Nosema Disease
Krankheiten
Nosema disease is the most common disease of adult bees.
Nosema disease is the most common disease of adult bees. It is caused by the microsporidia Nosema apis and Nosema ceranae, which infest the midgut epithelium as intestinal parasites. The spores are taken up orally with food and excreted again in the feces, so the infection spreads via soiled combs, robbing, and beekeeping work within and between colonies.
The two species show a different picture. Nosema apis is mainly a spring problem and is often accompanied by diarrhea: fecal spotting on combs, frames, hive, and at the entrance, weakened colonies, bee mortality, and sluggish spring development, in extreme cases so-called spring dwindling. Nosema ceranae can occur year-round and often proceeds without the typical fecal spotting, but with bees unable to fly, unexplained bee loss, declining colony strength, and increased winter losses.
A reliable diagnosis is not possible in the field. It is made in the laboratory by microscopic detection of spores, for which a sample of about a hundred bees is needed. Distinguishing between the two species is only possible with PCR and is usually chargeable. Fecal spotting alone does not prove Nosema disease; it also occurs with the non-contagious dysentery.
There are no approved medicinal products in either Germany or Austria. The only effective approach is beekeeping management: keeping colonies compact, providing good winter feed, promoting bee turnover through stimulation and care, melting down combs soiled with feces, cleaning and disinfecting hives, and requeening with a young, vigorous queen. Severely damaged colonies no longer capable of development are better dissolved.
Preventive measures include a sunny, wind-sheltered, and dry location, consistent comb hygiene, timely and sufficient feeding, and not leaving forest honey or melezitose honey in the colony as winter feed. Uniting diseased colonies with healthy ones and moving combs from conspicuous colonies should be avoided. There is no reporting requirement.