Amychus Pascoe 1876

Marris, John W. M. & Johnson, Paul J., 2010, A revision of the New Zealand click beetle genus Amychus Pascoe 1876 (Coleoptera: Elateridae: Denticollinae): with a description of a new species from the Three Kings Islands, Zootaxa 2331 (2331), pp. 35-56 : 36-39

Genus Amychus Pascoe 1876

( Figs. 1–26)

Amychus Pascoe 1876: 49 ; Pascoe 1877: 416; Candèze 1891: 177; Schwarz 1901: 193; Schwarz 1906: 219; Schwarz 1907: 231; Hudson 1934: 81. Type species: Amychus candezei Pascoe 1876: 49 (by monotypy).

Psorochroa Broun, 1883: 301 ; Broun 1886: 773; Schwarz 1906: 219; Schwarz 1907: 232, Pl. 6, fig. 2; Hudson 1934: 81, 200 (synonymy). Type species: Psorochroa granulata Broun 1883: 301 (by monotypy).

Adult Diagnosis: Body broad, moderately convex to strongly flattened; integument dull, appearance barklike, with a vestiture of orange to gold decumbent setae. Head prognathous. Mandibles bidentate. Antennae 11–segmented, subserrate from segment 4, short, reaching to about midlength of pronotum. Pronotum broad, moderately to strongly explanate, hind angles with sublateral carina. Mesocoxal cavity open to mesepimeron and mesepisternum. Tarsal claws simple, each claw with c. 4–8 lateral and dorsal, postbasal setae.

Adult Description: Form. Body( Figs. 1–3) elongate, oblong to parallel-sided; length (excluding head) 12.7 to 24.2 mm; relatively broad, 2.6–2.8 x longer (excluding head) than wide; moderately convex to strongly flattened. Integument dull, finely granulate; dorsum with numerous glossy pustules or pustules absent. Vestiture of sparse to moderately dense orange to gold decumbent setae; dorsum with velvet-like indumentum generally covering posterior part of head, the margins and posterior part of disc of pronotum and almost all of the elytra. Colouration of integument orange-brown to dark brown with patches of dark brown to black on disc of pronotum; vestiture yellow-brown to dark brown, forming indistinct transverse bands or mottled patterns on elytra (less conspicuous in worn specimens or due to surface oils from fat deposits in some museum specimens); overall appearance of dorsal surface dull, bark-like.

Head: Head( Fig. 20) oval, prognathous, flattened anteriorly. Frontal carina incomplete medially. Frons with a weak triangular depression medially; punctate to foveolate, punctation less dense mesally; vestiture sparse. Eyes small, EI 0.2–0.3, finely faceted. Mouthparts prognathous. Mandibles( Fig. 21) bidentate, second tooth positioned medially on incisor edge, punctation dense and deep laterally. Labrum fully exposed at base, semicircular, wider than long, with a weak, longitudinal, anteromedial carina. Maxillary and labial palps( Figs. 25, 26) with terminal segment securiform. Antennae( Fig. 24) short, reaching to about midlength of pronotum, 11-segmented, subserrate from segment 4; sensory elements beginning on segment 4; antennomere 1 robust, 2.1 x longer than antennomere 2, antennomere 3 1.3 x longer than antennomere 2, antennomere 4 subequal in length to antennomere 2.

