Tropilaelaps mercedesae Infestation Is Correlated with Injury Numbers on the Brood and the Population Size of Honey Bee Apis mellifera

SIMPLE SUMMARY: A global decline in the population of bee pollinators is regarded as a potential threat to species extinction and global food security. Mite infestation plays a vital role in contributing to the collapse of bee populations. However, the correlation between bee population and mite infestation remains unclear. This study investigated Tropilaelaps mercedesae mite infestations to the larval, pupal, and crippled adult stages of honey bee Apis mellifera, the relationship between mite infestation rate and injury numbers for each of bee larvae and pupae, and the relationship between mite infestation rate and population size per beehive. Mite infestations occurred in all developmental stages of the honey bees, and it was pronounced in the abdomens and the antennas of the honey bees. Mite infestation rate was positively correlated with the number of injuries per bee in each of the larvae and pupae and negatively correlated with the population size per beehive. Overall, our findings suggested that the use of a large population size of beehives can reduce the infestation rate. It also provided important information about the adaptation of mite/antibacterial immune competence of honey bees to different life stages and the breeding stock of bees for hygienic behaviors resisting mite infestations. ABSTRACT: Tropilaelaps mercedesae, one of the most devastating parasitic mites of honey bee Apis mellifera hosts, is a major threat to honey products by causing severe damage to honey bee colonies. Here, we recorded injury numbers caused by T. mercedesae to different body parts of the larval, pupal, and crippled adult stages of honey bee A. mellifera. We evaluated the relationship between infestation rate and injury numbers per bee for both larvae and pupae. We also noted the total bee numbers per beehive and examined the relationship between the infestation rate and population size. T. mercedesae infested all developmental stages of honey bees, with the highest injury numbers in the abdomens of bee pupae and the antennas of crippled adult bees. Although larvae received more injury numbers than pupae, both infestation rate and injury numbers decreased as the larval stage progressed to the pupal stage. The infestation rate increased as the population size per beehive decreased. This study provided new perspectives to the understanding of changes in the effects of T. mercedesae infestations on different developmental stages of honey bees. It also showed useful baseline information for screening honey bee stock that might have high defensive behaviors against mite infestation.