The petiole gall-makers (subgenus Euura, in part) are the next most specialized. Six species of Salix in all groups are attacked in California, but exactly how many species of sawflies are involved is not known. All but one are smaller (females are 5 mm or under) than either the stem or bud-gallers. Petiole-galling Euura pupate in the soil as do the Euura {Gemmura). By far the most common species of this type is the exceptionally large (8 mm) one on S lasiandra (Fig. 7 B). It is widespread from sea level along the Pacific Coast to above 2000 m in the Sierra Nevada. The gall is up to 40x20 mm, and may be on petioles, midribs, or both. Infestations are massive, and a single tree may have most leaves with several galls. Up to 4 pale green larvae may inhabit a single gall, and parasites rarely destroy all of them. Late instar larvae may cut holes in the walls of the gall and clean house as do P. proxima. The purple-gray last stage larvae depart over a period of 2 or 3 weeks from each gall. The presence of the petiole gall apparently inhibits abcisin formation, since infested leaves may remain on the branches until blown off or decayed. Montane and littoral specimens of petiole galling Euura on S. lasiandra appear to be the same species, but series are difficult to obtain, abundance of galls notwithstanding. While other petiole gall-makers present the same rearing problems as do the Gemmura, and are usually even less common, the Euura on S. lasiandra seems to have some peculiar diapause-breaking requirement. One can rear hundreds to the prepupa and never get an adult.

[Euura sp., petiole and midrib galls on S lasiandra]

[Photos of many examples of this gall appear in Figure 30, page 15 of the pdf]

Euura sp. A
Petiole-gall sawfly
[Page 216]

Host: Salix lasiandra

The surface of the gall is generally glabrous but with distinct rounded cross ridges or furrows.