Key to apterae of polyphagous aphids

This key includes the 35 most polyphagous aphid species, species which occur numerous times in the host lists of many plant genera, and in some cases on plants in many different families. When you use this key you will normally have been directed to it, or to some starting point within it, from some point in another key. However, it may also be used on its own if, for example, an aphid is found on a plant from which no aphids have previously been recorded, or when the aphid that you are trying to identify does not seem to correspond to any of the aphid species listed under a particular plant genus. If either of these two problems occur then you may of course have an undescribed species, but it is far more likely that the aphid is a polyphagous species not previously recorded from that plant. Almost all polyphagous aphids have a long list of synonyms, because they have been described as new species again and again when found on previously unrecorded hosts.

If you are going to spend much time identifying aphids then it is a good idea to learn to recognise these polyphagous species and their chief characteristics. So, for each of the 20-or-so most polyphagous Macrosiphini and Aphidini, we have included a few additional recognition features. It is advisable to check through these each time, in order to confirm that your aphid really is a common polyphagous species, rather than something new.

To provide further help with recognition of polyphagous aphids, links are provided to photographs of slide-mounted apterae of all except one of the 35 species in this key (the exception being Aphis solanella which is superficially indistinguishable from A. fabae).

[A separate key is provided to polyphagous aphids found on some trees, although it includes many of the same species. Clicking on the links to “polyphagous aphids”in some of the keys to tree-dwelling aphids will take you to that key.]

1SIPH absent. ANT PT/BASE less than 0.5. Eyes of 3 facets …..2
SIPH present, conical or tubular. ANT PT/BASE more than 1.25. Eyes multifaceted …..4
2Body and appendages conspicuously hairy. Primary rhinaria with naked, sclerotic rims. ANT II elongate, about 2 × ANT I and similar in length to ANT III. Anus in posterio-dorsal position, with anal plate enlarged and surrounded on 3 sides by the U-shaped ABD TERG 8…..Smynthurodes betae (Plate 2f)
Body and appendages with sparse, short hairs. Primary rhinaria with ciliated rims. ANT II not elongate, not much longer than ANT I and much shorter than III. Anus in normal posterio-ventral position …..3
3Wax pore plates present on head, thorax and abdomen, especially well developed marginally on abdomen. R IV+V 0.130-0.175 mm long, with 4-8 accessory hairs. Cauda and anal plate forming a dark, rounded posterior projection of the abdomen…..Prociphilus erigeronensis (Plate 2h)
Wax pore plates absent from head and typically also from thorax and margins of abdomen; usually with 4 (2 spinal and2 pleural) on each of ABD TERG 3-6 and 1 spinal pair on ABD TERG 7. R IV+V 0.08-0.12 mm long, with 0(-2) accessory hairs. Cauda and anal plate not produced posteriorly…..Pemphigus sp. (Plate 2g; check with host list for probable species)
4Head ornamented with numerous spicules, often in rows, usually both dorsally and ventrally (in one case only ventrally). ANT tubercles well developed, with inner faces steep, almost parallel, gibbous or apically convergent, or with forwardly-projecting processes …..5
Head without spicules, or with a few minute ones ventrally. ANT tubercles undeveloped or variably developed, if well developed then with smooth divergent inner faces …..15
5Distal half of SIPH tapering or cylindrical, with no point where it is thicker than in a more basal part …..6
Distal half of SIPH clavate, or with at least with some degree of swelling, so that at some point distally or subapically it is thicker than in a more basal part …..8
6ANT 0.5-0.6 × BL, with PT/BASE 1.7-2.8. ANT III without rhinaria. Dorsal abdomen with a pattern of dark intersegmental spots. SIPH coarsely imbricated, and often with a shallow “S”-curve. (Check also: R IV+V 1.1-1.3 × HT II, with 2 accessory hairs. SIPH 2.1-2.7 × cauda, which has 4-6 hairs) …..Myzus ornatus (Plate 18f)
ANT 1.1-1.5 × BL, with ANT PT/BASE 4.0-5.5. ANT III usually with 1-3 small rhinaria near base. Dorsal abdomen pale or with more extensive dark markings. SIPH moderately imbricated and rather straight …..7
7Dorsum with extensive dark markings, including a roughly horseshoe-shaped dorsal abdominal patch and paired large dark patches on thorax. SIPH less than 10 × midlength width, with a moderate flange. R IV+V 1.2-1.7 × HT II, with 2 accessory hairs. Inner faces of ANT tubercles apically convergent. (Al. with 14-26 rhinaria on ANT III and 2-8 on IV)…..Neomyzus circumflexus (Plate 19c)
Dorsum without dark markings. SIPH more than 10 × midlength width, with a large flange. R IV+V 1.1-1.4 × HT II, and usually with 6 accessory hairs. Inner faces of ANT tubercles approximately parallel. (Al. with 5-26 rhinaria on III and none on IV)…..Aulacorthum solani (Plate 22i)
8SIPH markedly clavate, so that maximum width of swollen part is more than 2 × minimum width basad. Dorsal abdomen with dark markings …..9
SIPH more moderately clavate, with maximum width of swollen part less than 2 × minimum width basad. Dorsal abdomen without dark markings …..10
9SIPH with swollen part 3.7-4.8 × thicker than the narrow cylindrical basal part, and a narrowly constricted subapical region with polygonal reticulation. ANT III without rhinaria…..Rhopalosiphoninus latysiphon (Plate 21a)
SIPH with swollen part not more than 3.2 × the minimum width of the rather thick basal part, and subapical region not narrowly constricted, with a few rows of transverse striae proximal to flange. ANT III usually with 1-4 rhinaria on a thickened part near base…..Rhopalosiphoninus staphyleae (Plate 21b)
10SIPH 0.82-1.34 × ANT III …..11
SIPH 0.54-0.81 × ANT III …..12
11ANT tubercles themselves rather low, but with scabrous processes extending forward from ANT bases. SIPH weakly swollen subapically (over about distal 0.25). Dorsum with an evident reticulate pattern. (Al. with broken dusky/dark dorsal abdominal cross-bands)…..Abstrusomyzus phloxae (Plate 17h)
ANT tubercles broadly rounded, without forwardly-directed processes. SIPH slightly to moderately and asymmetrically swollen over about distal 0.6. Dorsum without a reticulate pattern. (Al. with a dark dorsal abdominal patch, solid except for a small posterior window). (Check also: ANT PT/BASE 2.8-4.5, hairs on ANT tubercles 0.2-0.6 × ANT BD III, R IV+V 0.9-1.0 (-1.2) × HT II, with 2-7 accessory hairs)

