Macrolema Baly 1861

Reid, C. A. M. & Beatson, M., 2010, 2486, Zootaxa 2486, pp. 1-60 : 9-11

Macrolema Baly 1861

Type species: Macrolema vittata Baly 1861 , by original designation and monotypy

= Macrogonus Jacoby 1894 ; Seeno & Wilcox 1982 (synonymy). Type species: Macrogonus submetallicus Jacoby , by monotypy

Diagnosis

Length 8–15mm; shape elongate, with strongly narrowed base of pronotum compared with elytral width at humeri; dorsum not distinctly pubescent, but may have scattered minute setae; eyes large, gena c. 0.1–0.4x eye length; pronotum widest at middle, or middle and anterior, and width at posterior angles narrower than width at anterior angles; lateral margination of pronotum absent; prosternal process elongate, arched between coxae, apex truncate or slightly pointed; elytra partially striate, but striae may be obscured by large interstrial punctures; male tibiae straight; tibial spurs 1+2+2, or 0+2+2, or 0+1+1; claw simple, with slight angulation at base of ventral margin; ventrites I and II fused or rarely not entirely fused, with some movement at middle.

Description

Length 8–15mm, females larger than males on average (rarely overlapping); body ( Figs 3–16) elongateovate, length 2.5–3.0x width, but with prominent elytral humeri and narrow pronotal base, moderately to shallowly convex in profile, length 2.7–3.4x height. Dorsum shining and smooth, coloured metallic green or blue, or plain brown or black, with or without areas of pale yellow or red, glabrous except trichobothria adjacent to eyes and on each corner of pronotum, or with additional short setae on vertex, pronotum and/or elytra.

Head ( Figs 19–37): fronto-clypeus smooth, triangular, anterior margin shallowly concave, usually depressed between eyes and without elevated apex; vertex smooth; eyes ovate, height c. 1.5x width, inner margin shallowly concave; eye laterally projecting, posterior curvature contiguous with short temples, which are constricted to parallel-sided head capsule; head capsule generally without deep grooves or ridges, but a few species with deep median groove between eyes; gena 0.1–0.4x greatest eye length; antennae 4–6x socket diameters apart; antennae c. 0.6–0.9x body length; relative sizes of antennomeres variable, but 1 always enlarged cylindrical or widest at apex, 2 shortest (c. 0.5–0.67x first), 3 equal to or shorter than 1, antennomeres 8–11 almost parallel-sided, 7, or 7 and 11, or 5, 7 and 11 longest; antennomeres 1–4 shining and sparsely punctured, 6–11 dull and densely microsculptured, 5 intermediate; labrum not densely setose, with 1– 3 pairs of prominent setae; mandible with single apical tooth and two setose membranes (pulvilli) at middle and base of inner margin; apical maxillary palpomere elongate, fusiform to cylindrical, males with broader truncate apex; preapical palpomere triangular, length equal to or shorter than apical, and of similar width; mentum transverse, width c. 4x median length, but anterior angles narrowly produced.

Thorax ( Figs 3–16, 37–40, 42–43, 45–59): pronotum transverse, width 1.3–1.85x length, broadest anterior to middle (or anterior angles as well) and slightly to strongly contracted to anterior and posterior angles; disc with or without pair of depressions; anterior edge truncate to concave, posterior convex or medially truncate, lateral margins slightly convex to strongly sinuate or lobed; anterior (at least at sides) and base distinctly margined (except some individuals with border absent at hind angles), lateral margination absent; anterior and posterior angles laterally prominent, with single trichobothria; posterior trichobothria anterior to vertical plane above posterior margin of hypomeron, anterior displacement most pronounced in M. albascutica , least so in M. aenescens ; posterior edge of hypomeron projecting into hollowed base of elytra; prosternum flat and punctate between coxae and head; prosternal process narrow and strongly arched, with slightly pointed or truncate apex; procoxal cavities closed by insertion of hypomeral lobes into prosternal process; scutellum elongate-triangular, apex superimposed on sutural base; elytra broadest at base, with strongly developed humeri, with or without lateral or median depressions; with scutellary striole and up to 9 striae, plus series of large punctures at epipleural margin, striae often obscured; elytral epipleuron narrow, width <0.2x elytral width, entirely visible laterally, slightly sinuate, gradually contracted from base to apex; mesoventrite entirely visible, well-developed, punctured, with elongate and parallel-sided median process; anterior of mesoventrite process evenly curved or elevated with anteriorly facing ridge; wings fully developed; metaventrite shining, smooth or feebly transversely wrinkled, transverse, width c. 2x length, without femoral plates; metepisternum smooth and shining or weakly microreticulate, with sparse punctures; all femora fusiform, with base and apex narrowed, without longitudinal keels or ridges, all tibiae round in section, without keels, thin, with abruptly expanded apices; short spur on protibia present or absent, 1 ( M. longicornis ) or 2 on remainder; all first tarsomeres with oval patch of modified setae in males, with dense simple setae diverging from midline in females; apex second tarsomere concave; third tarsomere deeply bilobed, lobes at least 0.5x median length; claws simple, without basal tooth.

