Rooney said
Then for this year I got the hollowed out teasel idea from you. I would like to know how you guard the exterior of the reeds from predatary wasps depositing eggs through the walls?  

I've been using teasel for Osmia lignaria for about 10 years.  I take all of my houses down Memorial Day weekend and put them in our treehouse which has windows with screens (I leave the windows cracked open year round).  In my area (SW WA/PDX) the predatory wasps become active after Memorial Day.  Occasionally there are a few straggler bees also active until then so they are probably quite upset with me.  But the losses from mono wasps will be way worse than losing the eggs from a few stragglers.

I think the mono wasps have a harder time drilling through teasel vs. cardboard, paper, or phragmites reeds.  In fact if the teasel wall is thick, the wasps cannot drill through.  But the best option is to just protect the tubes by putting them in a shady, dry outdoor space that is protected from wasps and squirrels.  If you don't have an outdoor structure, I would put them in a tightly closed cloth sack and hang them under an eave on the north side of your house.

I've never had leafcutters so I cannot advise on those.

To John S:
& regarding ideas on building solitary bee homes. 

Since mason bees are emerging I set up new homes in hopes to find the truthfulness of my previous statement about 7 weeks ago about bees that bees possibly avoiding metal cans when choosing nesting sites. (so a few weeks down the road we will later get a pretty good idea as this experiment moves along with at least one more picture)

As well here's another test I noticed about pictures today. Each internet blog probably has different methods of uploading. Here pictures seem to me very simple and it might be because I stick to this one HOS to accomplish this. It went like this; 

I placed a private message to "John S" with this picture file of 3 constructed nesting sites, then sent another copy to myself which the HOS PM system never allowed to myself. But in the latter case the copy retained on the cloud, so in more detail of the latter here's what I did;

( i ) Sign in to HOS

( ii ) In forums find a user's post and click on that users PM icon 

(iii )Delete that user from the send to field

( iiii ) Click Upload Attachments from the lower area (this opens another area even lower on the screen)

( iiiii) Click add files (this opens your computer's browse function to be used by the owner to search the picture file)

( iiiiii ) Click start upload

( iiiiiii ) Send to blank user (ie. nobody)

Then if after this 6th and 7th step the system prompts you to find a legal user to send the message so just ignore. If the file you tried uploading is the correct type it stays locked onto the HOS system. 

At which point it is important to preview your message and then at which point it's incumbent on you to what ever operating system, browser, or cellphone you are using to gain the path from the image showing to you in the preview, using windows is the mouse right click, then copy functions to save it. For non advanced people most browsers allow for the pathway to be seen on screen by hovering mouse over the image in preview and scribble the path in pencil. All can later be entered on a forum post on the HOS system after you prove the path exists without spelling mistake in the browser URL.
( ie. https://forums.homeorchardsociety.org/wp-content/sp-resources/forum-image-uploads/rooney/2021/03/Edit_2021-03-27_1-1.jpg )

Worth noting that learning goes faster working at it backwards and forwards until both ends meet and then sticking to one method /one site is always a very productive way.

John S said
They don't prefer wood blocks. If you look on the Crown bees site, you can see that they greatly prefer natural reeds to them.  I bundle them in bungee cords so squirrels won't pull one out to eat the larvae. I make mine out of teasel and Himalayan honeysuckle stems, but others would work too.

John S
PDX OR  

John, ever since your doubting statements 9 weeks prior against using wood blocks it stirred my curiosity so in the last 9 weeks have proven you are 100% correct to cancel the use of blocks. 

Once the bees saw this nice weather spell start they have taken 5-6 days to fill up my 12 teasel home and left the outer two wood blocks alone as seen per above pictures. It's been a few days now and still no activity in the wood blocks at all. There must be something strange to them about wood and not reeds etc.

The metal cans thought I had (ie. 2-5-2021 4:54pm) is not a case of avoidance either, it attracted the females which emerged from the brick hole that had been going for probably the age of whoever built this house, is now having those females relocate to the original can that bees avoided last year. I placed it on the ground 3 feet below the brick hole. -The stipulation is that they return to the original birthplace first before going elsewhere.