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Colopha graminis

Elm-cutgrass cockscomb aphid (Elm cockscomb gall aphid)

On this page: Identification & Distribution Biology & Ecology Natural enemies Other aphids on the same host

Identification & Distribution

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.

Note: Several species are known as "Elm cockscomb gall aphid": Colopha compressa (Europe), Colopha graminis & Colopha ulmicola (US).

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

Alate Colopha graminis (see pictures below) 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.

Both images above by permission, copyright Claude Pilon, all rights reserved.

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.

 

Biology & Ecology

Natural enemies

The Colopha graminis in Canada shown in the pictures above were heavily parasitized by an Aphelinid parasitoid. The picture below shows their characteristic black mummies - all these mummies have emergence holes, indicating adult parasitoids have emerged.

Image above by permission, copyright Claude Pilon, all rights reserved.

An adult Aphelinus which emerged from one of these mummies is shown in the picture below.

Image above by permission, copyright Claude Pilon, all rights reserved.

We do not know which species this is, but it may well be the common and widely distributed Aphelinus mali which is known to parasitize Colopha graminis (see Japoshvili & Abrantes, 2006).

 

Other aphids on the same host

Primary hosts

Colopha graminis occurs on 2 species of elm (Ulmus americana, Ulmus rubra).

Secondary hosts

Colopha graminis occurs on 1 species of Carex (Carex brunnea), 1 species of Deschampsia (Deschampsia cespitosa), 2 species of Leersia (Leersia oryzoides, Leersia virginica) and 1 species of Tricholaena (Tricholaena teneriffae) - it has also been recorded from Zea-mays.

Acknowledgements

We are especially grateful to Claude Pilon for pictures of Colopha graminis (for more of her excellent pictures see).

We have made provisional 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).

Useful weblinks

References

  • Hottes, F.C. & Frison, T.H. (1931). The Plant Lice, or Aphiidae, of Illinois. Illinois Natural History Survey Bulletin 19(3), 123-447. Full text

  • Japoshvili, G. & Abrantes, I. (2006). Aphelinus species (Hymenoptera: Aphelinidae) from the Iberian Peninsula, with the description of one new species from Portugal. Journal of Natural History 40 (13-14), 855-862. Full text

  • Patch, E.M. (1910). Gall aphids of the elm. Maine Agricultural Experiment Station Bulletin No. 181 (May), 193-240. Full text