Abstract
Simple summaryParasitic mites are among the main causes of honeybee colony losses worldwide. Long-term selection has led to bees that are, in part, resistant to one specific mite, Varroa destructor. We investigated whether an important Varroa resistance trait, “hygienic behavior”, is also effective against Tropilaelaps mercedesae. T. mercedesae is another bee-parasitic mite of great economic importance and a lifecycle similar to that of V. destructor. “Hygienic behavior” means the ability of bees to recognize and destroy mite-infested bee brood, interrupting reproduction of the parasite. We also compared the expression of the behavior in two species of bees, one of which (Apis cerana) is thought to be resistant to T. mercedesae, while the other (Apis mellifera) is sensitive to it. We confirmed that both bees were able to express hygienic behavior also towards T. mercedesae. Moreover, we found that specialist bees destroying V. destructor-infested brood often also destroyed brood infested by T. mercedesae. This strongly suggests that hygienic behavior against the two mites is really the same trait, and selecting for V. destructor resistance likely also increases resistance to T. mercedesae. We also showed that A. cerana is more efficient at destroying T. mercedesae-infested brood, which may help to explain its resistance.The mites Varroa destructor Anderson and Trueman and Tropilaelaps mercedesae Anderson and Morgan are both serious threats to the Apis mellifera beekeeping industry. A trait frequently used in selection programs for V. destructor resistance is hygienic behavior, the selective removal of diseased/damaged brood. Here, we measured the level of association of the expression of hygienic behavior against both mites in A. mellifera, by observing whether the same individual bees would carry out the opening and removal of brood infested by the two parasites. The groups of bees showing these behaviors on cells artificially infested by either parasite showed a large overlap, making it appear likely that the two traits are at least closely coupled. Therefore, breeding for V. destructor resistance based on hygienic behavior could prepare A. mellifera populations for dealing with Tropilaelaps sp. mites, and vice versa. Using the same bioassay, we also compared the hygienic behavior of A. mellifera towards T. mercedesae to that of the Asiatic honey bee, Apis cerana. A. cerana workers eliminated a greater proportion of infested cells, which may in part explain the resistance of this bee to Tropilaelaps and the observation that Tropilaelaps reproduction on brood of this species is extremely rare.
Highlights
Parasitic mites and associated pathogens are among the most frequent causes of Apis mellifera (L.)colony losses in most parts of the world [1,2,3,4]
Unlike V. destructor, adults of T. mercedesae feed on early larval
In the cbees_cbrood experiments, insufficient numbers of cells were infested with V. destructor to carry out the test
Summary
Parasitic mites and associated pathogens are among the most frequent causes of Apis mellifera (L.)colony losses in most parts of the world [1,2,3,4]. In Europe, North and Central America, and most of temperate Asia, Varroa destructor (Anderson and Trueman) is by far the mite species with the greatest economic impact. In those parts of Asia in which the introduced A. mellifera coexists with autochthonous giant honey bees (Apis dorsata, Apis breviligula, and/or Apis laboriosa), mites of the genus. Tropilaelaps clareae and Tropilaelaps mercedesae, are known to cause damage to A. mellifera colonies, and at least T. mercedesae (Anderson and Morgan) is capable of transmitting Deformed Wing Virus as well as black queen cell virus [7,8]. Unlike V. destructor, adults of T. mercedesae feed on early larval
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