Nanomela, Leschen & Reid & Nadein, 2020

Leschen, Richard A. B., Reid, Chris A. M. & Nadein, Konstantin S., 2020, Generic Review of New Zealand Chrysomelinae (Coleoptera: Chrysomelidae), Zootaxa 4740 (1), pp. 1-66 : 47-51

Nanomela , gen. nov.

( Figs 10 , 12A,B , 14–16 )

Type species: Nanomela tiniheke , sp. nov.

Diagnosis. Body length less than 2.5 mm; oval and moderately convex; colour generally uniform pale-yellow to dark brown, without metallic reflection. Antennae clavate. Procoxal cavities externally closed. Hindwings absent. Anterior edge of metaventrite curved or rounded; metaventral lines parallel and not extending to middle of ventrite. First abdominal ventrite with subcoxal lines parallel to coxal cavity and not extending to middle of ventrite.

Description. Length 1.3–2.3 mm. Body oval and moderately convex. Colour pale-yellow to dark brown, lacking metallic lustre.

Head forming a short muzzle with genae extending a short distance beyond level of antennal and maxillary insertions, scarcely visible from above with mouthparts directed anteroventrally, wide vertex or frons, nearly flat to feebly convex; postantennal calli absent, pale areas present or absent. Eyes reduced to 1 or 2 (mainland species) or 15 (Snares species) facets, not protuberant, though resting on a small hump in some species; inner margin of eye without a small seta. Antennae long and clavate, antennomeres relatively short, most about as long as wide, weakly thickened apically, scape short and somewhat elliptic, shorter than the A2+3 combined, last 2, 3 or 5 antennomeres forming a club, reaching just beyond the hind margin of the pronotum; eye not contacting antennal insertion, with distance between insertion and margin of eye equal to or less than diameter of insertion, distance between insertions about 2 times length of the scape. Clypeus trapezoidal and weakly to moderately transverse, anterior margin straight; frontoclypeal suture present; postclypeal lines absent. Labrum rectangular to squared, anterior margin weakly or not emarginated and sides rounded, surface with 1 elongate seta per side, anterior margin at middle lacking distinct setal fringe, tormae long and thin, about 2.5 times longer than labral plate. Mandible with terebral edge serrate. Maxillary palpus relatively short, palpomere 1 not strongly flattened about as long as wide, palpomere 2 shorter than wide, palpomere 3 about 2 times longer than wide or less, greater in length than palpomere 2, conical. Labium with wide ligula, almost equal in width to the lengths of palpomeres 1 and 2 combined, apex very weakly divided at apex, palpal insertions separated by less than the width of the basal palpomere, palpi relatively short, palpomere 1 shorter than long, palpomere as long as wide, palpomere 3 conical, twice longer than wide with truncated apex. Mentum rectangular and transverse, width of mentum equal to or shorter than the length of labial palpomere 3. Intermaxillary process short and extending a short distance anteriorly beyond maxillary insertions, anterior edge concave to straight, delimited behind by a ridge or a bead.

Pronotum transverse and convex, with a bead along anterior and lateral margins; posterior edge as wide as the base of elytra; anterior margin not emarginated, anterior angles weakly projecting and rounded to acute; sides distinctly converging anteriad and straight or weakly curved, posterior margin weakly convex or sinuate; posterior angles rounded and not produced; disc convex without sublateral groove, trichobothria absent, coarse and dense punctures at middle of posterior margin absent (punctation uniform); lateral carinae complete. Prosternum not vaulted at middle, without transverse notches in front of coxal cavities; prosternal lines present and parallel and extending a short distance forward and not reaching anterior edge of sternite; prosternal process broad, short and extending a short distance behind procoxae, expanded laterally behind coxae and contacting the hypomeral process; posterior margin emarginated, procoxal cavities externally closed. Notopleural suture distinct. Scutellary shield visible and small, triangular with acute apex. Elytra moderately convex, humeral calli and mid-basal striae absent; surface smooth, punctures weakly impressed and striate, epipleura narrow and well developed, visible in lateral view, apex without ctenidium. Hind wings absent. Mesoventrite mostly hidden in ventral view, posterior portion between mesocoxae visible as a narrow strip; mesal part of mesoventrite with vertical surface confluent with prepectus. Meso- and metacoxae widely separated. Metaventrite shorter than abdominal ventrite 1 at midline, mesocoxal process broad with a curved anterior margin, metaventral lines parallel, discrimen and transverse metaventral (metakatepisternal) suture absent. Metendosternite lacking stalk and laminae, widely spaced lateral arms lacking subapical anterior tendons. Legs with tibiae flattened in cross section, meso- and metatibiae not clubbed, gradually widened towards apex with evenly vurved lateral margin, apically setose; tarsomeres 4-4-4 with tarsomeres 1–3 of equal or subequal lengths, T1 slightly longer than T2 or longer, about 1.1–1.3 times longer than wide (not greatly enlarged in male, but may be slightly more elongate than female), T2, T3 not deeply incised (bilobed), tarsomere 4 minute and fused to 5, T5 about 2–2.5 times as long as T3, claws simple.

