A Peculiar Patch of Pussytoes

This week (on account of tomorrow is the deadline) I got around to writing up the results of the two-day survey of leaf-mining moths that Julia and I conducted at Black Rock Forest at the end of August. I showed the list to Jason Dombroskie, who is compiling a list of the Lepidoptera of New York, and he informed me that 17 of the species we found have never been documented in New York before—not counting the four that don’t have names yet. And since he is keeping track of which species have been found in each of New York’s seven ecoregions, he was able to determine that another 27 species we found are new for the Lower New England / Northern Piedmont ecoregion. Not bad for a two-day survey!

Near the end of the second day—shortly after finding the previously unknown immature stages of a Bucculatrix species (more on that later, maybe)—we walked past a patch of pussytoes (Asteraceae: Antennaria ?neglecta) and I did a double-take: “That’s not what pussytoes normally looks like, is it?”

Nearly every rosette bore a dense cluster of leaves, extra densely covered with woolly white hairs.

These reminded me of some midge galls that occur on willows and goldenrods, but I’d never heard of such a thing on pussytoes. I opened one up and sure enough, it had a central cell with something inside…

…and since I recognized the “something” inside as the pupa of a parasitoid wasp, we filled several vials with galls, with the hope that at least one would contain a midge that wasn’t parasitized.

Over the next two weeks, nine eurytomid wasps emerged…

…along with that single midge I had hoped for:

In these last two shots, she’s showing off her incredible ovipositor, no doubt specially designed for piercing pussytoes plants.

Naturally, I sent her off to Ray Gagné at the Smithsonian. He had never found these galls before either, in over fifty years of studying gall midges, but he reported that the specimen matches the description of Asphondylia antennariae, which was described in 1889 from specimens reared from similar galls on plantain-leaved pussytoes (Antennaria plantaginifolia) collected in Milwaukee. In the key to Antennaria galls in Ray’s 1989 The Plant-feeding Gall Midges of North America, the galls of this species are distinguished from the similar galls of Rhopalomyia antennariae by the latter’s having recurved tips on some of the leaves that form the gall. Asphondylia antennariae galls are not supposed to have leaves that are recurved at the tips, but this turns out not to be a consistent difference, based on the galls I found.

The descriptions in Ray’s species accounts provide a more reliable distinction: the Rhopalomyia galls are polythalamous (multi-celled), whereas the Asphondylia galls are monothalamous, each containing a single larva in a central cell—as I found when I tore open the first gall.