A recent article by Colin Purrington explains 11 flaws encountered in commercially made houses intended for mason bees.
1. Nesting blocks, tubes, reeds are not removable
Glued nesting materials is the number one reason why most commercial bee hotesl can become death traps. Because the nesting material cannot be removed and cleaned (or just thrown out), over time there will be an increase in the population of parasitic wasps, parasitic bees, parasitic flies, kleptoparasitic mites, fungi, bacteria, and viruses. And you typically won’t see these dangers because the solitary bees will still use the hotel (they can’t help themselves). But inside, out of view, their eggs, larvae, and pupae are probably dying at a much higher rate than when you first installed the house. And if you leave that house out for years and decades, that pest-ridden hotel might be doing more to increase the population of pests than solitary bees.
You can read the full article here.