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Therioaphis viviparae may be apterous or alate (in one species they are only alate). 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 ones. 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 ononidis (Spotted restharrow aphid)
Adult apterae of Therioaphis ononidis (see first picture 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.
Second image above by permission copyright Ole Bidstrup, all rights reserved.
The alate Therioaphis ononidis (see second picture above) has brownish shadowing along the wing veins, ending in small brown triangular spots on the wing margins.
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.
Therioaphis riehmi (Sweetclover aphid)
Apterous viviparae of Therioaphis riehmi are very rare (but see Quednau (2003) for illustration of aptera). Fourth instar alatoid nymphs (see first picture below) are pale yellow whilst alatae (see second picture below) are dark yellow or yellowish-orange. In alate Therioaphis riehmi the antennal terminal process is 0.92-1.1 times the length of the base of antennal segment VI. Antennal segment III bears 9-12 secondary rhinaria. The apical rostral segment (RIV+V) is shorter than the second hind tarsal segment (HTII) (cf. Therioaphis ononidis on Ononis which has RIV+V longer than HTII). Abdominal tergites I-VII each bear 4 hairs, 1 pair spinal and 1 pair marginal (cf. Therioaphis trifolii which has more than 4 hairs on each of abdominal tergites I-VII). These hairs arise from pigmented tubercular bases, giving four longitudinal rows of dark sclerites on the dorsum; the paramedian sclerites are of medium size, oval and in pairs. Wing veins, especially the radial sector, are dark-shadowed. The siphunculi are pale, stump-shaped and flangeless. The cauda has a constriction and a knob-like apex. The anal plate is bilobed. The Therioaphis riehmi body length is 2.0-2.7 mm.
Both images above by permission, copyright Claude Pilon, all rights reserved.
The preferred host of Therioaphis riehmi is melilot, sweet clover (Melilotus spp.), where they feed on leaf undersides. They are also found on species of medick (Medicago spp.), fenugreek (Trigonella spp.) and clover (Trifolium spp.). There is no host alternation and sexuales (oviparae and alate males) develop in September. Although there is the potential for damage to sweetclover crops, such damage only occurs occasionally as natural factors usually depress midsummer populations (Manglitz & Hill, 1964). The sweetclover aphid is indigenous to Europe, North Africa, Middle East, India, Kazakhstan, China and has been introduced to North and South America. Read more...
Therioaphis tenera (Spotted alfalfa aphid)
All adult viviparae of Therioaphis tenera are alate. Immatures (see first picture below) are pale yellow, unspotted and bear capitate dorsal hairs. Alate Therioaphis tenera (see second picture below) are yellowish. Abdominal tergites I-VII each bear 4 hairs, 1 pair spinal and 1 pair marginal (cf. Therioaphis trifolii, which has more than 4 hairs on each of abdominal tergites I-VII). These hairs arise mostly from unpigmented or lightly dusky tubercular bases, some with dark edging, giving a largely pale dorsum with incomplete rows of small dark spots (cf. Therioaphis riehmi, which has the hairs arising from pigmented tubercular bases, giving four longitudinal rows of completely dark sclerites on the dorsum). The siphunculi are pale. The body length of alate Therioaphis tenera is 1.7-2.2 mm.
Both images above by permission, copyright Claude Pilon, all rights reserved.
There are two subspecies of Therioaphis tenera, one apparently has a specific host-plant association.
Therioaphis tenera feeds on Caragana spp.. Colonies can be found living dispersed on undersides of leaflets, mostly on lower branches. Fundatrices are present in June, and oviparae and alate males in late August-September. It is distributed through north and central Europe into Russia, Ukraine and Central Asia, and has been introduced to Quebec, Canada where the aphids pictured here were photographed. Read more...
Therioaphis trifolii (Spotted alfalfa aphid)
The apterae of Therioaphis trifolii 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 alatae are similar in appearance to the apterae 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.