Varroa mites in bees: why one treatment isn’t enough

Varroa infestation is now one of the most serious problems in modern beekeeping. Behind its spread is the mite Varroa destructor, which attacks adult bees and brood, weakens the whole colony and also transmits other dangerous diseases. In practice, that means that without regular checks and interventions, you can see a significant decline in bee numbers or even a full hive collapse. Completely eradicating the parasite is very difficult, so the aim is mainly to keep its levels as low as possible.

Where the mite came from and why it’s so dangerous

Varroa destructor originates from Asia and over a few decades has spread to almost the whole world. Its expansion is helped by the fact that it has no natural enemies capable of effectively slowing its reproduction. Even a treated colony can become reinfested, which is why the fight against varroa is long-term and never ends with a single treatment.

The parasite attacks adult bees as well as the developing stages of brood. Weakened bees tend to be lighter, live for a shorter time and cope worse over winter. If the brood is affected, newly emerged bees may show deformities, underdeveloped wings or a smaller abdomen. Infestation also significantly increases susceptibility to viral and bacterial diseases.

How to recognise an infested colony

The mite is visible to the naked eye. It shows up on adult bees and in brood cells. Females feed on bees, then slip into cells containing brood, where they continue reproducing. They often prefer drone brood, especially in darker combs that have been used repeatedly.

Infestation can be detected in several ways. Beekeepers monitor natural mite drop, check drone brood or watch for a colony losing strength. Warning signs also include deformed wings, reduced activity or poorer wintering. The earlier the problem is caught, the better the chance of keeping the bees in good condition.

Legal responsibilities of a beekeeper

In the Czech legal framework, bees are considered livestock, so their keeping is covered by veterinary regulations. The keeper must provide conditions that meet the health and biological needs of bees. Hives and other equipment should allow health inspections, sampling and, if needed, cleaning and disinfection.

A responsible beekeeper should monitor the health of their colonies continuously, not only when obvious signs of a problem appear.

When and how varroa is treated

Treatment has to be timed correctly. Most often, interventions are carried out in spring and in late summer to early autumn, when it’s still possible to reduce mite levels before winter. Effectiveness is often high at the end of wintering as well. It’s important not to rely on a single method, because mites can gradually develop resistance to some active ingredients.

Common products include treatments based on amitraz, thymol or flumethrin. Each active ingredient has its own advantages and limitations. Some are applied as strips, others as tablets or vaporising products. When using any treatment, it’s always necessary to follow the manufacturer’s instructions and use it at the right time to avoid contaminating honey or harming the bees.

Natural and organic approaches

In organically focused apiaries, the main tools are organic acids, for example formic, lactic, citric or oxalic acid. These substances are applied in different ways depending on the product type and the season. Their advantage is a lower burden on bee products when used correctly.

Some beekeepers also reach for supplementary methods, such as dusting with icing sugar or using herbal infusions and smoke. However, these approaches are usually not enough as the primary treatment and their effectiveness is limited. They can serve more as support within overall hive management.

Biotechnical methods as a useful add-on

Non-chemical interventions also play an important role. A common practice is cutting out drone brood, which mites readily enter. The beekeeper inserts a drone frame, lets it be capped, then removes it along with the infested brood. This mechanically removes part of the parasite population.

Another option is making nucleus colonies (splits), which divides not only the bees but also varroa pressure. In some cases, the queen is caged to create a brood break, because without brood the mite has worse conditions for survival. These procedures require experience and care so they don’t weaken the colony itself.

Don’t wait for visible damage

Varroa must not be underestimated. Even if the bees look healthy at first glance, the parasite may already be present in the hive and gradually undermining the condition of the whole colony. Regular monitoring, well-chosen treatment and combining several methods are the best way to keep colonies strong and viable.