…..Myzus persicae (Plate 18h)

[Note: mid- to dark green aphids running to M. persicae in this key and occurring in rather dense colonies on the undersides of leaves of certain plants may be M. antirrhinii; see text, and also couplet 9 of the key to polyphagous aphids on trees.]

12SIPH with a narrow basal stem, its narrowest part thinner than, or as thin as, hind tibia at midlength. R IV+V (1.3-)1.4-1.6 × HT II, with 7-15 accessory hairs. (Check also: ANT tubercles with inner faces almost parallel, SIPH 2.3-3.3 × cauda, with maximum diam. of swollen part 1.5-1.8 × minimum diam. of stem …..Myzus ascalonicus (Plate 19a)
SIPH thicker on basal half, its narrowest part thicker than hind tibia at midlength. R IV+V 0.9-1.4 (-1.5) × HT II, with 2-8 accessory hairs …..13
13ANT PT/BASE 2.5-3.3. SIPH very coarsely imbricated on swollen part. Tergum very rugose. (Al. with wing veins without dark borders) (Check also: ANT tubercles very scabrous, their inner faces convergent, with spatulate hairs 0.2-0.4 × BD III, femora strongly scabrous)…..Myzus cymbalariae (Plate 19b)
ANT PT/BASE 3.5-5.3 SIPH smooth or normally imbricated on swollen part. Tergum not rugose. (Al. with dark-bordered wing-veins) …..14
14BL 1.1-2.9 mm. Femora mainly pale, SIPH not conspicuously dark-tipped. ANT III without rhinaria. Head spiculose dorsally as well as ventrally. (Al. with wing veins broadly dark-bordered) …..Neotoxoptera oliveri (Plate 19d)
BL 2.3-3.9 mm. Femora dark except at bases, and SIPH conspicuously dark-tipped. ANT III usually with a single rhinarium near base. Dorsal side of head almost devoid of spicules. (Al. with unbordered wing-veins) …..Pseudomegoura magnoliae (Plate 22h)
15Cauda helmet-shaped, not longer than its basal width, with 4-6 hairs. SIPH smooth, pale, conical, with a subapical incision below the flange. ANT tubercles undeveloped. ABD TERG 1 and 7 without marginal tubercles (MTu). Spiracular apertures large and rounded. Dorsum without any dark markings …..Brachycaudus helichrysi (Plate 9i)
Cauda tongue-shaped, finger-shaped, tapering or triangular, usually much longer than basal width, if not then it has 10 or more hairs. SIPH pale or dark, imbricated, without any marked subapical annular incision. ANT tubercles variably developed, if weakly developed then ABD TERG 1 and 7 have MTu. Spiracular apertures reniform. Dorsum with or without dark markings …..16
16ANT tubercles well-developed, with divergent inner faces. SIPH pale or dark, but if entirely dark then with a distal zone of polygonal reticulation. ABD TERG 1 and 7 without MTu. Body tends to be spindle-shaped with length of SIPH much more than 0.5 of the distance between their bases …..17
ANT tubercles little developed, or if somewhat developed then with middle part of front of head also projecting forward somewhat, so that the outline is sinuous in dorsal view. SIPH dark or pale with dark apices, never with polygonal reticulation. ABD TERG 1 and 7 constantly with MTu (although these may be very small). Body oval with length of SIPH usually 0.5 or less than the distance between their bases …..22
