Now that I’ve put most of my bugs in the fridge for the winter, I can get back to catching up on sorting through my backlog of photos, which goes back to September of last year. I just reached the conclusion of a little story that started with this leaf mine on an oxeye (Asteraceae: Heliopsis helianthoides) growing along my driveway:
I see these mines in my yard regularly, but they are always empty so I have been unable to rear the larvae out to determine what species they are. On September 1 last year, I finally found this one mine with a larva inside. I spotted it just in time: the moment I picked it, the larva began to exit through a slit it had cut in the lower epidermis:
It jumped a few millimeters once it was all the way out, which would have propelled it to the ground if I hadn’t been holding the leaf upside-down. Within a few hours, its skin had hardened and contracted to form a puparium:
But alas, 24 days later, what emerged was not an adult fly but a figitid wasp, which had been living as a larva inside the fly larva all along:
Matt Buffington tells me (based on looking at the above photo) that the wasp is a Gronotoma species. This genus is in need of revision, and when I met him last December he told me that he probably won’t get around to that until after he retires.
There’s a good chance that the fly was Liriomyza arctii, the only species that has been reared from mines like this on Heliopsis (by yours truly, in Wisconsin). The species was named by Kenneth Spencer in 1969, who reared it from Arctium (burdock) in Canada. The fact that this apparently native fly was only known to feed on a nonnative plant was puzzling, until I reared it from Heliopsis and three other native genera of Asteraceae over the past few years. I’ve also repeated the rearing from burdock in my own yard, which is why I’m reasonably sure L. arctii is what is mining the oxeye and wingstem in my yard (probably also the Jerusalem artichokes and other sunflowers, but Helianthus is not yet a confirmed host for this fly). Here’s one I reared from nodding beggarticks (Bidens cernua), also not far from my house: