In my last post I wrote about a little wasp in Mexico that apparently spins silk over stink bug eggs after it inserts its own eggs inside them. Several people had told me confidently that it was a pteromalid, so I went with that. However, shortly after I published my post, Henry Hespenheide wrote:
I think the parasitoid is a eurytomid. Note the very large pronotum which is characteristic of the family. And a number of the genera have the wings infuscated like the ones you show. One of the subfamilies, Rileyinae, are egg parasitoids.
To be honest, I had thought it looked like a eurytomid too, but “it kinda looks like a eurytomid” is about as sophisticated as I get in identifying micro-wasps before appealing to someone else for help. What I was seeing, besides the general shape, was that it was rough-textured and black, just like most of the eurytomids I’ve reared from galls. For instance the one below, which came from a goldenrod rosette gall made by a fruit fly (Tephritidae: Procecidochares):
That one had been having trouble getting the antenna portion of its pupal skin off, but had just succeeded in removing the right “sleeve” when I took that photo.
Anyway, I guess the fact that I had only ever encountered eurytomids as gall parasitoids had kept me from considering that this stink bug egg wasp might be one. But as pointed out here, eurytomids have a wide variety of habits, and many even have vegetarian larvae that develop in seeds or stems. In fact, here is one I found in my yard this spring, a member of the genus Tetramesa, whose larvae are known as “jointworms” and cause galls in grass stems.
I only just learned that a few weeks ago, but my brain is so full of leafminers right now that everything else gets pushed out. Speaking of which, some eurytomids in the Neotropical genus Aximopsis are parasitoids of leaf-mining beetles (Buprestidae).
Anyway, I followed Henry’s advice and showed my last post to Mike Gates, the eurytomid specialist at the Smithsonian National Museum of Natural History. Mike confirmed that the wasp in Cheryl’s photos and videos is a eurytomid in the genus Neorileya, and said he would be interested in seeing specimens. He has never heard of Neorileya producing silk, and is interested in more concrete proof that this wasp was actually responsible for the silk, since we can’t actually see the wasp laying down silk in the videos, nor was Cheryl able to see silk coming out of the tiny wasp.
To me, the fact that Cheryl photographed the wasp on the egg mass over a period of several days, during which the silk covering gradually increased, is pretty convincing. There’s also this: right after I published my last post, Kelly, who had sent the photo of the original silk-covered egg cluster from Brazil, wrote to tell me that she had found another silk-covered stink bug egg cluster with a similar wasp on it:
Unfortunately the wasp flew away after she took several pictures, but she collected the egg mass and will save anything that emerges from it. Stay tuned…
Edit: Kelly just found another photo of a similar wasp taken in Brazil, here. As with Kelly’s photo above, the silk is in bands that stitch the eggs together, rather than covering them in a web as in Cheryl’s example from Mexico.
The photographer, Bruno Garcia, gave me permission to use his photo here, but if you want to see a larger version you can click the above link.