17SIPH with a distal or subapical zone of reticulation, comprisng at least 4-5 rows of closed polygonal cells …..18
SIPH without polygonal reticulation …..21
18SIPH pale or dark, with reticulation comprising a few rows of rather large polygonal cells on subapical 0.12-0.20 of length. Dorsal hairs not arising from pigmented scleroites. First tarsal segments with 3 hairs (all close to the apex) …..19
SIPH dark, with reticulation comprising many rows of numerous small polygonal cells on distal 0.25-0.43 of length. Some or all of dorsal hairs usually arising from small pigmented scleroites. First tarsal segments with 5 hairs (one pair placed laterally) …..20
19SIPH pale, or only dusky towards apices. ANT and legs mainly pale. MTu and STu usually absent.(Check also: ANT PT/BASE 5.3-6.2, longest hairs on ANT III 0.6-1.0 × BD III, R IV+V 0.8-1.0 × HT II, SIPH 1.7-2.2 × cauda …..Macrosiphum euphorbiae (Plate 25g)
SIPH dark, sometimes paler towards bases. ANT, femoral apices and tibiae usually dark. Abdomen often with MTu on some of ABD TERG 2-4, and ABD TERG 7 and 8 each usually with a pair of spinal tubercles (STu) …..Macrosiphum pallidum (Plate 25h)
20Cauda pale, contrasting with dark SIPH, which are 1.0-1.5 × cauda. Coxae pale. ANT III with 8-35 rhinaria. (Check also: R IV+V 1.15-1.43 × HT II with 7-9 accessory hairs, cauda with 16-27 hairs, MTu absent) …..Uroleucon ambrosiae (Plate 28d)
Cauda almost as dark as SIPH, which are 1.7-2.3 × cauda. Coxae dark. ANT III with 51-77 rhinaria. (Check also: R IV+V 1.1-1.4 × HT II with 7-9 accessory hairs, cauda with 10-23 hairs, MTu absent) …..Uroleucon compositae (Plate 28f)
21SIPH 0.75-1.0 × the thick black cauda, which bears 10-24 hairs. Femora and SIPH dark on distal halves …..Sinomegoura citricola (Plate 24i)
SIPH 1.8-2.2 × the pale cauda, which bears 6-12 hairs. Femora and SIPH pale. (Also check: longest hairs on ANT III 0.30-0.6 × BD III, ANT VI BASE 100-170 μm long, R IV+V 0.9-1.4 × HT II, with usually10-17 accessory hairs) …..Acyrthosiphon malvae (Plate 23a)
22SIPH almost cylindrical for most of length or with very slight swelling of distal part, constricted subapically and then broadened again to a well-developed flange (as if a noose had been placed around near the apex and tightened slightly). Tergum of thorax and abdomen with reticulate pattern of strings of small bead-like spicules arranged in polygons, most polygons enclosing one to many additional similar spicules …..23
SIPH tapering gradually over most of length, without any subapical constriction and usually with a small or moderate flange. Tergum smooth, wrinkled, or reticulated, but without bead-like spicules arranged in polygons …..24
23ANT usually 5-segmented with longest hairs on ANT III 3-5 × BD III. ANT PT often with an upward curve. ABD TERG 8 with 4-8 hairs…..Rhopalosiphum rufiabdominale (Plate 8h)
ANT 6-segmented with longest hairs shorter than BD III. ANT PT usually rather straight. ABD TERG 8 with 2 (-3) hairs. (Also check: ANT PT/BASE 3.5-5.6, SIPH 1.4-1.9 × cauda which bears 4-5 hairs) …..Rhopalosiphum padi (Plate 8g)
