Which disease (A9) ?

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Correct answer: 7 (Nosemosis)

The pathogen Nosema spp. is a unicellular parasitic fungus. Two species exist: Nosema apis, formerly widespread throughout Europe and still present in part, and Nosema ceranae, a newer species originating from Asia. Nosema ceranae is increasingly displacing Nosema apis, which is rarely found alone and usually occurs in mixed infections with Nosema ceranae.

Spores are ingested by adult bees with food or water or during cleaning of surfaces contaminated with spores. They reach the midgut and infect epithelial cells, where they multiply. New spores are excreted with feces. Symptoms and damage are observed mainly in spring. However, Nosema is present year-round in the gut of infected workers. Damage manifests as above-average bee mortality. Infested colonies weaken or collapse. Diseased queens stop laying eggs and may die. Nosemosis is a multifactorial disease: it occurs frequently, but spontaneous recovery is not uncommon. Weakened colonies facilitate the development of other pathogens (mixed infections). Nosemosis has often been diagnosed in association with viruses, for example Black Queen Cell Virus (BQCV).

Field symptoms and diagnosis

• Bees unable to fly, crawling or hopping, with swollen abdomens.
• Brown fecal spots on the landing board, inside the hive, and on frames.
• Gut test: remove the head of a dead bee; hold the abdomen between two fingers and gently pull the abdominal tip to extract the intestinal tract.
• In nosemosis, the midgut is cloudy, milky white, and swollen.
• In healthy bees, the midgut is translucent and brown.
• Patchy brood.
• Colonies develop slowly in spring or weaken and eventually collapse.

Prevention and control

• Create optimal conditions for good colony development, especially in spring: favorable location, good nectar flow, clean water source.
• Timely unite weak but healthy colonies, or eliminate them if in doubt.
• Regularly renew combs. Melt down old combs or those contaminated with feces. Do not use frames or tools soiled with feces.
• Select bees for high vitality.
• Destroy severely weakened colonies. In less severe infestations, create optimal conditions for spontaneous recovery by promoting colony development; artificial swarms may also be made. If after 4 weeks no signs of spontaneous recovery appear, destroy the colony. No therapeutic product against Nosema is registered.

What can the beekeeper do?

It is recommended to strengthen bees’ natural defenses against disease by applying the principles of good beekeeping practice. Colonies are healthy when they develop well (adult bees and brood), display good hygienic behavior, and produce good yields. In practice, these are referred to as strong or vital colonies (see cover image). Colony vitality depends on many factors. Beekeepers mainly have the following levers of influence:

• Apiary locations with good nectar flows (continuous food supply) and a suitable local climate.
• Regular creation of young colonies and replacement of weak colonies.
• Selection of queens with sufficient vitality traits (colony development, hygienic behavior).
• Regular renewal of combs.
• Varroa mite control in accordance with regulations – hygiene in the apiary.
• Caution when taking over bees from other locations (diseases!).
• Avoid any importation of bees from regions outside Europe.

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