Norroa for Varroa: RNAi Control That Stops Reproduction

If you’re a beekeeper like me, you’ve been waiting for a fresh mode of action to keep Varroa in check, Norroa just made real news. It’s the first RNA-based, mite-specific product registered by the U.S. EPA to control Varroa destructor—and it does so by turning off a single mite gene that’s essential for reproduction.

RNA interference (RNAi) in plain English

RNA interference (RNAi) is a natural process cells use to silence specific genes. The tool for that job is double-stranded RNA (dsRNA)—a short genetic “message” designed to match a target gene. When a pest ingests or contacts the right dsRNA, its cells recognize the matching sequence and chop up the pest’s own messenger RNA for that gene, so the protein never gets made. In pest management, that means we can shut down genes essential for survival or reproduction—without broad toxicity to non-targets because dsRNA works by sequence match.

Several studies (including lab and field work) show that feeding bees dsRNA can deliver it to Varroa, and engineered bee-associated microbes can produce dsRNA that triggers RNAi in the mite. The new work behind Norroa builds on this foundation to reduce Varroa reproduction rather than simply trying to kill adult mites.

What makes Norroa different: vadescana targets calmodulin

Norroa’s active ingredient is vadescana, a dsRNA that targets the mite’s calmodulin gene. Calmodulin regulates calcium signaling—crucial steps for egg activation and early development in many animals. By silencing calmodulin, vadescana prevents successful egg laying and daughter development inside brood cells, cutting the mite’s reproductive output without harming bees.

Click here to read the peer-reviewed paper

In controlled trials, mites exposed to vadescana showed distinct signs of failed egg laying (a white mass under the genital plate) and dramatically fewer viable daughters per foundress, even though adult mite survival wasn’t affected—precisely the point of a reproduction-blocking mode of action.

Safety note: The calmodulin dsRNA used for Varroa does not have ≥21-nt matches to honey bee calmodulin, and studies report no adverse effects on bee larvae, pupae, workers, or queens. Intact dsRNA is also quickly degraded in vertebrate digestion.

Quick refresher: what’s a foundress mite, and why stop her?

A foundress is an adult female Varroa that enters a bee larval cell a day or two before capping. After the cell is capped, she lays a male egg first, then female eggs about every 30 hours. By bee emergence, typically one or two daughters reach maturity and leave with the foundress—fueling exponential population growth. If you block foundress reproduction, you break this cycle and flatten the mite curve.

That’s exactly what vadescana does: most vadescana-exposed foundresses produce no viable daughters, sharply reducing within-hive mite recruitment.

Where Norroa fits in your IPM

Norroa is classified by IRAC as Group 35 (RNAi)—a brand-new mode of action for beekeepers. That novelty aids resistance management and gives us a non-acid, mite-specific option that’s compatible with colony health. In field work, a single pouch treatment maintained mites below 3/100 bees for up to 18 weeks when applied at low infestation levels.

Bottom line for beekeepers

• New science, practical outcome: Norroa uses dsRNA (vadescana) to silence the Varroa calmodulin gene, stopping foundress reproduction inside capped brood.

• Bee-first profile: No negative impacts observed on larvae, pupae, workers, or queens in the cited studies; dsRNA is sequence-specific and degrades rapidly.

• A true new MOA: IRAC Group 35 RNAi—valuable for resistance rotation.

• How to deploy: Works best when mite levels are low; aim for timing that protects winter survival. 

Availability & registration status

Norroa is federally registered by EPA, and state registrations are rolling out. As of now, Kentucky is approved, and additional states will follow. Norroa is sold exclusively through Mann Lake and its authorized dealers.