The freeze-kill (or "pin-kill") brood test is the standard field assay for hygienic behaviour — a heritable trait in which worker bees detect diseased or dead brood beneath its wax cap, chew it open, and remove the corpse before pathogens like Varroa mites or American foulbrood can multiply and spread. Breeders freeze a patch of sealed brood with liquid nitrogen or dry ice, then score how much of it the colony has uncapped and removed after 24 and 48 hours.
Because hygienic behaviour also strips capped cells that harbour Varroa mites before they finish reproducing, breeders use this same freeze-kill assay as a fast, low-cost proxy for selecting Varroa-tolerant stock without needing a live mite challenge.
A patch of sealed brood is killed by freezing, and worker bees detect, uncap and remove the dead pupae over the following 48 hours — the core field assay breeders use to score hygienic behaviour.
Each frozen cell gets a random removal time drawn from a rate tied to the colony's hygienic score. Cells step through capped → uncapping → fully removed, mirroring the real 24h and 48h scoring checkpoints and the ≥95% pass threshold.
Set the hygienic score and patch size, then scrub the time slider or hit Auto-run to watch the patch clear. Watch removal percentages and the pass/fail readout update against the 24h and 48h benchmarks.
Because hygienic removal also strips out Varroa-infested brood before mites finish reproducing, this same freeze-kill test doubles as a fast proxy for selecting Varroa-tolerant breeding stock.