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Aphididae : Aphidinae : Macrosiphini : Acyrthosiphon
 

 

Genus Acyrthosiphon

Acyrthosiphon aphids

On this page: Acyrthosiphon boreale cyparissiae kondoi lactucae loti malvae pisum primulae

Genus Acyrthosiphon [Macrosiphini]

Acyrthosiphon aphids are rather large broadly spindle-shaped, short-haired aphids with long antennae, legs, siphunculi and cauda. Acyrthosiphon aphids are usually green but sometimes brownish, pink, or yellow. There are sometimes small marginal tubercles on abdominal segments II-IV and small spinal tubercles on the head. The antennal tubercles are well developed, usually smooth with diverging inner sides. The median frontal tubercle is very small or absent. The antennae are about as long as the body or longer. Apterae have secondary rhinaria near the base of antennal segment III; alates have more rhinaria on III. The siphunculi are cylindrical or tapering, occasionally with 1-3 rows of hexagonal cells below the distinct flange. The cauda is tongue- or finger-shaped, often slightly constricted.

This is a genus of about 80 species worldwide living without host alternation on various dicotyledons, particularly Fabaceae, Rosaceae, and Euphorbiaceae.

 

Acyrthosiphon boreale (Northern cinquefoil aphid)

Adult apterae of Acyrthosiphon boreale are green with the anterior part of the body yellowish. Their antennal tubercles are well developed with diverging, rough inner sides. The antennae are 0.7-1.1 the body length and the terminal process is 4.6- 6.0 times longer than the base of the sixth antennal segment. The third antennal segment of the aptera has 2-14 (rarely less than 5) slightly raised secondary rhinaria mainly on the basal half.The dorsal cuticle is slightly sclerotized and wrinkled, but not pigmented. The siphunculi are cylindrical with a rather well developed flange. The siphunculi are 0.21-0.30 times the body length and 1.5-2.6 times longer than the cauda. The cauda is rather thick, not constricted and bearing 7-11 hairs.

The fundatrix is similar to the aptera, but the terminal process is only 2.7 times longer than the base of the sixth antennal segment. Males are apterous.

Acyrthosiphon boreale lives year round on cinquefoils (Potentilla) species. It has a boreo-alpine distribution including northern Europe, Greenland and Canada.

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Acyrthosiphon cyparissiae (Dark-legged euphorbia aphid)

Adult apterae of Acyrthosiphon cyparissiae (see first picture below) are green or less frequently brown. The front of the head is black, and in most of Europe they have mainly black appendages, but in warmer climates the appendages may be brown or brownish yellow (see below re. ssp. propinquum). The first tarsal segments have 5-7 hairs (cf. other Acyrthosiphon spp. on Euphorbia, which have 3 hairs on each first tarsal segment). The black siphunculi are long, thin and outwardly curving; they have no subapical polygonal reticulation, and no trace of swelling or constriction before the rather well-developed flange (cf. Macrosiphum euphorbiae, Macrosiphum euphorbiellum, and other Macrosiphum spp. on Euphorbia, which all have a zone of subapical polygonal reticulation on their siphunculi). The pale greenish-brown cauda is long and pointed. The body length of adult Acyrthosiphon cyparissiae apterae is 2.4-3.4 mm.

Both images above copyright Marko Šćiban, all rights reserved.

The alate Acyrthosiphon cyparissiae (see second picture above) has similar coloration to the aptera, with green and brown forms, apart from the thorax which is brown.

There are two subspecies:

  • Acyrthosiphon cyparissiae ssp. propinquum. This has the front of the head pale or dusky, and the antennae, tibiae and siphunculi mainly pale with only the apices dark. Blackman comments that this form may not be a true subspecies but merely an effect of the environment.
  • Acyrthosiphon cyparissiae ssp. turkestanicum, which has been recorded from several Euphorbia (Euphorbia esula ssp. tommasiniana, Euphorbia ferganensis, Euphorbia lamprocarpa) in Central Asia.

Acyrthosiphon cyparissiae feeds only on Euphorbia species - mainly on the upper sides of the upper leaves. Sexual forms develop in autumn with alate males. It is found in Europe (but not apparently in the UK), the Middle East, Central Asia and China. The observations reported here by Marko Sciban appear to represent the first on-host record of the species in Serbia.

