Andricus williami Melika, Nicholls & Stone, sp. nov.

Gall. (Figs. 273–274). An acorn gall, developing as a swelling external to the cotyledons around the base of the acorn inside the acorn cup (see also Weld 1960, Fig. 18). The larval cell intrudes into the body of the acorn; adults emerge through holes they create along the rim of the acorn cup. The gall is unilocular and consists only of the larval chamber ca 3 mm long and 1.5–2 mm in diameter, surrounded by a hard woody wall. Several galls may develop around the same acorn.

Biology. Only a sexual generation is known, which induces acorn galls on Q. arizonica. Weld (1960) also records this gall type from Q. gambelii, Q. rugosa and Q. turbinella. Galls mature in April, adults emerge soon afterwards.

Distribution. USA, Arizona, Chiricahua Mountains.

Comments. All known Callirhytis and Andricus species that induce acorn galls, whether pip galls (external to the acorn cup) or stone galls (within the acorn cup and/or also inside the cotyledons of the acorn), have their asexual generations making such galls. The only exception, other than A. williami, is the sexual generation of Andricus chrysobalani Weld, 1926 which develops on Q. chrysolepis and is known only from California.

- George Melika, James Nicholls, Warren Abrahamson, Eileen Buss, Graham Stone: (2021) New species of Nearctic oak gall wasps (Hymenoptera: Cynipidae, Cynipini)^©