Varroa Mites: Current Research and Control for Irish Beekeepers

Information updated: 5 August 2026

Varroa mites remain one of the greatest threats to honeybee colonies in Ireland. They weaken developing and adult bees, spread damaging viruses and can cause the loss of a colony when their numbers are not kept under control. Varroa management is therefore a routine part of responsible beekeeping rather than a problem that can be dealt with once and forgotten.

Research continues to improve our understanding of the mite and to produce possible new methods of control. However, no single treatment provides a permanent solution. The most reliable approach remains regular monitoring, timely use of authorised treatments, suitable biotechnical methods and careful efforts to breed healthier, more resilient bees.

What is Varroa destructor?

Varroa destructor is an external parasitic mite of the western honeybee, Apis mellifera. An adult female mite is reddish-brown, flattened and approximately 1.1 millimetres long by 1.6 millimetres wide. Its shape allows it to fit between the abdominal plates of a bee and to remain concealed while the bee moves around the hive.

Varroa mites were originally parasites of the Asian honeybee, Apis cerana. After adapting to reproduce on the western honeybee, they spread through much of the world. European honeybees have not had the same long period in which to develop effective natural defences.

The mite is now widespread in Ireland. A beekeeper should work on the assumption that Varroa is present, even when no mites can be seen on adult bees.

How does Varroa harm honeybees?

Older descriptions often say that Varroa mites simply suck a bee’s blood. The true relationship is more complex. On adult bees, the mites feed mainly on fat-body tissue. This tissue plays an important part in immunity, energy storage, detoxification and survival through winter. Mites reproducing inside capped brood cells also feed on and damage the developing bee.

The physical damage caused by feeding is serious, but the transmission of viruses can be even more destructive. Varroa is closely associated with deformed wing virus and can also carry other viral pathogens. A heavily infested colony may produce bees with shortened lives, reduced ability to forage and, in some cases, visibly deformed wings. Many infected bees show no obvious deformity, so the absence of damaged wings does not mean that the colony has a low mite burden.

Mite numbers can rise rapidly while the colony is rearing brood. If the population is allowed to become high in late summer, the long-lived bees needed to carry the colony through winter may be damaged before treatment begins. This is one reason why monitoring and treatment timing are so important.

The Varroa lifecycle

An adult female mite travels on an adult bee before entering a brood cell shortly before it is capped. Once the cell is sealed, the mite begins to lay eggs. Her offspring develop and mate inside the cell while the bee larva becomes a pupa. When the adult bee emerges, the original female mite and any mature daughters leave the cell and can infest other bees or enter new brood cells.

Varroa reproduces particularly successfully in drone brood because drone cells remain capped for longer. This preference can be used in drone-brood removal, although the method must be carried out correctly and should form part of a wider control plan rather than being treated as a complete solution.

Mites also spread between colonies. Drifting bees, robbing and the movement of infested bees or brood can all contribute. A colony that has been treated successfully may be reinfested from a nearby collapsing colony, particularly later in the season.

Why regular monitoring is essential

It is not possible to judge the level of infestation reliably by looking at adult bees during an ordinary inspection. By the time mites are easily visible or bees with deformed wings are common, the colony may already be badly affected.

Common monitoring methods include:

• Sugar shake: A measured sample of adult bees is coated with icing sugar and shaken through a mesh lid so that dislodged mites can be counted. The bees can then be returned to the colony.
• Alcohol wash or alcohol roll: A measured sample is washed in alcohol to dislodge the mites. This generally provides a dependable count but kills the sampled bees.
• Natural mite fall: Mites falling through an open-mesh floor are counted on a monitoring board over a known number of days.
• Drone-brood examination: Capped drone pupae are removed and checked for mites. This can provide useful supporting information when drone brood is present.

Take care not to include the queen when collecting a sample of adult bees. Use the same monitoring method consistently, record the result and note the date, colony and stage of the season. A series of comparable results is much more useful than an occasional unrecorded check.

When does a colony need treatment?

There is no single percentage that applies to every test, season and location. A result must be interpreted according to the monitoring method used and the time of year.

