Griburius posticatus (Suffrian, 1866)

Sassi, Davide, 2024, Revision of the Griburius posticatus (Suffrian, 1866) species group (Coleoptera: Chrysomelidae: Cryptocephalinae), Zootaxa 5406 (2), pp. 201-237 : 206-207

Key to species of the Griburius posticatus species group

In the following species identification key, some dorsal colour patterns are emphasized. However, it should be noted that coloration is highly variable within the species group, and intermediate specimens and outliers are quite common. Therefore, the shape of the median lobe of the aedeagus must always be studied for reliable identification (it is also recommended to check the diagnoses provided for each species).

1. Elytron black with narrow yellow stripe running along lateral margin from humeral callus and ascending without interruption along the suture up to basal margin beside scutellum (Fig. 8h). Occasionally, the dark elytral pattern is brown instead of black (Fig. 8g), or brown except in the peripheral area, resulting in a tricolored pattern (Fig. 8f). Pronotum strongly transverse with seven black spots arranged in two transverse rows (4 + 3)........................ G. tredecimpunctatus , female (Fig. 8)

-. Elytral colour pattern differently arranged.................................................................. 2

2. Elytron black (rarely with an oblique chestnut patch in the middle, Fig. 3f) with evident metallic hues. Elytral punctation extremely minute and, apparently, irregularly arranged but actually composed of nine almost regular striae and densely micropunctate interstriae with micropunctations only slightly different in size from punctures on striae. Pronotum reddish or metallic black. Abdominal ventrites often covered with short, appressed golden setosity........... G. hyacinthinus (Fig. 3)

-. Elytron without evident metallic hues. Elytral punctation usually stronger (but see also couplet 5). Ventral surface devoid of golden setosity....................................................................................... 3

3. Dorsal surface totally yellow or with faint hint of black colour pattern........................................... 4

-. Dorsal surface with clear black colour pattern.............................................................. 7

4. Legs and head totally black. Anterior tarsi clearly broadened in males........ G. posticatus , lighter coloured form (Fig. 4a)

-. Legs, at least median and posterior ones, mostly or totally yellow or brownish. Head usually at least partly yellowish..... 5

5. Ocular distance more than 13% of the body length in males and up to 16% in females. Overall oval profile, with elytral margins becoming more noticeably convergent towards apex, humeral calli only slightly protruding, pronotal margins regularly curved. Elytra proportionally shorter compared to the pronotum. Species distributed in the Amazon region..................................................................................... G. hyacinthinus , light coloured form (Fig. 3k)

-. Ocular distance less than 10% of the body length both in males and in females. Profile more elongated with elytral margins more parallel, humeral calli more pronounced, pronotal margins curving more angularly. Elytra proportionally longer compared to the pronotum. Species distributed to the south of the Amazon region........................................... 6

6. Le/Lp ratio about 2.4. Dorsal surface markedly flattened. Outline slightly wider: Bl/Bw about 1.4. Dorsal punctation stronger........................................................................ G. ephippiatus , light form (Fig. 2f)

-. Le/Lp ratio about 1.9. Dorsal surface more convex. Outline slightly narrower: Bl/Bw about 1.5. Dorsal punctation weaker. Anterior tarsi not broadened in males..................................................... G. sciurellus (Fig. 6)

7. Elytron yellow or reddish with one rounded black spot on posterior half just before clivus. Pronotum totally yellow or yellow with two (rarely four) rounded black spots transversally arranged............................................... 8

-. Elytron prevalently black or yellow with more extended black pattern........................................... 9

8. In ventral view, the edges of the aedeagal apex on both sides of the apical tooth are substantially arranged along the same straight line. Setose depression and glabrous depression on each side clearly separated from each other by a narrow partition septum (Figs 4k–m). Ductus of spermatheca usually long, slender, tightly coiled only along half toward bursa copulatrix and forming sort of tangle near vasculum (but check what reported in “Remarks” for G. consanguineus )............................................................................................... Griburius posticatus (Figs 4–5)

-. In ventral view, edges of the aedeagal apex on both sides of apical tooth converge obliquely in the distal direction. Partition septum obliterated or almost obliterated, so as the setose depression and glabrous depression on each side scarcely delimited from each other (Fig. 10k). The duct of the spermatheca is short and entirely coiled, without forming a secondary convolution (tangle) beside the vasculum................................................. Griburius consanguineus (Fig. 10)

9. Pronotum strongly transverse, flattened, yellow with seven black spots arranged in two transverse rows (4 + 3). Elytron yellow as well with three rather lengthened black spots, two close to basal margin and third one just before apical clivus........................................................................... G. tredecimpunctatus , male (Figs 8a, 8b, 8e)

-. Pronotum black or yellow with or without black pattern, but never in form of seven spots arranged in two rows......... 10

10. Pronotum totally ochraceous. Elytron surface black with ochraceous band entirely covering basal fourth of surface. Such band slightly more extended along lateral margin to cover whole epipleuron. Remainder of elytral surface black. Dorsal surface slightly flattened with almost parallel sides................................................. G. semiluteus (Fig. 7)

-. Pronotum at least partly black or, if totally yellow or ochraceous, light colour on elytra not arranged in a transversal band entirely covering basal fourth of elytron.................................................................. 11

11. In males pronotum totally ochraceous or reddish; in females pronotum black, sometimes with reddish patch near or along anterior margin (Fig. 9g). In both sexes elytron surface black, usually with reddish patch along anterior part of side (Figs 9b, h), more rarely a light patch on elytral apex as well (Fig. 9e), but, in any cases, lateral margin is mostly black. Dorsal surface characterized by very tiny, almost obliterated punctation, above all towards apex.................. G. bicoloratus (Fig. 9)

-. Pronotum black with often yellowish lateral and anterior margins. Elytron usually yellow with large black patch at middle forming a variously arranged transverse band sometimes prolonged laterally to reach humeral callus but, in any case, margins are left mostly yellow (However, melanistic samples can be observed. In this case correct identification can be problematic without the examination of genitalia). Dorsal punctation usually stronger........................................ 12

12. Apical region of the aedeagus more squarely shaped, with sides converging towards the apical denticle basically aligned in the same direction; setose depression distinct from the glabrous depression by a small but evident septum, which sharply separates the two structures (st in figs 4k–m). Spermathecal duct longer (Fig. 11d), often forming a tangle near the vasculum, without being coiled or coiled only along a minor part of its length (but check what reported in “Remarks” for G. consanguineus )............................................................. G. posticatus , “ rufomarginatus ” form (Figs 4f–h; 5b)

-. Apical region of the aedeagus less squarely shaped, with sides converging towards the apical denticle along two oblique directions. Dividing septum on the ventral surface basically lacking, resulting in a minimal separation between the setose depression and the glabrous depression. Spermathecal duct shorter (Fig. 11a), not forming any tangle next to the vasculum, either entirely coiled or coiled along the majority of its length... G. consanguineus , “ rufomarginatus ” form (Figs 10e; 10g)