Re: How do you KNOW that mites caused the hive to crash?
Perhaps I am misreading but the tone of the OP seems to be a challenge to prove what he may not accept and that is that varroa kills hives. It may not always do so overtly but it is an everpresent fact of life in beekeeping whether one chooses to accept it or not. Given the fact the op has only kept bees post varroa (his profile says he began in 1998) it is entirely understandable to not be able to completely understand how dramatically beekeeping changed in our apiaries when varroa showed up. We were all pretty ignorant at the time and assumed it would just become a non-factor or a minor pest like tracheal mites were becoming. Many beekeepers went out of business, most resorted to lots of different remedies that may have worked for for a short time only to see infestations return with a vengeance. Having been a commercial operator for nearly 20 years pre varroa and over 20 years since its impact let me say the differences are stark and unmistakable. The beekeepers who have survived in this industry have learned a lot in how to deal with varroa, bees are better able to withstand varroa pressures and there are better tools at our disposal, but the best tool is knowledge. Understanding as much as you can about your adversary and accepting that there is a problem is paramount in learning how to deal with it and deal with it safely and sanely. Many will simply choose never to do mite counts and assume all losses are totally unrelated to the worst pest our industry has ever dealt with. That's everyone prerogative, it's not the path I have chosen. There is lots and lots of information out there about how to identify varroa infestations and evaluate hive deaths you can choose to read it or to ignore it. To each his own.
"People will generally accept facts as truth only if the facts agree with what they already believe."- Andy Rooney