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A new method for monitoring the decline in bee populations may prove a useful tool in much-needed conservation efforts. It requires only a few hundred pan traps: bright shallow bowls partly filled with soapy water or propylene glycol.
When United Nations experts noticed that crop production was flagging in seven countries around the world, from Brazil to Nepal, they contacted Gretchen LeBuhn, an associate professor at San Francisco State University who studies bees.
“The U.N. thought that the problem might be tied to a decline in bee populations,” Dr. LeBuhn said. “I was hired to see if it would be feasible to monitor this decline.”
Her results, published in the most recent issue of Conservation Biology, outline the new monitoring method, which is remarkably cheap and efficient for tracking national, regional or global bee populations. At any of these scales, the pan traps can do the job at a cost of less than $2 million over five years.
Globally, insect pollination is responsible for almost $200 billion of agricultural production every year, with 70 percent of the main crops used for human consumption dependent on pollinators. The annual contribution of pollinators to essential ecosystem functions like water and habitat health, though not directly valued by markets, likely exceeds $200 billion.
Despite the economic stakes, a decades-long scientific narrative of bee decline and growing concern about an acceleration of this decline, there is no fixed network for tracking bee populations.
“No one really monitors bees,” said Sam Droege, a biologist at the United States Geological Survey and a co-author with Dr. LeBuhn. “Talk all you want about declines, but it’s based on nothing, really — no census, no survey.”
A critical feature of the published program is its ability to capture very slight population changes of 2 to 5 percent in a small window of time, thereby acting as an early-warning system. “Insect populations naturally go up and down a lot,” Dr. LeBuhn said. “Because they’re so variable, detecting a trend can be hard.”
An even subtler and more intractable challenge is identifying bees once they’ve been collected. Outside of about a half-dozen experts across the country, very few people can efficiently identify bees by genus, much less by species.
“A lot of effort will be required for retraining the next generation of taxonomists,” said Sydney Cameron, an entomologist at the University of Illinois at Urbana-Champaign and a science adviser to the Bumblebee Specialist Group at the International Union for Conservation of Nature.
For the most part, grants available to taxonomists have shriveled as specialties like genomics gain ascendance in biology, Dr. Cameron said. “But this may be a case of throwing out the baby with the bathwater,” she said. “We need taxonomy to understand what’s happening in the biological world.”
In the case of agriculture, poor productivity of a particular crop could be caused by the disappearance of a single, very efficient pollinator. Without data at the species level, this crucial fact might be overlooked.
Mr. Droege, who is among a handful of expert bee taxonomists, is using the findings from the article in Conservation Biology to build a national monitoring network that he hopes will include a partnership with Canada. He will probably be the project’s sole identifier of specimens.
But even with the development of a network, there is no central repository, federal or private, for the data. Dr. LeBuhn directs The Great Sunflower Project, a citizen-science program with 100,000 volunteers reporting daily pollinator observations. She is not sure what to do with the vast and growing collection of information.
“I’m sitting on an amazing data set,” she said. “If I got hit by a car tomorrow, somebody would probably do something with it, but it’s not feeding into anything like the U.S.D.A.”
To underline the importance of systematic monitoring, Dr. LeBuhn recounted how a former student, Quinn McFrederick, surveyed bumblebees in San Francisco’s urban parks in 2004 and discovered that a bee species that had been one of the city’s most common ones in the 1990s had disappeared entirely.
“Wow, I thought. The most common bumblebee in San Francisco disappeared, and none of us noticed, not even me, a biologist,” Dr. LeBuhn said. “That really got my attention.”