Queen bees exposed to nicotine-based insecticides become less active and lay fewer eggs, a University of Minnesota study released Friday shows.
It's an important finding in the growing understanding of why bee populations are in decline, and it comes as the state is considering new insecticide regulations.
The link between neonicotinoid insecticides and the drop in bees has been known for several years, but it's still not well understood. The study, published in the journal Scientific Reports, fills in some gaps in that knowledge.
It's all about colony size and timing, the study shows.
Honeybee colonies are typically smaller in the spring. Then the queen bee gets busy laying eggs and the colony grows rapidly. It should be at peak strength by the time summer flowers are in full bloom and ready for bees to perform their critical work as pollinators.
However, queen bees exposed to neonicotinoid insecticide become lethargic and lay fewer eggs, says Judy Wu-Smart, who's now an assistant professor at the University of Nebraska-Lincoln, but did this research while a graduate student at the University of Minnesota.
"We didn't know that the queens could be impacted so readily, we didn't know that at even lower doses that these queens would have reduced egg laying," she said.
Wu-Smart and her colleagues found that it wasn't only queens who were affected by insecticide exposure — worker bees were also less active. So they did a poor job of removing pests like varroa mites from the colony, and they collected less pollen.
"The pollen I think is an important aspect particularly because that's what's necessary for brood production," she said.
This study also shows that understanding the complex effect of insecticides on bees isn't simple. When the chemicals are applied to seeds or soil, the plant absorbs them along with water and nutrients.
So any time a soybean aphid or potato beetle bites a leaf, they get a dose of insecticide, which is designed to impair brain activity and kill them.
It's an efficient pest control. But the insecticide also affects beneficial insects like bees that feed on plant flowers.
Bees exposed to low amounts aren't killed, but behavior changes in ways consistent with brain impairment, which would explain why queens lay fewer eggs and the colony collects less food for young bees.
This study also found that size matters that the chemical effect was more pronounced on smaller colonies than bigger ones exposed to insecticide, but the reason for it remains a mystery.
Wu-Smart suspects it's because in a larger colony there are more bees doing the work and the insecticide effect is diluted. She says more research is needed.
Co-author and U of M bee expert Marla Spivak says just looking at the small colony data, it's clear the insecticide is a significant problem. But someone could look at just the larger colony data and say, see it's not a big problem.
"Both are the truth. When a colony is small in the spring they're really vulnerable to the effects of the neonicotinoid and the stronger colony may not be as vulnerable so the study is nuanced in that it shows when it's a problem, and when it may not be a problem."
Spivak says spring appears to be a sort of perfect storm of insecticide exposure and weaker bee colonies. And she says these findings build a stronger case for better management of how these pesticides are used.
"The bigger picture in general is we really need to be practicing more integrated pest management which is just not this widespread use of all kinds of pesticides, insecticides, herbicides, fungicides, but only treating when the problem needs to be treated," Spivak said.
This new research comes out as the state has been reviewing existing studies on the benefits of neonicotinoid insecticides, how they're used and risks to pollinators. That review could lead to new requirements for advisory label recommendations or regulatory changes up to a partial or complete ban.
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