Hey gavin....no idea why they do the all the control variables. It seems like fiddling around the edges to me as the model must be influenced by a million other things before considering sunshine etc. I'm not convinced that bumbles and honeybees come into contact much anyway. I wonder if a "DWV-like" virus is simply circulating in bumble bee populations anyway ? Much like DWV in honeybees was at benign levels until Varroa came on the scene ?

Anyway in the methods bit they say "we tested all of our DWV positive Bombus samples and a subset of DWV positive Apis samples for virus replication, a strong indicator for infection. DWV is a positive strand virus whose negative strand is only present in a host once the virus is actively replicating". So this is a bit technical BUT you do a reverse transcription using a specific DWV primer in your first strand synthesis. This then acts as the priming site for PCR and, importantly, would only show a product if you have detected negative strand virus...ie replicating virus. However you need to run a shed load of controls to be sure the original primer you used for tagging is not acting independently from the RT and giving you false positives. My bible....the BEEBOOK....has a chapter of virology in bees that talks about this.