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Norroa: controlling Varroa with RNAi, how does it work?
Varroa · New developments
Norroa: controlling Varroa with RNAi, how does it work?
Norroa uses RNA interference to disrupt reproduction in Varroa mites. It is a striking new technology, but it is not yet authorised in the European Union.
Controlling Varroa destructor remains one of the major challenges in beekeeping. Established treatments use active substances such as oxalic acid, formic acid or thymol. Norroa takes a very different approach: it uses RNA interference, or RNAi, to selectively disrupt a biological process in the Varroa mite.
That makes Norroa an interesting development to follow. The product has already reached markets outside Europe, while it is currently not authorised in the European Union as a veterinary medicine against Varroa. For that reason, Norroa is not yet available from Beekeepershop.
What is Norroa?
Norroa was developed to control Varroa destructor in honey bee colonies. Its active substance is vadescana, a double-stranded RNA molecule, usually abbreviated as dsRNA.
Instead of poisoning the mite directly with a conventional acaricide, vadescana is designed to reduce the expression of calmodulin-related genes in Varroa. Calmodulin is involved in several biological processes, including development and reproduction.
How does RNAi work against Varroa?
RNA interference is a natural mechanism that can reduce the activity of specific genes. The dsRNA in vadescana was designed for a genetic target in Varroa destructor. Research shows that treatment can suppress the expression of calmodulin and a calmodulin-like gene in the mite.
In brief
- ✔Bees are exposed to the dsRNA through the administered sugar solution.
- ✔The dsRNA reaches Varroa mites associated with the colony and developing brood.
- ✔The activity of specific genes in the mite is temporarily suppressed.
- ✔This mainly disrupts mite reproduction and embryonic development.
- ✔The approach is therefore not primarily based on rapidly killing adult mites.
Important nuance
Laboratory research found that adult foundress mites could remain alive after exposure while their reproductive output dropped sharply. Norroa therefore works differently from treatments designed mainly to produce a rapid mite drop.
Why is this technology interesting?
A new mode of action can be valuable in integrated Varroa management. Many existing treatment programmes rely on a relatively limited number of active substances. RNAi adds a completely different biological mechanism.
Field research has produced promising results, with lower mite levels maintained for extended periods in some trials. At the same time, efficacy can vary with location, infestation pressure, colony size, nectar flow and delivery conditions. It is therefore too early to view Norroa as a universal replacement for existing Varroa strategies.
What does the research show so far?
The technology behind Norroa has now been investigated in several laboratory and field studies. Useful publications include:
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A 2026 review explaining how Norroa works, what field trials have shown and which effects on bees and other non-target organisms have been studied.
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A field study in full-sized honey bee colonies, including efficacy and the influence of factors such as nectar flow and colony size.
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This study examined whether treatment with vadescana affected honey bee longevity and foraging behaviour.
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Research into the relationship between dose and efficacy of vadescana in full-sized honey bee colonies.
More research is still needed
The results are promising, but RNAi for Varroa control remains a young technology. Researchers themselves highlight variability between field trials and the importance of integrated pest and resistance management. Some studies also include researchers affiliated with the product developer.
Why is Norroa not yet available in Europe?
An authorisation outside Europe does not automatically apply in the European Union. A product presented for the treatment or control of varroosis in honey bees falls under EU veterinary medicinal product rules. Before such a product can be marketed for this purpose, the relevant European authorisation process must be completed.
That assessment covers areas including quality, efficacy, safety for bees, user safety and possible implications for honey and other bee products.
As of September 2026, Norroa, with vadescana as its active substance, is not authorised in the EU as a veterinary medicine against Varroa. We therefore do not offer the product at this time.
We are following Norroa closely
- ✔We monitor new scientific publications on vadescana and RNAi.
- ✔We keep an eye on the European authorisation status.
- ✔We look at efficacy as well as safety, practical use and its possible role in integrated Varroa management.
- ✔If European authorisation and practical availability move closer, we will share new information.
What can you use now?
Several veterinary medicines and treatment methods are already available for Varroa control. Two familiar options in our range are VarroMed and Thymovar.
VarroMed
VarroMed contains formic acid and oxalic acid dihydrate and is used as part of an integrated Varroa control strategy.
Thymovar
Thymovar contains thymol. The strips release thymol vapour inside the hive and are used as part of a Varroa treatment programme.
Always check whether a veterinary medicine is authorised in your country and follow the current package leaflet, dose, treatment period and legal instructions.
View VarroMed → View Thymovar
Posted by
Chiel Versluijs
News
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