For example, the FIBKA guidelines on Varroa give treatment levels for a sugar-shake sample of more than 2% in May and more than 3% in August. FIBKA provides separate seasonal tables for natural mite fall and drone-brood examination. These figures should not be mixed or applied to a different test without appropriate guidance.

The direction of travel also matters. A result below a published threshold does not mean that the colony can be ignored for the rest of the year. Mite numbers can rise quickly during brood rearing, and reinfestation can produce a sudden increase. Monitor again at a suitable interval and check the result after treatment to confirm that the chosen control has worked.

Integrated management of Varroa

Integrated Pest Management, usually shortened to IPM, combines several appropriate methods instead of relying repeatedly on one product. Its purpose is to keep mite numbers below damaging levels while reducing unnecessary treatment and slowing the development of resistance.

An effective Varroa plan may include:

• Regular monitoring with recorded results
• Authorised medicines selected to suit the season and condition of the colony
• Rotation between suitable active ingredients or modes of action
• Brood interruption, queen trapping or drone-brood removal where the beekeeper has the necessary knowledge
• Checking treatment effectiveness rather than assuming that it worked
• Reducing robbing and avoiding practices that unnecessarily spread mites between colonies
• Coordinating monitoring and treatment with nearby beekeepers where practical
• Selecting healthy colonies with useful resistance or tolerance traits for breeding

The correct combination will vary with the colony, season, level of infestation, local conditions and the products legally available at the time.

Using Varroa treatments legally and safely in Ireland

Irish beekeepers should use only veterinary medicines currently authorised for use against Varroa in Ireland. The current authorisation of a product can be checked in the HPRA database of animal medicines.

Every product must be used strictly according to its label and product information. This includes the dose, number and position of strips or trays, duration of treatment, permitted temperature range, use in colonies with brood, honey-super restrictions, withdrawal period and necessary protective equipment. A method described on an overseas website or in an older article is not automatically legal or suitable in Ireland.

Authorised Varroa medicines may use active substances such as thymol, organic acids, amitraz or synthetic pyrethroids. Each has particular advantages and limitations. “Natural” or “organic” does not mean harmless: incorrect use of oxalic or formic acid, for example, may endanger the beekeeper, harm the colony or leave the mite population inadequately controlled.

Brood conditions are important. Some treatments act mainly on mites carried on adult bees and have limited effect on mites protected inside capped cells. Treatments based on temperature-sensitive vapours or acids may also perform poorly or cause harm when used outside their labelled temperature range.

Do not use homemade formulations, agricultural products or unauthorised treatment combinations in a hive. An experimental mixture described in a research paper is not an approved treatment. Beekeepers should also keep the animal-remedies records required for medicines administered to their colonies.

Treatment resistance and the limits of amitraz

Varroa populations can develop resistance when the same type of treatment is used repeatedly, when treatment is incomplete or when products are left in a hive for longer or shorter than the label requires. Resistance has previously reduced the effectiveness of some synthetic pyrethroids, and amitraz resistance is now receiving increased attention.

A peer-reviewed USDA-led study published in February 2026 examined severe losses among large commercial beekeeping operations in the United States. Three viruses were found at unusually high levels, while a genetic marker associated with amitraz resistance was present in all of the mites collected for the study.

This is an important warning, but it should not be misrepresented. The research concerned affected American commercial operations and did not prove that amitraz-resistant Varroa alone caused all of the estimated 1.7 million US colony losses. The authors also identified possible contributions from nutritional stress, agrochemicals and other pressures. Nor does the study establish the level of amitraz resistance in every part of Ireland.

The practical lesson for Irish beekeepers is that no product should be treated as permanently reliable. Use authorised medicines properly, avoid unnecessary repeated dependence on one active ingredient, monitor after treatment and seek current advice if mite numbers do not fall as expected.

Why treatment timing matters

A good product applied at the wrong time may fail to protect the bees that matter most. In many colonies, controlling mites after the honey crop and before the production of winter bees is a particularly important part of the annual plan. Waiting until visible damage appears can mean that those bees have already developed in mite-infested cells.

