Glossary
The most damaging virus affecting honey bees, primarily transmitted by varroa mites. DWV causes shriveled, stunted wings in developing pupae, rendering affected bees unable to fly. It is the primary mechanism through which high varroa mite loads kill colonies.
When beekeepers say "varroa mites kill colonies," they are technically oversimplifying. Varroa mites weaken bees by feeding on their fat bodies and hemolymph, but the real killing blow comes from the viruses they inject during feeding. Deformed Wing Virus is the most devastating of these. When a varroa mite feeds on a developing pupa, it injects DWV particles directly into the bee's hemolymph (blood). At sufficiently high viral loads, the baby bee emerges with crumpled, withered wings that are useless for flight.
A colony can tolerate a low background level of DWV without obvious symptoms. But as varroa mite populations grow (doubling roughly every month during the brood season), the viral transmission rate escalates exponentially. At a critical threshold, the colony begins producing large numbers of deformed-wing bees that cannot forage, cannot defend the hive, and die within days of emergence. The colony's population crashes as more dead bees leave than new healthy bees emerge, and collapse follows.
Understanding the varroa-DWV connection transforms how beekeepers think about mite management. The goal is not to eliminate every mite (impossible in practice) but to keep mite populations below the level at which viral transmission reaches the tipping point. This is why the treatment threshold of 2 to 3 mites per 100 bees exists: above this level, viral loads are escalating toward the collapse cascade.
There is no treatment for the virus itself. The only management strategy is controlling varroa mite populations to prevent high-level viral transmission. Reducing mite loads below the treatment threshold keeps viral levels at subclinical levels where bees can coexist with the virus without obvious symptoms.
Bees with clinically active DWV emerge from their cells with crumpled, shriveled wings that look like crumpled paper. They are unable to fly and crawl aimlessly on the comb face or at the hive entrance. Their bodies may also appear shorter and darker than healthy bees. Seeing even a few DWV bees indicates a significant varroa problem.
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