Project Megapoda (1)
The search for Bombus occidentalis.
The Western Bumblebee Project
Ancient history (twenty years ago)
Before the mid-1990s, the Western Bumblebee (Bombus occidentalis) was one of the most important native pollinators in the western United States. Not only was it widespread, abundant across most of its range, and active through most of the year, but it is also one of relatively few species of bee capable of pulling off a physical trick (“buzz pollination”) that is necessary to pollinate many agriculturally important native American plants.
Its resume as a pollinator was so impressive that there was a serious effort underway to domesticate the species for year-round pollination in greenhouses.
A few years later, most of them were dead. No one really knows why. There are some compelling suspects (most notably a microsporidian parasite called Nosema bombi) but the decline was so rapid, and so unexpected, that it was essentially complete before anyone realized that it had begun. The opportunity to conclusively identify the pathogen was gone, and aside from the occasional storm-tossed transient from one of a few remnant populations in the intermountain West, the species apparently declined to extinction across most of its historical range.
Recent history (last year)
In the summer of 2013, I heard a year-old rumor that a Western bumblebee had been seen north of Seattle. No one knew whether it was another transient, or part of a nest that was somehow scratching out a living in the suburbs.
I decided to find out.
After a few hours on Google Earth and two more on foot, I discovered that the bees were still out there: not a large population, but enough to show that they had survived the preceding winter and were in good shape to settle down for the following year.
We got lucky. This looks like at least a partial recovery, and if it is, we found it while it was still getting underway. That means that the different ecological possibilities – the spread of a resistant population across empty habitat, the spread of a resistant gene across sparsely distributed surviving populations, the recovery of surviving local populations due to a decrease in virulence of the pathogen that killed them in the first place – are distinct from each other in ways that can be measured with cheap genetic tests. Unfortunately, some of those distinctions will fade as the new populations grow and interbreed.
Our existing surveys strongly suggest that one particular hypothesis – decline to extinction at most sites, followed by radiation from a resistant, remnant population – is true. If it’s not, our pollinator surveys are not good enough. That would be good to know, too.
We may also be able to work back to find out what killed them off in the first place. There is a strong candidate: an imported strain of Nosema bombi, a microsporidian parasite. During the late stages of the decline, a team from the USDA measured the association between B. occidentalis genotypes and the presence of Nosema, but the data are difficult to interpret: we don’t know which populations survived. Now, we can find out. If N. bombi really is the pathogen affecting B. occidentalis, there’s a good chance that we’ll be able to prove it – and a better-than-nothing chance that we’ll find out how.
Finally, if we get really lucky, we may be able to save some honeybees. N. bombi is a close relative of two other pathogens, N. apis and N. ceranae, that are major threats to commercial honeybee hives. If N. bombi really is killing bumblebees, and if we can ID the change that has suddenly allowed B. occidentalis to survive, then we will have learned something about keeping bees alive in the presence of Nosema.
There are too many questions about the state of the Western bumblebee to answer with a single experiment, so we’re going to approach it from a few different directions.
In some ways, the genetic analysis is the easy part. The USDA group that did the original work on B. occidentalis is willing to process our samples, and we have faculty volunteers from the UW Department of Genome Sciences to make sure that we keep our math in order.
The real challenge is to collect the data in the first place. Someone (or, better yet, some two) needs to travel to the sites where Western bumblebees have been found, and take cell samples. (We use a technique that doesn't cause much damage to the bees.) Even if we can find volunteers, that’s going to take a lot of gas.
Rich site observation
A team of trained volunteers will monitor bumblebee activity at a few sites that are known to have healthy populations of Western bumblebees. The data they collect will let us answer questions about the absolute numbers and overall health of the Western bumblebee that are hard to address with genetic data alone.
So far, we only know of one site rich enough to support the kind of analysis we want to do, so we will spend the summer of 2014 fine-tuning our field techniques while the genetic data collection team finds a few more sites.
Our friends at Xerces have recently launched an excellent platform for tracking the location and activities of native bumblebees: Bumblebee Watch. A group of student volunteers at UW are working on a way for volunteers to observe and track sightings in a systematic way, so that their Bumblebee Watch data can be used to detect regional trends in the bumblebee population.
High Country News