A broodless period may provide an opportunity to control mites that would otherwise be protected inside capped brood. However, beekeepers should not apply a generic calendar blindly. Weather, brood patterns, colony development and the instructions for the authorised product all matter.

Monitoring should continue after treatment. A post-treatment count helps show whether the product was effective and whether reinfestation is occurring. If the count remains high, check that the treatment was used correctly and obtain suitable advice rather than improvising an unapproved stronger dose or combination.

Biotechnical methods

Biotechnical methods alter brood production or remove the brood preferred by Varroa. They can reduce mite reproduction and may make an authorised treatment more effective by creating a broodless period.

Drone-brood removal

A frame or section of drone comb can be removed after it has been capped and before the drones emerge. Because Varroa reproduces readily in drone cells, this removes mites from the colony. The method must be timed carefully. Allowing heavily infested drone brood to emerge will increase rather than reduce the mite population, and excessive drone removal is undesirable.

Brood interruption and queen trapping

Temporarily interrupting brood rearing can break the mite’s reproductive cycle and expose more mites on adult bees. Queen caging, queen trapping and some artificial-swarm methods can be used for this purpose. They require planning, accurate timing and competent colony management. They should not be attempted casually, particularly where there is a risk of queen loss or disruption at an unsuitable point in the season.

Heat treatment

Controlled heat can kill mites, but the margin between a useful treatment and harm to brood or bees can be narrow. Specialised equipment and careful temperature control are required. It should not be presented as a simple do-it-yourself replacement for authorised treatment.

Breeding bees with greater Varroa resistance

Breeding for resistance or tolerance is an important long-term part of Varroa control. One useful behaviour is Varroa Sensitive Hygiene, or VSH. Bees expressing this trait can detect and remove brood in which mites are reproducing, interrupting the mite lifecycle.

VSH should not be confused with grooming. Removing mites from adult bees is a separate behaviour. A colony may show several useful traits, including hygienic removal of infested brood, grooming, reduced mite reproduction and the ability to maintain comparatively low mite levels.

Ireland’s native honeybee population is a valuable genetic resource. The University of Galway-led FREE-B project, launched in 2025, is studying the survival of free-living honeybee colonies in Ireland and elsewhere in Europe. Research of this kind may help identify biological, behavioural and environmental factors that support resilience.

However, reports of surviving free-living colonies or selected treatment-free apiaries should not be taken as proof that an ordinary managed colony can safely be left without Varroa control. Beekeepers wishing to select for resistance still need reliable records and regular mite monitoring. Stopping treatment without evidence that a colony is keeping mite and virus levels under control risks losing the colony and spreading mites to neighbouring apiaries.

New and experimental treatments

Research into alternatives is progressing, but an interesting experimental result is not the same as an authorised treatment that Irish beekeepers can use.

RNA-based Varroa control

In September 2025, the United States Environmental Protection Agency registered vadescana, a double-stranded RNA active ingredient used in the product Norroa. It works through RNA interference, preventing the expression of a gene needed by Varroa and substantially reducing mite reproduction.

Research published in 2026 found that results varied between sites and colony conditions. The treatment was more successful at keeping an initially low mite population under control than at suppressing a high and rapidly increasing infestation. It should therefore not be described as a cure for a colony already overwhelmed by mites.

Norroa is a significant development, but it is not authorised for use in Ireland as of 5 August 2026. Irish beekeepers must not use a US registration as permission to obtain or apply it here.

Fungal control and improved formulations

Researchers have also investigated fungi capable of infecting Varroa and ways of improving the performance of established active substances. A widely reported trial using a heat-tolerant strain of Metarhizium brunneum involved 30 colonies and was published in 2021, not 2025. The work remains experimental and has not produced a treatment authorised for Irish hives.

Similarly, research involving slow-release materials, adjuvants or new combinations should not be copied using homemade hive treatments. Any useful development must first be assessed, authorised and supplied with approved instructions for use.

