Varroa Treatment Methods

Successful varroa control does not come from a single medicine but from a year-round programme: regular counts, treatment at the right time, rotating methods and measuring the result again. The most critical periods are late summer, when the winter bees are reared, and early winter, when brood decreases or stops.

Measure first: how to determine the mite load

Judging by eye is not enough; by the time mites are visible on bees, the load is usually already high. Base your decision on counts.

• Alcohol (or soapy water) wash: About 300 bees (roughly half a glass) taken from a brood frame are shaken in a container and the dislodged mites are counted. This is the most reliable field method; the bees die.
• Icing sugar shake: The same sample is shaken with icing sugar and the mites are shaken out through a mesh. The bees can be returned to the hive; the result may be slightly lower than with a wash.
• Natural mite drop tray: An oiled or sticky tray is placed under the mesh floor and the drop over several days is converted into a daily average. Useful for following trends and seeing the effect of a treatment.
• Uncapping drone brood: Capped drone cells are opened with a fork and the pupae are checked for mites; this gives an early warning in spring.

Commonly used action thresholds: in summer and autumn, about 3 mites per 100 bees in a wash; lower in spring and in the broodless period (1–2 mites per 100 bees). If the official recommendation in your region is different, follow it.

Groups of methods

Organic acids

Formic acid is the only organic acid that can also act inside capped brood cells, so it can be used while brood is present. However, in great heat it evaporates quickly and can cause brood and queen losses, while in the cold its effect may be insufficient; strictly follow the temperature range on the product label.

Oxalic acid kills only the mites on the bees. It is very effective in the broodless period; when brood is present, a single application is not enough. It is applied by trickling or sublimation. Lactic acid, on the other hand, is sprayed onto the bees on the frames; it is suitable for swarms, package bees and small colonies. Details are on the relevant pages.

Synthetic acaricides

Authorised strip products are effective and practical; but repeating the same active substance year after year selects for resistant generations of mites. Resistance to amitraz and pyrethroids has been reported in many parts of the world. Flumethrin and tau-fluvalinate belong to the same group; if there is resistance to one, the other usually does not work either.

Biotechnical methods

• Drone brood removal: The mite prefers drone brood cells. In spring, an empty or shallow frame is given; once the drone brood built on it is capped, it is cut out and discarded before the bees emerge.
• Brood break: The queen is caged or the colony is split; once the capped brood has emerged, all the mites are on the bees and a single oxalic acid treatment is very effective.
• Trap comb: The queen is confined to a single frame at set intervals; the mites enter the brood on this frame, and the frame is removed after it has been capped.

Annual programme (sample outline)

1. Spring: Do a count; start drone brood removal. If the load is high, treat with a suitable method before the supers go on.
2. Summer (nectar flow): No medicines are applied while supers are on. Continue the biotechnical methods and count once a month.
3. Late summer (immediately after the harvest): The main treatment of the year. As the winter bees are reared at this time, delay means losing a healthy generation of winter bees.
4. Early winter (broodless period): Oxalic acid to clear the remaining mites. In regions with mild winters brood may not stop; take this into account before opening the hive.
5. After every treatment: Count again within a few weeks. If the expected drop has not occurred, treatment error, reinfestation or resistance should be investigated.

Rules for treatment

• Use only veterinary products authorised in your country; follow the amount, duration and temperature conditions on the label. Underdosing and strips left in too long speed up resistance.
• Do not treat while supers are on; observe the withdrawal period on the label.
• Rotate the groups of active substances from year to year.
• Do not put livestock medicines, unauthorised mixtures or home-made strips into the hive; they are the main source of honey residues and resistance problems.
• Treat all colonies in the same apiary at the same time; coordinate with neighbouring beekeepers if possible. Robbing and drifting carry mites back into a hive that has been cleared.
• Record the product, date, duration and count result for each hive.