Differential susceptibility to the tracheal mite Acarapis woodi between Apis cerana and Apis mellifera

In Japanese honey bees Apis cerana japonica, infestations of the tracheal mite Acarapis woodi have spread rapidly over the mainland of Japan, causing damage and the collapse of colonies. Meanwhile, infestations by mites in Apis mellifera have hardly been observed in Japan. In this study, we assessed and compared the susceptibility of the two species, A. cerana and A. mellifera, using an inoculation assay. We found that migrating female mites entered the tracheae of more newly emerged bees in both species but more frequently in A. cerana than in A. mellifera. Hence, the higher susceptibility in A. cerana is proposed as a factor causing the explosive epidemic of tracheal mites in only A. cerana in Japan. Moreover, we compared grooming behaviors between the two bee species using an observation assay as a preliminary experiment, although the bees were not exposed to the presence of tracheal mites. From these observations, the frequency of autogrooming (self-grooming) on the thorax in A. cerana was lower than that in A. mellifera. The difference in susceptibility to the mite between these two species may be due to the difference in grooming behavior frequency.