Amitraz Treatment

Amitraz is one of the authorised active substances used against the varroa mite; its most common form is strips hung in the brood area that remain effective for weeks. It kills only the mites on the bees and does not reach mites in capped brood cells. The keys to success are: measure first, treat at the right time and only with an authorised product, remove the strip when the period is up, and measure the result again.

What is amitraz and how does it work?

Amitraz is an acaricide (mite killer) from the formamidine group. It acts on the octopamine receptors in the mite's nervous system; the mite is paralysed, cannot feed and falls off the bee. It works by contact: as the bees rub against the strip, the active substance spreads through the colony.

An important limitation: amitraz kills only the mites carried on adult bees. Mites developing with the pupa in a capped cell are protected. For this reason, short-acting treatments are effective in the broodless period, while long-lasting strips are effective when they cover a period spanning several brood cycles.

Forms of application

• Slow-release strip: The most common and safest form. The plastic strip is hung between two frames in the brood area; the active substance is spread by the bees. The number of strips and the time they stay in the hive are given on the product label.
• Fumigant (smoke) form: Authorised fumigant products exist in some countries. Their effect is short-lived; on their own they are insufficient while brood is present.
• Unauthorised mixtures: Diluting amitraz liquids sold for cattle, sheep and goats and soaking them into cardboard or wooden slats, or spraying them into the hive, is both against the law and dangerous. The dose cannot be controlled; it leaves residues in honey and wax, speeds up resistance in the mite, and can poison the bees and the queen.

When is it applied?

• Main treatment: immediately after the honey harvest, in late summer. The bees that will overwinter are reared at this time. Winter bees reared while the mite load is high are short-lived, and the colony dwindles in winter. In most regions this period falls in August–September.
• It is not applied while supers are on the hive. No strips are put in during a nectar flow; the withdrawal period on the label is observed.
• Go by measurement, not the calendar. Monitor the mite level throughout spring and summer. If mites have risen early, waiting for the harvest can cost you the colony; early intervention with the supers removed may be necessary.

Many guides take a mite level of about 3% (3 mites per 100 bees) in a sugar roll or alcohol wash in late summer as the action threshold; waiting above this level is risky.

Strip treatment step by step

1. Measure first. Record the starting level with a sugar roll, alcohol wash or natural mite drop tray. You need this to compare the result.
2. Remove the supers. Leave only the brood chamber on the hive.
3. Put on gloves. Hang the strips between the brood frames, where the bees are most concentrated. In a double brood chamber, distribute them according to the label.
4. Correct position: The strip must not block the bees' passage or stick to the frame. A strip hung on an outer frame has little contact with the bees and remains ineffective.
5. Follow up. If the colony shrinks or the brood nest shifts, move the strip towards the cluster if the label allows.
6. Always remove the strips when the period is up. A strip forgotten in the hive keeps releasing the active substance at a low dose; this is the quickest way to select for resistant mites.
7. Disposal: Do not use a strip a second time; dispose of it according to the label instructions.
8. Measure again. Count the mite level again after the treatment has ended.

Measure the effect, catch resistance

Varroa populations resistant to amitraz have been reported in many countries. Using the same active substance alone for years, underdosing and unauthorised mixtures speed up resistance.

• Mite drop tray: Plenty of mites are expected on the tray in the first days of treatment. If the drop is low but the proportion of mites on the bees is high, the product may not be working.
• Post-treatment count: After the strip has been removed, count with sugar or alcohol. If the level has not fallen markedly, consider resistance or incorrect application; a second treatment with a product from a different group is needed before winter.
• Compare hives: The same failure in all the hives in the apiary is a sign of resistance. It is useful to report this to the local agriculture authority or to beekeeping research institutes.

Rotation

Do not use the same active substance every year; use different groups in turn. The main groups in varroa control are:

Non-chemical methods (drone brood removal, brood break, temporarily caging the queen) reduce the need for medicines and lower the pressure for resistance.

Bee, product and human safety

• At the label dose, amitraz is generally well tolerated by bees. Overdosing and unauthorised mixtures can cause bee deaths and harm the queen.
• Amitraz and its breakdown products can be found as residues in honey and wax. Do not keep frames with honey to be harvested in the hive during treatment.
• Residues accumulate in wax over time; renew brood combs regularly.
• Handle strips with gloves, do not eat or drink during application, and wash your hands afterwards. Store the product away from children and food.
• Record every treatment in your logbook with the date, product and hive number.

Common mistakes

• Treating out of a "this month every year" habit, without counting.
• Treating too late, after the winter bees have been reared.
• Hanging the strip on an outer frame, or not removing it when the period is up.
• Reusing a used strip the following year.
• Preparing your own mixture with amitraz used in livestock farming.
• Relying on amitraz alone for years without using any other group.