Mass produced pollinator houses can be harmful
Note: It is always good to read research and observations that others have compiled, and this is an interesting article from Pennsylvania. The flow chart for deciding whether to buy a particular type of mason bee house is very good. We would also add: no plastic straws as they are not breathable and likely will cause mold issues. While drilled holes have been recommended in the past, we do not recommend that option. Our reasoning is that (like bamboo) they cannot be easily cleaned, so build up of mites or the fungus chalkbrood is much more likely to cause death within 1-3 years. Having removable tubes in the holes is better than not having them, but it is still hard to sanitize that type of site.
Many of us in the Willamette Valley observed an apparent die-off of blue orchard mason bees this spring when the weather got into the mid to upper 90s much earlier than usual. Although, there were reports in some areas in the Valley where it appears the heat did not affect the bees. We will learn more about the effects of the extreme heat when we harvest our cocoons in mid-October through early November.
Yes, we are all still learning about how to best help the bees!
These posts are from Master Gardeners, as well as speakers we have had at various events concerning pollinators.