Beekeepers worldwide face numerous challenges in maintaining healthy bee colonies, and one of the most destructive threats is Deformed Wing Virus (DWV). This virus, closely linked with Varroa destructor mites, has become a major contributor to colony losses. DWV not only causes visible deformities in bees but also severely weakens the overall health of the colony. Understanding how DWV spreads, its symptoms, and how to manage it is crucial for every beekeeper.
What is Deformed Wing Virus (DWV)?
DWV is a highly contagious virus that primarily affects honeybees (Apis mellifera). It is named for the characteristic deformity it causes in the wings of infected bees. The virus can exist in bee colonies at low levels without causing visible symptoms, but when varroa mite infestations are present, DWV becomes far more damaging, as the mites serve as vectors, injecting the virus directly into the bee’s body.
How is DWV Spread?
While DWV can be present in bee colonies without varroa mites, the severity of its spread is amplified by mite infestations. Varroa mites feed on the hemolymph (bee blood) of both adult bees and developing brood, transmitting DWV during the feeding process. This direct injection of the virus allows it to bypass the bee’s natural defenses, causing a rapid increase in viral load within the colony.
In addition to transmission through mites, DWV can spread via:
- Bee-to-Bee Contact: Infected bees can transmit the virus to healthy bees during normal hive interactions.
- Feeding Brood: Worker bees that carry the virus can pass it on to larvae as they feed them, further infecting the next generation of bees.
Symptoms of DWV
The most visible symptom of DWV is the deformed wings that give the virus its name. Bees with DWV typically have:
- Crumpled or Shrunken Wings: Infected bees are often born with wings that are twisted or underdeveloped, rendering them unable to fly.
- Shortened Abdomen: Along with wing deformities, bees may also show an abnormally short abdomen.
- Weakness and Reduced Lifespan: Even bees that do not exhibit visible deformities may be infected with DWV, leading to a shortened lifespan and reduced foraging ability.
Bees that are visibly affected by DWV often die within hours or days of emerging from their cells, which puts significant strain on the colony’s worker population.
The Impact of DWV on Bee Colonies
The presence of DWV in a bee colony can have devastating effects, especially when combined with high varroa mite populations. Some of the major impacts include:
- Reduced Worker Population: As infected bees die prematurely, the colony may struggle to maintain a healthy workforce, reducing the number of foragers needed to collect pollen and nectar.
- Poor Brood Health: The virus can weaken or kill developing brood, resulting in fewer healthy adult bees.
- Colony Collapse: In severe cases, when DWV spreads rapidly through a colony, the combined effects of reduced foraging, weak brood, and dying bees can lead to colony collapse, especially during winter when strong bee populations are crucial for survival.
- Weakened Immune System: DWV-infected bees are more susceptible to other pathogens and environmental stresses, further compromising the health of the colony.
Managing Deformed Wing Virus
Since DWV is so closely linked with varroa mites, controlling mite infestations is the most effective way to reduce the spread and impact of the virus. Some management strategies include:
- Varroa Control:
- Miticides: Using chemical treatments can significantly reduce mite populations, helping to minimize DWV transmission.
- Mechanical Methods: Techniques like drone brood removal (as varroa prefer drone cells) and screened bottom boards can help reduce mite numbers without chemicals.
- Varroa-Resistant Bees: Breeding programs focus on developing bees with traits such as Varroa Sensitive Hygiene (VSH), where bees are able to detect and remove infected brood, helping to control mite levels.
- Monitor for Symptoms:
Regular hive inspections are critical. Look for bees with deformed wings, shortened abdomens, or signs of paralysis. If symptoms are present, assume the colony has high levels of both DWV and varroa mites, and act quickly to treat the hive. - Strengthen Colony Health:
Healthy bees are better equipped to deal with viruses. Providing adequate nutrition through supplemental feeding and ensuring that bees have access to a variety of forage plants can improve colony strength and resilience to disease.
Conclusion
Deformed Wing Virus is a significant threat to honeybee populations worldwide, and its impact is made worse by the presence of varroa mites. Beekeepers must remain vigilant in monitoring for DWV symptoms and controlling varroa infestations. By employing effective mite control measures, strengthening colony health, and staying informed about the latest research, beekeepers can help protect their colonies from the devastating effects of DWV.
Further Reading:
- Bee Informed Partnership – Understanding Deformed Wing Virus
- International Bee Research Association – DWV and Varroa Mite Interaction
- National Bee Unit – Managing DWV in Beekeeping