Resistance to American foulbrood disease by honey bee colonies Apis mellifera bred for hygienic behavior

Honey bee colonies, selected for hygienic behavior on the basis of a freeze -killed brood assay, demonstrated resistance to American foulbrood disease. Over two summers in 1998 and 1999, 18 hygienic and 18 non-hygienic colonie s containing instrumentally inseminated queens were challenged with comb se ctions containing spores of the bacterium Paenibacillus larvae subsp. larva e that causes the disease. The strain of bacterium was demonstrated to be r esistant to oxytetracycline antibiotic. Seven (39%) hygienic colonies devel oped clinical symptoms of the disease but five of these recovered (had no v isible symptoms) leaving two colonies (11%) with clinical symptoms. In cont rast, 100% of the non-hygienic colonies that were challenged developed clin ical symptoms, and only one recovered. All non-hygienic colonies had sympto ms of naturally occurring chalkbrood disease (Ascosphaera apis) throughout both summers. In contrast 33% of the hygienic colonies developed clinical s ymptoms of chalkbrood after they were challenged with American foulbrood, b ut all recovered. The diseased non-hygienic colonies produced significantly less honey than the hygienic colonies.