There have been several tweets lately reporting Bombus occidentalis sightings. This is exciting because this once abundant bee has been absent from much of its range for the past 10 plus years. For example, when I surveyed the Bumble Bees of San Francisco in 2003 & 2004, I found none, yet this bee was one of the most common San Francisco bees historically.
Although we don’t have a smoking gun, California’s leading Bumble Bee expert, Robbin Thorp, has long suspected a fungal pathogen, Nosema bombini. This invasive pathogen was likely introduced to North American bees by the commercial bumble bee industry when they shipped bees from the US to Europe then back again. If B. occidentalis recovers, it will be fascinating to learn if it has evolved resistance or if something else is happening.
It is too early to call this a recovery, but this is positive news for sure. There is a crowd-funded citizen science campaign starting up, which is really neat. There is also a citizen science reporting site called bumblebeewatch.org. These citizen science efforts will be really important to document the recovery if it indeed happens, and I encourage you to join in. I’m really rooting for this bee, and hope that someday I can see it in California again!
I’ve just had a new paper come out in FEMS Microbiology Ecology. As I work a lot with halictid bees, a theme running through my science has been to look at how host social structure affects transmission and evolution of symbionts. For this new paper, I used social and solitary bee nests from the socially polymorphic bees Megalopta genalis and Megalopta centralis. By socially polymorphic, I mean that these bees have both social and solitary nests in the same population on Barro Colorado Island in Panama. I was therefore able to compare bacterial communities from social and solitary nests to determine if having workers affects the microbial communities associated with the bees and their nests. If you have been following this blog for a while, these were the nests I was collecting while I was in Panama, which I blogged about quite a bit.
I found that the social nests and solitary nests did not have very different bacterial communities, for the most part they were dominated by the environmental lactobacilli that I’ve found in sweat bees and leafcutter bees. So social structure, at least for these bees that are just at the cusp of sociality, does not influence bacterial community structure. But I did find that Wolbachia - that interesting insect-associated bacteria that messes with the host’s sex ratio or acts as a mutualist,was differentially abundant in the two host species. This is really interesting because the two host species are ecologically very similar, so why Wolbachia is abundant in one and not the other needs further investigation.
I also found that the bacterial communities differ by host stage. That is, Lactobacuillus kunkeei is found on the pollen provisions before the larval bee hatches from its egg, and larvae acquire this bacterium from their pollen provision. But once they become pupae, they mostly lose L. kunkeei, which they seem to only regain once they begin to forage on flowers.
My students and I are working on floral transmission more at Fresno State, and we hope to start functional assays to figure out how L. kunkeei might affect bee health. So there are many more questions to answer with wild-bee associated bacteria!
Here is the main figure from the paper, you can see how Wolbachia is common in M. centralis and not M. genalis:
And here is the PDF.
I’m pleased to announce that I have a new paper out in the Proceedings of the Royal Society B – Biological Sciences. My coauthors and I (Ulrich Mueller of UT Austin and Rosalind James of the USDA) studied the bacteria and fungi associated with the alfalfa leafcutting bee (ALCB for short) Megachile rotundata. The ALCB is the second most important field crop pollinator (after the honey bee), but it also has a nasty fungal pathogen that causes the disease chalkbrood (the fungus is Ascosphaera aggregata).
We wanted to look for interactions between microbes, so we applied several treatments to the pollen provisions of the bees: 1) antibacterials 2) antifungals 3) Ascosphaera aggregata spores and 4) a no treatment control. We then sequenced bacteria and fungi from the guts of the larvae that we applied these treatments to.
We found that when we applied antifungals, fungal diversity went up. This seems odd at first, but when we looked at the data we saw that we were knocking down chalkbrood, which seemed to be allowing other fungi to grow. This could have been just been an artifact of sampling, i.e. the other fungi could be showing up simply because there were so many chalkbrood sequences in the other treatments that they were swamped out and not detected. So we did some more analyses that suggest that the finding is not an artifact but due to some sort of inhibition (competitive, inhibitive, or otherwise, we don’t know yet) of other fungi by A. aggregata.
One other really interesting thing we found was that my current favorite bacteria, Lactobacillus kunkeei, was resistant to the antibiotic cocktail that we threw at it. Nancy Moran’s group found that a honey bee-associated bacteria is resistant to antibiotics. L. kunkeei is also associated with honey bees (though not as part of the core honey bee gut microbiota), and we think that L. kunkeei may be exposed to antibiotics while associated with honey bees. This suggests that antibiotic treatments to honey bee colonies may have far-reaching effects on wild bees, which is a really novel result. This is a really interesting hypothesis that we need to test further.
If you want to see the whole paper, check out my publications page. Here is one of the more important figures in the paper, which shows the relative abundances of fungi and bacteria from our different treatments. Note that L. kunkeei is present in the antibacterial treatments, and fungi are more diverse in the antifungal treatment, but A. aggregata shows low relative abundance.
I will be giving a public talk at Peeve’s Public House at 7:00 PM on January 6. The talk will be non-technical and I will talk about my work as well as that of others. Peeve’s is in downtown Fresno on a pedestrian mall, and I hear it is a pretty great place.
The talk is part of Cafe Scientifique, which is a forum for public science talks in an informal environment. So come on down, get some food and drinks (Peeve’s has a great beer selection from what I hear), and learn about bee research.