Mason Bee & Parasitic Wasp

Asked April 13, 2020, 4:02 PM EDT

For the first time last late Spring, I noticed a small wasp going into the mason bee holes that originally had been resealed that Spring. Since the mason bees holes were all sealed by this time, I covered the nests with a light sheet so the wasp couldn't get to mud sealed holes. This spring I have had two mason bees covered with something, they couldn't fly and soon died. Do you think this small wasp was a parasitic wasp and it had laid eggs on these mason bee larvae last Spring? I have been keeping a close watch and all the other mason bees seem to be doing fine. Thank you.

Lane County Oregon

2 Responses

I am so sorry to hear about your dead mason bees. Thanks for the images; these are helpful in figuring out what went wrong. If you take a hand lens or magnifying glass you should be able to make out that these little creatures are pollen mites. The mites eat the pollen, but then hitch a ride to find new hosts on emerging bees. When loads are excessive the bee has trouble flying. Mites are controlled in the fall by washing the cocoons in a bleach solution. The technique is covered in the OSU Extension publication linked below. But you can also learn how to clean cocoons of mites by attending an OSU Master Gardener mason bee training in the fall.
https://catalog.extension.oregonstate.edu/em9130

Thank you very much. I really appreciate your assistance.