The authors investigated the impact of the recent dispersal of Varroa destructor on honeybee virome taking use of historical samples. These samples are collected from four independent regions of the world, i.e. Canada, United Kingdom, New Zealand and Scandinavia, during 2010-2013. The distribution of varroa mites in these areas offered a unique opportunity to quantify the effect of the invasive vector on its host virome. A total of 654 colonies were investigated, which represent a relatively large sample size. I found this study is valuable and providing significant information.
I have a few minor concerns to be discussed.
1. Despite 14 RNA viruses were included in the study, only 6 viruses were quantified in all samples. Is this number (6) of viruses sufficient to support “global” shift in conclusion? Even considering all of the 14 viruses, these may not represent the virome of honeybees, since honeybees harbor many more viruses. Please consider revising the title.
2. Samples were independently screened in different labs, but data were pooled for analysis. The accuracy and sensitivity of the method may vary among different labs, even they use the same protocols. Did you consider including controls to calibrate the variations of methodology among different labs?
3. Some text in figure 3 is overlapping. Please revise to improve clarity.