🦟 Seasonal Varroa Treatment Thresholds Lab

About this simulation

Varroa destructor mite counts are usually reported as mites per 100 bees (from an alcohol wash or sugar roll) or as a daily natural mite drop onto a sticky board. A single number, though, does not tell you whether to treat — the same count can be safe in June and dangerous in September. That is because the "action threshold" beekeepers compare their count against is not fixed: it moves with the colony's biology across the season.

Why the threshold shifts

• Spring build-up — the colony is expanding fast and brood volume is high, so mites are "diluted" across more bees; a slightly higher count is tolerated while numbers are checked.
• Summer peak — population is largest and turnover is rapid, giving the widest safety margin, but mite populations are also multiplying fastest inside capped brood.
• Late summer / autumn — this is the most critical window: mites feeding on the bees that will become long-lived "winter bees" spread deformed wing virus, so thresholds tighten sharply even though raw mite counts may look similar to summer.
• Winter prep — the goal is to send a nearly mite-free, virus-free cluster into winter, so the threshold is at its lowest of the year.

Controls

• Month — moves through the beekeeping season; the threshold curve, colony size and brood volume all respond.
• Mite load — sets the sampled mite count; watch the gauge and bees change colour as it crosses the seasonal threshold.
• Colony population — a smaller colony has less capacity to dilute or outgrow an infestation.
• Monitoring method — relabels the gauge to match how you actually sampled (wash, roll or board).

Did you know?

Because mites reproduce inside capped brood cells, an alcohol wash only ever samples the mites riding on adult bees — it systematically undercounts the total mite population when a lot of brood is present, which is one more reason spring and autumn readings of the same number mean different things.