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Spotted pea aphidsOn this page: Genus Therioaphis Therioaphis trifolii Therioaphis ononidis
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 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.
Therioaphis ononidis (Spotted restharrow aphid)
Adult apterae of Therioaphis ononidis (see pictures below) are rather small and yellowish. The apical rostral segment (RIV+V) is longer than second hind tarsal segment (HTII), and has 8-12 accessory hairs. The dorsal hairs arise from pigmented bases and are mostly long and capitate. Abdominal tergites I-VII usually each bear 4 hairs, one spinal and one marginal on each side (cf. Therioaphis trifolii which has 7-10 hairs on each of abdominal segments I-V). The dusky siphunculi are stump-shaped, flangeless, and very short. As with other Therioaphis species, the cauda of Therioaphis ononidis is rather large, and has a constriction and a knob-like apex. The body length of adult apterae is 1.8-2.2 mm.
The alate Therioaphis ononidis (shown below) has brownish shadowing along the wing veins, ending in small brown triangular spots on the wing margins.
Both images above by permission copyright Ole Bidstrup, all rights reserved.
Therioaphis ononidis feeds on rest harrows (Ononis species), especially common rest harrow (Ononis repens) and spiny restharrow (Ononis spinosa). It does not host alternate, but remains all year on restharrow. Oviparae and alate males occur in October, with eggs laid on the stems and leaves of its host. The spotted restharrow aphid is found throughout Europe, the Middle East and Central Asia. Records from North America are thought to be misidentifications of Therioaphis trifolii.