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Acyrthosiphon kondoi (Blue alfalfa aphid)

Adult apterae of Acyrthosiphon kondoi are bluish green. Their antennae are light brown basally, progressively darkening to the terminal process (cf. Acyrthosiphon pisum, invasive in America, which has dark bands at the apices of each antennal segment). The antennal terminal process is 4.7-6.0 times as long as the base of antennal segment VI (cf. Acyrthosiphon loti in Eurasia & South America, which has the terminal process 2.7-4.2 times the length of the base, and cf. Acyrthosiphon pisivorum (= ? Acyrthosiphon phaseoli) in China, whose terminal process is about 3 times as long as the base). The antennal terminal process is less than 0.2 mm long (cf. Acyrthosiphon pisum, which has a terminal process 0.25-0.40 mm long). The siphunculi are without a subapical zone of polygonal reticulation (cf. the cosmopolitan Macrosiphum euphorbiae & Macrosiphum creeli in North America, both of which a subapical zone of polygonal reticulation). The siphunculi are 1.6-2.1 times the caudal length (cf. Acyrthosiphon astragali in South Asia, which has siphunculi 2.0-2.6 times the length of the cauda, and cf. Acyrthosiphon gossypii in southern Europe and South Asia, which has siphunculi 2.5-3.5 times as long as the cauda). The siphunculi are only slightly attenuated distally (cf. Acyrthosiphon pisum, which has its siphunculi attenuated distally such that they are thinner than the hind tibiae at their respective midlengths).

Images above copyright Jesse Rorabaugh under a public domain (CCO) licence.

Alatae of Acyrthosiphon kondoi (see second picture above) have a darker brown thorax than Acyrthosiphon pisum, and have 7-9 secondary rhinaria confined to the basal half of antennal segment III.

Acyrthosiphon kondoi feeds on the stems and leaves of alfalfa (Medicago sativa), and other Medicago species, sweet clovers (Melilotus spp.), clovers (Trifolium spp.) and canary clovers (Dorycnium & Lotus spp.) as well as on milkvetches (Astragalus spp) and some members of the pea & bean family (Fabaceae). In its native Japan Acyrthosiphon kondoi is monoecious holocyclic, but seems to be anholocyclic in most other places. It is an important pest of alfalfa, most notably where it is invasive such as North and South America, South Africa, Australia and New Zealand.

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Acyrthosiphon lactucae (Lettuce seed-stem aphid)

Adult apterae of Acyrthosiphon lactucae (see first picture below) are pale yellowish green or pink. The dorsal surface has a pale grey wax bloom, often appearing as pale transverse stripes. The head is smooth, and the antennal tubercles are well developed with smooth broadly-divergent inner faces. The terminal process is less than 7.5 times as long as the base of antennal segment VI. Antennal segment III has secondary rhinaria and bears hairs that are less than 0.7 times the diameter of that segment. The fused apical rostral segment (R IV+V) is 0.6-0.7 times the length of the second hind tarsal segment (HTII), and has 16-25 accessory hairs (cf. Acyrthosiphon ilka, which has RIV+V 0.8-0.9 times the length of HTII, with 6-8 accessory hairs). There are no dark markings on the dorsum (cf. Nasonovia ribisnigri, which on the secondary host - lettuce - has dark intersegmental sclerites between each abdominal segment). Abdominal tergites I and VII usually have no marginal tubercles. The siphunculi are long and tapering with no polygonal reticulation (cf. Hyperomyzus lactucae, which has distinctly swollen siphunculi). The cauda is finger-shaped, clearly longer than its basal length. The body length of adult apterae is 1.7-2.9 mm. Immature apterous Acyrthosiphon lactucae (see second picture below) resemble the adult apterae, but have shorter siphunculi and cauda.

Both images above by permission, copyright Claude Pilon, all rights reserved.

Acyrthosiphon lactucae alatae (see second picture above of immature and adult alate of the pink form) show the same two colour forms as the apterae, but have somewhat dusky siphunculi.

Acyrthosiphon lactucae feeds on stems and undersides of leaves of lettuce (Lactuca species). It does not host alternate, remaining on lettuce year round. Sexuales develop in autumn, with alate males. Acyrthosiphon lactucae is a native Eurasian species and is found throughout Europe, the Middle East, Kazakhstan and Pakistan. In Britain the lettuce seed-stem aphid has only been found in southern counties. It was introduced to North America many years ago and is now widely distributed there. More recently Acyrthosiphon lactucae has been recorded from Argentina and Chile.

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Acyrthosiphon loti (Green trefoil aphid)

Apterae of Acyrthosiphon loti are green, or rarely pink, often with indistinct greyish transverse stripes. Their antennae have dark apices, but the individual antennal segments do not have dark apices. The antennae are 0.9-1.0 times the body length, and the antennal terminal process is 3.2-4.0 times longer than the base. The antennal tubercles of Acyrthosiphon loti are low and smooth and strongly diverging. The median frontal tubercle is low and flat. Acyrthosiphon loti siphunculi are dark tipped and are 1.2-1.6 times the caudal length. The siphuncular diameter at the midpoint is 1.0-1.4 times the diameter of the hind tibia at its midpoint. The body length of Acyrthosiphon loti is 1.7 to 2.9 mm.

The alate has rather indistinct marginal sclerites and pleural intersegmental sclerites. The third antennal segment has 3-19 rather large rhinaria, and the siphunculi are thinner than in the apterae. The apterous male Acyrthosiphon loti is greyish red with a very slender body.

