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Genus Sitobion

Species Overview: Genus Sitobion  Sitobion avenae  Sitobion fragariae 

Genus Sitobion [Macrosiphini]

Medium-sized green to dull brownish-green or reddish-brown aphids, with blackish antennae. 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 tergum. 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.

A large genus of over 80 species worldwide. A few species alternate from Rosaceae to 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. They are not attended by ants. At least one species is a serious pest of cereals.

 

Sitobion avenae (English grain aphid)

Identification:Sitobion avenae is a medium-sized spindle-shaped aphid. The apterae show colour polymorphism with green and brown forms (see pictures below) predominating. The antennae are black and somewhat shorter than the body. The legs are mostly yellow but with the distal parts of the femora, and the tips of the tarsi and tibiae dark. The siphunculi are cylindrical and entirely black and about one and a half times the length of the pale pointed cauda. The body length of the aptera is 1.3 - 3.3mm long.

 

The alate is 1.6 - 2.9mm long and also occurs in two colour forms - green and brown. The alate 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. The majority of the population produces only asexual morphs and overwinters as nymphs or apterae on grasses or winter cereals, but a small proportion of the population alternates parthenogenesis with sexual reproduction and overwinters as eggs which hatch in March.

The English grain aphid may be a pest on all cereals but especially on wheat and to a lesser extent barley and oats. It causes direct feeding damage reducing both the number and size of grains and also transmits Barley yellow dwarf virus. 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.

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Sitobion fragariae (Blackberry-grass aphid)

Identification: The aptera is spindle-shaped and a dirty yellowish green, 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 about twice as long as the pale pointed cauda and are usually entirely black, although they may have paler bases on the primary host. Compared to Macrosiphum funestum, the siphunculi are shorter relative to the cauda (only 2 ×) and are darker or black. The body length of apterae is 1.6-3.0 mm long.

 

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). The 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.

Acknowledgements

We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. Microscopic examination of preserved specimens was used for confirmation if necessary. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Stroyan (1977),  Stroyan (1984),  Heie (1980-1995),  and Dixon & Thieme (2007).  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

  •  Blackman, R.L. & Eastop, V.F. (2006). Aphids on the world's herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.

  •  Heie, O.E. (1980-1995). The Aphidoidea, Hemiptera, of Fennoscandia and Denmark. (Fauna Entomologica Scandinavica) E.J. Brill, London

  •  Stroyan, H. L. G. (1952). The identification of aphids of economic importance. Plant Pathology 1, 9-14, 42-48, 92-99, 123-129.

 

Identification requests

David Fenwick, 10 June 14

Have an interesting aphid for you, what appears to be a Sitobion. It was found on Wall Barley, Hordeum murinum, on a small pier at Newlyn today. 10.06.14. SW 46490 28497. Juveniles quite orange in colour.

Few adults, mostly juveniles on each inflorescence, grass also looked like it was going over, becoming dry and purplish.

Hope I have the right genus.

Image(s) copyright www.aphotofauna.com  all rights reserved.

   

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Think I have it, Sitobion avenae!

A variable little beastie!

Bob, InfluentialPoints:

  • I know it can be rather variable, but I'm not convinced it is Sitobian avenae.

    Even allowing for foreshortening due to perspective, the siphunculi are too long relative to the cauda. (S. avenae siphunculi are no more than 1.4 times the length of the cauda.)

    Given the host and the dark siphunculi, it is much more likely to be Sitobion fragariae, whose siphunculi are at least twice the length of the cauda.