Do you recognise this disease? Explain what you see.
- European foulbrood, a bacterial brood disease.
- Chalkbrood, a fungal brood disease.
- Deformed Wing Virus: DWV.
- Healthy colony with regular brood.
- Nosemosis, a disease affecting mainly adult bees.
- American foulbrood, a bacterial brood disease.
- Banded brood associated with wax moth.
Show answer
Correct answer: 5.
Nosemosis, a disease affecting mainly adult bees.
Why?
Nosemosis is linked to microsporidia of the genus Nosema, notably Nosema apis and Nosema ceranae. It mainly affects adult bees, in particular their midgut.
In the expected image, one looks above all for signs observable on the bees and in the hive: bees unable to fly, crawling or hopping, an abdomen that is sometimes swollen, brown traces of excrement on the alighting board, the combs, or the walls.
Unlike the foulbroods or chalkbrood, nosemosis is not recognised first by the appearance of the larvae. Patchy brood may appear indirectly if the colony weakens, but this is not the main sign.
What to understand
The spores of Nosema are ingested with food, water, or while cleaning contaminated surfaces. They multiply in the midgut and are then disseminated through the excrement.
Nosemosis is a multifactorial disease: it expresses itself more readily when the colony is weakened, stressed, confined for a long time, exposed to humidity, or installed in unfavourable conditions. The symptoms are often more visible at the end of winter and in spring.
Visual diagnosis remains limited. Traces of excrement may also be linked to dysentery or to other disorders. In case of doubt, the observation must be supplemented by competent advice or an appropriate analysis.
Key takeaways
Nosemosis concerns above all adult bees. The suggestive signs are crawling bees unable to fly, a swollen abdomen, and traces of excrement in or in front of the hive.
Prevention relies mainly on strong colonies, a dry and favourable location, good nutrition, a clean watering point, hygiene of the equipment, and regular renewal of soiled combs.
There is no simple solution to apply at the apiary. The priority is to improve the colony's development conditions, to prevent spread through contaminated equipment, and to assess very weakened colonies with caution.
Further reading
► Practical Guide: 2.5 Dysenteric diseases
► Review of Nosema parasites in bees