CORVALLIS, Ore. — By the time she was studying the mechanics of stag beetle pinchers as an undergraduate, Emily Carlson knew she had been bitten by the research bug.
Literally.
“Basically, I just got them really angry, saw how hard they could pinch and then dissected their heads,” Carlson said.
A disclaimer, she added: Beetles aren’t “true” bugs, though the term is commonly used in the United States.
“We’ve used hazard quotient for at least 10 years, and this is the first study to ask a basic question: How many sites do we need to monitor to understand how hazard changes over time?”
Carlson went on to work in natural resources nonprofits and local governance as she explored where to focus her scientific interests. That experience ultimately led her to pursue a doctorate at Oregon State University, where she conducted research in the Honey Bee Lab and Pollinator Health Program.
Carlson, who graduated in June, is lead author on a study published in PLOS ONE showing that a commonly used method for monitoring honey bee pesticide exposure fails to capture critical information. The findings provide an important reference for policymakers and researchers.
Her co-authors include Ramesh Sagili, professor of apiculture and Oregon State University Extension Service honey bee specialist, and Andony Melathopoulos, Extension pollinator health specialist and associate professor, both in Oregon State’s College of Agricultural Sciences.
Bees and pesticides
In 2013, a pesticide application in Wilsonville resulted in the largest documented mass mortality of bumblebees in North America. Subsequent research in 2021 doubled the estimated death toll to 100,000.
In response, the Oregon Legislature funded Oregon State’s Pollinator Health Program and the Extension pollinator health specialist position filled by Melathopoulos in 2016. Carlson’s research builds on that foundation by addressing a key gap.
“You can report on bee poisonings, but there is no system to understand what pesticides bees are exposed to over time,” Carlson said. Both the U.S. Environmental Protection Agency and the Office of the Inspector General in the U.S. Department of Health and Human Services have identified this as a significant challenge.
Monitoring exposure is complicated.
“Bees are a very unusual agricultural ‘product,’” Carlson said. “Unlike cows, you can’t put a fence around them. They’re going to forage where they want.”
Instead of tracking individual bees, researchers monitor the pollen bees collect. Pollen can be identified by plant species using unique protein structures and then tested for pesticide residues.
Understanding hazard quotient
Pesticide exposure is commonly assessed using a unitless metric called a hazard quotient, which estimates pesticide risk to bees.
Carlson explains hazard quotient by comparing it to coffee consumption.
“We know caffeine can be deadly at a high enough dose, so caffeine itself is a hazard,” she said. “But risk depends on exposure.”
Someone who drinks one cup of coffee a day has low exposure and therefore low risk. Hazard quotient aims to express that same relationship for bees and pesticides, using pollen as the exposure pathway.
While widely used in research and monitoring, hazard quotient has limitations. There is little guidance on how much pollen should be tested or how many sites are needed to reliably detect changes in risk.
That uncertainty is where Carlson’s study begins.
Testing the assumptions
Carlson set out to determine how many sampling sites — locations where pollen is collected — are needed to detect a 5% annual change in hazard quotient over five years. To do so, she analyzed pollen collected from hundreds of hives across multiple crop systems.
The results varied dramatically by crop. One system required just 139 sites, at a cost of less than $150,000, to detect changes in risk. Another required more than 7,000 sites and an estimated cost exceeding $3 million.
The findings show that hazard quotient can be both imprecise and expensive when used as a monitoring tool.
“I’m not saying we should throw hazard quotient out entirely,” Carlson said. “It’s still useful for understanding general hazard.”
Instead, the study calls attention to the need to test assumptions embedded in long-standing monitoring systems.
“We’ve used hazard quotient for at least 10 years, and this is the first study to ask a basic question: How many sites do we need to monitor to understand how hazard changes over time?” Carlson said.
The metric also obscures important details, she noted. For example, when pesticides are detected in pollen from carrot fields, it isn’t always clear whether the chemicals came from carrot production or from another nearby source.
Identifying the specific pesticide source could inform management decisions. Growers might invest in drift barriers, such as plantings that deflect spray, or adjust application timing to better protect bee colonies.
Shared goals for bees and agriculture
Concerns about pesticide exposure can sometimes be framed as a conflict between growers and beekeepers, but Carlson said the reality is quite different.
“Commercial beekeepers and growers are partners,” she said. “Beekeepers earn much of their income through pollination contracts with growers, because crops produce better yields when bees are present.”
Both groups have a strong interest in reducing pesticide risks, which is why they collaborated on the research.
“We’re incredibly fortunate to have beekeepers who trust us with their livelihoods and allow us to use their hives for research,” Carlson said.
“The bees are being paid to pollinate,” she added with a laugh, before correcting herself. “Well, the beekeeper is paid on behalf of the bees — but the bees get benefits, too.”
Carlson’s research was supported by the Oregon State Beekeeping Association, the U.S. Department of Agriculture’s Natural Resources Conservation Service, the Foundation for Food and Agriculture Research, and the National Science Foundation’s Graduate Research Fellowship Program.
