What is the mite bomb?

Varroa reproduce inside sealed brood cells, so their population tracks the brood — and brood-rearing peaks in midsummer. By the time the colony stops rearing brood in autumn, every mite in the hive is on an adult bee, and the adults being parasitised are the long-lived winter bees the colony depends on. A colony can look strong in August and be dead by November.

Why can I not just treat whenever I like?

Oxalic acid does not penetrate a sealed brood cell, so it only reaches the two-thirds of the mite population that are on adults — and only when there is no brood for them to hide in. Formic acid does penetrate the cappings, but it needs 10–30 °C to evaporate at the right rate and it will kill the queen outside that window. Thymol needs warmth too. That is why treatment timing, not treatment choice, is the thing beekeepers argue about.

Why did my colony swarm when I had supers on?

Supers give storage space, not brood space. A colony swarms when the brood nest is congested and the queen has nowhere to lay, which is a different problem — and an old queen makes it more likely.

Beekeeper — Three years, eight hives, and a mite that doubles every three weeks.

You are the beekeeper. Run an apiary through the year: watch the brood nest expand on the first pollen, the colony boil over into a swarm in May, the summer flow fill the supers — and, underneath all of it, a parasitic mite population doubling every three weeks towards the autumn collapse that kills most colonies that die. Every treatment has a window, and most of them are shut when you need them.

Timescale: 1–3 years. Model: Age-structured honey-bee colony model (BEEHAVE-inspired) with a varroa–virus sub-model

What you will learn

Why a colony that looks strong in August can be dead by November.
Why oxalic acid only works when there is no brood, and when that actually is.
Why the honey crop depends on having foragers *before* the flow, not during it.
Why splitting a colony is both a swarm-control measure and a mite treatment.

Scenarios

Sandbox — Three years, eight hives if you want them, nothing scored.
First Winter — One hive, one year. Get it to spring alive.
Mite Bomb — Three hives, heavy mite pressure, eighteen months. Treat correctly or lose them.
Honey Year — Five hives, two seasons, maximum honey and no losses.

What you control

Hives — More hives means more honey and more places for mites and disease to move between.
Starting strength (frames of bees) — A frame of bees is about 2 500 workers. Below about four frames a colony cannot keep its brood warm.
Starting mite load (mites per 100 bees) — The single number that decides whether a colony sees another spring. Three in autumn is trouble; six is usually fatal.
Queen quality — Peak laying rate as a multiple of a good queen’s 1 800 eggs a day. It falls with her age.
Climate — Sets the temperature, the rain, and how long the winter cluster has to survive on its stores.
Forage around the apiary — What is in bloom, when, and how far away. A gap between two flows starves a colony at its largest.
Treatment product — What the treat button applies. Each one has a different window, and using it outside that window wastes it — or kills the queen.
Supers per hive at the start — Storage space. It is not brood space, so it does not prevent swarming.
Syrup feed rate (kg/week) — How fast the feed button delivers syrup. Feeding in autumn saves colonies; feeding during a flow puts sugar in your honey.
Drone comb (fraction) — Mites prefer drone brood eight to one. A frame of drone comb is a mite trap — if you remove it before the drones emerge.

Questions

What is the mite bomb?: Varroa reproduce inside sealed brood cells, so their population tracks the brood — and brood-rearing peaks in midsummer. By the time the colony stops rearing brood in autumn, every mite in the hive is on an adult bee, and the adults being parasitised are the long-lived winter bees the colony depends on. A colony can look strong in August and be dead by November.
Why can I not just treat whenever I like?: Oxalic acid does not penetrate a sealed brood cell, so it only reaches the two-thirds of the mite population that are on adults — and only when there is no brood for them to hide in. Formic acid does penetrate the cappings, but it needs 10–30 °C to evaporate at the right rate and it will kill the queen outside that window. Thymol needs warmth too. That is why treatment timing, not treatment choice, is the thing beekeepers argue about.
Why did my colony swarm when I had supers on?: Supers give storage space, not brood space. A colony swarms when the brood nest is congested and the queen has nowhere to lay, which is a different problem — and an old queen makes it more likely.

What this model cannot do

One average bee. Real colonies have genetic variation in hygienic behaviour, mite resistance and temper, and it matters.
Foraging is a yield curve, not a landscape. There is no recruitment by dance, no patch depletion and no distance-dependent energy cost beyond a simple discount.
Only deformed wing virus is represented, and only through adult lifespan. Nosema, chalkbrood, European and American foulbrood, and pesticides are absent except as scripted events.
Swarming is a probability, not a decision. Real colonies raise queen cells over ten days and can be talked out of it.
Treatment efficacies are single numbers. In reality they vary with dose, method, temperature, colony size and mite resistance.
This is not advice about managing real bees. Follow the label and your local regulations.

Sources

Becher, M. A. et al. (2014), BEEHAVE: a systems model of honeybee colony dynamics — the model class this is a simplified version of
Martin, S. J. (2001), The role of Varroa and viral pathogens in the collapse of honeybee colonies — the mite–virus dynamics and the autumn collapse
Khoury, D. S., Myerscough, M. R. & Barron, A. B. (2011), A quantitative model of honey bee colony population dynamics — the precocious-forager feedback
Seeley, T. D. (1995), The Wisdom of the Hive
Rosenkranz, P., Aumeier, P. & Ziegelmann, B. (2010), Biology and control of Varroa destructor — reproduction rates and treatment efficacies