Key to Polyphagous Tree-dwelling Aphids

There are about 20 polyphagous aphid species that feed typically on herbs or shrubs, but occasionally occur on trees.  Apart from Longistigma caryae, which is a bark feeder, they are most frequently found on young growth of saplings, or on sucker growth of older trees.  The key that follows is intended to enable such species to be identified.  It should be used only after the host plant lists and tree-specific keys have been consulted, and in conjunction with the species descriptions in the Aphids section of the website.  It applies to apterae only, except where otherwise stated.  (Photographs of slide-mounted preparations of all these species except Aphis eugeniae and Myzus antirrhinii can be found in Blackman & Eastop 2000, pp. 416-466.)

 

1     ANT PT/BASE much less than 1.  SIPH on flat dark hairy cones (fig. 121A).  Very large aphid (BL more than 5 mm)                                                             .....Longistigma caryae

-      ANT PT/BASE much more than 1, and usually more than 2.  SIPH tubular, of varying shape.  BL less than 4 mm                                                                                             .....2

2     SIPH pale at least on basal third                                                                                    .....3

-      SIPH wholly and uniformly dark                                                                                .....12

3     Cauda long, dark and pointed, as long as or slightly longer than SIPH, which are dark on about distal two-thirds (fig. 121B)                             .....Sinomegoura citricola (Plate 24i)

-      Cauda pale or dusky, much shorter than SIPH, which are pale or dark only at apices

                                                                                                                                              .....4

4     SIPH long, with a subapical zone of polygonal reticulation extending over about distal 0.15 of length. Cauda long and pale (fig. 121C).  Spindle-shaped aphid, often rather large                                                                      .....Macrosiphum euphorbiae (Plate 25g)

-      SIPH without any subapical polygonal reticulation                                                       .....5

5     SIPH slightly to moderately swollen over distal 0.5-0.7 of length (figs 121D-H)        .....6

-      SIPH tapering from base to apex, without any trace of swelling (figs 121I-K)          .....10

6     SIPH markedly inflated over distal two-thirds, the swollen part being smooth and of maximum diameter more than 1.5× the minimum diameter of the stem.  Cauda triangular, usually with 5 hairs (fig. 121D)                     .....Rhopalosiphoninus staphyleae (Plate 21b)

-      SIPH slightly to moderately inflated, the swollen part being weakly or strongly imbricated and of maximum diameter less than 1.5× minimum diameter of stem.  Cauda triangular or finger-like with 6-8 hairs (figs. 121E-H)                                                   .....7

7     Head and ANT I and II dark, ANT III with 1-2 secondary rhinaria near base.  Legs mostly dark, and SIPH conspicuously dark-tipped (fig. 121E)

.....Pseudomegoura magnoliae (Plate 22h)

-      Head and ANT I and II pale, ANT III without any secondary rhinaria.  Legs mostly pale, SIPH not conspicuously dark-tipped                                                                    .....8

8     SIPH less than 0.8× ANT III, and coarsely imbricated even on swollen part.  Cauda triangular, about 1.5× its basal width (fig. 121F)

       .....Myzus (Sciamyzus) cymbalariae (Plate 19b)

-      SIPH more than 0.9× ANT III, and only weakly to moderately imbricated.  Cauda finger-like, about 2× its basal width                                                                              .....9

9     Usually dark green in life.  SIPH usually slightly dusky overall, with maximum width of swollen part usually more than 0.11× SIPH length (fig. 121G)           .....Myzus antirrhinii

-      Usually pale green, yellow-green or straw-coloured in life (but darker green in cold conditions).  SIPH usually quite pale except at apices, with maximum width of swollen part usually less than 0.11× SIPH length (fig. 121H)

       .....Myzus persicae (Plate 18h)

10   Dorsal abdomen with a large dark roughly horseshoe-shaped patch (fig. 121I)

       ..... Neomyzus circumflexus (Plate 19c)

-      Dorsal abdomen without a large horseshoe-shaped patch                                           .....11

11   Dorsal abdomen with an intersegmental pattern of dark ornamentation (fig. 121J).  ANT III without any secondary rhinaria.  ANT PT/BASE less than 2.5.  SIPH tapering, with

       a shallow S-curve, and coarsely imbricated.  BL less than 2 mm

       .....Myzus ornatus (Plate 18f)

-      Dorsal abdomen without any dark markings.  ANT III with a single rhinarium near base.  ANT PT/BASE more than 3.5.  SIPH fairly straight, weakly imbricated

