Advances in Paenibacillus larvae and American foulbrood monitoring in honey bee colonies from Argentinean apiaries

Abstract

American foulbrood (AFB), an infectious disease affecting the honey bee Apis mellifera L., is caused by the spore-forming bacterium Paenibacillus larvae. Being able to kill larvae and pupae, AFB leaves adult bees unaffected, which thus become asymptomatic carriers (Lindström, 2008). Given the fact that AFB can only be detected visually, the diagnosis of this disease is usually complex and late. The development of a monitoring tool capable of detecting this disease has therefore become critical. Several works on P. larvae spore transmission and distribution at the colony and apiary level have been published (Lindström et al., 2008; Lindström, 2008); yet none of them have focussed on the number of spores in relation to the degree of disease, and so allowed the establishment of a damage threshold regarding the spores: bee ratio. Studies of such a relationship could, however, become useful monitoring tools, capable of assessing the sanitary behaviour of the colonies based on the spore loads registered, and so prevent American foulbrood development. The aim of our study was to establish a relationship between the number of spores per bee and the extent of disease development in the colony. It was further to establish a minimum number of spores (threshold) from which the clinical symptoms of AFB start to appear in the colonies.