How does nosema disease affect queens?
Answer: By increasing their levels of pheromone!
We like to think of ourselves as individuals. Sure, we have families, live in a society, and interact with many friends, but in the end we're still individuals. But while we can think that we're alone in seclusion, even Robinson Crusoe was never truly alone. We always have plenty of symbionts in or on our bodies, which means that we're always a walking community of many different life forms.
Mutualists are symbiotic organisms that live together for shared need; each party requires the presence of the other to survive. We have plenty of mutualists, mainly in our digestive tracts, so that we can actually absorb many of the nutrients that we need. Without microbes (such as the "good" strains of E. coli), much of our food would pass through our system without us absorbing their nutrients. Bees have mutualists as well. For example, stored pollen becomes "bee bread" (the edible form that nurse bees can digest to make brood food) only by mutualist fungi species that help break down the cell walls of the pollen grains. Without them, bees can't get the proper protein from consumed pollen.
Parasites, on the other hand, are symbionts where one party (the host) is harmed where the other (the parasite) benefits. Some parasites are relatively benign (e.g., the tiny mites that live on our eyelashes and eat our dead skin cells), while others can be very harmful indeed (e.g., tapeworms that live all throughout our intestines and slowly sap away our nutrients). Clearly, honey bees have a similar suite of parasites, most notably the parasitic mites Varroa destructor and Acarapis woodi (the varroa and tracheal mite, respectively). While the former remains the top management concern for beekeepers, the latter has be relegated to a secondary pest status because of its rarity in recent years.
There is yet another parasite that is making a lot more headlines recently, switching roles with tracheal mites as the "public enemy #2" for beekeepers. Like most insect species, honey bees have their own specialized gut parasite, a microsporidian called Nosema. The traditional Nosema species of our bees is Nosema apis, and for a long time was considered a nuisance parasite that only reared its ugly head in times of prolonged confinement (typically during winter), giving bees dysentery but easily curable with fumigilin antibiotic. However, in recent years, a newer species of Nosema, Nosema ceranae, has become more and more of a problem for the beekeeping community. Not as much is known about this newer parasite, including its symptoms, life cycle, and effects on colony health and productivity. There is a natural assumption that it acts much like the original Nosema, but its becoming increasingly clear that is not the case.
A recent study out of France looked at the effects of Nosema ceranae on honey bee queens. Most studies on this parasite focus on worker health, since they are the ones that do the foraging, feed the brood, and conduct all of the tasks in the hive that make the colony productive. But what about the queen? We know that she is the only reproductive female in the colony, and without her egg laying colony productivity is moot. She also has numerous indirect effects on colony function, such as her pheromones that keep workers from raising a new queen and promote foraging. It has long been known that Nosema apis can have some indirect effects on queens, but what about N. ceranae?
The researchers found that the parasite does cause some problems with queen physiology. While they did not find any significant effect on queen fat-body content (their main stored energy source, important for egg laying), they did detect significant differences in vitellogenin titers (the main egg-yolk precursor protein, important for queen longevity and fertility), antioxidant capacity (her ability to resist aging), and pheromone levels. To great surprise, however, all of these levels were higher in the infected queens compared to uninfected controls. This means that, contrary to workers where infection is negative or even lethal, Nosema infection actually boosts some of the main physiological functions of queens!
These results are indeed surprising, but they should also be interpreted in the correct context. The queens were measured after only a short period following infection (8 days, to be exact). This means that it remains unclear what effects Nosema might have over the long term. In fact, an increase in physiological factors might be good in the short term but actually be bad over time. Given that many beekeepers are reporting early queen failure and other problems, these results may be consistent with that trend. What is clear, however, is that when you look at a queen, there may be more going on inside of her than you might think.
Alaux, C., M. Folschweiller, C. McDonnell, D. Beslay, M. Cousin, C. Dussaubat, J-L. Brunet, and Y. Le Conte. (2011). Pathological effects of the microsporidium Nosema ceranae on honey bee queen physiology (Apis mellifera). Journal of Invertebrate Pathology, 106: 380-385.