Geoica [Fordini]
Geoica are small to medium-sized pale-coloured aphids. A characteristic feature of their apterae is the presence of fan-shaped 'spatulate' hairs as well as normal hairs. The anus and anal plate are displaced dorsally, and the anal plate is enlarged to form a trophobiotic organ as in Baizongia. Apterae developing on grasses have 4- or 5-segmented antennae, whereas in alatae the antennae are always 6-segmented. There are no faceted wax glands and, like for example Forda, Baizongia, Paracletus, Prociphilus and some Trama, these aphids lack siphunculi. Geoica alatae have variably developed dorsal abdominal cross-bands, and a rather different trophobiotic organ from that in apterae. The anal plate and cauda are extended laterally to unite and form a sclerotised perianal ring, enclosing a membranous area with the anal aperture at its centre.
Most species of Geoica form globular galls near the bases of leaflets of Pistacia and migrate to and from grass roots. The complete cycle takes two years. Gall-forming populations are present in southern Europe and south Asia where they host alternate to grass roots. Permanently parthenogenetic, grass-feeding populations of two species have become widely distributed in northern Europe, Asia and North America.
Geoica setulosa (hairy-tailed pistachio-grass root aphid)
Adult Geoica setulosa apterae on their secondary host (grass roots) are light yellowish brown, off-white or pale greenish-grey (see first picture below). The primary rhinaria on the antennae are transversely elongated; slit-like, or of irregular shape with narrow diverticula. The dorsal body hairs are pointed, spatulate or fan-shaped. Geoica setulosa have the anal plate enlarged and extended or displaced dorsally, surrounded on three sides by the U-shaped abdominal tergite 8 so as to form a trophobiotic organ to retain honeydew for collection by ants. The anal plate has long and usually pointed hairs arranged in two longitudinal rows (see first picture above), as well as finer, shorter hairs grouped near their anus (cf. Geoica utricularia which has only scattered, shortish hairs on the anal plate, not arranged in two rows). The body length of the adult Geoica setulosa aptera is 1.6-2.6 mm. The body length of alatae on the secondary host is 1.8-2.3 mm.
The clarified slide mounts below are of adult viviparous female Geoica setulosa : wingless, and winged.
Clarified mount of aptera and alate, courtesy Favret, C. & G.L. Miller, AphID.
On the primary host, (Pistacia khinjuk) in Iran, Geoica setulosa forms galls at the bases of leaflets. These galls open in late August-October. Emigrant alatae found colonies on roots of grasses (e.g. Agrostis, Briza, Festuca, Holcus), attended by ants. Where the primary host Pistacia khinjuk does not occur (most of the aphid's range), the hairy-tailed pistachio-grass root aphid spends its entire life cycle on grass roots reproducing parthenogenetically, often overwintering in the nests of Lasius flavus. Geoica setulosa is found over much of Europe, and has been introduced to USA.
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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.
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