"It's fantastic that someone is doing this," says Rutgers University entomologist Rachael Winfree. "There are no long-term bee monitoring programs in North America, except for bumblebees. This is not a new idea, it's just no one is doing it."
Part of the reason there hasn't been a long-term, wide-scale bee monitoring program is because there wasn't an efficient way to collect the bees. Using nets takes time, and results vary depending on who swings them. Bowls of soapy water catch bees effectively, but the water evaporates quickly—meaning scientists have to check the traps frequently. "Figuring out how much and when to sample is tricky" with this method, Droege says. A third option uses malaise traps, which are large tent-like nets that funnel insects into jars of alcohol or propylene glycol, but these traps can cost up to $250 apiece.
Droege and his colleagues spent years cooking up a solution. They developed a trap made from painted plastic beer cups, soap and glycol. The paint colors attracts the bees, the soap kills them and the glycol preserves them. (Propylene glycol is "generally recognized as safe" by the U.S. Food and Drug Administration.) The foresters at each site set out the traps, collect the captured bees every two weeks and mail them to Droege for identification.
The program is in its third year of data collection, but doesn't yet have a name or funding. And so far they haven't needed it; most of the participating sites report that maintaining the traps requires very little money or effort. Henry McNab, a research forester at the Bent Creek Experimental Forest in North Carolina, estimates that on average the bee collections required 15 minutes per week and about $30 per year.
Some sites have collected more than 1,400 bees in one summer. They've found several rare bees, and discovered species in places that would typically be considered outside of their normal range or habitat—for example, scientists at the Maine site collected a squash bee (Peponapis pruinosa), a species that is most common in the U.S. Southwest and rarely found north of southern New England.
The two-year analysis is also uncovering hints at population trends, although several years' more data are needed to determine whether these hints are significant. "The main goal is to look at change over time," Droege says. "If we can foresee declines, we can intervene before it's too late."
By making the monitoring project simple and inexpensive, Droege has made it easy for the experimental sites to continue participating for a very long time. Michael Ryan, a research ecologist at the Manitou Experimental Forest in Colorado, said in an email that "As long as the Forest Service can afford to keep a site manager at Manitou, we'll continue. And even if the site manager goes away [due to budget cuts],” he added, “I'll work somehow to get it done."
The simplicity of the program could come at a slight cost. For now, foresters participating in the monitoring program set up the traps in an area of their own choosing, typically in an area that is most convenient. But bees respond strongly to local habitat changes, such as weeds flowering in a nearby field or a freshly mowed lawn, Winfree says. She suggested that by standardizing and controlling the environments around the traps it will be easier to detect large-scale changes in bee populations, rather than the effects of local changes.
As the project is still in its infancy, Droege continues to work out the kinks. After he has proved that the experimental design works, he says he'll ask for federal funding in hopes of scaling up the project and increasing data resolution. At the moment Droege alone is tasked with identifying the thousands of bees collected, so he only has time to categorize them down to the genus level. "To some extent, the really interesting and important questions are at the species level," Winfree says. "The problem with having genus-level data is that, say one species is increasing and one went extinct, you wouldn't even detect it," because the total number of bees would stay the same, she says.