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Genus Therioaphis

Spotted pea aphids

On this page: Genus Therioaphis  Therioaphis trifolii 

Therioaphis [Panaphidini]

Therioaphis viviparae may be apterous or alate (all alate for one species). They are rather small to medium-sized yellowish aphids. The terminal process is slightly shorter to slightly longer than the basal part of antennal segment VI. The antennal hairs are shorter than basal diameter of antennal segment III. The rostrum is short, not reaching the middle coxae. The dorsal body hairs are situated on individual pigmented scleroites. The front coxae are very much enlarged relative to the middle and hind coxae. The siphunculi are stump-shaped, flangeless, and variably rugose, lying just anterodorsal to the marginal sclerite of tergite 6. The cauda is rather large, with an elongate knob. The sclerotic markings of wings and body of alatae are pale to darkish grey or brown, not black. The head of the alate has a ventral dark band running transversely between the inner margins of the compound eyes.

Therioaphis feed on members of the pea and bean family (Fabaceae). There are about 30 Therioaphis species, of which half are restricted to south-east Europe and the Middle East. Others are confined to northern Europe, and a few have a cosmopolitan distribution.

 

Therioaphis trifolii (Spotted alfalfa aphid)

The apterae vary in colour from shiny yellow to greenish white, with rows of pigmented raised spots. The antennal terminal process is approximately equal in length to the base of antennal segment VI. Abdominal tergites I-V each have 7-10 hairs (cf. Therioaphis riehmi in which abdominal tergites I-V each have only 4 hairs, and Therioaphis luteola in which abdominal tergites I-V very rarely have more than 6 hairs each). Tergite VIII has 3-6 hairs. The hairs arise from pigmented bases and are mostly long and capitate. The dusky siphunculi are stump-shaped, flangeless, and very short. The cauda of Therioaphis trifolii is rather large and has a constriction and a knob-like apex.

The alate is similar in appearance to the aptera except that the dorsal body hairs are shorter and less strongly capitate. The ovipara (see first picture above) is similar to the viviparous aptera, but the posterior extremity is produced into an ovipositor-like extension, and the hind tibiae are somewhat swollen. The male (see second picture above) has a similar pattern of sclerotization to the alate vivipara, but has secondary rhinaria on antennal segments III-V inclusive.

Three subspecies with associated forms have been recognised:

  • Therioaphis trifolii ssp. maculata is the subspecies found naturally in Europe, North Africa, the Middle East, India and Pakistan. It has been introduced to
    1. eastern USA in the 1880s, a biotype (the yellow clover aphid) feeding mainly on red clover (Trifolium pratense), now found over much of North America.
    2. south-western USA in the 1950s, a biotype (the spotted alfalfa aphid) feeding mainly on alfalfa (Medicago sativa), now found throughout the USA and Mexico, and introduced to Australia and New Zealand.
    3. South Africa in the 1980s, a biotype feeding on Medicago and Trifolium.
  • Therioaphis trifolii ssp. ventromaculata feeds on milkvetch (Astrolagus onobrychus) in central Europe.
  • Therioaphis trifolii ssp. albae feeds on white melilot (Melilotus albus) in Ukraine.

Therioaphis trifolii feeds on feeds on various members of the pea family (Fabaceae) especially clovers (Trifolium), medicks (Medicago) or trefoils (Lotus). It does not host alternate, remaining on the same host all year. In temperate countries sexual forms develop in autumn, and the aphid overwinters in the egg stage. In warmer areas the aphid is anholocyclic.

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Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and sp accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . 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).

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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.