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Apterous viviparae of Atheroides spp. have an elongate slender, nearly linear, body or, in the case of Atheroides brevicornis, oval. The head and prothorax are not fused. Head + thorax +abdominal segment I is almost as long as abdominal segments II-VIII. The antenna are short, 5 segmented or, in the case of Atheroides brevicornis, 4 segmented. The frons is convex. The eyes are normal, with the ocular tubercles distinct. The rostrum is short, reaching to the middle coxae. Abdominal tergites II-VII are sclerotized and usually fused, although only partially fused in Atheroides karakumi. Tergite VIII is semicircular, covering the cauda (except in Atheroides hirtellus). The siphunculi are pore-shaped, placed at anterior margin of abdominal segment V. The cauda and anal plate are broadly rounded. Alatae are rare and sexual morphs of several species are unknown.
There are 7 Atheroides species recognised worldwide. Six are palaearctic (Atheroides brevicornis, Atheroides doncasteri, Atheroides hirtellus, Atheroides karakumi, Atheroides persianus), one is either invasive in America or naturally holarctic (Atheroides serrulatus) and one is a recently discovered species (Miller et al., 2014) in the nearctic (Atheroides vallescaldera). They feed on grasses (Poaceae) and some sedges (Cyperaceae), with some species found on many different species of grasses; others are more specific (e.g. Atheroides doncasteri is only known from the grass Deschampsia caespitosa). Wieczorek (2009) fully reviewed the genus, with a key and illustrations of apterae of six species.
Atheroides brevicornis (Dark saltmarsh grass aphid)
Adult apterae of Atheroides brevicornis (see first two pictures below) have a very elongated oval, nearly linear blackish-brown body. The head is semicircular with the front convex. The antennae are very short, 4 or 5-segmented, and only 0.14-0.17 times the body length (cf. Atheroides serrulatus, Atheroides hirtellus and Atheroides doncasteri, which all have the antennae greater than 0.20 times the body length). The terminal process is stumpy, about 0.5 times as long as the last antennal segment. The head and prothorax are fused, but their suture is very distinct. The mesothorax, metathorax and first abdominal tergite are free; abdominal tergites II-VII are fused, the second sometimes partly free; tergite VIII is semicircular and free. The dorsum is strongly sclerotic, usually uniformly dark, very coarsely corrugated, covered with club-shaped or inverse bottle-shaped hairs with blunt, sometimes emarginate (=notched at the margin) apices. The hair bases look like perforations of the dark sclerite. Tergite VIII has a number of thick, long, spiny hairs on large bases along the margin; the two longest stand rather far apart, with two club-shaped or cylindrical hairs between them. The siphunculi are reduced to very small pores on the anterior margin of tergite V (cf. Laingia psammae, which has siphunculi as slightly raised pores with sclerotic rims on abdominal tergite VI). The body length of adult Atheroides brevicornis apterae is 1.5-2.4 mm.
The alate (not pictured) has the head and thorax sclerotic and dark. The abdomen is mostly membranous with paired, very large, usually fused spinal sclerites; pleural sclerites are often absent and marginal sclerites are large. Tergites VII and VIII are uniformly sclerotic. Their antennae are as in the apterae, with 4, rarely 5, segments, but with the third segment bearing 2-4 secondary rhinaria.
Atheroides brevicornis lives in rows on the upper sides of grasses especially those growing in salt-marsh habitats such as Deschampsia cespitosa, Puccinellia spp., Festuca ovina and Festuca rubra. There is no host alternation and sexual forms develop in autumn. The dark saltmarsh grass aphid is found in coastal habitats around northern Europe and the Black Sea, as well as in salty pond-side habitats. Atheroides brevicornis has been found to be extremely common along the muddy seashores of the Netherlands where it feeds on common saltmarsh grass (Puccinellia maritima = Festuca thalassica) and reflexed saltmarsh grass (Puccinellia distans = Festuca distans), the two typical species of grass growing there.
Atheroides serrulatus (Orange grass aphid)
Adult apterae of Atheroides serrulatus (see first two pictures below) are yellow to yellowish-brown with elongate and slender bodies and visible rugose sculpture. The dorsal carapace is always solidly sclerotic from abdominal tergites II-VII. The antennae just reach the anterior margin of the prothorax, with the antennal 'flagellum' (=segments III-V/VI) more than 0.25 mm long (cf. Atheroides brevicornis, which has the antennal flagellum less than 0.25 mm long). The terminal process is 1.1-1.3 times the length of the base of the last antennal segment (V). The apical rostral segment (RIV+V) is blunt and about 0.75 times the length of the second hind tarsal segment (HTII). The dorsal body hairs and those on antennal segment III (when present) are less than 0.03 mm long, and less than one-third as long as basal part of last antennal segment. The siphunculi of Atheroides serrulatus are borne on the fifth abdominal segment, and reduced to 'siphuncular pores'. Abdominal tergite VIII bears 11-17 pointed, thorn-like hairs, and has a somewhat rounded, overhanging hind margin which normally conceals the cauda (see clarified mount below). The Atheroides serrulatus cauda has 4 hairs. The body length of adult Atheroides serrulatus apterae is 1.7-2.4 mm.
Atheroides serrulatus alatae (see image below) have the head and pterothorax blackish sclerotic, and the dorsal abdominal carapace of apterae replaced by separate segmental dark bands and marginal sclerites on the tergites. Secondary rhinaria are few, with up to 7 in a single row on antennal segment III, and rarely 1 on IV. Siphuncular pores are located on the inner front angle of marginal sclerite of abdominal tergite V.
Atheroides serrulatus is found, often singly, on the leaves of many different grasses (Poaceae) and possibly on species of sedge (Cyperaceae). Most specimens are obtained by the use of sweep nets, so the identity of the host plant species is often indeterminate. There is no host alternation. Sexual forms (apterous males and oviparae) develop in autumn. Atheroides serrulatus is widespread and often common in Europe as well as parts of Asia and Canada.