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The thistles form the tribe Cynareae in the daisy family (Asteraceae). Most species have prickly leaves, stems or flowers. Over 100 species of aphids feed on the more than 2500 species of thistles worldwide, mainly in temperate Europe and Asia. The majority of these aphids are in just four genera, namely Aphis, Brachycaudus, Capitophorus and Uroleucon. Here we show the commonest species found on thistles in Britain from those genera. Please refer to Blackman & Eastop  for formal identification keys and further information on thistle aphids found worldwide (the link will take you just to aphids on Cirsium).

The species below are those we have found most frequently, listed in rough order of abundance. Some assistance on identification of common thistles is given below. 

 

Aphis fabae cirsiiacanthoidis (Black spindle-thistle aphid)

A black or very dark brown species with a variable abdominal sclerotic pattern - confined to abdominal tergites 6-8 in smaller apterae but broken bands present in larger ones. The siphunculi and cauda are dark. The antennae have joints of III-IV and base of V usually quite pale. Marginal tubercles are protuberant but small. The longest femoral and tibial hairs are longer than the least width of tibiae. Apterae often, and immatures very often, have discrete white wax spots. The body length of apterae is 1.2-2.9 mm.

Another subspecies of the black bean aphid (Aphis fabae solanellae ), now sometimes given specific status, is also found on thistle. It can be differentiated from Aphis fabae cirsiiacanthoidis by the length of hairs on the antenna and hind femur. Aphis fabae cirsiiacanthoidis has the longest hair on the third antennal segment 35-50 um and the longest hair on the hind femur 60-85 um. Aphis fabae solanellae has the longest hair on the third antennal segment 15-25 um and the longest hair on the hind femur 45-70 um.

 

The black spindle - thistle aphid host alternates between spindle (Euonymus europaeus) as the primary host and thistles (especially Cirsium and Cynara species) as secondary hosts. In many tropical and subtropical countries it may reproduce parthenogenetically all year round. Aphis fabae has a cosmopolitan distribution.

 

Brachycaudus cardui (Plum - thistle aphid)

Identification:The apterae are brownish-yellow, pale green or brown, with a large black spot situated dorsally on the abdomen and 2 or 3 black stripes at the tip. The siphunculi are black, thick and cylindrical and 1.7-3.4 the length of the cauda. The rostrum is long and reaches the hind coxae. The body length of apterae is 1.8-2.4 mm.

 

The primary hosts are various Prunus species, mainly cherry, plum and apricot. Aphids migrate to various wild and cultivated daisies (Asteraceae) especially thistle (Carduus and Cirsium spp.) and borage (Boraginaceae). Infested leaves undergo severe curling. Dense colonies occur at the base of flower heads and on the leaves. The plum-thistle aphid is found throughout Britain and Europe as well as in Asia, north Africa and North America.

 

Uroleucon cirsii (Large thistle aphid)

This rather large aphid is a bronzy or reddish brown with pale legs that are darkened towards the apices of the segments. Abdominal hairs are placed on pigmented scleroites. Spinal scleroites are fused into larger sclerites, each normally with three hairs. A crescent shaped sclerite is present in front of each siphunculus. The siphunculi are 0.25-0.34 times the body length, and 1.6-2.2 times the length of the cauda, with polygonal reticulation on less than the distal 0.25 of their length. The slightly dusky cauda has 20-33 hairs.

 

The large thistle aphid lives on the leaves and stems of the creeping thistle (Cirsium arvense) and related species. The young of Uroleucon aphids are quite distinctive as they are usually reddish-brown. Urolueucon cirsii is common throughout Europe and across Russia to Siberia, and has been introduced to North America.

 

Uroleucon jaceae (Large knapweed aphid)

This is a large blackish aphid. The abdominal tergites 2-4 often have small marginal tubercles about the size of hair bases. The femora have the basal half pale and distal half dark, with a rather sharp transition between them. The tibiae are totally black. The siphunculi are reticulated over the distal 0.16-0.27 of their length and are 1.3-1.8 times the length of the cauda. The cauda is dark and bears 18-30 hairs. The body length of apterae is 3.0-4.5 mm long.

