Hormaphis cornu (Shimer, 1867)

Hamamelistes cornu Shimer, 1867.
Hormaphis hamamelidis Osten-Sacken, 1861 [secondary homonym of Hamamelidis Fitch 1851].
Hormaphis hamamelidis (Fitch): Walsh, 1867; Pergande, 1901; von Dohlen and Gill, 1989 [misidentifications].
Hormaphis hamamelidis Osten-Sacken: Thomas, 1877 [misidentification].
Pemphigus hamamelidis (Fitch): Thomas, 1877 [misidentification].

Gall: Conical but usually constricted at the base, tapered tip often bent to one side, protruding from upper leaf surface and usually on a major leaf vein; length from tip to base on leaf underside 8.2-19.4 mm (mean - 13.5) and 4.0-8.1 mm (mean = 5.6) at greatest width. Underside of gall on lower leaf surface circular and somewhat swollen beyond leaf; the opening at first obstructed by plant hairs, later forms a small circular exit hole. Color pale green, turning yellow in early summer.

Biology: Fundatrices hatch in late March from overwintering eggs laid on the bark of witch-hazel, form cone-shaped galls on leaves and produce virginoparous emigrants into mid-June. Alate virginoparae depart from galls in June and migrate to river birch to produce the first aleurodiform generation on the undersides of leaves. Two more aleurodiform generations follow; the last produces sexuparous nymphs. Mature sexuparae depart from leaves of river birch and fly back to witch-hazel in mid-September to early October and deposit sexual nymphs. Sexuales mature in late September to late October and mate. Ovipara produces several overwintering eggs which are laid in crevices in the bark or occasionally at the base of leaf buds. See von Dohlen and Gill (1989) for additional information.

Summary: Hormaphis hamamelidis forms small, conical galls usually without basal constriction, is autoecious on witch-hazel, and lives at high elevations in northern regions of the eastern United States. Hormaphis cornu forms larger, conical galls that are usually constricted at the base, is host-alternating between witch-hazel and river birch, and is found at low elevations in the mid-Atlantic and southern regions of the eastern United States.

Range: VA, DC

- Carol von Dohlen, Manya Stoetzel: (1991) Separation and redescription of Hormaphis hamamelidis (Fitch 1851) and Hormaphis cornu (Shimer 1867) (Homoptera: Aphididae) on witch-hazel in the eastern United States^©

Reference: https://www.biodiversitylibrary.org/item/54815#page/559/mode/1up