Approaches and Challenges to Managing Nosema in Honey Bee Colonies
Its a tough time to be a pollinator.
Bee, butterfly, and bat populations are in decline across the globe. Even the honey bee, perhaps the best-studied pollinator, has suffered great losses as beekeepers and researchers struggle to identify the causes. In recent years, its become clear that no one factor is responsible — honey bees face an onslaught of pressures, ranging from pesticides to viruses to parasites.
A recent Journal of Economy Entomology paper puts a spotlight on just one of these problems, the honey bee pest Nosema. Summarizing decades of intensive research from across the globe, two University of Minnesota and Pennsylvania State University entomologists outline precisely why Nosema represents an intractable problem for beekeepers. Their sobering conclusion — that far more research and resources are still needed to equip beekeepers with the right tools for managing Nosema infections — throws into relief the challenge of understanding and reversing global declines not just in honey bees, but in many other pollinators as well.
Nosema species, two of which are known to infect honey bees, belong to a group of fungi known as microsporidians. These fungal parasites live out their days within the cells of a host animal, which, in the case of N. apis and N. ceranae, is the digestive tract of honey bees. Perhaps as a result of this lifestyle, microsporidians such as Nosema evolved stripped-down versions of mitochondria. Unable to manufacture enough energy themselves, Nosema relies instead upon the energy produced by its honey bee hosts cells, with sometimes-grave consequences for the host.Nosema spores (red arrows) in a sample with pollen and tissue debris.Anchored in the midgut and munching on its hosts energy molecules, Nosema can effectively starve infected honeybees. This can accelerate a bees normal development, causing worker bees to mature earlier into foragers — but poor ones at that. Nosema-infected bees take longer rests, are less efficient at gathering pollen and nectar, and are more likely to become disoriented than their uninfected counterparts. The parasite spreads when spores leave the digestive tract. When enough of a colonys inhabitants are infected, the colony suffers or even collapses.
Nosema spores (red arrows) in a sample with pollen and tissue debris.
So whats a beekeeper to do? The first obstacle is to determine whether a colony is, in fact, suffering from a Nosema infection.
One of the major challenges of diagnosing Nosema is that there are no 100 percent reliable clinical symptoms, said lead author Holly Holt. Without a microscope or molecular tools, its impossible to visually inspect a colony with the naked eye and know with certainty whether Nosema of either species is present.
Several promising methods of diagnosis are on the horizon, including a pregnancy test-like dipstick that confirms the presence of Nosema, but none are widely tested and available yet.
More challenges await the beekeeper that does overcome the hurdle of diagnosis. Theres a desperate need, Holt and co-author Christina Grozinger stress, for guidelines and best practices as to when a beekeeper should intervene and treat Nosema. After all, not every Nosema infection results in colony collapse. Some dont even require treatment.
Image courtesy of entomologytoday.org