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Aphididae : Eriosomatinae : Eriosomatini : Colopha
 

 

Genus Colopha

Cockscomb gall aphids, elm-sedge aphids

On this page: Colopha compressa graminis

Colopha [Eriosomatini]

Colopha is a small aphid genus, related to the genus Kaltenbachiella. Apterae on the secondary host differ from Kaltenbachiella apterae in having the fore-tarsi parallel-sided, with a ventral hair arising from a distal protrusion. Alatae have a once-branched media in the fore wing and one oblique vein in the hind wing.

There are 6 Colopha species worldwide, all in the northern hemisphere. Three of these have a sexual stage, and host alternate from elm, where they live in cockscomb-like galls, to grasses or sedges, where they live on the roots or aerial parts. Three species have lost their primary host and their sexual stages and live parthenogenetically year-round on grasses and sedges.

 

Colopha compressa (Elm cockscomb gall aphid) Europe, West Asia

The fundatrices of Colopha compressa induce laterally compressed cockscomb-shaped galls along the midrib on the upper surface of elm leaves (see first picture below). These galls are yellowish, often tinged with red. Fundatrices (not shown) are yellow or yellowish green and are lightly covered with waxy powder. Their antennae are about 0.12 times as long as the body. The body is oval or elongate, with wax plates on each of the thoracic and abdominal segments, and small siphuncular pores - which may be present or absent. The yellowish offspring of the fundatrices (see second picture below) develop to green alatae which leave the gall. These produce dark yellow apterae on the secondary host which have a body length of 0.9-1.5 mm, and secrete flocculent wax.

Both images copyright Maria Fremlin, all rights reserved.

Alatae emerge from their galls on elm (Ulmus) in July, from an opening on the underside of the leaf, and colonise the roots of sedges (Carex) and cottongrass (Eriophorum). Alate sexuparae return to elm in September-October, although some populations may persist on the roots of sedges throughout the winter months. Colopha compressa is found throughout Europe, east to Turkey, Ukraine and Kazakhstan, and has been introduced to Siberia.

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Colopha graminis (Elm-cutgrass cockscomb gall aphid) North America

The primary host of Colopha graminis is elm (Ulmus), where they induce cockscomb-like galls on the upper leaf-surface on the leaf lamina between the veins indistinguishable from Colopha ulmicola (first picture below). These galls are about 2.5 cm long, 0.6 cm high, and are wrinkled irregularly like a rooster's comb. Galls are reddish-green at first, but turn brown as they mature. Winged aphids emerge from the galls in June/July and migrate to grasses (Deschampsia, Leersia) where they form colonies both above and below ground.

The aptera of Colopha graminis on grass (see second picture below) is orange-brown and is covered in grey woolly wax. Their eyes are 3-faceted and both antennae and legs are greatly reduced, their antennae being less than 0.1 times the body length. The apical rostral segment (RIV+V) is 1.0-1.35 times the length of the second hind tarsal segment (HTII) (cf. the European Colopha compressa, which has RIV+V 1.8-2.8 times as long as HTII). Wax glands are present on all segments, each comprising a ring of cells surrounding 1-2 smaller central cells. Siphunculi are absent. The body length of Colopha graminis apterae is 1.2-1.8 mm.

First image above copyright Howard Ensign Evans under a under a Creative Commons Attribution 3.0 Licence
Second and third images above copyright Claude Pilon, all rights reserved.

Alate Colopha graminis (see third picture above) are orange-brown and have the media vein of the forewing once-branched (cf. Colopha ulmicola which have the media of the forewing unbranched). The body length of alatae is 1.0-1.6 mm.

Colopha graminis gall the leaves of elm, especially American elm (Ulmus americana), in spring. In summer they host alternate to the above & below ground parts of certain grasses, in particular cut-grasses (Leersia) and hair-grasses (Deschampsia). In autumn sexuparae develop to adults on the leaves of the secondary host, before returning to elm in October. After mating the female deposits a single egg under the rough bark of the elm tree. Patch (1910) provides a good summary of the morphology and biology of the elm-cutgrass cockscomb aphid under the name Tetraneura graminis, while Hottes & Frison (1952) discuss its generic/subgeneric rank. Colopha graminis is widely distributed in North America.

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Acknowledgements

We especially thank Maria Fremlin and Claude Pilon for the images of Colopha compressa and Colopha graminis shown above.

Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors 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).

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References

  • Blackman, R.L. & Eastop, V.F. (2006). Aphids on the world's herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.