Two common gut parasites have been found to alter the behaviour and physiology of honeybees in ways that could harm the health and productivity of entire colonies.
A recent study published in the International Journal for Parasitology shows that the parasites — Nosema ceranae and Lotmaria passim — reduced the production of vitellogenin, an important protein for bee health and development, which in turn triggered earlier foraging.
Nosema ceranae is a common parasitic fungus that can replicate rapidly in the digestive tract of honeybees, explains lead author Courtney MacInnis, who conducted the research as a doctoral candidate in the Department of Biological Sciences.
"It's a highly specialized fungus and it's really environmentally resistant, so when it gets into the bee it's difficult to treat," she says.
"The parasite has been associated with increased colony mortality, changes in bee behaviour and physiology, as well as changes in bee learning and memory."
Like Nosema ceranae, Lotmaria passim — a trypanosomatid parasite related to parasites that are involved in Chagas disease and sleeping sickness in humans — is found worldwide and commonly infects honeybees. However, it was only identified in 2015, so researchers are still seeking more information about its transmission and influence.
"We don't really know a whole lot about Lotmaria beyond that it seems to affect bee survival in cages, and can affect bee behaviour and physiology," says MacInnis, who was part of the team responsible for starting the Lotmaria culture at Agriculture and Agri-Food Canada's (AAFC's) Beaverlodge Research Farm that was used for this experiment.
The researchers studied the effects of the parasites both individually and when bees were infected with both, finding that the lowest vitellogenin levels were found in bees that had both parasites.
The two parasites, both individually and together, ultimately change the division of labour in the colony among worker bees because they reduce vitellogenin production and thereby alter foraging behaviour.
As MacInnis explains, honeybees have an "age-based division of labour" — they have different jobs within the colony depending on their age.
The process of transitioning to a different role in a honeybee's lifespan is sparked by vitellogenin, a "protein that's produced in the fat body of the bee, kind of analogous to the human liver," as well as juvenile hormone, a hormone that regulates bee behaviour and development.
When bees are young, their roles in the colony typically involve tasks like nursing larvae, cleaning out cells, and feeding and attending to the queen, says MacInnis. As they grow older, they transition to tasks outside the colony, like foraging for nectar and pollen or guarding the colony.
Young bees have larger amounts of vitellogenin and not much juvenile hormone, and the balance switches as they age, with older bees producing less vitellogenin and much more juvenile hormone. By reducing vitellogenin levels, the parasites shift this balance and accelerate the bee's internal clock.
"The parasite can change that transition, so you get bees doing tasks that are advanced for their age."
On an individual level, this has the potential to wear out a bee's flight muscles at an earlier age, which can reduce lifespan. But the main disruption is to the colony as a whole, with potentially long-lasting effects.
"If you have younger bees foraging earlier than they should, you can be missing a group of bees inside the colony doing a critical job," says MacInnis. This can mean a smaller colony overall or one that produces far less honey or doesn't have an adequate population to keep itself warm and sustained through the winter months. If critical tasks such as nursing the larvae to adulthood are neglected, it can even lead to the colony dying out.
Though the two parasites are known to be associated with colony losses, there hasn't been much research done at the colony level because it's a very challenging undertaking.
"It requires culturing the parasites, infecting the bees and individually putting them back into colonies," explains Stephen Pernal, a research scientist at Beaverlodge Research Farm and national lead of the AAFC's Apiculture Research Program. "A whole lot of effort and skills are required to do it."
MacInnis, now a postdoctoral fellow at the University of Lethbridge, is still working with the Lotmaria culture. There's currently no management strategy for the relatively new parasite, so more knowledge about its impact on honeybees could be vital.
She plans to examine how temperature affects transmission and infectivity, as well as whether susceptibility to the parasite differs in bees from different colonies around the world.
The research was funded by Agriculture and Agri-Food Canada. MacInnis also received an Alberta Graduate Excellence Scholarship and Project Apis m. Costco Scholarship.
