The role of resistance to varroa destructor and deformed wing virus in the European honey bee (apis mellifera)

Kevill, J

Abstract

The European honey bee (Apis mellifera) is of global importance as a pollinator. Over the past 30 years an increase in colonies lost during winter has occurred, particularly in the northern hemisphere. These losses are attributed to the ectoparasitic mite Varroa destructor that acts as a vector of RNA viruses, most notably Deformed wing virus (DWV). Three master variants of the DWV have been discovered; Type-A, B, and C. The increase in overwinter colony losses are closely linked to DWV. At the same time DWV may also offer protection to colonies via superinfection exclusion (SIE), which may be linked to Varroa-tolerant colonies. However, the role of each DWV variant in colony survivorship and mite-tolerance is limited, so the main thrust of the thesis is to address this issue.


Firstly, the detection of all three DWV master variants was only possible via Next Generation Sequencing (NGS), therefore I developed a reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) assay that enabled the detection of all three DWV master variants. This allowed me to re-analyse historic samples, and revealed that type-A and C were involved in the untimely demise of treated colonies.


Secondly, I used the new assay to survey the three DWV master variants in English and Welsh honey bee colonies. DWV type-B was found to dominate colonies regardless of season, whilst overwinter losses remained low. English and Welsh Varroa tolerant colonies were also shown to have DWV viral loads similar to colonies which receive Varroa treatment throughout the year.


Thirdly, I conducted a similar study as Chapter two except in the USA. Here DWV type-A was dominant and linked to overwinter colony losses. Varroa tolerant bees also had DWV loads similar to Varroa treated colonies, a result which suggests mite-tolerant traits evolve over time.


Fourthly, DWV populations were assessed in Varroa-tolerant colonies from the Arnot forest, USA. This study disproved that avirulent DWV infections were present and supports the importance of other life history traits being involved in the survival of these colonies.


Finally, the role of DWV viral recombinants were investigated on a landscape scale using samples from England and Wales, and the USA. This provided further evidence that viral recombinants are not as fit as parent genomes.


Together these results deepen our understanding of DWV variants and their impact on colony survivorship.

Citation

Kevill, J. (in press). The role of resistance to varroa destructor and deformed wing virus in the European honey bee (apis mellifera). (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Mar 29, 2019
• Deposit Date: Apr 9, 2019
• Publicly Available Date: Apr 9, 2019
• Additional Information: Projects : ReViVe