Oh crum, new study finds "Freeze Killed Brood" assay ineffective at predicting colony mite load.

The FKB assay (brood cells are killed with liquid nitrogen within a ring, and then counted for clearing at 24 hours) is widely used as a proxy for "hygenic behavior". The protocol is core to the selection of "Minnesota Hygenic Bees". However a replication of the protocol in an unselected population show no correlation with mite loading. They assay is ineffective in detecting resistant bees.

Cite: Hygienic removal of freeze-killed brood does not predict Varroa-resistance traits in unselected stocks
Gil Leclercq Journal of Apicultural Research, 2018
Vol. 57, No. 2, 292299

The situation in our unselected stocks is summarized as:
(1) We found no significant correlation between the
mite load and the FKB removal at 24 h (nor at 48 h). In
future studies, other periods of time should probably
also be tested