The epizootiology of European foulbrood of the larval honey bee, Apis mellifera Linnaeus

Larvae, artificially infected when 0 to 1 day old with Streptococcus pluton (White) and placed in colonies, were usually ejected by adult bees. Ejection was delayed from colonies deprived either of unsealed brood or their queen, or which were reinforced with adult bees. The feces of surviving larvae whose weight was subnormal, contained many viable cells of S. pluton. Colonies reinforced with unsealed brood removed more infected larvae than usual. It is concluded that infected larvae are ejected when larval food is merely adequate, as it may be when a colony is growing rapidly ; and they are kept when larval food is more abundant, as it may be when brood rearing is retarded. Natural outbreaks of disease occurred when brood-rearing, in colonies heavily infected with S. pluton, was increasing during nectar flows, which was also when secondary infection with Bacterium eurydice White increased. At such times, larvae heavily infected with both organisms may die quicker than they are being removed. At the same time infection of new larvae with S. pluton seemed to decrease: transmission of S. pluton was presumably checked by the death and ejection of unsealed larvae. Thus outbreaks usually seemed to be self-limiting. Colonies eject introduced larvae even more readily after the main nectar flows which may account for the difficulty in causing disease artificially at this time.