Blue orchard mason bees (Osmia lignaria) and horned-face mason bees (Osmia cornifrons) both only produce one generation of bees per year.
Knowing this fact makes it easier for us to protect the developing larvae from one of the biggest threats that hole-nesting bees face: gnat-sized parasitic wasps.
Monodontomerus, known as mono, is a very small parasitic wasp that lay their eggs inside of growing mason bee larvae. You may see the female mono wasp inspecting your mason bee house flying in a zig-zag pattern. The bee larvae finish eating their pollen loaf, spin their cocoons, and die when the mono eggs hatch. Mono larvae are then hidden within intact mason bee cocoons and can be hard to detect until the following spring as you discover why your cocoons did not hatch.
Our nesting materials are designed to reduce the ability of mono to access mason bee larvae but these parasitic wasps can be very sneaky. The best way to protect against mono is to remove and protect filled nesting materials and place the filled nesting holes into a fine mesh bag that keeps mono out.
Two timing options to remove nesting holes from the bee house:
Reusable wood trays:
Wait until all female mason bees are done nesting, about 6-8 weeks after you released your cocoons. The timing could be longer or shorter based on your weather patterns.
Loose nesting holes:
For spring cardboard BeeTubes, spring cardboard BeeTubes and Inserts, or spring natural reeds, you may remove individual filled nesting holes as soon as they are capped with mud. The best time to remove individual tubes and reeds is after dusk when the bees are done flying for the day. You can add additional nesting holes if the bees are still nesting. Removing nesting holes at night can help nesting bees reorient in the morning.
Protect the filled nesting trays or tubes by placing them with the mud-capped end facing up inside of our fine mesh BeeGuard Bag. Place loose tubes into a clean empty jar or can to keep them sturdy. Storing with the mud end up keeps the egg on top of its pollen loaf. Cinch the top of the bag closed.
Store the filled nesting materials in an unheated and un-airconditioned garage or shed. The mason bee larvae need the warmth of the summer to develop and you want to follow nature's temperatures as closely as you can. It's a good idea to check on the nesting materials every so often.
Removing and protecting filled mason bee nesting holes will also keep the bees safe from birds and ants. If rodents are an issue, place filled nesting materials into a plastic container.