Abdominal ventrite 1 long, longer than ventrites 2–5 combined, with a broad metacoxal process that is wider than long and with a straight apical margin, ventrites 2–4 equal in length and much shorter than ventrite 1, ventrite 5 longer than ventrites 3 and 4 combined with rounded posterior margin; first abdominal ventrite with subcoxal lines parallel to coxal cavity that do not extend to middle of ventrite. Aedeagus variable, weakly curved in lateral view and dorsoventrally compressed in cross section; apex in dorsal view acute to arrow-shaped; flagellum. Ovipositer with coxite over 2 times longer than wide, stylus absent. Spermatheca U- shaped, collum present with spermathecal duct inserted onto base, spermathecal gland absent.

Comments. Nanomela is restricted to the South Island, Stewart Island, and subantarctic Snares Islands. Here we describe one species from the Snares, but the genus will require more detailed work because specimens tend to be rarely collected and morphologically similar, often with very subtle differences between localities. For example, sorting based on general colour (light tan to dark-brown and black) and general body shape (elytra that are broadly rounded to somewhat tapered, Figs. 12A,B ) has revealed at least 4 species that may be sympatric in the southern portion of the South Island (Fiordland (FD), Central Otago (CO), Stewart Island (SI), and Southland (SL)) and allopatric populations from Mt. Robert (NN), Mt. Arthur (NN), Karamea (NN), Mt. Faraday (BR), and Arthurs Pass (NC). The male genitalia among these taxa are very similar with subtle differences in the apex and specimens from several South Island localities are probably conspecific, but these require genetic sequencing, dissection, and further sampling. We decided to include a description of these referred to as the “mainland group”.

Most specimens have been collected from leaf litter or moss, apart from one series from Karamea that were collected via soil washing (J. Nunn, pers. comm., 2017). Those from the Snares Islands have been collected from a variety of habitats. Two species have been collected in reasonable numbers from pitfall traps set in Takahe Valley, Fiordland during a period of 4 years indicating that species are habitat specialists, with one species at lower altitudes associated red tussock ( Chionochloa rubra ) and another at higher altitudes associated with snow tussock ( C. teretifolia ) ( Poaceae ).

The reduced eyes, head elongated anterior to antennae forming a short muzzle, simple unexpanded 3rd tarsomere and distinct body form of Nanomela will distinguish this genus from all other Chrysomelinae and renders it difficult to recognise as a member of this subfamily, for example it fails to identify from the key to subfamilies in Reid (2000). However the mouthparts, ventral thoracic, modifed male tarsal setae and genitalic characters are typical of Chrysomelinae . Nanomela may be most closely related to Aphilon which also has clavate or clubbed antennae, but Nanomela differs from it by the elliptical body form and reduced eyes. Nanomela and Aphilon have the head scarcely visible in dorsal view, subcoxal lines parallel to the coxal cavity on abdominal ventrite 1, and relatively flattened tibiae, characters which are also present to some degree in Maurodus , Zeaphilon , and most Caccomolpus .

Etymology. The genus name is derived from “nanos” (ancient Greek—dwarf, midget) and “- mela ”, body, a common ending in the names of Chrysomelinae genera. The new genus contains some of the smallest members of the subfamily worldwide.

Distribution. South Island, Stewart Island, Snares Islands.

Figures

FIGURES 10A–F. Habitus of Nanomela spp.; A, Nanomela sp., dorsal, length 1.5 mm; B, Nanomela sp., ventral, length 1.5 mm; C, Nanomela tiniheke, dorsal, length 2.2 mm; D, Nanomela tiniheke, ventral, length 2.2 mm; E, Nanomela sp., lateral, length 1.5 mm; F, Nanomela tiniheke, ventral, length 2.2 mm.

FIGURES 12A–N. Habitus and genitalia; A, Nanomela sp., dorsal, scale = 1 mm; B, Nanomela tiniheke, dorsal, scale = 1 mm; C, Maurodus maculatus, aedeagus, dorsal view; D, Maurodus maculatus, aedeagus, lateral view; E, Maurodus occiduus, aedeagus, dorsal view; F, Maurodus occiduus, aedeagus, lateral view; G, Maurodus nunni, aedeagus, dorsal view; H, Maurodus nunni, aedeagus, lateral view; I, Maurodus supernus, aedeagus, dorsal view; J, Maurodus supernus, aedeagus, lateral view; K, Zeaphilon marskeae, aedeagus, dorsal view; L, Zeaphilon marskeae, aedeagus, lateral view; M, Zeaphilon mirandum, aedeagus, dorsal view; N, Zeaphilon mirandum, aedeagus, lateral view.

FIGURES 14A–D. Ventral SEMs of Nanomela spp.; A, Nanomela sp., body; B, Nanomela sp., prothorax; C, Nanomela sp., meso-, meta-, and abdominal ventrites; D; Nanomela tiniheke, meso- and metaventrite.

FIGURES 15A–H. SEMs of Nanomela structures; A, Nanomela tiniheke, head, dorsal view; B, Nanomela sp., head, frontal view; C, Nanomela sp., head, frontal view; D, Nanomela sp., metatarsus, ventral view; E, Nanomela sp., male mesotarsus, dorsolateral view; F, Nanomela sp., left elyton, ventral view; G, Nanomela sp., male middle leg, anterior view; H, Nanomela sp., male middle leg, anterolateral view. Photo B by Sue Lindsay, Australian Museum.

FIGURES 16A–E. Nanomela structures; A, Nanomela sp., aedeagus, dorsal view; B, Nanomela tiniheke, aedeagus, dorsal view; C, Nanomela sp., spermatheca; D, Nanomela tiniheke, abdomen showing spermatheca, ventral view; E, Nanomela sp., hindleg, posterior view.