An incoming colony of unknown origin is placed in a separate quarantine yard, already carrying an undetected infection. Whether it ever reaches the main apiary — and how far a leak spreads once it does — depends on the layered controls on the left.
Daily infection exposure per healthy hive i:
E_i += k · M_layout · M_sanitation · M_robbing · n_infected_neighbors · dt
k = 0.06 / day · infected neighbor
hive turns infected once E_i >= 1
Quarantine gate (brood-cycle rule):
release day >= 21 -> symptoms caught first, colony destroyed, never merged
release day < 21 -> colony merges into the apiary while still infectious
- Apiary layout — straight rows with aligned entrances increase forager drift between neighbors (M_layout = 1.0); a varied, staggered arrangement cuts it by 60% (M_layout = 0.4).
- Quarantine period — the isolation window before a new colony is allowed to mix. A first brood cycle (~21 days) is usually long enough to notice foulbrood, chalkbrood, or an abnormal mite load.
- Tool sanitation — flaming the hive tool between colonies cuts transmission by 60% (M_sanitation = 0.4 when on).
- Robbing screens — reduced entrances on weaker colonies cut opportunistic robbing spread in half (M_robbing = 0.5 when on).
None of these layers is foolproof alone; together they are what actually keeps a leak from one colony becoming an apiary-wide outbreak.