Abdomen ( Figs 61–65, 68–80, 82–95, 97, 99–112, 114–127, 129): pygidium (tergite 7) not strongly sclerotised except at apex, basal half membranous, apical half pubescent and punctured, without median groove; ventrite I with triangular intercoxal process and without femoral plates; ventrites I and II usually completely fused; ventrite V smooth, not medially depressed, and truncate or convex at apex in both sexes, but shorter in male; dense sclerotisation of sternite VIII of male variable, fan-shaped, Y-shaped, or linear; sternite IX of male Y-shaped; male tegmen present, enclosing penis, U- shaped, thinly sclerotised and with slight internal median keel; penis simple, flattened tubular, apex sparsely microspiculate, basal foramen c. 0.4x length of penis; vas deferens with long thickened sperm pump; female tergite VIII well-developed, sternite VIII with transverse to elongate basal apodeme; ovipositor with thin bacillus wrapped around base of paraprocts, which are well-developed, partly enclosing basal half of palpi, pair of well-defined elongate proctigers dorsal to these; vaginal palpi 2-segmented, gonocoxite massive, not divided, gonostylus variable in size and shape; membranous pad between gonocoxites lacking sclerite; spermatheca generally falciform, surface microreticulate, with long spermathecal duct; kotpresse absent, rectum without band of spinules.

Notes

The diagnostic description for Spilopyrinae provided in Reid (2000) needs to be modified to accommodate all species of Macrolema as follows: gena 0.1–1.5x eye length; antennomeres 8–11 to 6–11 densely setose and microsculptured; anterior pronotal border complete or effaced at middle; articulated tibial spurs 0+1+1, or 0+2+2, or 1+2+2, or 2+2+2; third tarsomere shallowly or deeply bilobed; kotpresse (faecal plate organ) present or absent.

The synonymy of Macrolema and Macrogonus Jacoby has been briefly dealt with ( Reid 2000), but is explained in full here. Macrogonus was defined by possession of lateral lobes on the pronotum ( Jacoby 1894). This feature is a grade, at its most extreme in M. submetallicus and M. ventralis , but with varying degrees of expression in between. Differences in other features such as prothoracic morphology, elytral depressions, male and female genitalia, do not conform with development of the pronotal lobes, therefore the synonymy is justified. However the synonymy was originally based on a misunderstanding by Lea, who confused males and females of a species with lateral lobes ( M. atripennis ) and one without ( M. longicornis ) ( Lea 1921a). Curiously, having decided that Macrogonus and Macrolema could not be distinguished except in males, Lea described M. ventralis in Macrogonus on the mistaken assumption that the holotype was a female specimen ( Lea 1921b). This action has led to considerable confusion in Australian collections, which have been dominated by material identified by Lea.

Sexual dimorphism

Sexual dimorphism is slight. Males are smaller on average, with larger cephalic sensory organs: apical maxillary palpomeres broader, antennae longer, eyes proportionally larger. Males also have first tarsomeres broader and ventrite 5 shorter.

Distribution and biology

Macrolema is confined to Australia and New Guinea; it occurs on the eastern ranges of Australia, from Barrington Tops, New South Wales, in the south, to Cape York Peninsula, Queensland, and the eastern ranges of New Guinea ( Figs 130–134). A number of early Australian specimens appear to have erroneous locality labels as they have come from two poorly curated collections (see under species descriptions). Ignoring these suspect labels, the 11 Australian Macrolema species are restricted to only 4 of the 85 recently designated Australian bioregions ( Anonymous 2009): Wet Tropics (6 species), Central Mackay Coast (1), Southeast Queensland (3), New South Wales North Coast (2), all of which are dominated by high rainfall forests.

The species are generally rarely collected, although large and conspicuous. Two species have been collected at light ( M. metallica , M. quadrivittata ), and two other species ( M. pulchra , M. ventralis ) have probably been collected in similar circumstances, as specimens are clothed in lepidopteran scales. Almost all Macrolema adult specimens have been collected from October to January and the sex ratio is approximately 1:1. The basic biology of Macrolema is unknown and remarkably not even the foodplant is accurately recorded for any species. The absence of a kotpresse may indicate that Macrolema species do not coat their eggs in plates of excrement, unlike Spilopyra species ( Reid 2000) . However it does not preclude use of excrement as an egg covering, as this is done by many Eumolpinae which also lack the kotpresse (pers. obs., CAMR).

A first-instar spilopyrine larva collected and described by CAMR ( Reid 2000) probably belongs to this genus ( Fig. 17). The pale-green larva was collected at the entrance to Red Cedar Flora Reserve, Nymboida- Binderay National Park, New South Wales, the same locality as a specimen of Macrolema vittata Baly collected 12 years later by our colleague José Jurado-Rivera. As no other spilopyrines have been collected at this locality, we consider that this larva is almost certainly a specimen of M. vittata . Compared with other Spilopyrinae , the larva is characterised by a massive circular terminal plate with a fringe of long setae, an undivided frons and only two pairs of eggbursters, on the meso- and metathorax ( Reid 2000). The external morphology is most similar to the larva of Stenomela Erichson (Jerez 1995) , which is freeliving, feeding on leaves.

There is strong evidence for mimicry between Macrolema species and other Chrysomelidae , especially species of Oides Weber (Galerucinae) . For example, the distribution of the two colour forms of M. vittata closely mirrors the distribution of two similar colour forms of O. fryii ( Clark 1864) . Oides species are conspicuous and relatively common rainforest beetles, belonging to a subfamily well-known for strong chemical protection ( Pasteels, Braekman & Daloze 1988; Pasteels, Rowell-Rahier, Braekman & Daloze 1994). Macrolema species are rare and do not appear to be chemically protected and the mimicry would appear to be Batesian ( Pasteur 1982).

Two Australian species of Macrolema are only known from a small amount of old material and may reasonably be considered ‘Endangered’ in conservation status (International Union for Conservation of Nature 2001): M. giya sp. nov., one specimen, last collected before 1919; M. submetallicus (Jacoby) , eight specimens, last collected 1951. Given the infrequency of collection, it is quite likely that further species await discovery, especially in New Guinea.