I have a mason bee barn and it looks like some of the "hollows" are being filled in. So I have been trying to find information on what to do next spring as they start to hatch? Do you have any good references/articles? or educational sessions scheduled?
Linn County Oregon mason bees
Thanks for reaching out about how best to care for your mason bees!
The "filled" areas contain cocoons inside of which the next generation of bees is developing. These developing bees are vulnerable to parasites and predators, but you can increase survival from about 30% to as much as 90% by bringing the "barn" inside once the life cycle of adult bees has ended, and (for models that can be disassembled) cleaning cocoons in the fall. It's late to bring them in, but you might as well do it now and then get an earlier start in 2020.
Here's an OSU Extension publication about mason bee care, detailing how to do this on page 5: https://catalog.extension.oregonstate.edu/em9130
Better yet, you can learn how to do this person with Master Gardener volunteers who are skilled stewards of blue orchard mason bees. Registration opens in September for our FREE fall cocoon care classes. Check out this list of Linn County classes and save the date for one near you: https://extension.oregonstate.edu/linn/events/linn-county-mason-bee-cocoon-care-classes