Total RNA Extraction and DWV Quantification

Total RNA extraction and DWV absolute quantification were performed as previously described [18 (link)]. Briefly, individual heads and abdomens were separately homogenized using a TissueLyser II (Qiagen), total RNA was extracted with RNeasy mini Kit (Qiagen), eluted in 30 μl RNase-free water and quantified with RiboGreen RNA Quantitation Kit (Invitrogen, Carlsbad, CA, USA). Ten microliters of each RNA were used as template to determine the viral load by RT-qPCR. Samples with RT-qPCR amplification signal were considered positive and those without signal negative. Results were expressed as viral copy number per microgram of RNA.