Varroa mites: signs and treatment options
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Varroa mites (Varroa destructor) are parasites of the western honey bee that reproduce inside capped brood cells and feed on the fat body of developing and adult bees; untreated colonies typically fail within a few years. Registered options include synthetic acaricides, formic and oxalic acid, and thymol products, rotated and combined with drone brood removal and brood breaks, and guided by regular mite counts.
Varroa destructor is the most damaging parasite of the western honey bee. It reproduces inside capped brood cells and feeds on the fat body of developing and adult bees, and colonies left untreated typically fail within a few years. Only products registered for use in beehives may be used against it.
How do varroa mites damage honey bees?
Varroa shifted from the Asian honey bee, Apis cerana, to Apis mellifera in the twentieth century and is now present almost worldwide. A female mite enters a brood cell just before capping, lays eggs, and her offspring mate inside the cell before the bee emerges. Drone brood is preferred because its longer development allows more mite offspring. Outside the cell, mites ride on adult bees and feed on the fat body tissue, weakening bees and shortening winter bee lifespan.
How do you check a hive for varroa mites?
Estimate infestation with an alcohol wash or sugar roll of about 300 bees from the brood nest, expressed as mites per 100 bees, or with sticky boards under a screened floor. Monitor in spring, midsummer and before winter bees are raised. Thresholds vary by region and season; many extension programs use about 2 to 3 mites per 100 bees as a trigger for action in late summer. Record counts per colony each time.
Which treatments control varroa mites?
Registered options include synthetic acaricides (amitraz, fluvalinate, coumaphos), organic acids (formic and oxalic acid) and thymol products. Resistance to fluvalinate and coumaphos is widespread, and amitraz resistance has been reported. Rotation and non-chemical methods (drone brood removal, brood breaks) are part of every program. Vegalab has no product registered for use in beehives. Thymol appears in our crop portfolio at 1% in Spore Control; that is a plant product and must not be used in hives.
Key takeaways
- Varroa reproduces inside capped brood cells and prefers drone brood.
- It feeds on honey bee fat body tissue, weakening bees and shortening winter bee lifespan.
- An alcohol wash or sugar roll of about 300 bees gives mites per 100 bees.
- Many extension programs use about 2 to 3 mites per 100 bees as a late-summer trigger for action.
- Resistance to fluvalinate and coumaphos is widespread, and amitraz resistance has been reported.
Key facts
- Varroa destructor feeds primarily on honey bee fat body tissue rather than hemolymph (Ramsey et al. 2019, PNAS 116:1792)
- Varroa reproduces in capped brood cells and prefers drone brood (Rosenkranz et al. 2010, J Invertebr Pathol 103:S96)
- Resistance of Varroa to fluvalinate and coumaphos is documented in multiple regions (Rosenkranz et al. 2010, J Invertebr Pathol 103:S96)
- Oxalic acid was registered by US EPA for varroa control in honey bee colonies in 2015 (US EPA, Oxalic Acid registration decision, 2015)
How our delivery technology applies
Thymol hive treatments already depend on controlled release: gel and matrix formats meter the vapor so mites are exposed without overdosing bees. That is a delivery problem encapsulation addresses in principle, holding release within a temperature-dependent window. A hive product carries its own registration, and we follow this as a research direction.
Questions
What are the treatment options for varroa mites?
Registered options include synthetic acaricides (amitraz, fluvalinate, coumaphos), organic acids (formic and oxalic acid) and thymol products. Rotation and non-chemical methods such as drone brood removal and brood breaks are part of every program. Only products registered for use in beehives may be used.
How does a sugar roll check for varroa mites?
A sugar roll, like an alcohol wash, tests about 300 bees from the brood nest and expresses the result as mites per 100 bees. Sticky boards under a screened floor are another option. Record counts per colony each time.
When should you treat for varroa mites?
Thresholds vary by region and season, and many extension programs use about 2 to 3 mites per 100 bees as a trigger for action in late summer. Monitor in spring, midsummer and before winter bees are raised.
Why do varroa treatments stop working?
Resistance to fluvalinate and coumaphos is widespread, and amitraz resistance has been reported. Rotating treatment classes and using non-chemical methods helps keep programs effective.
Protect apiaries: review pollinator precautions before any nearby treatment.