This “underside tentiform” mine in a hazelnut leaf was made by a larva of the moth Phyllonorycter intermixta (Gracillariidae).
As seems to be the case more often than not with leaf mines, what emerged from it was not the insect that produced it. Most often, the parasitoid wasps I get are members of the family Eulophidae; sometimes they are braconids, and occasionally non-eulophid chalcids (e.g. torymids). So when I trained my lens on the two-millimeter wasp that came out of this hazelnut leaf mine, I was surprised to see something that looked more like an ant than like any of the above-mentioned wasps.
The resemblance to an ant is no coincidence; this wasp belongs to the family Bethylidae, which, like ants (Formicidae), belongs to the Aculeata, or stinging wasps–as opposed to the “Parasitica,” an artificial group that includes all the hymenopterans that are neither sawflies nor stinging wasps. Not everything in the “Parasitica” is parasitic (e.g., gall wasps, Cynipidae), and bethylids are among the many parasitic wasps that are not in the “Parasitica.”
I could check the 332-page Bethylidae of America north of Mexico (H. E. Evans, 1978) out of my local library, but I don’t see myself having time to deal with that any time soon and I’d probably get it wrong anyway. So, if there is anyone out there who would be willing and able to identify this wasp to species, I’d be happy to send it. I’m also still seeking a braconid specialist interested in examining the dozens of braconids I’ve reared from assorted leaf mines and galls.