Andricus opertus
Bisexual generation

Andricus fimbrialis Weld, new synonymy

[Photos of this gall appear on page 4 of the pdf]

Galls: Galls appear as reddish swellings on the midrib of the leaf, mostly on the upper surface when the leaf is about three-quarters grown. Soft fimbriate dark red spines soon develop, usually growing diagonally away from the leaf base. Galls vary from single ovate cells, about 2 mm long, with little swelling or spinulation, to several cells over most of the leaf length, with individual gall length up to 15 mm; on young terminal growth, the whole stunted leaf may be utilized. Galls are most common on small slow-growing trees, but also occur on larger more robust trees. Often many galls are restricted to a few trees which are apparently the same as other, uninfested trees in the same area. Adults emerge amid the spines of the gall, leaving a fuzzy pale-brown mass of chewed fiber at the exit holes. Leaves with dead galls usually fall with the other leaves.

Range: from southern Oregon to central California

Adults of the bisexual generation emerge during late May through July. Oviposition occurs within 5 days in the small lateral buds on new growth. Galls and immature adults are fully formed by mid-September

- David Evans: (1972) Alternate generations of gall cynipids (Hymenoptera: Cynipidae) on Garry oak^©

Reference: https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/alternate-generations-of-gall-cynipids-hymenoptera-cynipidae-on-garry-oak/2C1A55FDA766653C05B65896CC288EC0