Honey bees rely on more than just good nutrition to stay healthy, but also depend on a stable and diverse gut microbiome. This internal community of microbes supports digestion, strengthens immunity and helps honey bees resist disease. But parasites like Nosema spp. can invade the gut and disrupt their microbiome, threatening colony health.

Bee Alert: Attack of the Microsporidia

Nosema spp. are a microsporidian parasite that attacks the midgut of adult honey bees¹. The genus is being reviewed as Vairimorpha.  It is a spore-forming organism that is phylogenetically related to fungi ². Three types of microsporidia are known to infect honey bees Nosema apis, Nosema ceranae, and Nosema neumanni ³. Of these, N. apis and N. ceranae are the most common and widespread. The size of N. apis is about 6x3 μm, and N. ceranae are around 4.7 x 2.7 μm ³.  Transmission occurs when bees ingest spores through contaminated food or during grooming ³. Once inside the digestive tract, the spores attack the gut lining, damaging the tissue and can potentially spread to the hemolymph, which may cause septicemia ³.

Nosema ceranae specifically targets the midgut epithelium, which is the tissue responsible for nutrient absorption ⁴. As infection occurs, the bee’s ability to digest and absorb nutrients declines. This damage may lead to dysentery and weakened immunity. Dysentery is more common in N. apis ³ with the dominant species being N. ceranae. While most beekeepers might assume that increased sucrose consumption is a sign of healthy, active bees, infected bees often consume more sucrose and are less likely to share food with their colony, which can disrupt social dynamics due to behavioural changes and impact the whole colony ⁴.

Figure 1: Nosema Spores (circled) Viewed Under a Microscope (400X) (ATTTA©2020)

Beyond damaging the gut lining, Nosema spp. also disrupts the balance of beneficial microbes that live in the bee’s digestive system. Core bacteria like Snodgrassella alvi play a crucial role in maintaining gut health. Snodgrassella consumes oxygen in the ileum, creating an anaerobic environment for beneficial microbes ⁶. It also forms biofilms that protect the gut lining and has been shown to reduce spore loads of N. ceranae in infected bees ¹. These microbes are essential in stabilizing the gut environment and supporting immune function.

However, the effectiveness of microbial defense against pathogens can be influenced by diet. A recent study has shown that nutritional stress can accelerate the reproduction of N. ceranae, especially in early stages of infection ⁵. Bees fed low-quality pollen, such as Eucalyptus grandis, which lacks essential proteins, lipids, and the amino acid isoleucine, tend to carry higher spore loads than those fed diverse, polyfloral pollen ⁵. This highlights the importance of a nutritionally rich diet in maintaining gut health and resisting infection.

Figure 2: Healthy Bees (ATTTA©, 2024)

Poor nutrition does not just affect the spore loads of Nosema but also alters the composition of the gut microbiome. From studies, it has also been found that poor diets can have a reduction in bacteria like Lactobacillus and Bifidobacterium, which are both core gut bacteria in honey bees ⁵. Bifidobacteria, for example, are involved in producing hormones and signal molecules that may influence immunity and development in the gut ⁶. When these microbes decline, bees may become more vulnerable to infections like Nosemosis, as their immune defenses are compromised ⁷. This disruption in the microbiome can have broader implications for colony health, like reduced longevity and overwintering success.

The honey bee gut is not just a site of digestion but also an important ecosystem that is vital for defending against pathogens and supporting proper health. When parasites like Nosema spp. damage the midgut, they disrupt nutrient absorption and the balance of beneficial microbes, making bees more vulnerable to disease. Beekeepers should regularly monitor for Nosema to help protect colony health. The Atlantic Tech Transfer Team of Apiculture offers Nosema testing to help detect this disease. Supporting gut health through good nutrition and monitoring to identify when treatment is necessary helps maintain strong and healthy hives!

Written by Kaitlyn Newton, ATTTA Seasonal Apiculturist 

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

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References:

1    Motta, E.V. and Moran, N.A., 2024. The honeybee microbiota and its impact on health and disease. Nature Reviews Microbiology, 22(3), pp.122-137.

2.     Zhang, Y., Su, M., Wang, L., Huang, S., Su, S. and Huang, W.F., 2021. Vairimorpha (Nosema) ceranae infection alters honey bee microbiota composition and sustains the survival of adult honey bees. Biology, 10(9), p.905.

3.     Galajda, R., Valenčáková, A., Sučik, M. and Kandráčová, P., 2021. Nosema disease of European honey bees. Journal of Fungi, 7(9), p.714.

4.     Lau, E., Maccaro, J., McFrederick, Q.S. and Nieh, J.C., 2024. Exploring the interactions between Nosema ceranae infection and the honey bee gut microbiome. Scientific Reports, 14(1), p.20037

5.     Castelli, L., Branchiccela, B., Garrido, M., Invernizzi, C., Porrini, M., Romero, H., Santos, E., Zunino, P. and Antúnez, K., 2020. Impact of nutritional stress on honeybee gut microbiota, immunity, and Nosema ceranae infection. Microbial ecology, 80, pp.908-919.

6.     Bonilla-Rosso, G. and Engel, P., 2018. Functional roles and metabolic niches in the honey bee gut microbiota. Current opinion in microbiology, 43, pp.69-76.

7.     Meehan, D.E. and O’Toole, P.W., 2025. A Review of Diet and Foraged Pollen Interactions with the Honeybee Gut Microbiome. Microbial Ecology, 88(1), pp.1-14.