mono, the pest of mason bees


The monodontomerus, or “mono” is a parasitic wasp that lays its eggs on the larva, usually within the cocoon of the mason bee.  The eggs then hatch and the mono larvae (10-15) eat the mason bee larva.  They take about 6 weeks to develop from eggs to emerged adults, so if there are flying adults of monodontomerus among the cocoons, or thin-walled nests while the mason bees are still larvae or early pupae, there will likely be a lot of dead mason bees and another crop of mono flying soon.

mono larva and cocoon

Mono females typically deposit their eggs through the side of a thin-walled straw.  They insert their ovipositor (see the long “stinger looking thing” in the above photos) through the side and deposit their eggs on the surface of their host larva.  In this video by Sherian Wright, you will see the mono tapping the straw with her antenna to sense what’s below in the straw.

Unfortunately, the parasitic wasp is also a beneficial insect that preys on sawflies in woodland.  It is raised and released to control the sawflies in North Carolina.  Quite the conflict of interest to our poor native solitary bees!


Video by Sherian A. Wright (top)

Control solutions:

  • Remove nesting straws from the monodontomerus environment.  If you see the mono flying around your mason bee nesting house in late May, remove your straws and store them away from this pest.  Read more.
  • It is possible to reduce the number of monos by using a misting spray of water and removing them.
  • If you suspect you have mono already within your colony, you can reduce further infestation by putting the nests in a dark room with a black light suspended over a tray of baby oil. The mono adults are attracted to the black light and drown in the baby oil.  A bug zapper works just as well.  A word of warning, however, is that there are other, even smaller parasitic wasps in this group that are not attracted to the black light (tetrasicus).
  • If during harvest, you suspect that mono is within your cocoons, you can candle the cocoons.  Here’s a video of what we mean by “candling”.

  • The most sensible solution is to use thicker straws, reeds or nest blocks they cannot penetrate with their ovipositor.  The EasyTear straw is just thick enough to stop most of them, yet is easy to open.