24Dorsal abdomen with an extensive solid black sclerite centred on ABD TERG 4-5. Cauda black like SIPH, tongue-shaped, rather pointed and usually bearing 4-7 hairs. (Also check: ANT PT/BASE usually 1.4-3.0, longest hair on ANT III 0.3-0.8 × BD III, R IV+V usually 0.9-1.2 × HT II, alata with 3-8 secondary rhinaria on ANT III, none on IV) …..Aphis craccivora (Plate 6d)
Dorsal abdomen with or without dark markings, but without an extensive solid black sclerite. Cauda pale or dark, but if black then usually with more than 7 hairs …..25
25Stridulatory apparatus present, consisting of a pattern of ridges on ventro-lateral areas of abdominal sternites 5 and 6, and a row of short, peg-like hairs on the hind tibia …..26
Stridulatory apparatus not present …..28
26SIPH much shorter than (0.4-0.6 ×) cauda. ANT PT/BASE 2.5-3.0…..Aphis odinae (Plate 8a)
SIPH 0.9-1.5 × cauda. ANT PT/BASE 3.5-5.0 …..27
27Longest hairs on ANT III 12-27 μm long, 0.5-1.0 × BD III. Longest hairs on hind tibia up to 60 μm long, less than 0.6 × HT II. Cauda with 10-26 hairs (rarely more than 20). BL often less than 2 mm. Forewing of alata with a very dark pterostigma, and media usually once-branched ….. Aphis (Toxoptera) aurantii (Plate 8b)
Longest hairs on ANT III 29-64 μm long, 1.5-2.0 × BD III. Longest hairs on hind tibia up to 80-110 μm long, 0.7-1.0 × HT II. Cauda with 19-54 hairs (rarely less than 25). BL usually more than 2 mm. Forewing of alata with pterostigma much paler than distal parts of femora, and with media twice-branched …..Aphis (Toxoptera) citricidus (Plate 8c)
28SIPH less than 0.1 × BL. ANT III with 0-12 rhinaria. ANT PT/BASE 1.4-2.1. ANT PT 1.0-1.5 × R IV+V. Cauda bluntly triangular. Dorsal abdomen usually with variably developed dark markings …..Protaphis middletonii (Plate 7e)
SIPH 0.10-0.26 × BL. ANT III usually without rhinaria (except in alatiform specimens). ANT PT/BASE 1.4-4.7. ANT PT 1.7-3.2 × R IV+V. Cauda usually tongue- or finger-shaped. Dorsal abdomen with or without dark markings …..29
29ABD TERG 1-4 (-5) and 7 with large flattish or domed marginal tubercles (MTu). SIPH 2.2-4.5 × cauda. Cauda short and rounded, not much longer than its basal width, with 13-21 hairs …..Aphis sambuci (Plate 7a)
MTu only sporadically occurring on ABD TERG 2-5 and then small and placed on marginal sclerites (if these are present). Cauda tongue- or finger-shaped, distinctly longer than its basal width, with 4-24 hairs …..30
30SIPH mainly pale or dusky, only dark towards apices. (Also check: ANT PT/BASE 1.8-3.5, longest hair on ANT III 0.4-0.7 × BD III, R IV+V 1.0-1.2 × HT II, SIPH 0.9-1.6 × cauda which bears 5-11 hairs, alata with secondary rhinaria distributed ANT III 8-16, IV 1-6, V 0-2) …..Aphis nasturtii (Plate 6g)
SIPH uniformly dark …..31
31ANT PT/BASE 3.4-4.7.R IV+V 1.25-1.6 × HTII. SIPH 1.7-2.7 × cauda …..Aphis nerii (Plate 6h)
ANT PT/BASE 1.4-3.5.R IV+V 0.85-1.3 (-1.5) × HT II. SIPH 0.7-2.5 × cauda …..32
32Cauda pale, dusky or dark, bearing 4-7(-8) hairs. Longest hind femoral hairs only 0.4-0.7 × diameter of trochantro-femoral suture. (Also check: ANT PT/BASE 2.0-3.5, R IV+V 1.1-1.5 × HT II, SIPH 1.3-2.5 × cauda, alata with secondary rhinaria distributed ANT III 3-15, IV almost always 0)