Thorax: Prothorax wider than long; pronotal index 67–83; sides arcuate to weakly sinuate, not explanate to strongly explanate; disc flattened to convex. Pronotum with a weakly impressed median longitudinal depression, obsolete anteriorly, faint to obsolete posteriorly; anterior angles strongly produced extending beyond midpoint of eyes; lateral margins entirely carinate; base with two short sublateral carinae and incisions, notched in front of scutelleum; hind angles prominent, broad, carinate, weakly convergent to weakly divergent. Prosternal suture straight, marginate along hypomeral border. Prosternum rounded anteriorly, projecting to form a chin piece, marginate around procoxal cavities. Hypomeron sparsely punctate with punctures shallow to moderately deep, densely punctate anteriorly with punctures separated by less than their diameter. Prosternal spine( Fig. 22) moderate to long, proportion posterior to procoxae 1.0–1.7 x procoxal cavity width; extending horizontally to weakly deflexed dorsally behind procoxae, without a ledge immediately behind procoxae, with subapical tooth. Scutellum broadly rounded anteriorly; anterior margin well defined sharply angulate and steeply declivous to prescutum; vestiture sparse. Mesosternal cavity deep, with glossy median groove extending to floor; cavity opening broadly ovate (viewed ventrally), extending posteriorly to about the anterior 1/3 rd to 2/5 th of mesocoxal cavity; sides moderately steeply declivous. Mesosternum (viewed laterally) weakly declivous anteriorly, horizontal posteriorly; posterior margin steeply declivous, forming a distinct depression at the junction with the metasternum. Mesocoxal cavity open to mesepimeron and mesepisternum. Metasternum with distinct discrimen extending the length of metasternum. Elytra 2.6–2.7 x length of pronotum; sides weakly curved to parallel-sided anteriorly, tapering from about posterior 3/5 th; apex narrowly rounded; disc moderately convex to flattened; weakly sculptured to strongly tuberculate; striae weakly to moderately impressed, weakly to moderately punctate, with punctues widely separated; vestiture sparse. Hind wings brachypterous (at most reaching to apex of elytra) ( Fig. 6) to micropterous ( Figs. 4–5); if brachypterous about 3.0 x as long as wide; wedge cell absent; apex of wing without sclerotisations; without transverse apical fold in repose; venation as in Fig. 6; venation varies in some specimens as follows: Radial cell (R) sometimes with 1–3 internal cross veins or partial cross veins in proximal area; MP 3 extended proximally to join base of MP 1+2 to form cell; MP 1+2 –MP 3 cross vein sometimes branched and forming small triangular cell. Legs robust. Tibiae with two short apical spurs. Tarsi simple; laterally compressed; distal margins oblique in lateral view; densely pilose ventrally. Tarsal claws ( Fig. 23) grooved laterally; each claw with ca. 4–8 lateral and dorsal, postbasal setae.

Abdomen: Abdomen with ventrites 1–4 connate, ventrite 5 tapering to a narrowly arcuate apex, ventrites with sparse to dense punctation laterally and apically, punctures shallow to deep. Female segment 8 with narrow membrane connecting sternite and tergite. Sternite 8 spiculum elongate, spiculum 0.6–0.7 x length of sternite; apex narrowly arcuate. Male tergite 9 deeply notched at midline.

Female genitalia: Ovipositor( Fig. 10) stout; elongate, about 0.5–0.6 x length of abdomen (measured medially). Coxites divided into two parts; with subapical palpiform styli. Paraprocts elongate, 2.9–3.7 x length of coxites, 0.7–0.8 x length of ovipositor. Vagina( Fig. 11) elongate; anterior end enlarged; without sclerotised structures. Collaterial glands formed as weakly developed outgrowths anterior to common oviduct. Bursa copulatrix tubular, elongate, U-shaped posteriorly, narrowing anteriorly; without sclerotised armature. Two spermathecae present; posterior spermatheca long, weakly curved; anterior spermatheca moderately long, coiled and weakly sclerotised apically. Tubular extension elongate, running from apex of bursa to a complex, multi-armed spermathecal gland. There are no evident differences in structure between species.

Male genitalia: Aedeagus ( Figs. 7–9) 3.4-4.8 x long as wide. Median lobe almost straight in profile; apex narrowly rounded, extending beyond apices of parameres. Basal struts 0.26–0.28 x length of median lobe. Parameres articulated with median lobe, convergent apically; apex simple; apical angle narrowly rounded, with a group of c. 9–16 latero-apical setae. Basal piece distinctly separate; 0.21–0.28 x length of aedeagus.

Pupa Description: See pupal description for A. candezei , below.

Larva Description: Body elateriform, subcylindrical, shallowly convex dorsally; maximum length ca. 27.5 mm, width 4.5 mm (final instar); dorsum orange-yellow with brown highlights, mandibles black; pleural and ventral areas pale yellow. Spiracular atria subparallel; ecdysial scar adnate to atrial margin.

Head. Head ( Fig. 16) with frons pedunculate; frontal sutures lyriform, broadly truncate at cervical margin. Mandibles strongly arcuate, attenuate; with large, stout retinaculum at midlength. Antenna ( Fig. 17) 3– segmented, integument darkly sclerotized; segment 1 with 3 large setae at midlength, one dorsolateral, two ventrolateral; segment 2 with one conical apical sensorium; segment three with 5 minute apical setae. Stemma present. Frons with nasale unidentate, slightly widened subapically, with 5 large basal setae each side; paranasalar lobe with 2 large anterior setae and 1 posterior seta; posterofrontal setae one each side. Cranial setation: dorsal anteroepicranial 2, ventral anteroepicranial 1, dorsal lateroepicranial 2, ventral lateroepicranial 1, dorsal epicranial depression with 6–7 large and 1–3 small, ventrosulcus 10–11. Stipes with single anterolateral seta. Labial palpus with 2 setae on basal segment. Prementum with 4 setae. Postmentum subrectangular, with setal sockets of both anterior and posterior pair surrounded by sclerotization. Cardo triangular, longitudinally oriented, with single seta. Gula with a single central seta.

