that doesn’t mean there aren’t any. There could be a cumulative threat from neonicotinoids: the greater exposure and die-off of female workers, the more the colony will have to adapt its demographics. What was only a slight imbalance could create a pressure that might be easily exacerbated if other stress factors were introduced, for example parasites or a shortage of food. This could account for the sudden collapse of colonies, though of course that would have to be scrutinized by further experiments.

It’s worth noting, too, that figures for 2014 show that honeybees had suffered the second-highest rate of die-off since records began in the United States. So clearly it’s probably a combination of factors that are driving down their numbers.

It’s also true that the data suggests honeybees are actually far more resilient to pesticides than had once been thought. That might be good news for them, but other insects and even other kinds of bees have been shown to struggle far more. The above finding may signal how neonicotinoids can make insects vulnerable. That of course doesn’t even touch on the fact that cumulative insecticide exposure appears to be negatively impacting other species, like birds.

This research, then, is important because it appears to support – subsequent to more tests – that neonicotinoids do drive up mortality rates in bees as had been shown in the lab. That will be important as policies surrounding insecticides continue to be debated. For example, the EU issued a ban on neonicotinoids in 2013 but that must be renewed this year. The UK government has fought heavily to keep using neonicotinoids, saying that the science simply isn’t there to prove that neonicotinoids do harm bees. This research may serve to reinvigorate that debate and give greater insight into the connection between insecticides and our declining pollinator numbers.

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