Stem miner (Diptera: Agromyzidae) in Aquilegia

In the first example of this miner examined in the current study, I located the stem mine but it was not immediately clear if the insect itself was still present. The mine, observed in late August 2021, was very subtle and difficult to discern except for small but conspicuous black lumps or short strips of frass scattered along its length. The lumps were rather amorphous in shape and the short strips alternated between the parallel sides of the mine. By following these agglomerations of frass I was able to track the mine from its apparent starting point near the top of a peduncle down to the base of the main stem. In addition to the scattered lumps and short strips of frass, parts of the mine also showed subtle reddish-brown discoloration, sometimes including a pattern of repeating semicircular marks left by the larva's mouthparts as it fed.

Closer examination of the plant material revealed a puparium appressed to the stem, wedged between the petiole of a basal leaf and the very base of the stem. The puparium was formed externally, less than a millimeter away from an exit slit in the stem epidermis. It was a light reddish-brownish color, somewhat dorsoventrally flattened, with anterior and posterior spiracles both held on short stalks; the anterior spiracles were black.

In a similar stem mine found in early August the following year, I managed to locate the oviposition site in the peduncle. It consisted of (1) a round hole in the epidermis partly surrounded by a raised collar of tissue, (2) a small area immediately adjacent to the hole that showed no discoloration relative to the surrounding stem tissue but was evidently the location where the egg had been placed under the epidermis, and (3) the beginning of the stem mine, a pale, whitish track leading away from the egg location. Further down the peduncle from the egg-laying site, the mine assumed a more subtle yellowish color with traces of reddish-brown discoloration; it also contained alternating lumps of black frass.

Additionally, in mid-September 2022 I located a puparium near the base of a main stem of the host. It was black in color and formed underneath the stem epidermis, and its posterior spiracles resembled those of the first example.

The overall body shape and the general spiracle morphology of the 2021 and 2022 puparia resembled those of Ophiomyia spp. I observed on other host plants, but I did not rear adults. The peduncle mining I found appears somewhat similar to that found by E. LoPresti on Aquilegia eximia in California, as reported in Eiseman (2022).