        (fig. 121K).  BL usually more than 2 mm                     ......Aulacorthum solani (Plate 22i)

12   SIPH with a distal zone of polygonal reticulation                                                       .....13

-      SIPH without any polygonal reticulation                                                                    .....14

13   Cauda black (fig. 121L). Tibiae mainly pale               .....Uroleucon compositae (Plate 28f

-      Cauda pale (fig. 121M).  Tibiae mainly dark              .....Uroleucon ambrosiae (Plate 28d)

14   Dorsal abdomen almost wholly covered by an extensive solid black sclerite.  Cauda black and usually bearing 4-7 hairs (fig. 121N)                             .....Aphis craccivora (Plate 6d)

-      Dorsal abdomen without an extensive solid black sclerite.  Cauda if black then usually with more hairs                                                                                                             .....15

15   Stridulatory mechanism present, consisting of a conspicuous pattern of ridges on ventrolateral areas of abdominal sternites 5 and 6, and a row of short peg-like hairs on the hind tibia (fig. 122)                                                                                                .....16

-      Stridulatory mechanism not present, although peg-like hairs are sometimes present along part of hind tibia                                                                                                          .....18

16   SIPH much shorter than (0.4-0.6×) cauda (fig. 121O).  ANT PT/BASE 2.5-3.0

       .....Aphis odinae (Plate 8a)

-      SIPH usually longer than (0.9-1.5×) cauda (figs 121 P, Q).  ANT PT/BASE 3.5-5.0

                                                                                                                                            .....17

17   Longest hairs on ANT III 12-27 µm long, 0.5-1.0× basal diameter of segment.  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

       .....Aphis (Toxoptera) aurantii (Plate 8b)

-      Longest hairs on ANT III 29-64 µm long, 1.5-2.0× basal diameter of segment.  Longest hairs on hind tibia 80-110 µm, 0.7-1.0×HT II.  Cauda with 19-54 hairs (rarely less than 25).  BL usually more than 2 mm

       .....Aphis (Toxoptera) citricidus (Plate 8c)

18   Dorsum with variable dark markings, usually consisting of at least dark sclerotic bands on pronotum, mesonotum and ABD TERG 7 and 8, and small dark marginal sclerites (fig. 121R); often also with small dark sclerites scattered over other abdominal tergites.  Cauda with 12-24 hairs                                                                                                .....19

-      Pronotum, mesonotum and ABD TERG 7 and 8 without dark sclerotic bands and marginal sclerites not deeply pigmented.  Cauda with 4-22 hairs                               .....20

19   Longest hair on ANT III 35-50 µm, longest hair on hind femur 60-85 µm.  R IV+V 0.85-1.05× HT II.  SIPH 0.9-1.6× cauda and 0.10-0.17× BL.  ANT PT/BASE 2.4-3.4

       .....Aphis fabae (Plate 6e)

-      Longest hair on ANT III 15-25 µm, longest hair on hind femur 45-70 µm.  R IV+V  1.05-1.30× HT II.  SIPH 1.3-1.8× cauda and 0.14-0.20× BL. ANT PT/BASE 2.9-3.4

       .....Aphis solanella

20   HT I with 3 hairs (i.e., medial sense peg present), first tarsal chaetotaxy 3:3:3.  Cauda black with 9-22 hairs (e.g. fig. 121S)                                                                           .....21

-      HT I with 2 hairs (no medial sense peg), first tarsal chaetotaxy 3:3:2.  Cauda pale, dusky or black with 4-12 (-15) hairs                                                                                       .....22

21   ANT PT/BASE 3.5-4.8.  R IV+V 1.3-1.6× HT II.  Hind tibiae black

       .....Aphis nerii (Plate 6h)

-      ANT PT/BASE 2.5-3.5.  R IV+V 1.1-1.3× HT II.  Hind tibiae only dark towards apices

       .....Aphis eugeniae

22   Femoral hairs long and fine, the longest of them being longer than the diameter of the femur at its base.  Cauda black, usually with a distinct constriction about one third from base, and bearing 6-12 hairs (fig. 121T)                                .....Aphis spiraecola (Plate 7b)

-      Femoral hairs all rather short, not exceeding the diameter of the femur at its base.  Cauda pale or dark, but usually clearly paler than siphunculi, tongue-shaped without a constriction, and bearing 4-7 hairs (fig. 121U)                         .....Aphis gossypii (Plate 7c)