bee-keeperIf there's one reason a modern beekeeper can't afford to relax, it's varroa. The mite Varroa destructor feeds on the bee's fat body and spreads viruses that deform wings and kill brood. A colony that looks strong in August can collapse by November if varroa isn't kept in check. The good news: varroa is manageable — but only if you monitor it and act in time.
Why it's so dangerous
Varroa breeds in capped brood, right where you can't see it. The more brood a colony has, the faster the mite multiplies. The problem isn't just the mite itself, but the viruses it spreads — which is why even a small number of mites can do great damage when viruses are present.
How to measure infestation
The biggest mistake is treating “blindly” or “when the neighbour does”. First measure how many mites you have:
- Alcohol wash — take about 300 bees (half a decilitre) from a brood frame, shake them in alcohol and count the mites that fall; the most accurate method
- Powdered sugar — the same idea, but the bees survive; less accurate but kinder
- A screened bottom board — count the mites that drop naturally over 24–72 hours
The goal is to get the number of mites per 100 bees, because only the number tells you whether and when to treat.
When it's too much
A rough rule: during the season, more than about 3 mites per 100 bees (3%) is the alarm and a call to action. The threshold is lower before winter, because winter bees must be healthy for the colony to survive. Measure several times a season, not just once.
Treatments and when to use them
- Oxalic acid — most effective when there is no brood (winter, at a cold 5–12 °C), because then no mite is hidden in the brood
- Formic acid — penetrates even capped brood, so it works even with brood present (best at 15–25 °C)
- Thymol and other organic acids — per the manufacturer's instructions, usually in late summer
The most important treatment of the year is the one right after harvest, in late summer — that's when you save the winter bees. An additional winter oxalic-acid treatment “mops up” whatever remains.
The harvesting rule (withdrawal period)
After treating with a medicine, respect the prescribed withdrawal period — the time during which you must not harvest — so the honey stays clean and safe. In the app you log the treatment and it calculates and shows you a “do not harvest until” warning for that date, so you never mix medicine and honey.