Nosema Apis - Symptoms

Symptoms

The symptoms of Nosema are relatively nonspecific. This makes it easy to confuse with other diseases of the honeybee. It arises mostly in the spring after periods of bad weather, although it may also be a winter disease that is only noticed in the spring when beekeepers first inspect their hives. The female worker bees are most strongly afflicted, less so the drones. The queen bee is rarely infected since afflicted bees rarely participate in feeding the queen. The most notable symptom is dysentery. This appears as yellow stripes on the outside of the hive and in severe cases, inside the hive. Bees may be unable to fly ("crawling") due to disjointed wings.

Further symptoms include increased girth of the abdomen, missing sting reflex, and early supersedure of the queen. If the queen is infected, her ovaries degenerate and ovum production drops due to atrophy of the ova, after which she is likely to be superseded. The disease pattern described by Higes et al.. in Spain for Nosema ceranae is slightly different than with Nosema apis. The changes in the digestive system were substantially more serious than with Nosema apis, related to particularly heavy and spacious cell lesions. On the other hand, classical symptoms were missing from Nosema ceranae, such as diarrhea, crawling, large numbers of dead bees in the apiary etc. Bees tend to die away from the apiary, which causes a reduction in food gathered and can eventually lead to colony collapse. Ritter (CVUA Freiburg) reports symptoms can arise throughout the year from Nosema ceranae, in contrast to Nosema apis. In the winter some colonies died within a short time and the bees lay dead in the box (in Spain, hives usually remained empty). Whether these features are related to the new form of Nosema cannot be conclusively proven.