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Willowherb aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Ant attendance Natural enemies Other aphids on the same host
Identification & Distribution
Adult apterae of Aphis epilobii are dark blackish-green to reddish-brown (see first picture below) which often appears dark-grey to pinkish-brown (see second picture below) because of a rather uniform powdering of wax (cf. Aphis grossulariae which is dull green to light green with only a light wax bloom). The apical rostral segment (R IV+V) is 1.28-1.55 times the length of segment II of the hind tarsus (HT II) (cf. Aphis grossulariae which has R IV+V 1.42-1.68 times the length of HT II). 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. 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 first 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. Immatures (see second picture below) resemble the adults with blackish-green and reddish-brown forms.
The images below are micrographs of an apterous adult and an alate in isopropyl alcohol.
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. The overwintering eggs hatch in spring and by late summer most plants of broad-leaved willowherb will have colonies of aphids especially on the growing shoot and flowers (see picture below).
They are often in mixed species colonies with other Aphis species found on Epilobium, especially the host-alternating Aphis grossulariae which overwinters on gooseberry. The picture below shows a mixed species colony of Aphis epilobii (dark green) and Aphis grossulariae (pale green).
By late September they start to produce sexual forms. Oviparae are reddish brown or greenish black with the hind tibiae more or less distinctly swollen on the basal half. The picture below shows a reddish brown ovipara.
Pictures below show (first) several green or brown wingless oviparae and (second) 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.
Unlike Aphis grossulariae, a species with which they often form mixed species colonies, Aphis epilobii are not usually ant attended. However, we have found oviparae of Aphis epilobii being attended (see picture below).
By egg-laying time, many of the colony may have been killed by parasitoids which mummify their aphid hosts (see picture below). The form of the mummy suggests Lysiphlebus fabarum is the parasitoid in this case, a parasitoid also reported by Rakhshani et al. (2013).
The mummy of another parasitoid species attacking Aphis epilobii is shown below.
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:
Aphis epilobii has been recorded from 13 Epilobium species.