Varroa treatment: the five mistakes to avoid for your colonies

Varroa treatment: the 5 mistakes to avoid to protect your bees

Understanding varroa treatment before taking action

Varroa treatment is a strategy for fighting Varroa destructor, a parasitic mite that weakens bees and promotes viral diseases. It does not simply consist of placing a medicine in the hive. It requires a good schedule, reliable counting, rigorous application and a check after intervention. Are you wondering whether your hives are truly protected after a treatment? The answer often depends on the mistakes avoided before, during and after application.

Varroa destructor affects the domestic bee, Apis mellifera. It feeds mainly on bee tissue and reproduces in capped brood. As a result, it directly threatens bee health, the longevity of winter bees and honey production.

This article examines five mistakes to avoid, without claiming to rank them by frequency. You will find the points to check on a leaflet and a way to prepare a usable report with your sanitary contact. No single schedule or treatment recipe is proposed.

Mistake 1: starting varroa treatment too late in the season

Treating too late exposes winter bees to parasitic pressure that is already established. This is one of the most damaging mistakes for a colony.

Why is the schedule important for bees?

Winter bees must live for several months. They ensure the colony's survival until spring. However, if they are born in a heavily infested hive, their life expectancy decreases. Their immunity also drops. As a result, the colony may seem fine in September, then collapse in winter.

The main treatment is often placed after the last honey flow, once the supers have been removed. However, waiting until late autumn may be too late. At this stage, some of the winter bees have already been parasitised during their development.

Warning signs

A significant infestation can show up as bees with deformed wings, a mottled brood pattern, weakened bees in front of the hive or high natural drop counts on a greased board. However, the absence of visible signs does not prove the absence of varroa mites.

Good news: regular monitoring makes it possible to anticipate. It is better to measure before observing serious symptoms.

Recommended veterinary solutions

The choice depends on the specific medicine, the brood, outdoor conditions and the apiary's strategy. Apivar, Apiguard and Oxybee are not interchangeable. For Oxybee, the absence of brood is a condition of use; "almost broodless" is not an equivalent. Read the document for the presentation actually used.

According to French beekeeping sanitary guides, control must combine monitoring, authorised treatment and efficacy checking. If in doubt, consult your veterinaire before any treatment.

Mistake 2: treating without measuring the varroa infestation

A varroa treatment without counting amounts to intervening blindly. This mistake makes it harder to choose the right time and to assess the result.

Why does counting protect bee health?

The level of varroa mites varies according to the colony, the season, the presence of brood and the apiary's environment. Two neighbouring hives can show very different parasite loads. Thus, a strategy based solely on the calendar remains insufficient.

Monitoring methods include natural drop counts on a board, alcohol wash, detergent wash, icing sugar or CO2. Each method has its limits. However, the principle remains the same: you need to measure in order to decide.

Issues linked to lack of monitoring

Without counting, the beekeeper may treat a colony too late, overlook a heavily infested hive or believe a treatment has succeeded. Moreover, they may confuse an application failure with reinfestation coming from other colonies.

Checks after treatment complement the initial measurements. Their interpretation depends on the method, the timing and the colony's context. On their own, they do not constitute a percentage of the medicine's efficacy.

A comparable record rather than a 0-21-42 calendar

The duration of one medicine is not the same as another's. Setting the same checks at 21 and 42 days for every situation risks confusing ongoing treatment, withdrawal and assessment. Plan the checks with your sanitary contact according to the leaflet and the method chosen.

For each result, record the hive concerned, the date, the method, the collection period or sample size, the result and its unit. In particular, distinguish between a number of varroa mites dropped per day and a result reported relative to a number of bees. These values cannot be compared directly.

Also note whether the record was made before, during or after treatment. A drop caused by a medicine is not a natural drop. A high total may show that parasites have fallen, without indicating how many remain. A low total may have several explanations. Have the whole picture interpreted rather than the figure alone.

Example of a useful note: "Hive A, board checked after a known period, treatment ongoing since such a date, brood observed at the last visit." If a piece of information is missing, state it. Avoid converting a raw result into an infestation rate from memory.

Mistake 3: misapplying the medication or altering the dosage

Following the instructions, dose and duration is necessary for the proper use of an apicultural medicine. This does not guarantee full effectiveness: monitoring the colony remains essential.

Why does dosage matter so much in beekeeping?

Treatments against Varroa destructor act within a living environment. The size of the colony, the volume of brood, the circulation of bees and the temperature all influence the result. A strip placed incorrectly may remain too far from the bee cluster. A product removed too early may leave too many parasites alive.

Conversely, overdosing is not a solution. It can stress the bees, increase residues and fall outside the scope of the AMM.

Common mistakes during application

• Placing the strips at the edge, far from the brood.
• Using a number of strips not suited to the instructions.
• Removing the treatment before the recommended duration.
• Leaving a medicine longer than intended.
• Treating with supers intended for harvest.
• Storing a product under poor conditions.
• Using an expired or poorly preserved medicine.

These mistakes reduce effectiveness. They can also encourage resistance, particularly when mites survive insufficient exposure.

Recommended veterinary solutions

Before any application, read the medicine's instructions. Check the temperature of use, the presence or absence of supers, the duration, the number of units and handling precautions. Also note the batch and date in your breeding register.

The FNOSAD guides and ANSES resources highlight the importance of proper use of veterinary medicines in beekeeping. This rigor protects the colony, the beekeeper and the quality of hive products.

Mistake 4: ignoring the presence of brood and weather conditions

The presence of brood strongly affects the effectiveness of a varroa treatment. Many varroas hide in capped cells.

Why does brood complicate the fight against Varroa destructor?

