Factors affecting development of chalkbrood disease in colonies of honey bees, Apis mellifera, fed pollen contaminated with Ascosphaera apis

Abstract

Using improved methods, colonies of honey bees, Apis mellifera, selected and bred for resistance and for susceptibility to chalkbrood disease caused by the fungus, Ascosphaera apis, were inoculated with the pathogen in pollen patties. Good hygienic behavior, defined as uncapping and removal of freeze-killed sealed brood by worker bees, was correlated with resistance to the disease in most of the test colonies. Resistant colonies had fewer hive substrates contaminated with the pathogen than susceptible colonies. Most bee bread (stored pollen) samples from susceptible colonies contained the pathogen, but few from resistant colonies did. Bee bread and guts of nurse bees were the major sources of the pathogen in susceptible colonies. A higher percentage of bee bread samples from resistant colonies contained yeasts and molds other than A. apis. Tests of bees, brood, bee bread, and honey for antimycotic substances active against A. apis revealed that microorganisms, primarily molds, produced inhibitory substances. Most of these organisms were isolated from bee bread. The largest zones of inhibition were produced by Rhizopus sp. and unidentified Mucorales. These organisms may have been introduced by the bees.