Another Mystery Host Plant

Last week Owen Lonsdale gave me a first batch of identifications from the big box of agromyzid fly specimens I sent him a few months ago. Unfortunately, of the ten species represented, he was only able to put species names on three (of these, it appears that one is a new host record, one a new state record, and one a new US record). Four were only identifiable to genus because the specimens were all females. The remaining three were new species.

Two of the three new ones are from New England, and their host plants are species I know well. The third emerged last spring from leaf mines I collected in Iowa the previous September. The host plant was growing in a small patch at the base of a bur oak in the middle of a huge lawn in a park. There were only basal leaves (no flowers or fruits to help identify it).

At the time I had the impression that it was a waterleaf (Hydrophyllum), but on looking at the photos later, I was pretty sure it wasn’t. This shot of the leaf mine gives a better view of the leaf margin and vestiture.

When I asked John Pearson, who had initially agreed with my thought that it was a waterleaf, to take another look, he suggested that it was a buttercup, and maybe early buttercup (Ranunculus fascicularis). That looks like a plausible match to me, but I’d like to be as sure as possible before I go reporting that as the host plant of this new species. So if anyone out there has other suggestions, or has experience with R. fascicularis and can confirm John’s suggestion, please let me know.

The fly itself, incidentally, looks like this:

Externally, it looks awfully similar to many other Phytomyza species. The identification is all about the male genitalia–which Owen says place it in the Phytomyza aquilegiae group. This group is associated with the buttercup family (Ranunculaceae), so John’s suggestion is certainly on the right track.

Not all of the new species that have been emerging from my collected leaf mines are so cryptic. I brought these moths to Dave Wagner a few months ago, and upon taking one quick look, he said he thought they represented a new genus. He saved one for DNA analysis and sent the rest off to Don Davis at the Smithsonian, to join the hundreds of other unnamed gracillariid species awaiting description.