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Aphids on willow

Blackman & Eastop list over 120 species of aphids  as feeding on willows worldwide, and provides formal identification keys for aphids on Salix. The main genera are Chaitophorus, Pterocomma and Cavariella.

The species below are those we have found most frequently, listed in rough order of abundance. Assistance on identifying the various species of willow is given below. 

 

Aphis farinosa (Small Willow aphid)

A small mottled green and yellow-orange species with the abdominal dorsum entirely membranous or with at most a narrow band across tergite 8. Siphunculi are pale usually with a dusky tip. The cauda is about as dark as the tibial apices. The pigmentation of legs and antennae is variable. The alates are dark green and their siphunculi are more or less dusky. The oviparae are dull green and the apterous males are reddish orange.

 

The small willow aphid is fairly common in dense colonies on the young shoots of Willows (Salix spp.) especially common sallow (Salix caprea) in spring and early summer. They do not host alternate and are attended by ants. They have a sexual stage in the life cycle with oviparae and males appearing from July onwards, although occasionally populations of viviparae persist until August or September. The species occurs throughout northern temperate parts of the world (North America, Europe & Asia) and in South America (Argentina).

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Cavariella pastinacae (Willow-umbellifer aphid)

Adult apterae of Cavariella pastinacae are rather light shiny green with appendages pale except for the base of antennal segment VI and the tarsi which are dark. Their antennae are about 0.45 times the length of the body and the terminal process is 3.0-4.0 times the base of the last antennal segment. The siphunculi are 2.3-3.0 times as long as the cauda and are slightly swollen towards the tip. The supracaudal process is broadly tongue-shaped,with a flat apex and is 0.5-0.8 times the length of the cauda. The body length of apterae is 1.8-2.9 mm. The Cavariella pastinacae alate has a dark abdominal patch formed by more or less fused cross bands on tergites III-VI. The antennae, cauda, supracaudal process and distal halves of siphunculi are dark.

The willow - umbellifer aphid host alternates between willows (Salix spp.) and some umbellifers mainly hogweed (Heracleum), wild parsnip (Pastinaca) and Angelica. Cavariella pastinacae is common over most of Europe and in North America.

 

Cavariella theobaldi (Willow - parsnip aphid)

Adult apterae are green with the tips of the antennae and apices of the legs dark. The antennae are 0.50 times the length of the body and the terminal process is 2.1-3.5 times the base of the last antennal segment. The siphunculi are more than twice as long as the cauda and are cylindrical or tapering from base to the apex; they are not swollen (distinguishes from Cavariella pastinacae which has the siphunculi slightly swollen towards the tip). The supracaudal process is more or less quadrangular and small, about 0.3-0.7 times the length of the cauda. The body length of apterae is 1.8-2.8 mm.

The willow - parsnip aphid host alternates between willows (Salix spp.) and some umbellifers mainly wild parsnip (Pastinaca) and hogweed (Heracleum). Common over most of Europe and in North America.

 

Cavariella aegopodii (Willow - carrot aphid)

The apterae are small and greenish or reddish. The tips of the antennae and apices of the legs are brownish. The antennae are about 0.4 times the body length, with the terminal process about 0.85-1.5 times the basal part of segment VI. The siphunculi are swollen and about twice as long as the cauda. The supracaudal process is 0.75-1.05 times the cauda, broadest at the base and oblong triangular to conical. The body length of apterae is 1.5-2.8 mm.

The willow-carrot aphid host alternates from willows (Salix spp) to umbellifers (Apiaceae). The preferred primary hosts are crack willow (Salix fragilis) and white willow Salix alba, although some Willow species seem only to be colonized in spring, by winged forms from populations which have overwintered parthenogenetically. Preferred secondary hosts are cultivated umbellifers such as carrots (Daucus carota) and fennel (Foeniculum vulgare) and several wild umbellifers. It is widespread throughout temperate and warm temperate parts of the world.

