Ask any beekeeper what keeps them up at night, and chances are the answer is Varroa destructor. These parasitic mites spread quickly through colonies, weakening bees and transmitting deadly viruses like Deformed Wing Virus (DWV). But not all bees take it lying down – some have evolved a powerful defence known as Varroa Sensitive Hygiene (VSH).
VSH bees can detect, uncap, and remove brood that’s infested with reproducing mites, breaking the mite’s breeding cycle and helping colonies survive with fewer chemical treatments. In this article, we’ll explore how VSH works, how to recognise it, and what it means for the future of mite management.
What Is Varroa Sensitive Hygiene?
Varroa Sensitive Hygiene (VSH) is a natural behaviour shown by certain honeybee colonies. Worker bees with this trait can smell or sense when a developing bee (pupa) is infested by a reproducing varroa mite. They open the cell (uncapping), remove the infected pupa, and clean the cell before resealing it for the queen to lay again.
This behaviour interrupts the mite’s life cycle – because the mite’s offspring die when the host pupa is removed. Even though the colony sacrifices a few developing bees, the long-term gain is huge: fewer mites and healthier brood.
The Science Behind VSH
We don’t yet fully understand how bees detect infested cells, but research suggests they respond to changes in odour – likely from stressed or virus-infected pupae, not the mites themselves. Studies have shown that VSH bees are particularly good at recognising pupae infected with highly virulent viruses, such as aggressive strains of DWV.
In effect, VSH is not just a fight against mites – it’s a defence against the viruses they carry. Colonies showing strong VSH behaviour tend to stay healthier overall, even when mites are present.
Signs of VSH in Your Hive
You can often spot hygienic behaviour without opening a single frame. Here’s what to look for:
- Pupal exoskeletons on the bottom board: A sure sign that bees are removing mite-infested pupae.
- Uncapped or recapped brood cells: Bees sometimes open and reseal suspect cells. Recapping (partial uncapping and then resealing) disrupts mite reproduction, reducing their numbers without sacrificing all brood.
- Steady mite counts: Colonies showing hygienic behaviour often maintain lower mite loads even without treatments.
Some beekeepers leave the monitoring boards in all year to observe mite drop and hygienic activity – especially useful in cooler months when hives shouldn’t be opened.
Can VSH Be Bred or Encouraged?
Yes. Breeding programs, such as those by Arista Bee Research, have been selectively breeding bees with high levels of VSH while maintaining productivity and temperament.
Beekeepers can also test for general hygiene using freeze-killed brood assays or pin tests – both involve killing a patch of brood and measuring how quickly the colony removes it. However, these tests measure general hygienic behaviour, not necessarily VSH. The best indicator of true mite resistance is how well a colony maintains low mite levels over time.
If you’re interested in starting with VSH stock, look for queens advertised as “VSH” or “Varroa-resistant.” Keep monitoring mite levels as usual – even resistant bees can be overwhelmed under certain conditions.
The Role of Uncapping and Recapping
Recent studies show that bees don’t always remove the infested pupae outright. Sometimes, they’ll uncap the cell, inspect it, and then recap it. This “recapping” disturbs the mite’s environment just enough to stop reproduction.
Interestingly, bees don’t seem to perform this on drone brood, where mites prefer to reproduce. This mirrors behaviour seen in the Asian honey bee (Apis cerana), which naturally limits mite populations by confining them to drone cells.
Why VSH Matters for Beekeepers
VSH represents a shift toward sustainable, treatment-free beekeeping. Instead of relying solely on chemical controls, beekeepers can work with the bees’ natural defences. Colonies with hygienic traits often:
- Require fewer treatments
- Show stronger overwintering survival
- Maintain better brood health
- Exhibit slower mite population growth
However, VSH isn’t a silver bullet. Mite monitoring, brood management, and good nutrition are still essential. Think of VSH as part of an integrated pest management (IPM) strategy – a long-term ally in keeping your colonies healthy.
The Future of Varroa Resistance
Natural selection is already shaping honey bee populations to better cope with Varroa. In places like the Arnot Forest in New York, wild colonies have survived for decades without treatment, thanks to traits like VSH and smaller, naturally managed colonies.
Bees are learning, adapting, and evolving. Our job as beekeepers is to support that process – by keeping strong colonies, avoiding overuse of miticides, and selecting queens from survivor stock.
Conclusion
Varroa Sensitive Hygiene is a remarkable example of how honey bees can fight back against one of their deadliest parasites. By recognising and removing infested brood, VSH bees limit mite reproduction, reduce virus transmission, and improve colony survival.
For beginner beekeepers, understanding and supporting this behaviour can mean fewer treatments, healthier bees, and a step toward more natural beekeeping. The more we select and support hygienic colonies, the closer we get to a sustainable future where bees manage Varroa themselves.
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