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 colonies containing instrumentally inseminated queens were challenged with comb sections containing spores of the bacterium Paenibacillus larvae subsp. larvae that causes the disease. The strain of bacterium was demonstrated to be resistant to oxytetracycline antibiotic. Seven (39% ) hygienic colonies developed clinical symptoms of the disease but five of these recovered (had no visible symptoms) leaving two colonies (11% ) with clinical symptoms. In contrast, 100% of the non-hygienic colonies that were challenged developed clinical symptoms, and only one recovered. All non-hygienic colonies had symptoms of naturally occurring chalkbrood disease (Ascosphaera apis) throughout both summers. In contrast 33% of the hygienic colonies developed clinical symptoms of chalkbrood after they were challenged with American foulbrood, but all recovered. The diseased non-hygienic colonies produced significantly less honey than the hygienic colonies