Thorax. Thorax with nota sparsely set with large, shallow, setiform punctures. Pronotum with 4 anterolateral and 5 posteriolateral setae. Meso- and metanota lacking anterior and lateral setae, posterior setae 3–4. Presternum 4-partite, lateral portion with single anterolateral setae, posterior portion with 2 setae. Episternum with 2 large setae each side. Legs with each segment heavily spined laterally and along ventral margins; trochanter and femur each with 2–3 large ventral setae; tarsungulus claw-like, with two basal setae.

Abdomen. Abdominal terga 1–8 ( Fig. 18) with numerous small, shallow, and finely setate punctures, on terga 1–7 each puncture adjacent to a transversely undulating, moderately sclerotized carinula that partially forms the puncture margin, punctures and carinulae becoming obsolescent in posterior third of each tergite; anterolateral carina with short branches, each a series of undulating carinulae, with anterior branch reaching less than halfway to ecdysial suture; posterolateral margin with 6–12 large setae. Tergite 9 ( Fig. 19) with disc depressed, coarsely wrinkled, striate, and coarsely punctured, with 2 large setae near anterior margin; circumdiscal ridge shallow, undulate, 4-tuberculate dorsolaterally, with anterior pair low, indistinct; base of urogomphus ( Fig. 19) with large acuminate dorsal tubercle; urgomphus broadly obtuse at apex, with short blunt preapical tubercle; terminal emargination angularly oval, with narrow gap between urogomphal apices. Pleurites 2-partite, sparsely setate. Sternites 5-partite, sparsely setate. Segment 8 spiracle anterad of midlength. Pygopodium tubular, with narrow ring sclerite.

Included species. Three species are included: A. candezei , A. granulatus , and A. manawatawhi , sp. nov.

Distribution. Restricted to the New Zealand archipelago: Three Kings Islands (TH), 60 km northwest of Cape Reinga at the northern tip of the North Island of New Zealand; some islands of the Marlborough Sounds and Cook Strait (SD) in the north east of the South Island; North Canterbury (NC) in the east of the South Island (a single subfossil specimen); and the Chatham Islands ( CH) c. 870 km east of New Zealand.

Remarks. Hudson (1934) erroneously synonymised the species Amychus candezei and Psorochroa granulata (see Remarks for A. candezei ) but, in doing so, correctly synonymised the genera Amychus and Psorochroa . The synonymy of Amychus and Psorochroa is supported by this revision.

General biology. Amychus adults are nocturnal and have commonly been collected from on tree trunks at night where they tend to favour gnarled, knot-holed trees that presumably offer refugia during the day. Beetles have also been found under logs, rocks and low growing vegetation, and by pitfall trapping. Adults were found feeding on sap oozing from tree trunks ( Marris 1996, Marris unpublished data) and on algae and lichens on tree trunks ( Meads 1990). Collection records show A. granulatus specimens were collected in all months except June and October and A. candezei has been collected over the summer months and in July. Few records exist for A. manawatawhi due to the inaccessibility of the Three Kings Islands, and these are limited to November, December and April. Thus, adult beetles are probably present throughout the year and individually long lived.

Larvae attributed to A. candezei were associated with a pupa and adults through the elimination of other candidate elaterids and their known larvae and pupae from the small and well documented Chatham Islands beetle fauna ( Emberson 1998, 2002). Both larvae and the pupa were collected within the habitat and close proximity of adults. The larvae of A. granulatus and A. manawatawhi were collected from small island localities where, like Amychus candezei , there is a limited elaterid fauna and thus few possibilities for adult associations along with the same basic morphological features shared with A. candezei larvae.

Amychus larvae have been collected from in rotten wood, in soil at the base of tussock grasses and from litter. Elaterid larvae, especially denticolline and agrypnine species, are usually predaceous or omnivorous (e.g., Lawrence et al. 1999, Johnson 2002), and the predaceous habit is apparently true for Amychus larvae. Two larvae of A. candezei were reared through four moults on sections of yellow mealworm larvae ( Tenebrio molitor L.) over three years but died before pupating (Marris, unpublished data). Only one pupa is known from the genus, a specimen of A. candezei collected from in soil at the base of tussock grasses.

Amychus species are restricted to offshore islands which, with the exception of Chatham Island, are free of introduced mammalian predators. Subfossil evidence shows that A. granulatus was also once present on the South Island mainland ( Worthy and Holdaway 1996, see Remarks for A. granulatus ) but became extinct there presumably due primarily to predation by rodents. The beetles are found in habitats including mature forest, coastal scrub and sward. The subfossil record of A. granulatus from near Waikari, c. 20 km inland from the east coast of the South Island, shows that this species was not restricted to its present maritime range.