Hi Stephen, In response to your note of 27 April, I do use wooden nest blocks for Osmia but they can not be opened to clean out infested cells. I have heard of the treatments using Amitraz and Fluvalinate for honeybee mites and may try these materials in the future. At this time, the Osmia are in full nesting mode and seem to be using treated and untreated blocks about equally. While cleaning out some of last years unopened cells I noted quite a bit of what I suspect is chalkbrood. I have heard of some experiments using Benlate to cure this in honeybee colonies but have never tried it as my one chalkbrood hive produces at least as well as my un-infected hives. Any comments? Finally, thanks to everyone for the interesting discussions on this line! I'm really enjoying "listening in". Cheers! Dave Pehling, WSU Cooperative Extension Washington State [log in to unmask]