Caryomyia cilidolium Gagne, new species

Hosts: Carya cordiformis

Gall (Figs. 51-52). — Occasional, known only from C. cordiformis of the Apocarya section; found singly, usually on lower leaf surface, rarely on upper, usually between but occasionally on veins; 3.1-3.9 mm in height, spheroidal, slightly longer than wide, base broadly rounded to truncate in profile, apex with small central nipple surrounded by extensive areola that with pressure can separate from gall; surface not sticky, occasionally slightly bumpy, tan to brown, with few to many short, fine, white hairs not obscuring surface, areola usually paler than surrounding surface; base with deep, wide, circular indentation; wall firm, brittle, almost uniformly thin, larval chamber glabrous, with longitudinal ridges. For notes on galls of related species, see below under affinities.

Affinities. — Caryomyia cilidolium, C. hirtidolium, C. tuberidolium, and C. viscidolium form similarly shaped, spheroidal, thin walled galls (Figs. 43-52). At their apex is a large, circular areola surrounding a small central nipple. With a little pressure the circular apex can be broken off as a unit from the rest of the gall and forms the exit from which pupae emerge in spring. Galls of C. cilidolium occur only on bitternut of the Apocarya section of Carya, usually on the lower surface, and are covered with sparse, fine, short hairs. The other three species of this group occur on the Eucarya section. Galls of C. hirtidolium are hairy, much more so than those of C. cilidolium, so that the long hair obscures the gall surface. Galls of C. tuberidolium and C. viscidolium are both sticky, the former very much so and also bumpy and more spherical, the latter merely slightly resinous and smooth. A major difference between these two last species is that C. tuberidolium occurs on the underside of the leaf (except for one example known to me) while C. viscidolium occurs on the upperside. This difference indicates a different egg-laying strategy by the female. The pupal stages are known for all except C. hirtidolium, both sexes for C. cilidolium and C. viscidolium, and the female for C. tuberidolium.

Biological notes. — In mid-June in the eastern panhandle of West Virginia fresh galls were green and brittle and with either second or third instars. In London, Arkansas, galls collected on Sept. 14 still contained second instars.

Range: AR, CT, MD, MO, NJ, NY, PA, TN, VT, WV