Riethia zeylandica Freeman 1959
Creators: name: Cranston, Peter S.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Chironomidae
Riethia
Riethia zeylandica

description: Riethia zeylandica Freeman 1959
(Figs. 1F, 2M, 4O, 6P)
Riethia zeylandica Freeman, 1959: 422
[not Riethia zeylandica Freeman 1961: 680]
Type material. Holotype ♂, pinned, hypopygium on celluloid mount, NEW ZEALAND, Ohakune,. xi.1922 (T.K. Harris) BM 1923-13 (BMNH). Examined, hypopygium drawn, September 1998.
Other material (all Cranston ANIC / NZAC): NEW ZEALAND: N. Island, 24 Pe, Pukete Forest, 1–2 order stream (unnamed), 35°12.52’S 173°47.43’E, 12.i.2000; Le/P ♂, 35°12.41’S 173°47.37’E, 30.i.2006; 2L, P ♂ same (MV NZ 10PSR1-2, PSRP1) 27.xiii.2010.
Description. Male, n=1–3 [based on Freeman 1959, re-examination of holotype by Cranston; the only new specimens are teneral within pupa]. Body pale green with light brown thoracic bands; wing and legs pale, without markings. Antennal ratio 1.05 [Freeman states 1.3]. Legs with all tarsomeres missing, ratios unable to be calculated [Freeman ‘slightly more than 1]. Hypopygium (Fig. 1F) [Freeman 1961: fig. 3a] with 4–6 clustered stout setae on anal tergite near posterior margin and interspersed with regular setae. Gonocoxite slightly narrowed at junction to gonostylus, gonostylus tapering to point. Superior volsella (Fig. 2M) with basal ‘heel’ prior to non-microtrichiose elongate, non-tapered, bare lobe bearing 4–6 simple setae and without pectinate scales. Pseudovolsella an angular protrusion (not a tubercle) bearing 3 slightly approximated long setae. Inferior volsella well developed, microtrichiose, curved medially, subapically with 7–8 pectinate setae and several simple setae. Mensural details, see Table 1.
Female unknown.
Pupa. Almost hyaline except for yellowish dorsal thorax, anterior wing sheaths; tergal spinules golden, apophyses almost invisible except on VIII; comb yellow-brown. Frons with short warts, cephalothorax smooth, with one row of tubercles each side of dorsal ecdysial line. Prealar tubercle modestly developed as rectangular to elongate rounded lobe. Continuous hook row on II occupying 30–35% width of segment II; continuous conjunctival spinule band on III, IV and sparser on V. Pedes spurii B absent, vortex very weak. Tergite I bare, II–V with quadrate armament of quite dense spinules, without strongly delimited anterior or posterior transverse band; VI with more patchily distributed spinules although essentially quadrate; VII and VIII bare. Segment V with 3L setae, all non-taeniate, VI–VIII with 0, 4, 4, 5 taeniate LS, on VIII more or less evenly spaced (Fig. 4O). Sternites bare. Tergite VIII posteriorly with yellow apophyses meeting comb comprising few golden spines, the strongest directed posteriorly, and innermost directed more posteromedially. Anal lobe with 40–50 biserial taeniae.
Larva. The head is evenly pale pigmented with postoccipital margin broad and dark, and mentum and inner mandibular teeth distinctly brown. The clypeus (Fig. 6P) has an indented lateral margin with clypeal (S3) setae located midway between anterior and posterior margins. Antenna with short pedestal; AR c. 1.4, each segment shorter than preceding (thus 3 rd shorter than 2 nd). Premandible with very small basal-most tooth, essentially with 4 teeth. Mandible with gold apical tooth and 4 dark inner mandibular teeth, seta subdentalis arising from pointed lobe, with 1–2 molar spines. Mentum relatively narrow with ventromental plates of similar width. Mensural details, see Table 2.
Diagnosis. The adult male closely resembles the Australian R. azeylandica, differing mainly in the pseudovolsella. In both species it bears 3 setae, but in R. zeylandica these arise from a distinct angular lobe (Fig. 2M), whereas there is no such lobe in R. azeylandica (Fig. 2A), with setae arising from the inner contour of the gonocoxite.
The pupa, with continuous hook row and conjunctival spinule bands on II, IV and V, is unlike any taxon in the ‘zeylandica’ grouping from Australia. The conjunctive of V has a sparse, perhaps narrowly medially-divided band of spinules, well separated from posterior tergal spinules and weaker than in possibly conspecific Australian specimens, all of which have a denser band on V. The absence of taeniae on the lateral segment V is unique in the genus, and led to early inability to recognise the pupal exuviae as belonging to Rietha due to (0), 4, 4, 5 pattern of taeniate LS.
The larva with an AR of 1.4 with consecutively shorter segments and smooth clypeus probably is only confidently identifiable by its restriction to New Zealand, whereas look-alikes are Western Australian.
Remarks. The resemblance of the adult male of R. zeylandica to Australian specimens allocated by Freeman (1961) to this species is evident and misidentication is quite understandable.Although molecular data shows distinction, and the pupae provided strong morphological confirmation, particularly in the non-taeniate LS on segment V and weak to absent vortices on IV, differentiation of the male and larva from some Australian congeners remains uncertain.
Intensive searches around the type locality of Ohakune revealed no Riethia in any life stage. Since Harris’s original collection in 1922, the local volcano Mount Ruapehu has erupted several times, and conceivably local stream conditions no longer suit Riethia. The species was found much further north in Pukete Forest (Northland, Kerikeri) from drifting pupal exuviae in 2000, with larvae and pharate adults found in 2006 and larval molecular material collected in 2010. The life history association derives from molecular data of 2 unreared larvae and a pharate pupa with clearly visible male genitalia within.
Distribution and ecology. Pukete Forest in northern New Zealand is a large intact tract of native forest dominated by ancient Agathis (Kauri) trees. The low order streams where Riethia occur are of modest gradient, with rocky substrate and filled with leaf litter. Apparently represented by the sole species, Riethia has been found nowhere else in the country despite widespread sampling across both North and South islands, including in other ancient forested streams (see above).
description: Published as part of Cranston, Peter S., 2019, Riethia (Kieffer 1917) (Diptera: Chironomidae) revised for the Austro-Pacific region, pp. 461-500 in Zootaxa 4646 (3) on pages 489-490, DOI: 10.11646/zootaxa.4646.3.3, http://zenodo.org/record/3351058