 

The large knapweed aphid lives on various knapweeds (Centaurea spp.) and a few other species of Asteraceae, but not generally on other thistles. It is found across Europe to the Middle East and much of Asia.

 

Capitophorus carduinus (Thistle oleaster aphid)

The wingless viviparae are pale greenish white to yellowish green, almost translucent, with two indistinct darker green longitudinal stripes. The terminal process of the antenna is 4.6-6.3 times the length of the base of the last antennal segment. They have long capitate hairs on the head and posterior abdominal segments. The siphunculi are pale, slender and cylindrical, and are 2.4-3.5 times the length of the cauda. The siphunculi have no distal reticulation and are without dark apices. The body length of wingless viviparae is 1.6-2.2 mm.

 

The thistle oleaster aphid does not host alternate. It lives on the stem and the undersides of the lower leaves of thistles (Carduus and Cirsium spp.). It is found in Europe and in various Asian countries.

 

Capitophorus elaeagni (Common oleaster aphid)

Apterae in spring populations are pale green. The abdominal dorsum is reticulate or sculptured, and abdominal tergites 1-4 each have 6-8 hairs, usually one pair each of spinal, pleural and marginal hairs. The siphunculi are cylindrical or tapering. The body length of wingless viviparae on the primary host is 1.9-2.5 mm. Winged viviparae produced on the primary host have a black head and thorax, black antennae and a blackish dorsal abdominal patch. Wingless viviparae on the secondary host (see below) are greenish white to yellowish green with dark tips to the siphunculi. The body length of wingless viviparae on the secondary host is 1.4-2.5 mm.

 

The common oleaster aphid host alternates from oleaster (Elaeagnus) or sea buckthorn (Hippophae) to various thistles and daises (Asteraceae). It is found over most of the temperate and warm temperate parts of the world. We have so far only found it in Britain on its primary host (oleaster).

Species of thistle (Cynareae) 

Most of the plants in the tribe Cynareae are commonly termed thistles, including Cirsium, Carduus, Carlina, Cynara and Echinops. One exception to this is the genus Centaurea which comprises the knapweeds. These have typical thistle-type flowers, but the leaves are not usually prickly. Probably the commonest thistle species in Europe is the creeping thistle (Cirsium arvense) (below first) which is a major weed pest on agricultural land. Another common species on calcareous land is the spear thistle (Cirsium vulgare) (below second).

 

The flowers of the creeping thistle are small and purple and at the tips of the stems. The leaves are deeply divided with prickly margins. The inflorescence of the spear thistle is flask-shaped. Its stem is winged and its leaves are deeply cut with a wrinkled grey green appearance.

Two further species are the marsh thistle (Cirsium palustre) (below first) and the carline thistle (Carlina vulgaris) (below second).

 

The marsh thistle is tall and grows in damp places. The leaves are decurrent and spinous and the flower heads are clustered. The carline thistle is a short species that grows on calcareous grassland. The leaves and outer bracts are spinous and the inner bracts are whitish, spreading like rays.

The other main genus of thistles is Carduus including the nodding thistle (Carduus nutans) (below first) and the less common and localized shore thistle (Carduus tenuiflorus) (below second).

 

The lower leaves of the nodding thistle are smooth with a prominent white mid-rib. The stem is spiny and the flower often tips downwards - hence nodding thistle. The stem of the shore thistle is winged and spinous throughout. The florets are small, not exceeding the length of the bracts.

The next two species are native to southern Europe but are widely cultivated elsewhere. The globe artichoke (Cynara cardunculus) (below first) is grown for food, whilst the globe thistle (Echinops ritro) (below second) is grown for its ornamental value.

 

The globe artichoke has long arching deeply lobed glaucous green leaves and a large edible flower bud. The globe thistle has divided prickly dark green leaves which are whitish beneath and rounded, violet-blue flower heads (not yet out in the picture) on silvery branched stems.

The common knapweed (Centaurea nigra) (below first) is a common plant which has a thistle like flower head, but spineless leaves and stem. The greater knapweed (Centaurea scabiosa) (below second) is mainly found in chalk grassland.

 

The common knapweed has the leaves of the upper stem lanceolate, and the bract appendages blackish concealing the base. The greater knapweed has the leaves toothed and the bracts green, not fully covered by the dark fringe.

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