A couple of years ago we set up the provap vapouriser with an inverter and a battery in a box, and an anderson plug off the ute to charge it up and happily drove around the countryside fogging hives in late summer/early autumn to supplement our thymol treatments. We decided to closely monitor one site. To begin with it had really low levels of mites on the one side (4 pairs of hives on each side of the vehicle) and a lovely gradient on the other side with the hives having increasing numbers of mites up to a mite bomb hive on the end. To our amazement the low mite hives gradually increased their mite counts as they soaked up the mites from the mite producer colony, despite our repeated fogging. Did fogging help? I have no idea, but i sure wish we had blocked the entrance of the mite producer hive the moment we discovered it, as it took out about 1/3 of the hives eventually. Of course at the time of monitoring it was perfectly healthy to look at and we thought we were going to kill some varroa with our new gadget. So my 2c worth is to put the time and effort into mastering something like the oxalic strips, and exhaustive monitoring. I imagine fogging could be a very cost effective tool in a varroa IPM programme, but reinvasion is the bane of all non-synthetic treatments. Also, the provap kept giving problems, it was a really overprived bit of kit in my opinion.