 

Cavariella archangelicae (Willow - angelica aphid)

The adult apterae are green or yellowish. The antennae are 0.35-0.39 times the length of the body and the terminal process is1.5-2.0 times the base of the last antennal segment. The siphunculi are more than twice as long as the cauda with the distal half somewhat swollen in a nearly symmetrical way. The supracaudal process has a broad basal part and is tongue-shaped about 0.7-1.0 times the length of the cauda. The body length of apterae is 1.5-2.6 mm.

The willow - angelica aphid host alternates from willow (Salix spp.) to angelica (Angelica). Sexual forms occur in October. Its distribution is cosmopolitan.

 

Chaitophorus capreae (Pale sallow leaf aphid)

The apterae are white to yellowish-white. The body is not markedly narrow with the body length 1.8-2.1 times the maximum body width (this characteristic distinguishes Chaitophorus capreae from Chaitophorus horii bethuani which is narrower). The cauda has a distinctly knobbed apex. The body length is 0.8-1.9 mm. Both the apterae and the alates have no distinct dark dorsal abdominal markings. This picture below shows an aptera on a sallow leaf. The knobbed cauda, lack of dorsal markings, and body length to width ratio of 2.0, along with the food plant all indicate this is Chaitophorus capreae.

The pale sallow leaf aphid lives mostly on sallows (broad-leaved Salix spp.) especially common sallow (Salix caprea) and grey sallow (Salix cinerea). Aphids are usually scattered on the undersides of leaves and are not attended by ants. Oviparae and yellow apterous males occur in October-November. The species is widespread in Europe, and eastward to Central Asia.

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Tuberolachnus salignus (Giant willow aphid citrus aphid)

Tuberolachnus salignus are very large aphids with a body length of 5.0-5.8 mm. Apterae are mid-brown to dark brown with several rows of black sclerotic patches. The body is covered with numerous fine hairs, which give a greyish-golden sheen to the abdomen. There is a large dark brown tubercle in the centre of the back, just in front of the siphunculi which are on large dark cones. The antennae are less than half the body length. Alates have the forewing membrane unpigmented but the pterostigma and costal margin are dark brown.

  Tuberolachnus salignus (Giant Willow Aphid) alate on Salix alba (White Willow) at Woods Mill, West Sussex, UK on 2/9/11 at 15.09 h.

The giant willow aphid lives on the stems and branches of numerous Willows & Sallows (Salix spp.) and is also very occasionally recorded from Poplar (Populus). Its distribution is almost cosmopolitan wherever willows are grown.

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Pterocomma salicis (Black willow bark aphid)

Wingless 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 siphunculi are bright red or orange and strongly swollen. Winged viviparae 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. It is widely distributed in Europe and Asia and has been introduced into North America.

 

Pterocomma pilosum sp. group (Hairy willow bark aphid)

Wingless viviparae 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. All abdominal segments have marginal plates but the pleurospinal plates are discontinuous or absent. The siphunculi are yellowish and not swollen. Winged viviparae have abdominal cross-bands on abdominal segments 2-8.

Most authorities recognize three species (or subspecies) within this group: Pterocomma populeum (on poplar) and Pterocomma konoi and Pterocomma pilosum sensu stricto both on willow. The species we picture would appear to be Pterocomma pilosum ss. since unlike Pterocomma konoi it lacks well-developed marginal tubercles on the prothorax and abdominal tergites 1-7.

 

All forms of the species we picture were greenish and ant-attended, and (at least in Sussex/Surrey, UK) seem to be largely restricted to feeding on broad leaved willows (Salix cinerea and Salix caprea), sometimes under loose bark. The hairy willow aphid generally lives on the twigs and branches or in bark crevices of numerous Salix spp., and usually attended by ants. Sexual forms occur in October. It is found in Europe eastward to Pakistan.

 

Pterocomma rufipes (Rufous willow bark aphid)

Wingless viviparae 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 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. It occurs in north-west and central Europe, Mongolia, Siberia, and has been introduced to Canada .

