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Sea aster aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution
Apterous Aphis tripolii are apple green with a dusky head and no wax powdering. The abdominal dorsum is entirely pale. There are always 4 marginal tubercles on abdominal segments I and VII, and 1-6 smaller ones on segments II-IV. The siphunculi are yellowish with dusky apices, and are 0.86-1.22 times the length of the cauda. The dusky cauda is long, narrow, and blunt with 5-9 hairs. The body length of Aphis tripolii is 1.3-2.45 mm. Aphis tripolii nymphs have a faint dorsal pattern of wax powdered spots (see second picture below on left).
Alate Aphis tripolii (see second picture above) have rather pale marginal and postsiphuncular sclerites, and sometimes pale and inconspicuous bands across tergites 7-8. The siphunculi of alates are uniformly dusky sclerotic.
The second picture above is a micrograph of an aptera of Aphis tripolii showing the dusky siphunculi and cauda.
The sea aster aphid does not host alternate but remains all year on the upper parts of the leaves and on the flowers of Tripolium pannonicum (sea aster). Sexual forms are produced in autumn. The winged male has the antennae brown and the siphunculi and cauda pale brown. Aphis tripolii is found in coastal salt marshes or on mud flats in a few European countries including Britain. Our record for Hampshire appears to be a new one for that county as Aphis tripolii is previously only known from the coastal fringe from Kent round to Norfolk and in Wales.
Biology & Ecology
We have found Aphis tripolii several times in southern England, especially at Keyhaven Marshes in Hampshire (see picture below) and Rye Harbour in East Sussex.
At Keyhaven Marshes we searched numerous large healthy sea aster plants (see first picture below) until we finally found a colony on a lone, rather sad-looking plant growing on the sea wall (second picture below).
The tendency to get aphids on stressed plants is well known, as happens in unusual and marginal microhabitats. A similar preference for stressed plants has been reported for an American species of saltmarsh aphid, Uroleucon ambrosiae, which lives on salt marsh elder (Iva frutescens) (Hacker & Betness, 1995), although in that case the apparent reason was that coccinellid predators favoured taller more productive plants.
There has been very little research done on Aphis tripolii. Foster & Treherne (1976) observed that in a submerged colony, the only aphids that died were those that moulted whilst immersed. Also the winged adults were unable to fly after submergence (hardly a great surprise!). We have only found large numbers of developing alatae when we visited the saltmarsh in July. The image below shows a number of alatoid fourth instar nymphs.
The faint dorsal pattern of wax powdered spots on the immatures is reminiscent of aphids in the Aphis fabae group. Aphis tripolii was for some time considered to be a member of this group (sensu lato), but Jorg & Lampel (1995) have subsequently excluded the species on the grounds of its morphology, especially the green colour, and its genetic identity.
Hopkins et al. (2002) showed that the proportion of species that are rare in a particular group increases as host plant range declines. By extrapolating this pattern in well known insect groups to the less well known group of aphids, he predicted which aphid species were indeed rare and in need of conservation measures. Aphis tripolii was included on this basis in his "rare aphids" category.
Unlike the sea lavender aphid, the green sea aster aphid is often attended by ants, as can be seen in the pictures below.
The ant shows a superficial resemblance to the common black ant (Lasius niger), but we would appreciate identification from anyone who is more 'up' on ants than we are.
Other aphids on same host:
Blackman & Eastop list 6 species of aphid as feeding on sea aster (Tripolium pannonicum) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists all 6 as occurring in Britain (Show British list).