Acraspis quercushirta (Bassett, 1864), sexual generation

[Many synonyms given but all are taken to apply to the agamic generation; see table on that page]

Gall (Fig. 13). Sexual galls develop in the innermost scales in apical and lateral buds, a brittle, thin-walled, seed-like, sub-ovoid cell approximately 2 mm long, tan or orange-brown when mature, with faint longitudinal striations and sparse, pale hairs. Galls form in the basal portion of the scale and often leave the scale apex intact, which extends as a flat flap beyond the gall.

Biology. Galls of the sexual generation usually occur singly, but up to six galls were found around a single bud. Galls and inhabitants survived freezing in late April 2005 in Edmonton that destroyed new shoots on many bur oaks. Emergence typically occurs through holes chewed near gall apices. Empty galls can persist around bases of new shoots for weeks or months, but are easily detached as bud scales slough off during shoot maturation. Adults of the sexual generation emerged in Edmonton from late May to early June.

Distribution. USA: Connecticut south to Virginia, Illinois, Michigan, Texas, Utah (Burks 1979), Colorado, New Mexico, Oklahoma (Kinsey 1930). Canada: Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick. Probably everywhere east of the Rocky Mountains in the USA and Canada where white oaks occur (Kinsey 1930) or have been introduced as urban trees (e.g., bur oak in Alberta).