Differential autogrooming response to the tracheal mite Acarapis woodi by the honey bees Apis cerana and Apis mellifera

The infestation of honey bees by the endoparasitic tracheal mite Acarapis woodi was first discovered in Apis mellifera on the Isle of Wight, England, and the mite has since spread to all continents except Australia. Since 2010, this tracheal mite has spread rapidly in the Japanese honey bee, Apis cerana japonica, of mainland Japan, causing considerable colony mortality. In contrast, infestations by the mites in the imported and managed European honey bee, A. mellifera, have rarely been observed in Japan. A previous laboratory experiment revealed a difference in susceptibility by demonstrating that the tracheal mite more frequently enters tracheae of A. cerana than those of A. mellifera. In this study, we compared autogrooming responses of A. cerana and A. mellifera by depositing a mite on each honey bee’s mesoscutum, and we then assessed the efficacy of autogrooming to remove the mite. The bees that received mites more frequently showed an autogrooming response compared to unchallenged bees in both bee species. However, a significantly greater proportion of A. mellifera individuals autogroomed compared to A. cerana. In addition, when bees autogroomed, A. mellifera removed the tracheal mite more effectively than A. cerana. When considering all bees in the mite-deposited group, the proportion of mite removal in A. mellifera was almost twice as high as that in A. cerana. Thus, the difference in susceptibility to the tracheal mite between these two bee species is attributed to the difference in the behavioral response threshold to mites and the effectiveness of mite removal by grooming.