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Genus Pterocomma [Pterocommini]

Pterocomma are brownish, grey or green aphids with conspicuous white, yellow or red siphunculi. The frons is almost straight with very low antennal tubercles and sometimes with a distinct median tubercle. The body is wax powdered, especially along segment borders, and is densely hairy. The antennae and legs are similarly hairy. The antennae are about half as long as body. The siphunculi are longer than wide, cylindrical or swollen with a more or less distinct flange.

The Pterocomma genus comprises about 30 species of robust, hairy aphids living on willows (Salicaceae) in the northern hemisphere. They have a sexual stage in the life cycle, but do not host alternate. Their colonies on the bark of branches and twigs are almost always attended by ants.

 

Pterocomma pilosum (Hairy willow bark aphid)

The wingless viviparae (see first picture below) of Pterocomma pilosum are greenish, greyish or brownish. The terminal process of the antenna is 1.0-1.9 times as long as the base of the last antennal segment. The base of antennal segment six has 5-10 long hairs (cf. Pterocomma rufipes which has only 1-3 long hairs on the base of antennal segment six). All abdominal segments have marginal plates but the pleurospinal plates are discontinuous or absent. Pterocomma pilosum siphunculi are yellowish and cylindrical (cf. Pterocomma rufipes which has slightly or markedly swollen siphunculi). The body length of the viviparous aptera is 2.3-4.0 mm.

Winged viviparae (see second picture above) have more or less fused abdominal cross-bands on abdominal segments 2-8 and marginal sclerites.

Two subspecies of Pterocomma pilosum are recognised:

  • Pterocomma pilosum pilosum: has no or very small marginal tubercles on the prothorax and abdominal tergites 1-7.
  • Pterocomma pilosum konoi has well-developed marginal tubercles on the prothorax and abdominal tergites 1-7.

They feed on both broad leaved willows (Salix cinerea and Salix caprea) and on narrow leaved willows (Salix alba), where they live in large colonies along the twigs and branches or partly concealed in crevices in the bark. The hairy willow bark aphid is nearly always attended by ants. Sexual forms occur in October. Pterocomma pilosum is found in Europe eastward to Pakistan. It has also been found in North Africa, and has been introduced to North America.

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Pterocomma populeum (Hairy poplar bark aphid)

Pterocomma populeum apterae are yellowish grey or brownish with paired dark patches on at least the posterior abdominal tergites (see first picture below). There are intersegmental cross-bands of greyish white wax. The second antennal segment has 4-6 hairs (cf. Pterocomma tremulae which has 8-12 hairs on that segment). Pterocomma populeum siphunculi are pale yellow and almost cylindrical with hardly any swelling. The body length is 2.7-4.5 mm.

Pterocomma populeum alates have broad dark dorsal abdominal bands (see second picture above).

The poplar bark aphid feeds on branches, or two year old twigs, of many poplar (Populus) species. Oviparae and alate males may be found in October to November. The species is nearly always ant attended. It is widespread in Europe and has been recorded from North Africa and parts of Asia. Pterocomma populeum has been introduced to North and South America.

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Pterocomma rufipes (Rufous willow bark aphid)

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 spp.). 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.

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Pterocomma salicis (Black willow bark aphid)

Wingless Pterocomma salicis viviparae are greenish black to black with greyish white wax powder including a spinal stripe and lateral spots. There are marginal plates on all abdominal segments and pleurospinal plates on segments 7 and 8. The rostrum reaches to the hind coxae and the apical segment of the rostrum (RIV+V) is 0.8-0.9 times the length of the second hind tarsal segment. The siphunculi are bright red or orange and strongly swollen. The body length of the adult apterous vivipara is 3.2-4.5 mm.

Winged viviparae of Pterocomma salicis have the same pattern of abdominal plates as the wingless viviparae.

The black willow bark aphid forms dense colonies on two-year-old twigs and wands of willow (Salix spp.). It is usually attended by ants. Apterous males and oviparae occur in October-November. Pterocomma salicis is widely distributed in Europe and Asia, and has been introduced into North America.

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Pterocomma tremulae (Aspen bark aphid)

Apterae of Pterocomma tremulae (see first picture below) are dark warm brown or olive brown and are dusted with powdered wax. The terminal process is 1.5-2.0 times as long as the base of the last antennal segment. The second antennal segment has 8-12 hairs (cf. Pterocomma populeum which has 4-6 hairs on that segment.) The third antennal segment has 4-79 secondary rhinaria and the fourth antennal segment has 0-9 secondary rhinaria (cf. Pterocomma populeum which has none on the third antennal segment).The abdomen has large marginal and pleurospinal sclerites and marginal tubercles on the abdominal tergites. The pale yellowish siphunculi are slightly swollen. The body length of Pterocomma tremulae is 2.5-4.3 mm.

Pterocomma tremulae is usually found on suckers and two-year-old twigs of aspen (Populus tremula). No sexual morphs have been recorded, which is surprising given its northerly distribution. It is nearly always attended by ants. Pterocomma tremulae is found in northern, central and eastern Europe and west Siberia.

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Acknowledgements

We are extremely grateful to Jon Martin of the Natural History Museum, London for assistance in identifying the greenish Pterocomma found living under loose bark on Salix cinerea.

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).

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