for the ID, Joseph. From the Info tab, food is "unknown cyclorrhaphid fly. reared from mushrooms." Is that still all that is known of the host for Mesocrina?

With parasitoid wasps, we know more about what we don't know than about what we do know. That being the case with Mesocrina, the fact that we have a record of its association with fungi tells us that it probably finds its fly host in fungi. If that's the case, this narrows down what the host may be. As far as known, all alysiines oviposit on flies that pupate in specialized structures called puparia (Cyclorrhaphous flies). In fact their mandibles are adapted to dig themselves out of these puparia. According to a British study in the early 1950's, the 4 cyclorrhaphous families with the most species breeding in fungi are the Phoridae, Syrphidae, Drosophilidae, and Muscidae. Given the small size of alysiines, I'd place my bet with Phoridae and/or Drosophilidae for Mesocrina - but that's all it is: an informed guess.

I had no idea such a wide variety of flies fed on fungi as larvae. I have not yet finished the linked article, but I have saved it to my harddrive and fully intend to read it carefully. It is amazing how much there is to learn about the natural history of my little suburban yard and garden (though it undoubtedly helps that there have been no pesticides sprayed on my property for the fifteen years I have lived here; when we moved in, there was nothing but barren weed-free lawn).