Aulacidea hieracii
Canada hawkweed stem gall wasp

Host: Canada hawkweed (Hieracium umbellatum).

Gall location: On the stem, often near the apex but sometimes developing further down.

Description: Rounded, fleshy, medium-sized galls, usually 1-3 centimeters in length. Sometimes with abundant soft, pale hairs, but sometimes entirely without hairs. Green when fresh to brown when old and dry.

Range: In North America, this species may be found in several North Central US states including Minnesota and Wisconsin as well as adjacent parts of Canada including Manitoba and Ontario.

This species has apparently been introduced, but its only known host plant in North America, Canada hawkweed, is indeed native to both Europe and North America. As a result, it is unclear whether this species was truly introduced or is native in its current range. Complicating this question further is the unclear taxonomy of this species; it is possibly a complex of multiple closely-related species that each prefer a different species of hawkweed. In Europe, where this species is native, it induces galls on several hawkweed species. Overall, further research is necessary to substantiate the identity of the North American population.

Similarly, the subterminal hawkweed gall wasp (Aulacidea subterminalis) may also have been introduced to North America. Its galls apparently occur on the stolons rather than on the main stem. However, like the Canada hawkweed stem gall wasp, its status in North America is unclear.

Gall (Plate 8.3-4). In stems, multilocular, differently shaped, large-sized, hard and fuzzy galls; the stem is malformed. The gall growing on the stem or at the base of the leaf rosette, 40 mm long, 10-15 mm in diameter, usually spindle-like, sometimes rounded. During the development, leaves are coming out from it. The surface of the gall is covered with hairs. The gall loosing its hairs after overwintering and only the bases of hairs are visible on a glabrous epidermis. The parenchyma of the gall soft, spongy-like, with rounded larval cells. The number of larval cells decreasing towards the center of the gall. The gall is green when young and growing, turns brown when mature. The shoot above the gall malformed, abnormally short. Sometimes galls develop on the leaves which are lying on the ground. [This latter point almost certainly refers to a distinct species - LFN, 3 March 2026]
Biology. Monovoltine. Galls mature in autumn, larvae overwintering in the gall, adults emerge next spring, in May (Zerova, Diakontschuk & Ermolenko, 1988). Host plants: Hieracium vulgatum, H. umbellatum L., H. murorum L. and H. virosum Pall. Diakontschuk (2001) mentioned this species from the Primorskij Kraj, Far East of Russia, from galls on Saussurea spp., however, this is incorrect data and concern a recently described species, Aulacidea tobiasi Melika, 2004 (Melika, 2004). Kierych (1979) also mentioned Linaria vulgatum Fries. as a host plant in Poland, but it must be confirmed.

Aulacidea hieracii (Linnaeus, 1758)

Synonyms. Aulax graminis Cameron, 1875, Aulax artemisiae Thomson, 1877, Aulax foveigera Thomson, 1877, Aulax crassinervis Thomson, 1877, Aylax sabaudi Hartig, 1840, Aulacidea cacaliae Belizin, 1959.

Gall. In stems, multilocular, differently shaped, large, hard and fuzzy galls; the stem is malformed. The gall develops on the stem or at the base of the leaf rosette, 40 mm long, 10-15 mm in diameter, usually spindle-like, sometimes rounded. During the development, leaves are coming out from it. The surface of the gall is covered with hairs. The gall loosing its hairs after overwintering and the bases of hairs are visible only on a glabrous epidermis. The parenchyma of the gall soft, spongy, with rounded larval cells. The number of larval cells is decreasing towards the center of the gall. The gall is green when young and growing, turns brown when mature. The shoot above the gall is malformed, abnormally short. Sometimes galls develop on the leaves which are lying on the ground.

Host plant. Hieracium murorum L., H. umbellatum L., H. verruculatum Link, H. virosum Pall., H. vulgatum L. (Asteraceae). Biology. Galls mature in autumn, larvae overwinter in the gall, adults emerge next spring, in May (Zerova et al. 1988).

Distribution. Iran, Lorestan (Ghelaei or Gharaei) and Azerbaijan-e Gharbi provinces (vicinity of Kelïsä Kandï village, 37º29′N, 45º01′E, 1600 m a.s.l., 2.5 km SW Urmia) -- a new record for Iran. Europe (Melika 2006), Far East of Russia (Kovalev 1965), Transcaucasus (Zerova et al. 1988).