Nosema is the most widespread of the adult honey bee diseases. A single celled animal named Nosema apis, a small, unicellular parasite specific to the honeybee, causes it. Nosema cannot exist in a laboratory culture, as with most bacteria and fungi. It will only thrive and multiply in the epithelial cells of the honey bee ventriculus which causes dysentery. Queens, drones and workers are all susceptible to Nosema. The spores of the Nosema must be ingested for the bee to be infected. The spore takes root in the midgut, where they will penetrate a midgut cell and grow by absorbing nutrients from that cell. The parasite will increase in size until it is large enough to divide in half. Each new parasite will continue to feed on the nutrients of the cell until they are depleted. In a matter of time, about 6 to 10 days, 100 new spores are formed in the infected cell. The infected cell when depleted of all the nutrients ruptures releasing all the newly formed spores into the midgut to start the process again. The damaged intestinal tissue is susceptible to secondary diseases. Dysentery is a common symptom of this disease. You will be able to spot the dysentery on the outside of the hive by the little brown spots, but the diseased bees will also defecate inside the hive. contaminating combs with millions of infectious spores. The disease is spread to other colony members through fecal matter.

Nosema having infected one bee will be spread to others in the colony. The disease lowers the life span of the bees. If you have a colony of bees infected with Nosema in late fall, come spring it is likely that most of the colony will have died off.

Nosema is a difficult disease to diganose without using laboratory equipment. Decapitating a bee and pulling out the last abdominal segments usually will remove the intestinal tract while still intact. An infected midgut will become swollen, whitish and lose its visible constrictions. However, other causes of dysentery, such as ingesting honeydew, fermented syrups, etc. can result in similar intestinal changes.

Treatment for Nosema is based on the most appropriate times to prevent comb contamination and to prevent the development of disease in bees that clean up fecal deposits from combs while they are still trying to expand the brood nest. A few bees are always infected, but the diseased late season bees are the only one of any concern. If they develop high levels of infection, they defecate on the combs in October, November, and December, and then they die. The use of fumagillin has been field tested by some beekeepers with acceptable results. When treating use the manufacturer's instructions.