17Honey bee parasitic mites (Tropilaelaps mercedesae and Varroa destructor) detect 18 temperature, humidity, and odor but the underlying sensory mechanisms are poorly 19 understood. To uncover how T. mercedesae responds to environmental stimuli inside a 20 hive, we identified the sensilla-rich sensory organ on the foreleg tarsus. The organ 21 contained four types of sensilla, which may respond to different stimuli based on their 22 morphology. We found the forelegs were enriched with mRNAs encoding sensory 23 proteins such as ionotropic receptors (IRs) and gustatory receptors (GRs), as well as 24 proteins involved in ciliary transport. We also found that T. mercedesae and Drosophila 25 melanogaster IR25a and IR93a are functionally equivalent. These results demonstrate 26 that the structures and physiological functions of ancient IRs have been conserved 27 during arthropod evolution. Our study provides insight into the sensory mechanisms of 28 honey bee parasitic mites, as well as potential targets for methods to control the most 29 serious honey bee pest.
31The number of managed honey bee colonies has declined across North America and 33 Europe in recent years 1 . Pollination by honey bees is critical for maintaining 34 ecosystems and producing many agricultural crops 2,3 . Prevention of honey bee losses 35 has, therefore, become a major issue in apiculture and agriculture. Although there are 36 many potential causes for the observed declines, ectoparasitic mites are considered to be 37 major threats to the health of honey bees and their colonies 1,4 . Varroa destructor is 38 present globally (except Australia) and causes both abnormal brood development and 39 brood death in honey bee colonies 5 . The mites feed on hemolymph and also spread 40 honey bee viruses, particularly deformed wing virus (DWV) 6,7 . In many Asian 41 countries, another honey bee ectoparasitic mite, Tropilaelaps mercedesae, is also 42 prevalent in Apis mellifera colonies 8,9 . These two emerging parasites of A. mellifera 43 share many characteristics 10 . For example, they have similar reproductive strategies 11 44 and both are vectors for DWV [12][13][14][15] . As a result, T. mercedesae or V. destructor 45 infestations have similar negative impacts on A. mellifera colonies [16][17][18] . Although T. 46 mercedesae is currently restricted to Asia, it has the potential to spread and establish 47 worldwide due to the global trade in honey bees.
48V. destructor prefers temperatures of 32 ± 2.9 ℃, reproduces best at 49 32.5-33.4 ℃, and has been shown to discriminate temperature differences of 1 ℃ 19-21 .
50Furthermore, its reproduction also depends on humidity of 55-70 % 22 . These results 51 demonstrate thermo-and hygrosensation of V. destructor play important roles to adapt 52 to the honey bee hive environment; nevertheless, chemoreception must be most 53 important in the various interactions between mites and their honey bee hosts. For 54 example, V. destructor prefers to parasitize nurse bees rather than foragers during its 55 phoreti...