Nosema

1 . What is Nosema?

Nosema is a microsporidia which are a group of spore-forming, unicellular parasites. Although they were once classified as protozoans, they are now recognized as fungi or closely related to fungi. In honey bees, the most important microsporidia are Nosema apis and Nosema ceranae. Microsporidian spores are highly specialized. Each spore contains a tightly coiled polar tube, which functions like a microscopic harpoon. When a bee ingests spores, this tube rapidly ejects, penetrating the gut epithelial cells and injecting infectious material into the cell. These parasites produce highly resistant spores that can survive outside the host for extended periods, allowing them to persist in the environment. The spores are typically oval-shaped and are only visible under a microscope.

2 . How does Nosema affect honey bees?

Infection occurs when bees ingest spores present in contaminated food, water, or hive surfaces. Once inside the gut, the parasites multiply and damage the gut lining, impairing digestion and nutrient absorption. Spores are shed in the feces of infected bees, facilitating transmission throughout the colony. During cold weather, when bees are unable to leave the hive to defecate, fecal contamination inside the hive increases. House bees that clean contaminated comb and surfaces are then exposed, leading to further spread of infection within the colony.

3 . What are symptoms of Nosema infection?

Bees crawling outside the hive Distended abdomens Reduced colony buildup Dysentery (in some cases, but not always) Note: Dysentery alone is not a reliable indicator of Nosema infection.