Pterocomma rufipes

Identification & Distribution:

Wingless viviparae of Pterocomma rufipes are variably pigmented, grey or dull reddish brown to dark brown with spots of powdery wax. The antennae are about half as long as the body with the terminal process that is 1.3-2.2 times as long as the base of the last antennal segment. All abdominal segments have large marginal plates. There are conspicuous pairs of large pleurospinal plates on segments 6 and 7 and a crossband on segment 8. The siphunculi are yellowish and slightly or markedly swollen.

Winged Pterocomma rufipes viviparae have variably developed dorsal abdominal cross-bands.

The rufous willow bark aphid lives on twigs and young branches of many species of willow (Salix species). Colonies are often visited by ants. Sexual forms occur in September. Pterocomma rufipes occurs in north-west and central Europe, Mongolia, Siberia, and has been introduced to Canada.

Biology & Ecology

We have found Pterocomma rufipes in various locations in East & West Sussex, on willow, usually in May or June. This species is usually somewhat less common than its close relative, Pterocomma pilosum.

Molnar et al. (2003) looked at the population dynamics of Pterocomma rufipes on willow. There were two peaks of abundance, in mid-May and mid-October, with the spring peak larger than that in the autumn. Like Pterocomma pilosum they were parasitized by the specific parasitoid Euaphidius cingulatus, but rates of parasitism were much lower.

Pterocomma rufipes may or may not be attended by ants. The picture below shows an alate being attended by a jet black ant (Lasius fuliginosus). Molnar et al. (2000) found that Lasius fuliginosus was responsible for most of the ant-aphid interactions on willow.

We found this Formica lugubris attending a Pterocomma rufipes mummy.

If no ants in attendance, there may be large numbers of predators around colonies. The picture below shows an adult harlequin ladybird (Harmonia axyridis) in close proximity to several immature Pterocomma rufipes.

The first picture below shows a coccinellid larva about to capture am immature Pterocomma rufipes. The second picture shows an adult Pterocomma rufipes with solidified wax around its siphunculi, testament to a past predator attack upon said aphid.

Dixon (1958) was the first to correctly identify the defensive capability of siphunculi. They produce wax, which rapidly solidifies on the mouthparts of an attacking predator (Edwards, 1966) - as well as (usually) releasing an alarm pheromone, which alerts other aphids to the danger (Bowers et al., 1972).

Another hazard faced by Pterocomma aphids is parasitism by trombidiid mites as shown in the picture above. An aphid will probably survive attachment by a single mite, albeit the aphid's reproductive rate will be reduced, but multiple infestations can kill an aphid (Zhang, 1998). We provide more information about mites parasitizing aphids in Mites parasitizing aphids and predatory mites.

Other aphids on same host:

Pterocomma rufipes has been recorded on about 36 Salix species.

Blackman & Eastop list over 120 species of aphids as feeding on willows worldwide, and provides formal identification keys for aphids on Salix.

• Of the 41 aphid species Blackman & Eastop list as feeding on white willow (Salix alba) (Show World list), Baker (2015) lists 24 as occurring in Britain (Show British list).

• Of the 30 aphid species Blackman & Eastop list as feeding on common sallow (Salix caprea) (Show World list), Baker (2015) lists 24 as occurring in Britain (Show British list).

• Of the 26 aphid species Blackman & Eastop list as feeding on grey sallow (Salix cinerea) (Show World list), Baker (2015) lists 21 as occurring in Britain (Show British list).

• Of the 26 aphid species Blackman & Eastop list as feeding on crack willow (Salix fragilis) (Show World list), Baker (2015) lists 20 as occurring in Britain (Show British list).

Acknowledgements Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

References Bowers, W.S. et al. (1972). Aphid alarm pheromone: isolation, identification, synthesis. Science 177, 1121-1122. Dixon, A.F.G. (1958). The protective function of the siphunculi of the nettle aphid, Microlophium evansi (Theob.). Entomologist's Monthly Magazine 94, 8. Edwards, J.S. (1990). Defense by smear: Supercooling in the cornicle wax of aphids. Nature 211, 73-74  Full text Molnár, N. (2003). Population dynamics features of willow-feeding aphids. Acta Phytopathologica et Entomologica Hungarica 38 (1-2), 125-135. Full text Molnár, N., Kovács, É. and Gallé, L. (2000). Habitat selection of ant-tended aphids on willow trees. Tiscia 32, 31-34. Full text Zhang, Z. (1998). Biology and ecology of trombidiid mites (Acari: Trombidioidea). Experimental & Applied Acarology, 22, 139-155. Full text