Wu, Yunfei
(2020)
Characterization of the cross-interactions between Deformed Wing Virus (DWV), honey bee, and ectoparasitic mite, Tropilaelaps mercedesae.
PhD thesis, University of Liverpool.
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Abstract
Recently, honey bee colony losses have been reported to be associated with both presence of the pathogen Deformed Wing Virus (DWV) and ectoparasitic mites. The DWV vectoring role of Varroa destructor is well established while the role of Tropilaelaps mercedesae in viral transmission has not been fully investigated. In this project, I examined the effects of both mite species infestation on honey bee by comparing the DWV copy number and alteration of DWV variants of individual pupae and their infesting mites. Infestation with either mite species causes increased DWV copy number in honey bee pupae, which proves the vector role of V. destructor on honey bee and as well as suggesting a similar viral vectoring role for T. mercedesae. Through artificial infestation and wound induction experiments, a biological and mechanical vector role for T. mercedesae has been established. I also identified a positive correlation between DWV copy number in pupae and copy number in infesting mites, which forms two clusters with either high or low copy number in both honey bee pupae and infesting mites. The same DWV type A variant was present in either low or high copy number in both honey bee pupae and infesting V. destructor or T. mercedesae. These data suggest a previously proposed hypothesis that DWV suppressed the honey bee immune system when DWV copy number reaches a specific threshold, promoting greater replication. Tropilaelaps mercedesae infestation induces Hymenoptaecin and Defensin-1 expression in honey bee pupae; however, they are associated with two independent events, mite feeding activity and DWV replication, respectively. DWV can be transmitted from honey bee to mite via intake of fat body or other tissues through feeding activity, which is supported by the observation of accumulated DWV in the mite’s intestinal region. During feeding activity, induced Hymenoptaecin is ingested by mite as well and it has a negative role, down-regulating vitellogenin synthesis, which further influences mite’s reproductive capability. Hymenoptaecin expression induced by mite feeding exerts the negative feedback on the mite reproduction, and may help establishing an equilibrium between host (honey bee) and parasite (mite). I also explore the critical factors for DWV infection/replication, including 1) the host with A/T-rich genome and a skewed codon usage; 2) an intact accessible VP1-P domain on the viral virion; and 3) certain factors critical for viral replication and at least exclusively present in honey bee rather than V. destructor, T. mercedesae nor C. sonorensis.
| Item Type: | Thesis (PhD) |
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| Uncontrolled Keywords: | Honey bee, DWV, Tropilaelaps mercedesae, Varroa destructor, infection and replication, immunity |
| Divisions: | Faculty of Health and Life Sciences > Institute of Systems, Molecular and Integrative Biology |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 14 Aug 2020 09:04 |
| Last Modified: | 18 Jan 2023 23:49 |
| DOI: | 10.17638/03090688 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3090688 |
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