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Found in Translation
Honey Bee Gut Parasites
By: Jay Evans, USDA Beltsville Bee Lab
Varroa is truly enemy #1 for honey bee health, by chewing the fat and spreading devastating viruses. Still, many other nasties can shorten bee lifespans, change behaviors and destabilize bee nutrition. These parasites share the trait of being quick on their feet, even those lacking feet. There is a famous disease analogy to the Red Queen from “Alice in Wonderland”, whereby a host (human, plant, cow, bee, etc.) seeking to avoid disease must constantly ‘run just to stay in the same place’, as did the Red Queen. Human flu viruses provide a prime example of agile threats. Just when you’ve worked out a good plan for one strain, new ones pop up to chase you.
Lotmaria Passim
Scientists have observed similar changes in two unrelated parasites that thrive in honey bee guts. Nosema apis was a legitimate parasite of western honey bees for decades, and likely for millennia, before being almost completely replaced in recent years by a new species, Nosema ceranae. The late, great, Ingemar Fries felt sorry for N. apis as he observed this takeover, even suggesting a Nosema apis Endangered Species Society to mark the decline. A second parasite suffered the same fate at about the same time. Crithidia mellificae was the first trypanosome gut parasite studied in honey bees, but it was quietly and almost completely replaced by a new species, Lotmaria passim, whose main shared trait was a thirst for honey bees. No one really knows what caused these flips, or exactly how the new flavors traveled the world so quickly. Nevertheless, Nosema ceranae and Lotmaria passim are now found in honey bees worldwide and both are linked with colony losses.
Courtney MacInnis and colleagues in Alberta, Canada put together a very nice study showing how Nosema and Lotmaria impact honey bees (MacInnis, C.I., Luong, L.T. & Pernal, S.F. (2023) “A tale of two parasites: Responses of honey bees infected with Nosema ceranae and Lotmaria passim.” Scientific Reports 13, 22515,. https://doi.org/10.1038/s41598-023-49189-9). They carried out controlled lab experiments, following up on widespread genetic studies that found these parasites to be present more often than expected during colony loss events. Bees inoculated with a field-relevant dose of N. ceranae died nearly ten days earlier than control bees and eight days earlier than those inoculated with Lotmaria. Not all bees died at once, but that was the time point at which 50% of the bees in any given trial had succumbed. Interestingly, bees given both parasites did better than bees given Nosema alone, suggesting some sort of interaction between parasites and their bee hosts that decreased the impact of Nosema. What is really interesting is that bees infected with either parasite showed a significantly greater hunger for sucrose. Prior work had shown that bees infected with Nosema consumed sugar stores quicker than healthy bees, and this current work suggests the same is true for Lotmaria infections. Consequently, even when a parasite does not kill you, it could have costly effects. Put another way, if a colony of 40,000 is full of infected individuals, the food stores of that colony will be used up more quickly. This dynamic could help explain the connection between parasites and Winter colony losses when food stores are limited. If you are worried about either parasite in a yard after completing diagnostics, it might be wise to over-provision colonies in that yard. Stay tuned for additional studies exploring just how much extra sugar bees consume while fending off disease.
Your bees are not idle victims of nutrient-robbing parasites, nor do they fight disease impacts simply by eating more. Like almost all organisms, honey bees mount an immune response to disease. Many studies have shown immune responses to parasites can be a positive thing. Nevertheless, these responses are costly. Since the main immune responses in bees involve attacking parasites with proteins, it follows that bees with poor protein nutrition could be more vulnerable to disease. I have discussed before how pollen-rich diets can help bees through some disease challenges, including viruses. It seems as though these pollen sources might differ in their abilities to help bees confront gut parasites. Evan Palmer-Young, working in our USDA group, screened an apothecary of plant compounds and found several pollen chemicals that seemed to reduce Lotmaria growth in controlled settings (Palmer-Young, E. C., Markowitz, L. M., Grubbs, K., Zhang, Y., Corona, M., Schwarz, R., Chen, YP, Evans, J. D. (2022). “Antiparasitic effects of three floral volatiles on trypanosomatid infection in honey bees”. Journal of Invertebrate Pathology, 194, 107830, https://www.sciencedirect.com/science/article/abs/pii/S002220112200115X). Similar work has found that pollen chemicals could reduce Nosema disease and there is a good chance your farm could provide a pharmacopeia for diseases that otherwise might be rampant. Several research groups are working to confirm and expand these results, aiming for a treatment solution involving either medicines or medicinal plantings.
Fumadil-D (based on the chemical fumagillin) is the only registered drug for either parasite, and it seems on the whole to have beneficial effects on Nosema and arguably bee health, based on a recent review of 50 research studies (Peirson, M., & Pernal, S. F. (2024). “A systematic review of fumagillin field trials for the treatment of Nosema disease in honeybee colonies”. Insects, 15(1), 29. https://doi.org/10.3390/insects15010029). The hard work by these authors to track down so many studies reveals that fumagillin as a Nosema control (based on both prevalence and spore count) is at least as effective with the current species, N. ceranae, as with the former, N. apis. Adverse effects, while possible for fumagillin and its breakdown products, were not evident in the reviewed studies. Any treatment should involve consultation with local experts, including your state inspectors, since timing, seasonality, and colony type (from package to large overwintered colony) will all impact your success.
These thoughts are not meant to scare beekeepers about monsters within and without. A possible silver lining to all of this work is the clear evidence that bees can mount immune responses to gut parasites. Immune responses help your bees endure and actively clear out many of the demons they face. As long as bees are healthy and not facing undue stress, they can keep both of these gut parasites in their place as sporadic, minor nuisances.
