Geoica utricularia induces a smooth, globular yellowish gall on its primary hostPistacia terebinthus (see first two pictures below). Adult apterae are very plump-bodied, off-white, cream or yellowish, usually with scattered globules of wax. The head, prothorax, appendages and anal region are brownish. Geoica utricularia has no siphunculi (cf. Tetraneura ulmi which has small siphunculi). The anal plate has scattered, shortish, sometimes spatulate or flabellate (=fan-shaped), hairs. They are not arranged in two longitudinal rows (cf. Geoica setulosa which has the anal plate with long and usually pointed hairs arranged in two longitudinal rows). The body length of adult apterae is 1.6-3.0 mm.
The name Geoica utricularia is conventionally applied to anholocyclic populations of this group on grass roots throughout Europe and in North Africa (Morocco), the Middle East, Central Asia, North America, and China (as subpecies urunquiensis Qiao). However Blackman notes that these populations vary considerably in chaetotaxy (=the arrangement of bristles), particularly of the apical rostral segment, abdominal tergite 8, cauda and anal plate, and it is possible that more than one species is involved, or that the name is being applied incorrectly.
First image above, by permission, copyright Ben van As
Second image above, copyright Houard 1909;
Third image above, by permission, copyright Mariusz Kanturski all rights reserved.
Micrographs of clarified mounts courtesy Favret, C. & G.L. Miller, AphID. Identification Technology Program, CPHST, PPQ, APHIS, USDA; Fort Collins, CO.
Geoica utriculariaalatae have a dark head and thorax and a pale yellowish-green abdomen with dark transverse bars, longer on the more posterior tergites.
On its main primary host, Pistacia terebinthus, in the Mediterranean area and south-west Asia Geoica utricularia usually forms its gall near the base of a leaflet, close to the main vein. Colour, texture and shape seem to vary somewhat with the host species, but on this Pistacia species they are smooth and yellowish with a pinkish tinge. These galls open in July-October. Emigrant alatae found colonies on roots of grasses (such as Agrostis, Avena, Bromus, Deschampsia, Festuca, Hordeum, Lilium, Phleum, Poa), attended by ants.
Where none of the primary hosts occur (most of the aphid's range), the short-haired pistachio-grassroot aphid spends its entire life cycle on grass roots reproducing parthenogenetically. Geoica utricularia is found throughout Europe and in North Africa, the Middle East, Central Asia and North America.
Other aphids on the same host
Geoica utricularia is found on 4 or 5 Pistacia species (Pistacia chinensis, Pistacia integerrima, Pistacia palaestina (?), Pistacia terebinthus, Pistacia vera).
Blackman & Eastop list 19 species of aphid as feeding on those species of Pistacia worldwide, and provide formal identification keys.
Of those aphid species, Baker (2015) lists 6 as occurring in Britain .
We are extremely gratefulto Ben van As for his picture of the gall on Pistacia terebinthus in Greece, and to Mariusz Kanturski for the excellent images of Geioca utricularia on grass roots in Poland; also to Willem Ellis, bladmineerders.nl, for putting us in touch with Mariusz.