Hormaphis is a small genus of rather atypical aphids which induce conical galls on their primary host (see first picture below), but live as inconspicuous aleurodiform (=whitefly-shaped) morphs on the secondary host. The antennal tubercles are undeveloped, and the front of the head is convex. Compound eyes are present in alatae, but absent in apterae; triommatidia are present in both apterae and alatae. The antennae are 3-segmented in the alata and fundatrix of the nearctic species, but 5-segmented in those morphs in the palaearctic species; they are reduced to small inconspicuous papillae with 1 or 2 segments in the aleurodiform stage. The terminal process is short in the fundatrix, and absent in the alate and aleurodiform stages. Primary rhinaria are absent in the fundatrix and aleurodiform stages, but there are numerous annular secondary rhinaria present on segment III of alatae. The fore wings of the alate have reduced venation, with an unbranched media vein and the branches of the cubitus arising from a short common stem. Siphunculi are absent, and the cauda is knobbed. The anal plate is bilobate.
The genus Hormaphis has 3 species, 2 nearctic and 1 palaearctic. They either host alternate from witch hazel (Hamamelis) to birch (Betula) or they are monoecious on witch hazel.
Hormaphis hamamelidis & Hormaphis cornu (witch hazel cone gall aphids)
Witch-hazel cone gall aphids 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, we now know that there are two species of aphids involved - Hormaphis hamamelidis which is monoeciousholocyclic on witch hazel, and Hormaphis cornu which host alternates between witch hazel and birch.
First image above copyright Katja Schulz, second image above copyright Beatriz Moisset
both under a Creative Commons Attribution License.
Third image above by permission copyright J.R. Baker, NC State University, all rights reserved.
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. 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 is 0.29-0.36 mm.They give rise to the sexual morphs (oviparae and males) on the leaf undersides, where the oviparae deposit overwintering eggs. Hormaphis hamamelidis occurs in north-eastern North America mostly at high elevations and latitudes north of 41°N.
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. The emigrant alate (see second picture above) 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 length of 0.35-0.44 mm. They migrate to river birch (Betula nigra), where they produce very small aleurodiform apterae (see third picture above) 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. After three generations on birch leaves sexuparae are produced, which fly back to Hamamelis in September-October. Hormaphis cornu is found in eastern North America, mostly at low elevations and latitudes south of 41°N.
We have used the genera descriptions of Foottit & Richards (1993), 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).
Foottit, R.G. & Richards, W.R. (1993). The Insects and Arachnids of Canada. Part 22. The Genera of the Aphids of Canada (Homoptera: Aphidoidea and Phylloxeroidea). Research Branch, Agriculture Canada. Publication 1885. 766 pp. Full text