I’m working on a little paper summarizing observations I’ve made of leaf-mining chrysomelid beetles, and this has caused me to spend some time scanning through a few years’ worth of photos. One of the species involved is Odontota scapularis, which specializes in groundnut (Fabaceae: Apios americana). On June 15, 2011, I found lots of adults of this species congregating on the groundnut outside my house.
It’s always amusing to see a three-beetle stack, but I was looking for photos of their eggs, to see if I could come up with an approximate number of eggs per cluster. The female coats the eggs in soupy excrement, which had hardened by the time I photographed them five days later:
When I got to this photo, I noticed something I hadn’t seen at the time I took it. Those aren’t beetle larvae developing in those eggs…
…but little parasitoid wasps. I remembered having seen a eulophid wasp hanging around the egg mass, which at the time I assumed was getting ready to parasitize the eggs.
Taking a closer look at the first shot of the egg mass, it seems likely that this wasp had just emerged–note that there’s a missing pupa or two at the right side of the photo. I didn’t get any good photos of the wasp, but they’re clear enough to identify it as a Closterocerus species (Eulophidae). Apparently no one has ever reared a Closterocerus from an Odontota species, but two Closterocerus species have been reared from the eggs of Baliosus nervosus, a related leaf-mining beetle known as the “basswood leafminer” (so far I’ve never found it on basswood, but have found the larvae mining leaves of at least three other, unrelated trees). Presumably these eggs had been laid more than five days before, if the wasps were already starting to emerge.