…..Aphis gossypii (Plate 7c)

[Note: specimens running to A. gossypii on certain plants, especially in Europe, could belong to a member of the very similar A. frangulae group, especially if they have ANT PT/BASE in range 2.6-4.2, ABD TERG 8 with a dusky/dark cross-band, and al. with 1-3 rhinaria on ANT IV; see text under both these names.]

Cauda always dark like SIPH, and bearing 7-24 hairs. Longest hind femoral hairs usually more than 0.7 × diameter of trochantro-femoral suture …..33
33Dorsal abdomen without any dark markings. Cauda usually with a midway constriction, and bearing 7-15 hairs. (Also check: ANT PT/BASE 1.9-2.9, longest hairs on ANT III 0.5-1.7 × but usually 0.7-1.0 × BD III, SIPH 0.9-1.7 × cauda, alata with secondary rhinaria distributed ANT III 6-11, IV 0-5) …..Aphis spiraecola (Plate 7b)
Dorsal abdomen with dark bands on ABD TERG 8, or 7 and 8, and often with dark markings anterior to SIPH …..34
34ANT I is dark, but ANT II is pale or dusky, concolorous with basal half of ANT III. Dorsal abdomen is usually without any dark markings anterior to SIPH (except for dark intersegmental muscle sclerites). ANT III 1.05-1.95 × PT, (1.6-)2.0-4.0 (-5.0) × R IV+V, and 1.5-2.5 (-2.8) × cauda. SIPH 1.2-2.9 × cauda. HT I with 3 hairs (sense peg present). ABD TERG 8 with 2-11 hairs. (Alata with 14-40 rhinaria on ANT III) ….. Aphis asclepiadis (Plate 6i)
ANT I and II are both dark, contrasting with ANT III. Dorsal abdomen usually has some dark markings anterior to SIPH (in addition to dark intersegmental muscle sclerites). ANT III 0.65-1.3 × PT, 1.2-2.6 (-3.0) × R IV+V and 1.2-1.6 (-1.9) × cauda. SIPH 0.7-1.6 × cauda. HT I with 2 hairs (no sense peg). ABD TERG 8 with 2-5(-7) hairs. (Alata has 10-23 rhinaria on ANT III) ….. 35
35SIPH 2.4-5.4 × longest marginal hair on ABD TERG 1-3. Longest hair on ANT III 17-69 μm (mostly 35-60 μm, and only less than 30 μm in hot weather dwarfs). Longest hair on hind femur 45-100 μm (mostly 70-90 μm, and only less than 60 μm in hot weather dwarfs). SIPH 2.8-5.1 × their diameter at midlength, 0.8-1.6 × cauda and 0.08-0.17 × BL. R IV+V 0.85-1.12 × HT II. ANT PT/BASE (1.8-)2.1-3.4 (-3.8) …..Aphis fabae (Plate 6e)
SIPH 5.4-17.0 × longest marginal hair on ABD TERG 1-3. Longest hair on ANT III 15-35 μm (mostly 20-30 μm). Longest hair on hind femur 45-75 (-82) μm. SIPH 3.5-7.5 × their diameter at midlength, 1.3-1.9 × cauda and 0.13-0.20 × BL. R IV+V (0.98-)1.03-1.30 × HT II. ANT PT/BASE 2.8-4.1 …..Aphis solanella