Witch-hazel cone gall aphids (the Hormaphis hamamelidis sp. gp.) induce conical galls on witch hazel (Hamamelis virginiana). Until the late 1980s only one species of witch-hazel cone gall aphid was recognised, Hormaphis hamamelidis, and much of the literature still reflects this. However, von Dohlen & Gill (1989) showed that there are two species of aphids involved - Hormaphis hamamelidis which is monoeciousholocyclic on Hamamelis virginiana and Hormaphis cornu which host alternates between witch hazel and birch. We cover both species on this page, but since the pictures on this page were mostly taken south of the 41st parallel north (see distribution below), they most probably only represent Hormaphis cornu.
Only the alate morph (see pictures below) can be reliably identified to species. Alatae of both Hormaphis hamamelidis and Hormaphis cornu have only three antennal segments, no siphunculi and opaque wings with one oblique vein in the hind wing (cf. Hormaphis betulae on birch, which has five antennal segments and 2 oblique veins on the hindwing).
The alate (sexupara) of Hormaphis hamamelidis has 19-27 rather spaced-out annular secondary rhinaria on antennal segment III. The forewing is 1.5-2.0 mm long. The length of the hind tibia of is 0.29-0.36 mm.
The emigrant alate of Hormaphis cornu has 26-40 rather close-set annular secondary rhinaria on antennal segment III, a forewing length of 1.9-2.2 mm, and a hind tibia 0.35-0.44 mm long.
Apterous fundatrices of Hormaphis hamamelidis induce conical galls on Hamamelis virginiana with little or no basal constriction. The fundatrices are dark purple with white wax on the abdomen and a body length of 0.9-1.3 mm. There is an abbreviated life cycle on witch hazel with no host alternation - the aphids remain on witch hazel all year. Alatae that leave the galls from late July to September are sexuparae, with a body length of 1.1-1.7 mm. They give rise to the sexual morphs (oviparae and males) on the leaf undersides, where the oviparae deposit overwintering eggs.
Apterous fundatrices of Hormaphis cornu induce conical galls on Hamamelis virginiana with basal constriction. The galls are slightly larger than those of Hormaphis hamamelidis. The fundatrices in the galls are dark purplish brown with a body length of 1.3-2.0 mm. The alatae (body length 1.3-1.9 mm) that leave the galls in June are emigrant alatae. They migrate to river birch (Betula nigra), where they produce very small aleyrodiform apterae (see picture below) which are dark brown to black with a fringe of radiating wax filaments and feed on the leaf undersides. Sexuparae return to witch hazel in autumn.
Image above copyright J.R. Baker, NC State University.
There is also a record from paper birch (Betula papyrifera) by von Dohlen & Stoetzel (1991). After three generations on birch leaves sexuparae are produced, which fly back to Hamamelis in September-October.
Hormaphis hamamelidis occurs in north-eastern North America mostly at high elevations and latitudes north of 41°N. Hormaphis cornu is found in eastern North America, mostly at low elevations and latitudes south of 41°N.
Other aphids on the same host
Hormaphis hamamelidis and Hormaphis cornu occur on one Hamamelis species (Hamamelis virginiana).
Control on witch-hazel is possible by application of orthene (acetaphate) at bud break, although it is probably better to leave it to the natural enemies since the damage is minimal. On birch sooty moulds may develop as a result of heavy deposits of honeydew. Insectidal soap or horticultural oils should give adequate control.
We have used the species accounts of von Dohlen & Gill (1989) and von Dohlen & Stoetzel (1991), together with information from Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).
von Dohlen, C. D. & Gill, D.E. (1989). Geographic variation and evolution in the life cycle of the witch-hazel leaf gall aphid, Hormaphis hamamelidis. Oecologia78, 165-175. Full text
von Dohlen, C.D. & Stoetzel, M.B. (1991). Separation and redescription of Hormaphis hamamelidis
(Fitch 1851) and Hormaphis cornu (Shimer 1867) (Homoptera: Aphididae) on witch-hazel in the eastern United States. Proc. Entomol. Soc. Wash.93(3), 533-548. Full text