Arctesthes siris (Hudson, 1908)

Patrick, Brian H., Patrick, Hamish J. H. & Hoare, Robert J. B., 2019, Review of the endemic New Zealand genus Arctesthes Meyrick (Lepidoptera, Geometridae, Larentiinae), with descriptions of two new range-restricted species, Alpine Entomology 3, pp. 121-136 : 121

Arctesthes siris (Hudson, 1908) Figs 7, 8, 15, 24, 25, 31, 35 (map)

Lythria siris Hudson, 1908. Transactions and proceedings of the New Zealand Institute 40: 106.

Type material.

Lectotype: male (designated by Dugdale (1988: 171)), ‘725a’ [corresponding entry in G.V. Hudson collection register: 'Old Man Range at about 4000 ft. Feb '06 (J.H. Lewis)'] (MONZ) (not examined but photograph seen).

Diagnosis.

Arctesthes siris is similar to A. catapyrrha , but on average smaller. It is easily distinguished by the proximal line of the forewing, which has a distinct concave curve below the middle of the wing; the proximal line in A. catapyrrha is convex (bowed away from the wing base). The hindwing pattern also differs strongly from that of catapyrrha : in siris , the orange coloration is only present as rather narrow V-shaped band beyond the basal blotch and as scattered scales elsewhere; in catapyrrha , orange is the dominant hindwing colour. The dark antemedian line that borders the hindwing basal blotch is much more strongly V-shaped than in catapyrrha .

Redescription.

Adult male (Figs 7, 15): Wingspan 14-16 mm. Male antennal pectinations shorter than in A. catapyrrha , up to ca 3 –4× flagellum width. Labial palpi without hairlike scales projecting laterally, with moderately short, erect white to reddish brown hairlike scales ventrally. Head and thorax deep pinkish mixed with black and white; strip of pure white to deep pinkish scales along antero-ventral margin of eye. Forewing ground colour (areas between transverse markings) pale greyish brown, usually suffused with deep pinkish at least towards costa and dorsum and along veins distally; proximal line white, with slight concave curve below mid-wing; antemedian line white, gently sinuous; discal dot black, more or less equidistant between antemedian and postmedian lines or closer to antemedian; central fascia usually pallid, greyish in central band around discal dot, suffused pale brown exteriorly, dark lines or bands either side of this band contiguous with antemedian and postmedian lines; postmedian line white, strongly sinuous, with large V- to U-shaped evagination centrally, section between evagination and costa straight to very weakly convex; veins not lined blackish beyond discal cell; distal line grey, indistinct; fringe greyish, not chequered. Hindwing ground colour yellow-orange, but this colour only present as rather narrow V-shaped band beyond basal blotch and as scattered scales elsewhere; antemedian line strongly V-shaped and near wing centre; rest of wing suffused blackish without distinct lines; fringe brownish, paler distally. Forewing underside (Fig. 15) pale orange, with costa sometimes suffused deep pinkish; antemedian line absent; discal dot very small but distinct, black; postmedian line usually distinct, blackish, not double, with strong median evagination; no white spot on costa beyond postmedian line; subterminal fascia and subterminal line absent; terminal fascia represented at most by scattered suffusions of black scales. Hindwing underside pale orange, unmarked except for distinct black V-shaped antemedian line. Abdomen blackish, sprinkled white and orange, distal margin of each segment not usually distinctly paler; anal tuft mixed orange and white.

Male abdomen and genitalia (Figs 24, 25): S3-4 and 6 moderately elongate (rectangular), S5 more squarish, all sternites evenly sclerotised; T2-6 more or less evenly sclerotised but may have faintly desclerotised lines centrally and laterally. Uncus digitate, moderately robust basally, attenuate apically; labides rather short, broad, slightly curved, obliquely truncate apically; dorsal scobinate portion of manica with rather numerous blunt teeth; juxta triangular, with keel-like ventral lobe (juxta tending to flip over towards saccus in slide preparations); valva very short, rather narrow, with rounded-truncate apex; basal costal sclerite with straight costal edge, ending in short blunt process distinctly projecting beyond valval costa; sacculus process lobe-like to distinctly pointed, just reaching valval apex, not scobinate; saccus very short, blunt, somewhat recurved under genital capsule. Phallus (Fig. 25) with tongue-like apical process; vesica with 2 moderately long and a comb-like group of smaller cornuti (longer cornuti more basal in uneverted vesica).

Adult female (Fig. 8): Wingspan 16 mm. Similar to male, but antennae without pectinations; labial palpi more or less as in male; forewing and hindwing both tending to be slightly narrower than in male; forewing tending to be slightly paler with middle portion of central fascia more whitish grey (though in specimens with narrower central fascia, entire fascia may be pale brownish and discal dot absent).

Female genitalia (Fig. 31): Total length ca 1.9 mm. Ovipositor lobes subtriangular, apically blunt. S8 with weakly concave lamella postvaginalis not clearly distinguished from remaining S8 sclerite. Ostium round, narrow; antrum not differentiated from posterior portion of ductus bursae; ductus bursae not sclerotised, but thickly membranous, with weakly rugose posterior portion roughly equal in length and width to smooth anterior portion. Corpus bursae membranous, round.

Distribution.

(Fig. 35). Confined to Central Otago: occurs between 1050-1140 m on the Lammermoor Range and 1200-1380 m on the Rock and Pillar Ranges of eastern CO, 1050-1150 m on South Rough Ridge further inland, 1150-1620 m on the Garvie Mountains, Old Man and Old Woman Ranges of nuclear CO, and 1700- 1850 m on the Pisa Range further west. The species is not known from the adjacent Umbrella Mountains or The Remarkables, but may have been missed there.

CO.

Biology.

Confined to mountains, where it lives in cushion wetlands and snowbanks. The adults fly by day low over the open vegetation and are found between early December and mid April; they can be locally common in these habitats. Larvae have not been described but have been observed to feed on various low-growing plants including Plantago and Coprosma (BHP, pers. obs.); unfortunately no photographs are available.

Remarks.

This local Central Otago endemic was discovered by railwayman J.H. Lewis in February 1906, high (over 1320 m) on the Old Man Range. BHP has recorded it 37 times since 1982 from seven discrete alpine areas (see Distribution above). In low alpine habitats of Central Otago, both Arctesthes catapyrrha and A. siris can sometimes be found flying together in cushion wetlands, such as at 1400 m on Symes Road on the Old Man Range [45°20.5'S, 169°13.7'E].