The image across the top of my blog is a leaf mine of Tischeria quercitella (Tischeriidae), a moth, in an oak leaf. The whitish area is the mine, and the brownish streaks are excrement* smeared on the underside of the leaf’s upper epidermis. The brightest white area is where the moth larva has constructed a circular “nest” (nidus) in which to overwinter. It is more clearly visible in this mine in a dry leaf:
This fall I collected several oak leaves containing these mines, hoping to get a chance to photograph the moths that emerge from these beautiful mines. Yesterday I spotted somebody in the bag of leaves, but it wasn’t a moth.
It was a tiny eulophid wasp, which had parasitized one of the moth larvae. This wasn’t terribly surprising, since most of the time when I try to raise leaf-mining, -rolling, or -tying moth larvae, I end up getting eulophid wasps. They come in a variety of forms and patterns but are often iridescent like this one. This one is noteworthy because, as far as I can tell, it’s the first documented parasitoid of Tischeria quercitella (although plenty have been documented from other Tischeria species).
Thanks to Ross Hill for identifying the wasp (and most of my other tiny parasitoid wasps) on BugGuide.Net.
* At least, that’s what I’ve always thought. Since writing this post, I’ve read that this species pushes its excrement out of the mine, as do many other tischeriids. In that case I have no idea what the streaks are.