The female varroa reproduces in capped brood. When the cap seals the cell, some treatments reach the parasites less effectively. Thus, a treatment effective on phoretic varroas may leave a reserve of varroas in the brood.

This is why oxalic acid gives its best results in the absence of brood. Conversely, some late-summer treatments aim for a longer action, in order to cover several emergence cycles.

Weather must be compared against the instructions of the exact product

Do not rely on a temperature range valid for all thymol or all organic acids. For Apiguard gel 12,5 g, the French RCP states in particular not to use the product if the expected maximum daily temperature is below 15 °C, if the colony's activity is very low, or if the temperature exceeds 40 °C. This reference applies to this specific specialty.

A temperature recorded at the time of application does not summarize upcoming conditions. Prepare the forecasts, the state of the colony and the handling constraints for the sanitary intervention. If a condition is not compatible, do not compensate with a modified dose or a homemade preparation.

Useful biotechnical solutions

In addition to medicines, certain methods improve the strategy. Removing drone brood traps part of the varroas in spring. Temporarily caging the queen can create a break in egg-laying. Afterwards, a suitable treatment targets phoretic varroas more effectively.

These methods require precision. They are better suited to trained beekeepers. They do not replace an authorized medicine when parasitic pressure is too high.

Mistake 5: forgetting post-treatment monitoring and reinfestation

A completed treatment does not always mean the apiary is secured. Reinfestation can revive varroa pressure within a few weeks.

Why does reinfestation threaten hives at the end of summer?

At the end of the season, some colonies weaken. Robbing, drifting and contact between bees facilitate the transfer of varroas. A properly treated hive can therefore receive parasites coming from a neighboring colony.

This situation explains certain apparent failures. The product may have worked, but the colony became reinfested after the intervention.

A disappointing result calls for investigation, not an immediate conclusion

A rise in counts does not by itself prove reinfestation; an insufficient drop does not demonstrate resistance. The FNOSAD guide describes several possible causes: high initial infestation, brood, application, storage, parasite sensitivity and outside contributions. ADA France documents emphasize the importance of examining other explanations before concluding there is resistance.

Gather the box, the batch, the dates, the storage conditions, the placement and the successive results. Note any change in measurement method. This information allows for discussing an appropriate response and, if necessary, reporting a suspected lack of efficacy through the pharmacovigilance channel with the veterinarian.

Coordination between beekeepers can help limit reinfestations. It does not authorize applying exactly the same product to all colonies without checking their situation. Discuss the constraints of the area and the monitoring of weak colonies with your GDSA or the relevant sanitary contact.

Resistance: why alternate strategies?

The repeated use of the same family of molecules can select for less sensitive varroas. Reasoned alternation of substances, under sanitary advice, helps preserve the effectiveness of available treatments.

Do not multiply treatments at random. Rely on counts, local GDSA recommendations, the medicine's instructions and the advice of a veterinarian or an apicultural sanitary technician.

Three medicines: conditions of use to distinguish

These references illustrate differences in presentation and use. They do not constitute a ranking of the best treatment. Read the full current leaflet of your box and have the choice confirmed for your apiary.

Apivar: contact, placement and removal

The sheet Apivar, 10 lanières corresponds to a medicine based on amitraz. Its SPC specifies the placement of the strips and their duration depending on the brood situation. Monitoring their contact with the bees matters; do not leave them indefinitely in the hive.

The official document requires that it not be used at the same time as another antiparasitic medicine. An improvised combination is therefore not an answer to a count deemed too high. Also check the restrictions related to supers and honey.

Apiguard: distinguishing the gel and temperature conditions

The presentation Apiguard gel, 10 récipients de 50 g contains thymol. The SPC consulted concerns the gel 12,5 g to be used inside the hive. Do not transpose without checking the instructions of another packaging or another specialty.

The honey flow period and temperatures are among the points to check before use. The origin of the substance does not exempt from respecting the precautions for the operator, the bees and the honey.

Oxybee: absence of brood and absence of supers

Oxybee is a preparation based on oxalic acid dihydrate for hives. Its product information provides for application in colonies without brood and without supers. A colony still having little brood does not automatically meet this condition.

Do not confuse the routes of administration of different medicines containing oxalic acid. A technical powder or a recipe found online does not replace the authorised specialty. The protections and preparation conditions of the leaflet must be respected.

Before the intervention: a simple equipment check

Prepare the exact medicine, the leaflet, the required protections, clean equipment and the register. Check that you will be able to ensure the possible removal and the planned check. This organisational work avoids discovering a constraint once the box has been opened. If a point remains ambiguous, get the answer before application.

Preparing a usable apiary assessment

Group the results by colony and keep the units. Separate observations, interventions actually carried out and hypotheses. A short but precise table is better than a graph mixing several methods. ITSAP offers VarroAppli to record and visualise readings; the tool does not replace their sanitary interpretation.

Find the catalogue references from the product links above. Before renewing an order, check what has been used, what remains available and the conditions of the colonies. The objective is to build a followed strategy, not to accumulate treatments.

The five mistakes come together on one point: a treatment is not just about applying it. The calendar must be adapted, the measurements comparable, the application compliant and the result reassessed. Keep a record of the uncertainties to discuss them without concluding too quickly about efficacy, failure or resistance.

Sources

• FNOSAD — Varroa et varroose.
• FRGDS Auvergne-Rhône-Alpes — guide Varroa, 2020.
• ADA France — Apitech, causes de défaut d’efficacité.
• ITSAP — surveillance et stratégie de lutte.
• ITSAP — VarroAppli.
• Anses-ANMV — RCP Apivar.
• Anses-ANMV — RCP Apiguard gel 12,5 g.
• Base européenne des médicaments vétérinaires — Oxybee.
• RCP Oxybee, document hébergé par la FNOSAD.