Which disease (A8) ?

View answer

Correct answer: 6 (Deformed wing virus: DWV)

Deformed wing virus (DWV) is present at all developmental stages of bees, from the egg to the adult. Infected nurse bees transmit the virus to young larvae via larval food (royal jelly). Adult bees also transmit the virus through trophallaxis.

DWV is generally weakly pathogenic. It can therefore be transmitted vertically (from one generation to the next). An infected queen does not die quickly and transmits the virus to her eggs. Likewise, transmission of the virus from a mother colony to a swarm is considered a vertical transmission route.

DWV has also been detected in semen, honey, feces, and pollen. It has been established that DWV can replicate not only in the bee but also in the Varroa mite. Colonies contaminated with DWV often show no apparent damage for a long time. However, most often—especially in combination with other infections—colonies develop very slowly or collapse. The combination with Varroa destructor is the most dangerous for bees. It is assumed that DWV becomes more virulent when it switches hosts, i.e., when passing from Varroa to the bee.

Field symptoms and diagnosis:

The typical symptom of this disease is deformed wings in bees. Bees may also show a range of other symptoms, such as reduced body size and pigmentation defects.

Prevention and control

• Treat colonies against Varroa properly and in a timely manner.
• Favor vital and strong colonies. Unite weak colonies in time (only if healthy) or eliminate them.
• Select for vitality and hygienic behavior. Do not keep queens that are too old.
• Replace combs regularly.
• Melt down contaminated combs. Viruses do not survive wax melting. House strong colonies as swarms in clean hives and allow them to build foundation. Eliminate weak colonies.
• Create more young colonies and place them at a sufficient distance from production colonies.
• Do not use the same beekeeping equipment at different apiaries (hive tools, gloves, etc.).

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.

► PDF poster: Recognizing diseases

► Next question ►►