1.7. Hygienic behaviour
Hygienic behaviour is defined as the bees’ ability to detect and remove diseased brood from the nest (Rothenbuhler, 1964). Hygienic behaviour was first described in the 1930s when researchers sought to determine the mechanism by which some honey bee colonies were resistant to American foulbrood (reviewed in Spivak and Gilliam, 1993). In the 1980s, it was shown that hygienic behaviour was also the primary mechanism of resistance to chalkbrood (Gilliam et al., 1983), although resistance to this disease involves other factors as well, such as differences in the susceptibility of different colonies or even between patrilines within colonies (Invernizzi et al., 2009; Jensen et al., 2009b).
Hygienic behaviour assays, involving killing brood by freezing or by piercing pupae with a pin (methods described in the BEEBOOK paper on queen rearing and selection (Büchler et al., 2013) are indirect, and record the proportion of dead brood removed by a colony after a particular amount of time. Most, but not all colonies, show a good correlation between removal of freeze-killed brood and resistance to chalkbrood. However, researchers and beekeepers cannot assume that the ability of a colony to remove dead brood within a certain time will ensure colony-level resistance to chalkbrood. It is very important, especially for breeding purposes, to directly challenge colonies with A. apis in addition to the freeze-kill or pin-kill brood assay (See paragraph 1.5.1. Infection bioassay of colonies) and subsequent observation of the bees’ response to the challenged brood (Palacio et al., 2010).