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Willowherb aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Natural enemies Other aphids on the same host
Identification & Distribution:
Aphis epilobii is a blackish-green to reddish-brown aphid which appears dark-grey to pinkish-brown because of the rather uniform powdering of wax (see pictures below). The apical rostral segment (RIV+V) is 1.28-1.55 times the length of segment II of the hind tarsus The abdominal dorsum of Aphis epilobii is membranous with only a dusky narrow band across tergite 8 and sometimes 7. There are small conical marginal tubercles on tergites 1 and 7 (visible if you can expand the first micrograph image below), but not on tergites 2-6 (cf. Aphis grossulariae which has marginal tubercles on most tergites). The siphunculi and basal parts of the antennae are pale, but the cauda is dusky or dark. The siphunculi are 1-1.6 times the length of the cauda. The body length of Aphis epilobii apterae is 1.3-2.1 mm.
The alate (see second picture below) has marginal, postsiphuncular and small marginal sclerites, but no dorsal cross bands in front of the siphunculi. The antennal terminal process is about 3 times the length of the basal part of antennal segment 6. Antennal segment III has 30-32 secondary rhinaria, segment IV has 17, and V has 7-9.
The ovipara is reddish brown or greenish black with the hind tibia more or less distinctly swollen on the basal half. The winged male (see pictures below) is dark but has an entirely membranous dorsum.
The willowherb aphid does not host alternate. Sexual forms occur in autumn. It feeds on broad-leaved willowherb (Epilobium montanum) or more rarely other Epilobium species. Aphis epilobii is not usually ant attended. It is widely distributed throughout Europe.
Biology & Ecology:
Aphis epilobii is usually a very common aphid, and by late summer most plants of broad-leaved willowherb will have colonies of aphids especially on the growing shoot and flowers. By late September they start to produce sexual forms. The pictures below shows several brown wingless oviparae with immatures feeding on the stem - and winged males, which were moving up and down the colony seeking suitable mates.
Mating takes place on the drying stems of Epilobium.
The oviparae then lay the shiny black eggs along the dead stems of the host plant shown below.
By egg-laying time, many of the colony may have been killed by parasitoids, in this case by a Praon species which give the characteristic mummies shown below.
Two species of Praon have previously been found on Aphis epilobii in Europe, Praon dorsale (see M&uouml;ller et al., 1999) and Praon abjectum (see Kavallieratos et al., 2004). Other parasitoids recorded are Binodoxys angelicae (Kavallieratos et al., 2004) and Lysiphlebus fabarum (Rakhshani et al., 2013).
Little else seems to have been published about the ecology of Aphis epilobii, although O'Doherty & Ring (1987) found that this species was capable of surviving considerable supercooling. They noted however that this seemed to be a general property of aphids rather than specific to those species encountering such conditions.
Other aphids on same host:
Blackman & Eastop list 13 species of aphid as feeding on broad-leaved willowherb (Epilobium montanum) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 11 as occurring in Britain (Show British list).