Drat about specimen quality, but good that it might be something interesting. I'll look again next year. Meanwhile, anything I can do here (besides increasing numbers) to enhance the probability of quality specimens? At least for me, the flies are hard...

I think these hadn't emerged yet when you sent the package, so it wasn't anything you did. The problem was that one was teneral and not fully emerged from its puparium, and the other was a somewhat moldy female. Both were long dead when I photographed them on July 26. That was the month I went to Colorado; I don't remember you sending me a package before I got home, but I was probably overwhelmed with everything I'd collected and just didn't get to them in time.

This will likely turn out to be an Agromyza. The only described Asteraceae-feeding species in that genus is A. ambrosivora, but there are at least two undescribed ones, and A. virginiensis (known only from Virginia) is suspected of being an Asteraceae feeder too.

It's uncanny how much the mine looks like Nemorimyza posticata. I think I did rear that species from Vernonia this year, but Owen hasn't gotten to those specimens yet.

I sent you a female yesterday, but in the next shipment I'll send along the male. I saw a lot of these mines this year, but with one exception I found them too late.

I've reared Nemorimyza posticata from seemingly identical mines on Vernonia. Hopefully this is in fact the Agromyza (tip of the abdomen not white). Were you able to preserve the mine?

I think the mine might have already been sent to you. But the abdomen is whitish. I will email you a picture (not yet downloaded).