In honey bees (Apis mellifera L.), hygienic behavior of workers against Varroa destructor provides the colonies with some resistance to this parasite. The removal of freeze-killed brood (FKB) has often been used as a proxy to assess the removal of Varroa-infested brood. The question is whether this approximation is reliable enough to estimate the benefits induced by the removal of Varroa-infested brood in unselected stocks. For this purpose, we investigated the relation between the removal of FKB and three other variables: (1) the percentage of pupae and workers infested by V. destructor; (2) the share of mites in brood compared to phoretic mites; and (3) the reproductive success of mites. To be a reliable estimate, the removal of FKB should correlate with these three variables. Since hygienic behavior is naturally expressed and highly variable in unselected stocks, we chose to use such stocks to get a wide range of FKB removal. There was no correlation between FKB and the three other variables. We conclude that removal of FKB is not a good estimate for hygienic behavior towards Varroa mites in unselected stocks.
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