A practical Varroa plan for Irish beekeepers

1. Assume Varroa is present. Do not wait until mites or deformed bees are easily visible.
2. Monitor using a recognised method. Record the method, result, date and colony.
3. Interpret the result correctly. Use thresholds appropriate to the test and season, such as those in the FIBKA guidance.
4. Plan ahead. Pay particular attention to protecting the bees that will carry the colony through winter.
5. Choose a suitable authorised medicine or biotechnical method. Consider brood, temperature, honey supers, colony strength and the treatment’s mode of action.
6. Follow the label exactly. Do not change the dose, timing, formulation or treatment period.
7. Check the result. Monitor after treatment to confirm that mite numbers have fallen.
8. Reduce resistance and reinfestation. Rotate suitable modes of action and coordinate with nearby beekeepers where practical.
9. Keep learning. Product authorisations, resistance patterns and research findings change, so consult current Irish sources rather than relying on an old treatment routine.

Asian hornet and other pressures

Varroa is not the only threat facing Irish honeybees. Two Asian hornet nests were found and destroyed in County Cork in 2025. According to the latest official information available on 5 August 2026, there was no confirmed evidence that the species had successfully overwintered or become established in the Republic of Ireland. Beekeepers should remain vigilant and report a suspected Asian hornet through the official Asian Hornet Reporter.

Asian hornet vigilance should not distract from the continuing need to control Varroa. Mites and the viruses they transmit are already present and place colonies under pressure every year. Nutrition, weather, queen health, pesticides and other diseases may add to that pressure, making good overall colony management essential.

Keeping Varroa under control

Varroa management has become more demanding as resistance develops and new research reveals the limits of familiar treatments. The answer is not to chase every newly publicised product or to rely indefinitely on one medicine. It is to know the mite level in each colony, respond at the appropriate time and confirm that the response has worked.

New technologies and resistant-bee research offer genuine hope, but they do not remove the need for careful management today. Irish beekeepers can give their colonies the best protection by combining monitoring, authorised treatments, suitable biotechnical methods, accurate records and cooperation within the local beekeeping community.

Frequently Asked Questions

Does every honeybee colony in Ireland have Varroa?

Varroa is widespread throughout Ireland. Beekeepers should assume that their colonies are exposed and monitor them, even if no mites can be seen during ordinary inspections.

What percentage of Varroa means I should treat?

There is no universal percentage for every method and season. FIBKA’s sugar-shake guidance gives treatment levels of more than 2% in May and more than 3% in August, with different tables for natural mite fall and drone-brood examination. Always interpret the result using guidance appropriate to the test you performed.

Can I tell whether a colony has Varroa by looking at the bees?

Not reliably. Visible mites and deformed wings may indicate a serious problem, but many affected bees look normal. A recognised monitoring method is needed to estimate the infestation.

Can Varroa mites become resistant to treatment?

Yes. Resistance has affected several synthetic treatments, and amitraz resistance is an increasing concern internationally. Correct label use, suitable rotation and post-treatment monitoring help preserve treatment effectiveness.

Is amitraz still authorised in Ireland?

Product authorisations can change. Check the current HPRA animal-medicines database before purchasing or using any Varroa treatment, and follow the approved product information exactly.

Can I use Norroa in Ireland?

No. Although vadescana products have been registered in the United States, Norroa was not authorised for use in Ireland as of 5 August 2026.

Are organic-acid treatments completely safe?

No. Oxalic acid and formic acid can be effective when used in authorised products according to their labels, but incorrect handling or application can harm the beekeeper or colony. Appropriate protective equipment and all product instructions must be followed.

Can resistant bees be kept without treatment?

Some colonies and selected populations show useful resistance or tolerance traits, but this does not justify leaving an ordinary colony unmonitored. Treatment decisions should be based on reliable mite counts and evidence from the particular colony, not on general claims about treatment-free beekeeping.

Where can Irish beekeepers find current Varroa advice?

Consult the FIBKA Varroa guidelines for monitoring information and the HPRA animal-medicines database for current product authorisations. Your local beekeeping association can also provide practical training and help interpret monitoring results.