Recent spread of Varroa destructor virus-1, a honey bee pathogen, in the United States

Eugene V Ryabov,Dennis Vanengelsdorp,Yanping Chen,Shayne Madella,Anna K Childers,Ashrafun Nessa,Jay D Evans

doi:10.1038/s41598-017-17802-3

Abstract

RNA viruses impact honey bee health and contribute to elevated colony loss rates worldwide. Deformed wing virus (DWV) and the closely related Varroa destructor virus-1 (VDV1), are the most widespread honey bee viruses. VDV1 is known to cause high rates of overwintering colony losses in Europe, however it was unknown in the United States (US). Using next generation sequencing, we identified VDV1 in honey bee pupae in the US. We tested 603 apiaries the US in 2016 and found that VDV1 was present in 66.0% of them, making it the second most prevalent virus after DWV, which was present in 89.4% of the colonies. VDV1 had the highest load in infected bees (7.45*1012 ± 1.62*1012 average copy number ± standard error) compared to other tested viruses, with DWV second (1.04*1012 ± 0.53*1012). Analysis of 75 colonies sourced in 2010 revealed that VDV1 was present in only 2 colonies (2.7%), suggesting its recent spread. We also detected newly emerged recombinants between the US strains of VDV1 and DWV. The presence of these recombinants poses additional risk, because similar VDV1-DWV recombinants constitute the most virulent honeybee viruses in the UK.

Highlights

The European honey bee (Apis mellifera) is the most commonly managed bee in the world and a key contributor to pollination of food crops and wild plants
The major Varroa destructor virus 1 (VDV1) variants in the samples tested by next-generation sequencing (NGS) were full-length, we demonstrated that in addition to the full-length VDV1 and Deformed wing virus (DWV), United States (US) honey bees harbor VDV1-DWV recombinants, similar to those found in Europe with respect to genome organization, but showing sequence-level traits from the VDV1 and DWV parental virus strains typical of the US
The reads were aligned to the reference DWV and VDV1 sequences to reveal complete coverage for both viruses, suggesting that full-length VDV1 and DWV constituted the majority of the DWV-like populations in the sampled pupae (Fig. 1B)

Summary

Introduction

The European honey bee (Apis mellifera) is the most commonly managed bee in the world and a key contributor to pollination of food crops and wild plants. Parasites and pathogens are strongly implicated in honey bee colony losses, impacting pollination services[4,9]. In Europe and the US, elevated losses of honeybee colonies are associated with the mite Varroa destructor[13] This parasite feeds on the internal tissues of both pupal and adult honey bees, and in the process can vector a number of RNA viruses[13,14]. These include Deformed wing virus (DWV)[15], referred to as DWV-A16, and DWV-like viruses such as the Varroa destructor virus 1 (VDV1)[17], (Fig. 1A), referred to as DWV-B16. When planning antiviral treatments, including RNAi-based methodologies, consideration of the sequence differences between VDV1 and DWV will be important to ensure their efficacy

Methods

Results

Conclusion