Well here is something new for those that like to buy fancy expensive gadgets. Seen one today at the UBKA conference, it seems to be a simple 14.5kHz sound generator cost buttons to make running of a 12V alarm lead acid battery. Does it work - well these have been around for a while now and not a lot publicity so draw your own conclusions.
https://www.varroa-killer-sound.com/...ducts/Varroa01 A tad expensive at £86 squid for a few electrical componants easily obtainable on ebay and circuits easily found on the web

I'm nearly tempted to make one for evaluation , so has anyone tried it?