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Genus Sitobion [Macrosiphini]Sitobion are medium-sized green to dull brownish-green or reddish-brown aphids, with blackish antennae. Their adult viviparae may be winged or wingless. They typically have an intersegmental sclerotic pattern, but some species may have a more or less completely brownish sclerotic dorsal surface. The siphunculi are rather long, blackish and sclerotic, with the apical part reticulated and a small, but distinct flange. The cauda is pale, elongate and finger-shaped from half to nine-tenths as long as siphunculi. Sitobion is a large genus of over 80 species worldwide. A few species alternate between Rosaceae and grasses, but the majority of species remain on grasses (Poaceae) all year. On grasses they may or may not have a sexual stage. Even within one species, clones may produce males and egg laying females in the autumn - or only produce parthenogenetic females. Sitobion aphids are not attended by ants. At least one species (Sitobion avenae) is a serious pest of cereals. Sitobion avenae (English grain aphid) Europe, North Africa, Middle East, AsiaThe adult aptera of Sitobion avenae (see first picture below) is medium-sized and spindle-shaped. It shows colour polymorphism with green and brown forms predominating (immatures are green or red.) The antennae are black and somewhat shorter than the body. The legs are yellow but with the tips of femora, tarsi and tibiae dark. The siphunculi are cylindrical and black and somewhat longer (1.1-1.5 ×) than the pale pointed cauda (cf. Sitobion fragariae which also occurs on grasses, but has its siphunculi 1.7-2.7 × the length of the more rounded cauda). The body length of the aptera is 1.3-3.3 mm. long.
The alate (see second picture above) is 1.6-2.9 mm. long and also occurs in two colour forms - green and brown. It has distinct dark intersegmental markings on the upper surface of the abdomen. There is no host alternation and the species spends its entire year on cereals and grasses. It occurs on all cereals including rice and maize and can develop on most grasses (Poaceae), as well as on some rushes (Juncaceae) and sedges (Cyperaceae). The majority of the population is anholocyclic (produces only asexual morphs) and overwinters as nymphs or apterae on grasses or winter cereals, but a small proportion of the population is holocyclic (alternates parthenogenetic with sexual reproduction) and overwinters as eggs which hatch in March. Sitobion avenae is widespread throughout the world, with a preference for temperate climates. It occurs widely in Europe, North Africa, the Middle East and Asia. Sitobion berkemiae (Bear willow aphid) South-east AsiaAdult apterae of Sitobion berkemiae have a deep green abdomen, a brown head and prothorax and black sclerotic siphunculi. Their antennae are black, six segmented, with a terminal process about 6.6 times as long as the base of antennal segment VI. The apical rostral segment has 4-6 accessory hairs. The dorsum is largely membranous apart from darkened postsiphuncular sclerites. The femora are greenish basally and black distally; the tibiae and tarsi are jet black. The tapering siphunculi are about 1.6 times the length of the cauda. They have a small but distinct flange, and reticulation on the distal 0.32-0.44 of their length (cf. Sitobion berchemiae in China, which have reticulation on the distal 0.25-0.33 of their siphunculi). The cauda is pale yellow-green. The body length of adult Sitobion berkemiae apterae is 1.3-1.8 mm.
Image above by permission, copyright Akihide Koguchi, all rights reserved. We can find no description of the alate vivipara of Sitobion berkemiae, but it is likely to be similarly coloured to the aptera apart from increased sclerotization on the head and thorax, and possibly black abdominal markings. Immatures (see picture above) are coloured as the adult aptera, except that immature alatae (and probably immature apterae of instars 1-III) have only the distal part of their siphunculi dark. The only known host of Sitobion berkemiae is bear willow (Berchemia racemosa) in the buckthorn family (Rhamnaceae). They feed along the leaf veins (see picture above). The life cycle of the aphid is unknown. Sitobion berkemiae is only known from Japan. Sitobion fragariae (Blackberry-grass aphid) Europe, Asia, South Africa, North & South AmericaThe Sitobion fragariae aptera is dirty yellowish green (see first picture below), with small brown intersegmental sclerites on the abdominal dorsum. The antennae are about the same length as the body, with the basal segments paler than the rest. The siphunculi are usually entirely black, although they may have paler bases on the primary host. They are 1.8-2.7 times longer than the pale pointed cauda (on blackberry cf. Macrosiphum funestum, which has the siphunculi 2.5-3.5 times the length of the cauda; on grass cf. Sitobion avenae, which has the siphunculi 1.1-1.5 times the length of the cauda). The body length of Sitobion fragariae apterae is 1.6-3.0 mm long.
The alates (see second picture above) have a pattern of dorsal dark intersegmental markings that is usually more extensive than in Sitobion avenae. The blackberry - grass aphid host alternates from blackberry (Rubus fruticosus agg.) and occasionally other Rosaceae to grasses (Poaceae) especially Holcus spp. and some sedges (Carex spp). Sitobion fragariae eggs hatch in spring and the young nymphs feed on the breaking buds. Colonies build up and in summer alates migrate to cereals and grasses. A return migration takes place in autumn. Sitobion fragariae is native to Europe and Asia, but has been introduced to South Africa, North and South America and (probably) Australia and New Zealand.
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