 

Chaitophorus salicti (Sallow leaf-vein aphid)

Adult apterae in spring are black with a pale spinal stripe in spring, but in summer are light yellowish-green with reddish-brown or greyish-black dorsal markings (see picture below). The body length is 1.3-1.8 mm. The siphunculi are sometimes surrounded by a membranous ring, at other times fused solidly into the dorsal carapace. The alates are dark, with broad dorsal abdominal cross-bands. The picture below shows a colony of sallow leaf-vein aphids in summer. The aphids are light yellowish-green with greyish-black dorsal marking and dusky siphunculi.

Sallow leaf-vein aphids live along the veins on the underside of leaves of various sallows (Salix caprea, Salix cinerea, Salix aurita). Unlike the other Chaitophorus commonly occurring on sallows (Chaitophorus capreae), they are usually ant-attended. Oviparae and apterous males occur in September-October. They occur throughout the Palaearctic region, parts of Africa, and are introduced and widespread in North America.

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Chaitophorus salijaponicus niger (Dark willow leaf aphid)

Adult apterae are usually blackish-brown with a pale ring around the bases of the siphunculi. The antennae, legs and cauda are mainly pale. However, there is considerable variation in dorsal sclerotization and in some populations individuals may be entirely pale. Alates are dark, with broad dorsal abdominal cross-bands. Nymphs are wine red with a yellowish suffusion around the siphunculi. The first picture below shows two apterae, one fully mature and black, the other recently moulted and brown along with some nymphs. The second picture shows an alate - the body is fairly uniformly dark, but the pale legs and antennae are useful distinguishing features.

 

Dark willow leaf aphids live separately or in small colonies on leaves of willow (narrow-leaved Salix spp.), only rarely visited by ants. Oviparae and males occur in September-November. Whether males are apterous or alate seems to depend on geographical location. They are found in Europe and across Asia to Siberia, but are replaced by a different subspecies in China and Japan.

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Chaitophorus truncatus (Green willow-leaf aphid)

Chaitophorus truncatus apterae are elongate oval in shape. In spring they are pale green with three darker green interrupted longitudinal stripes. In early summer and autumn some are solidly blackish on the dorsum. Their antennae are half the length of the body, and the terminal process is 2.2-3.2 times as long as the base of the last antennal segment. The siphunculi are pale, as are the legs and antennae. The body length of Chaitophorus truncatus is 1.2-2.4 mm.

 

Images copyright www.aphotofauna.com  all rights reserved.

Chaitophorus truncatus alates have separate, narrow, often broken bars across abdominal segments 3-8.

The green willow leaf aphid lives in small colonies on leavers of various narrow leaved willows including Salix purpurea, Salix amygdalina, Salix alba and Salix triandra. Apterous males and oviparae can be found in autumn. Chaitophorus truncatus does not host alternate, and is not ant attended. It is distributed throughout Europe and east to Iran and Kazakhstan.

 

Species of willow

We cover four species of willow, Salix caprea (common sallow or goat willow), Salix cinerea (grey sallow), Salix fragilis (crack willow) and Salix alba (white willow).

The sallows are broad-leaved trees. Common sallow (Salix caprea) is a tree or many stemmed shrub growing to 12 m. The leaves (see first picture below) are oval with pointed tips with the length usually less than or equal to 1.5 times as long as wide. The buds spread from the shoot. Grey sallow (Salix cinerea) is very similar to common sallow (and often hybridizes with it), but the leaves (second picture below) are usually 2-3 times as long as wide, and the buds are more or less adpressed to the twig.

 

The willows are narrow-leaved trees. Crack willow (Salix fragilis) usually grows to about 20 m. It is so named because the twigs break of easily and cleany with an audible crack. The lanceolate leaves (first picture below) are bright green with a finely serrated margin; although hairy when young, they soon become hairless. The leaf shown has galls caused by the sawfly Pontania. White willow (Salix alba) is a large tree up to 30 m tall. The lanceolate leaves are covered in silky white hairs, especially on the underside. However, it can be difficult to tell from crack willow with which it readily forms natural hybrids.

 

Acknowledgements

We have made provisional 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

  •  Blackman, R.L. & Eastop, V.F. Aphids on the world's plants An online identification and information guide. Full text