Oak Marginal Fold Gall

A couple of weeks ago, me and several of my Extension colleagues came across so-called marginal leaf fold galls on an oak on the OSU campus during a photography workshop. Since that time, I'm commonly finding these galls on oaks belonging to the "red oak group" as well as a similar gall on black locust in southwest Ohio.

So-called marginal leaf fold galls are appearing on oaks in the "red oak group" in southwest Ohio.  The galls appear as rolled or folded leaf margins and are produced by a gall-making midge fly, Macrodiplosis erubescens (Family Cecidomyiidae).  As with the vast majority of oak galls, the leaf fold galls cause no appreciable harm to the overall health of affected oaks.  However, the gall has become notorious in recent years for its connection to a non-native predaceous mite (Pyemotes herfsi) that may feed on the gall-making midge fly larvae (maggots).  The mite...