Horizontal transmission of Paenibacillus larvae spores between honey bee (Apis mellifera) colonies through robbing

Surprisingly little is known about transmission rates between honey bee colonies of Paenibacillus larvae, the causative agent American foulbrood. We studied the rate of horizontal transmission of P. larvae spores between colonies as a function of physical distance between colonies by culturing for the spores from sequential samples of adult bees. The results demonstrate a direct effect of distance to clinically diseased colonies on the probability of contracting high spore levels, as well as on the probability of developing clinically visible disease symptoms. The results also demonstrate that colonies may develop considerable spore densities on adult bees without exhibiting visible symptoms of disease. Furthermore, the data suggest that transmission of AFB between apiaries occur within 1 km distance from clinically diseased colonies, but is significantly lower at 2 km distance or longer when colonies dead from AFB are allowed to be robbed out.