Greg Laden's Blog

The conservation of insect pollinators is drawing attention because of reported declines in bee species and the 'ecosystem services' they provide. This issue has been brought to a head by recent devastating losses of honey bees throughout North America (so called, 'Colony Collapse Disorder'); yet, we still have little understanding of the cause(s) of bee declines. Wild bumble bees (Bombus spp.) have also suffered serious declines and circumstantial evidence suggests that pathogen 'spillover' from commercially reared bumble bees, which are used extensively to pollinate greenhouse crops, is a possible
cause. We constructed a spatially explicit model of pathogen spillover in bumble bees and, using laboratory experiments and the literature, estimated parameter values for the spillover of Crithidia bombi, a destructive pathogen commonly found in commercial Bombus. We also monitored wild bumble bee populations near greenhouses for evidence of pathogen spillover, and compared the fit of our model to patterns of C. bombi infection observed in the field. Our model predicts that, during the first three months of spillover, transmission from commercial hives would infect up to 20% of wild bumble bees within 2 km of the greenhouse. However, a travelling wave of disease is predicted to form suddenly, infecting up to 35-100% of wild Bombus, and spread away from the greenhouse at a rate of 2 km/wk. In the field, although we did not observe a large epizootic wave of infection, the prevalences of C. bombi near greenhouses were consistent with our model. Indeed, we found that spillover has allowed C. bombi to invade several wild bumble bee species near greenhouses. Given the available evidence, it is likely that pathogen spillover from commercial bees is contributing to the ongoing decline of wild Bombus in North America. Improved management of domestic bees, for example by reducing their parasite loads and their overlap with wild congeners, could diminish or even eliminate pathogen spillover.

The paper is very technical and you would be bored to death with the details. Of course if you want the details just read the papers as this is an Open Access publication do you do not have to be special to read it. I just want to make a few observations of general interest.

This topic touches on what could be called the Anthropocentric Class of Fallacies. Let me give you an example: Many people (mainly younger folks who are not science oriented) know that sexually transmitted diseases are a problem for humans but they do not realize that this is the case for (probably) all sexually transmitted diseases. This may be because religious leaders sometimes point out that this or that STD is a vengeful act of god against a sinner (someone who has sex, or is gay, or whatever). The same class of fallacy includes thinking that you can give your cat an aspiring if (you think) it has a headache. The anthropocentric class of fallacies includes both assuming that humans are entirely special and assuming that whatever we know for humans is generally true even when it is not. The fallacy is not how we think about the world specifically, but rather, the process of always referring to humans as the anchor point, the measuring stick, the calibration, etc. for our observations.

It is not the case that diseases come out of nature and whack humans now and then. Well, that is true, but it is only a tiny part of a bigger picture. Pathogens generally evolve in relation to their hosts in such a way that virulence is reduced over time (usually). Viability of a pathogen across species is generally limited. However, a pathogen may cross species boundaries now and then and have a brief period of high virulence followed by ... well, a lot of different things including becoming less virulant, or simply dieing out.

Between species generally. Not between humans and non-humans. And by species I don't mean just animals. And so on.

The study summarized in the abstract above is important becuase it is a detailed look at the relationship between a pathogen and multiple species that may host it. That is important for a lot of reasons, ranging from conservation to human public health. If you don't think this is important now, you will change your mind when some disease (from a human, a dog, a fly, whatever) suddenly stumbles, as a highly virulent and deadly critter, into the world's genetically non-diverse cattle population and the beef industry collapses within weeks. Or some chicken gets coughed on by a sparrow and that's it for eggs and drumsticks for a while. Or the corn. The corn all goes bad and then it's curtains for al of us (because that is pretty much all we eat these days).

One might think this sounds like crazy apocalyptic arm waving ... after all, such a thing has never happened before, why should it now? The problem with that reasoning is that the circumstances by which this sort of thing can happen or only a few decades old, and otherwise, it actually has happened before. I'll give you two examples. Wild cattle (cape buffalo) in southern Africa are now more rare than rhinos because of disease, and humans during the early 20th century as affected by the Great Influenza Epidemic.

Cover your mouth when you cough. On a chicken.

source

Otterstatter, M.C., Thomson, J.D., Adler, F.R. (2008). Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators?. PLoS ONE, 3(7), e2771. DOI: 10.1371/journal.pone.0002771