Validation of the methods of hygienic behaviour evaluation in the honeybee

The aim of this study was to determine which method of hygienic behaviour assessment is more reliable: the evaluation of the pierced brood removal rate or the evaluation of the freeze-killed brood removal rate. Additionally, we aimed to determine whether freeze-killed brood should be placed in colonies when defrosted or still frozen. Defrosted freeze-killed brood was removed faster within a 24 h period. The removal rates for pierced brood and frozen freeze-killed brood were similar in hygienic colonies. In non-hygienic colonies, pierced brood was removed at a significantly slower rate than frozen or defrosted freeze-killed brood. The mechanisms of removing frozen and defrosted freeze-killed brood were similar to each other and different from those observed in the case of pierced brood. The defrosting of brood prior to its introduction into colonies seems inadvisable, as it accelerates brood removal. Our results confirm the hypotheses of those researchers who believe that the frozen freeze-killed brood removal test is not always appropriate. A good solution is, therefore, to perform the frozen freeze-killed brood and pin-killed brood removal tests simultaneously. The time from the beginning of the tests to the moment 50% and 75% of dead-brood cells have been cleaned up should be assumed as the appropriate duration of the hygienic behavior evaluation tests.