Key to Australian, Indomalayan and southwest Pacific species of Altica Geoffroy

Note: specimens of Altica aenea, A. birmanensis, A. corrusca and A. cyanea are only reliably separated by careful examination of the genitalia, and some females of A. aenea and A. birmanensis may not be distinguishable at all. Host plants and distribution may provide useful diagnostic information (Table 2).

1. Eyes relatively smaller (Figs 8–10, 12–13), EG <7.5 (usually <7), IE>1.15 (usually>1.25), HG <16 (7.5–15.3); elytra (Figs 1–3, 5–6) without lateral ridges, or with short keel (usually weak) from humerus to middle; dorsum usually deep blue, less commonly bronze, purplish, dark green or with blue pronotum and green elytra; penis (Figs 23–24, 27–28) shorter, 1.5–2.15mm, without ridges on venter; vaginal palpi (Figs 30, 47–51, 54–57) less elongate, length ≤1.5x width (elytra & hypomeron not microreticulate).......................................................................... 2

- Eyes relatively larger (Figs 11, 14), EG>7 (usually>8), IE <1.25 (usually <1.15), HG>16 (17–22.2); prominent longitudinal ridge (sometimes additional ridges in females), usually present on elytra (Figs 4, 7) from humerus to 2/3 length of elytron, rarely absent; dorsum usually bronze-green to greenish-blue, rarely purplish or dark blue; penis (Figs 25–26, 29) longer, 2.25–2.5mm, strongly transversely or obliquely ridged on dorsum and venter; vaginal palpi (Figs 31, 52–53, 58–61) more elongate, length ≥1.5x width (first antennomere usually entirely dark; outer face of midtibiae flat; habitat in wetlands)..... 5

2(1) External face of midtibia at midpoint convex, often with longitudinal keel as well; penis (Figs 23, 24, 28) usually longer, 1.65–2.15mm, straighter in lateral view, shallowly transversely ridged on middle of dorsal surface (except A. aenea in New Ireland); tignum (Figs 32–36, 39–42) with prominent lateral arms (north & east Australia, New Guinea, south and east Asia, west and central Pacific)............................................................................... 3

- External face of midtibia at midpoint flat with thin median ridge; penis (Fig. 27) usually shorter, 1.5–1.7mm, more curved in lateral view, without transverse ridges on either face; tignum (Figs 30, 39–40) with broad base and short or absent lateral arms (length 4.2–6.1mm; antennae black, rarely reddish at apex of first antennomere; male eyes relatively small, male EG 3.0–3.3, male HG 7.4–8.6; apex penis not kinked in lateral view; hostplants variable but including non-littoral genera; south-east Australia).............................................................................. corrusca (Erichson)

3(2) Eyes generally larger and more convex (Figs 8–9), male IE 1.20–1.55, female IE 1.2–1.5, female EG 3.5–6.85, female NE 1.93–2.23 (small-eyed forms present in both sexes but infrequent); at least apical quarter of first antennomere orange to reddish-brown, or rarely dark brown (some NW Victorian specimens); anterior of clypeus generally smoother, edge less strongly raised; apicoventer of penis (Fig. 23) with short pair of depressions (0.2–0.25x penis length), apex of penis abruptly bent in lateral view (only slightly so in some New Guinea specimens); tignum usually shorter, 0.85–0.95mm (length 4.6–6.4mm; hostplant Ludwigia, in wetlands and the littoral zone; north and east Australia to 37°S, southeast Asia and west Pacific).................................................................................................. aenea (Olivier)

- Eyes generally smaller (Figs 10, 13), less convex, male IE 1.32–1.85, female 1.4–1.8, female EG 2.9–3.8, female NE 2.33–2.70; first antennomere variable, black or with orange apex; anterior of clypeus generally more rugose or strigose, edge more strongly raised; apicoventer of penis (Figs 24, 28) with longer pair of depressions (0.25–0.3x length), apex of penis straight or almost so in lateral view; tignum usually longer, 0.94–1.35mm (length 5.0– 7.3mm; hostplant Polygonum or Melastoma; absent from Australia and Pacific Islands)............................................................ 4

4(3) Anterior of clypeus more rugose (Fig. 13), anterior edge usually sharply ridged; elytra (Fig. 6) without short keel behind humerus; apicoventral depressions of penis (Fig. 28) separated by a sharp ridge, usually also internally finely ridged; vaginal palpi (Fig. 56–57) short, almost ovate, with rounded to truncate apex and straight or convex inner margin; tignum (Fig. 42) with base expanded, broader than stem of apex, and broad triangular lateral arms; host Melastoma (length 5.0– 6.1mm; heathland, disturbed ground, Malay Peninsula to Java and Borneo)....................................... cyanea Weber

- Anterior of clypeus smoother (Fig. 10), anterior edge flatter; elytra (Fig. 3) usually with short keel behind humerus; apicoventral depressions of penis (Fig. 24) smooth, separated by broad flat ridge (ridge may be medially depressed at apex); vaginal palpi (Figs 50–51) short, almost conical, with obliquely truncate apex and concave inner margin; tignum (Figs 35–36) with thin acute base, narrower than stem of apex, and small triangular or thin lateral arms; host Polygonum (length 5.0– 7.3mm; wetlands, edge of rainforest, ditches; southeast Asia to Timor and New Guinea)...................... birmanensis (Jacoby)

5(2) Elytra and prothoracic hypomeron duller, microreticulate (Fig. 7); penis (Fig. 29) slightly expanded from middle to apex, apicoventral grooves smooth-edged, lateral ventral ridges fewer, more oblique, subtending <90° at midline; tignum (Figs 43–46) with base broader than shaft and without lateral spurs; palpal apodeme (Figs 58–61) broader, at least 1/3 width base of vaginal palp (length 5.6–7.2mm; usually entirely dark bronze-green; host Myriophyllum, in wetlands; Australia, except southwest)....................................................................................... gravida (Blackburn)

- Elytra and hypomeron shining, without microsculpture (but often soiled) (Fig. 4); penis (Figs 25–26) parallel-sided or broadest before apex, apicoventral depressions laterally sharp-edged, lateral ventral ridges more numerous, usually less oblique, subtending approximately 90° at midline; tignum (Figs 37–38) with base as narrow or narrower than shaft, with or without short lateral spurs; palpal apodeme (Figs 52–53) narrower, <1/3 width base of palp (length 5.6–7.0mm; entirely dark blue [typical colour in Indonesia], purplish, or dark green, or bicoloured [common in Australia], with contrasting pronotum and elytra; host Ludwigia, in wetlands; north & east Australia to 29°S, southeast Asia to New Guinea)................ caerulea (Olivier)