The green trefoil aphid does not host alternate. Sexual forms occur in autumn and males are apterous or alate. It feeds on various members of the pea family (Fabaceae) especially trefoils (Lotus, Anthyllis and Hippocrepis) and lucerne (also known as alfalfa, Medicago sativa). Acyrthosiphon loti is found in Europe, eastward to Turkey, and has been introduced to Argentina.

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Acyrthosiphon malvae (Geranium aphid, Pelargonium aphid)

Acyrthosiphon malvae apterae are green, yellowish or greyish green, or pinkish red (see first two pictures below). The femora and siphunculi are pale. The terminal process of antennal segment VI is 4.8-5.8 times the length of its base. The longest hair on antennal segment III is 0.7-1.0 times the diameter of that segment and the apterae have 1-24 secondary rhinaria on that segment. The fused apical rostral segments are 1.1-1.4 times the second hind tarsal segment. Their siphunculi have no polygonal reticulation, are cylindrical on the distal half and are 1.8-2.2 times the pale caudal length. The body length is 1.5-3.2 mm.

The alate Acyrthosiphon malvae (shown giving birth in third picture above) has antennae longer than the body with 12-31 secondary rhinaria on antennal segment III. The abdomen is usually unsclerotized but may have small spinal and intersegmental pleural sclerites. The siphunculi and cauda are more slender than in the apterae.

Acyrthosiphon malvae is found on many plants, but particularly herbaceous Rosaceae. There are many subspecies, mostly with specific host-plant associations.

  1. Acyrthosiphon malvae sensu stricto are pale green or red aphids on many Geraniaceae and Malvaceae worldwide, as well as plants in other families.
  2. Acyrthosiphon malvae subspecies agrimoniae is yellowish green and found in flowerheads or on undersides of leaves of Agrimonia species (agrimony) in Europe and western Asia.
  3. Acyrthosiphon malvae subspecies poterii is bright salmon pink, yellowish or green and found on Poterium sanguisorba (= Sanguisorba minor) (salad burnet), and is only known from England.
  4. Acyrthosiphon malvae subspecies potha Börner is pale yellowish or greyish green and associated with Alchemilla species (lady's mantle) throughout Europe.
  5. Acyrthosiphon malvae subspecies rogersii (Theobald) is green or yellow-green, often shiny, and may form large colonies on young leaves of Fragaria (strawberry) in north and west Europe (Blackman & Eastop 2006).

The geranium aphid does not host alternate. All subspecies spend their entire life cycles on their respective host plants, overwintering in the egg stage. Distribution varies according to subspecies (see above).

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Acyrthosiphon pisum (Pea aphid)

Acyrthosiphon pisum apterae (see first picture below) are pale green or pink with red eyes. The antennae of Acyrthosiphon pisum are 1.0-1.6 times as long as the body. The antennal segments, tibiae and siphunculi have dark apices (cf. Acyrthosiphon loti which does not have the antennal joints darkened). The siphunculi are tapering and very thin with the diameter of a siphunculus in the middle less than the diameter of the hind tibia; the siphunculi are 1.2-1.9 times the length of the cauda. The cauda is long and tapered. The body length of Acyrthosiphon pisum apterae ranges from 2.2 to 5.0 mm long.

The alate viviparous female (see second picture above) has the head and thorax only slightly darker than the abdomen which is pale with small marginal sclerites.

The pea aphid can be found feeding on about 20 genera in the family Fabaceae but especially on Medicago, Melilotus, Trifolium, Dorycnium and Lotus. Acyrthosiphon pisum is a major pest of peas and alfalfa, partly because of direct feeding damage and partly because of virus transmission. Adults readily fall to the ground if the plant is disturbed. The pea aphid is found worldwide in temperate climates.

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Acyrthosiphon primulae (Primrose aphid)

Adult apterae of Acyrthosiphon primulae (see first picture below) are shiny pale yellow to greenish yellow. They have dark tips to the antennae and legs, but not to the siphunculi which are entirely pale. The median frontal tubercle is slightly developed. The siphunculi are 2.2-3.1 times longer than the cauda. The cauda of Acyrthosiphon primulae is 1.3-1.6 times longer than the base of antennal segment 6 (cf. Acyrthosiphon malvae which has the cauda 1.8-2.6 times longer than the base of antennal segment 6).

The Acyrthosiphon primulae alate vivipara (see second picture above) has dark distal cross-bands and postsiphuncular sclerites.

Acyrthosiphon primulae lives on the underside of leaves of Primula species, especially cowslip (Primula veris) and Kew primrose (Primula X kewensis). It reproduces solely by parthenogenesis and no sexual forms are known. Acyrthosiphon primulae is found in Britain and some European countries, and has been introduced to Tasmania, New Zealand and California.

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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

  •  Blackman, R.L. & Eastop, V.F. (2006). Aphids on the world's herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.