The photos on BugGuide seem to support the idea that the overwintering generation of the Vitaceae feeders at least usually have that spot, whereas the summer generation at least usually does not. Based on what I've seen here from Charley Eiseman, it seems like a rearing experiment would work wonders with them, since it seems unclear exactly how many species there are and which hosts they utilize, never mind how they might be told apart from adult morphology.

This summer, I found a number of completed vitegenella mines on Vitis down the road from my house, unfortunately with only one adult eclosing from the several pupae I collected. I also successfully reared ampelopsiella from a completed mine on Parthenocissus, which is common around the house, and found a vacated upper surface mine of an unknown species. (I based the identifications on appearance of the mines.) I would imagine most if not all of the adults I see at home are from the virginia creeper, but I almost certainly get adults from Vitis at at least one blacklighting location, and I have definitely never seen this black spot in the summer at my porch lights or elsewhere. All 5 individuals, three from my house and two from a blacklighting trip a couple miles away, I have seen during weekend visits to Block Island in the fall in the last two years have had this spot.

I took in just a few leaf mines and galls this year with limited success. Next year I'll have to go out looking for for a wide variety of leaf mines and hopefully get to associate the adult moths with the host.

I got a number of new species for the island list that way. I mostly focused on a handful of common plant species I can recognize, but I’d like to expand my efforts a bit next summer.