Caryomyia thompsoni (Felt)

Hormomyia thompsoni Felt 1908: 388; Felt 1918d: 47 (Caryomyia).
Caryomyia consobrina Felt 1909: 292. New synonym.
Caryomyia similis Felt 1909: 292. New synonym.

Hosts: Carya ovata, laciniosa, floridana, texana, pallida, glabra, tomentosa

Gall (Figs. 23, 112-115): One of the commonest Caryomyia galls, on Eucarya hickories; usually in clusters, on lower leaf surface between veins; 1.5-2.6 mm in height, depressed-spheroidal, often distended to one side, with deep dimple at center top; hair whitish gray, either sparse and not obscuring green to brown shiny surface or dense and obscuring gall surface; base of gall at center with deep, central, circular, shallow depression, the leaf without exfoliation surrounding connection; wall of uniform thickness, firm, woody, the larval chamber invaded from both apex and base by vertical cylindrical intrusions, the apical intrusion bearing crinkly hairs, both intrusions nearly abutting one another at center of larval chamber. Galls of this species vary considerably in hairiness, ranging from sparsely haired (Fig. 113) to so hairy as to obscure the gall surface (Fig. 115). Sparsely and densely haired examples are commonly found intermixed and closely adjacent on a leaf (Fig. 112). The gall is unique for the vertical column through the center of the larval chamber made of the combined apical and basal intrusions of the gall wall. The only other Caryomyia gall with any intrusion is that of C. holotricha, but the intrusion in the latter is only of hair growing inward from the apex of the gall.

Affinities. — In adult, pupal, and larval characters this species is similar to C. holotricha. The two species are the only congeners with an apical intrusion of hairs into the larval chamber. The galls are otherwise distinct in that those of the present species have an additional intrusion into the base of the larval chamber and the apex of the gall is dimpled, not conical.

Biological notes. — In central Maryland, very tiny to full-size galls were found on the same leaflet as early as May 23. Young galls were greenish white turning light yellow with bright white hair. The larvae were all first instars. By June 9, galls appeared full-size and brittle but the larvae were still all first instars. In mid-June through mid-July galls were mostly hard, brittle, and brown to black and contained second instars, but during this time soft galls could still be found with first instars. By the beginning of August galls contained second or third instars and by mid- August more than half the larvae were third in- stars. Adults emerged in late March and early April from galls collected in New York, New Hampshire, Maryland, and Texas.

Range: AL, AR, CT, FL, GA, IL, KY, LA, ME, MD, MA, MS, MO, NH, NJ, NY, NC, OH, OK, Ontario, PA, SC, TN, VA, DC, WV

- Raymond J. Gagne: (2008) The Gall Midges (Diptera: Cecidomyiidae) of Hickories (Juglandaceae: Carya)^©

Reference: https://www.biodiversitylibrary.org/page/38636615#page/81/mode/1up