I came across this paper yesterday, which appears to be a very good and well-balanced summary of the Varroa mite problem. 'Natural Adaptation' is given a good airing, and the only obvious 'error' I can see is that organic acids are considered to be effective only during broodless periods - which may well have been the established opinion back in 2009. Despite the date of publication, I still think this paper is well-worth reading.