Thera Stephens, 1831

CHOI, SEI-WOONG, 2000, A Cladistic Analysis of the Therini: A New Synonym of the Cidariini (Lepidoptera: Geometridae, Larentiinae), American Museum Novitates 3295, pp. 1-26 : 21-22

Thera Stephens, 1831

TYPE SPECIES: Geometra variata [Denis and Schiffermüller, 1775] .

DIAGNOSIS: Members of Thera have filiform male antennae; central fascia of the forewing thin and medially and dorsally narrowed; male genitalia with hook-shaped uncus, transtilla thin, platelike, saccus medially projected, costa of valva strongly sclerotized with medial and distal projections, sacculus large, rounded, aedeagus slender with spinular processes distally; and female genitalia having lamella antevaginalis sclerotized, rounded; ductus bursae thin, long without a colliculum and the corpus bursae ovate without a signum.

DISCUSSION: All species of Thera (except firmata ) are united by four synapomorphies: male antenna filiform (character #0-0), saccus medially projected (#23-2), dorsal edge of sacculus vertically sclerotized (#28-1), and lamella antevaginalis two doughnutlike structures without a seta (#37-2). The basal clade comprising Thera and T. firmata is supported by one synapomorphy: transtilla large, platelike (#22-1).

Stephens (1831) proposed the genus Thera by separating it from Chesias Treitschke based on differences of the palpi, wing pattern and host plant (fir or juniper). Viidalepp ( 1980) defined the monophyly of Thera : saccus tender and round; costa and sacculus of valva distinct; ductus bursae membraneous; and sterigma sclerotized. Choi ( 1997) redefined the monophyly of the genus using 11 synapomorphies and listed four uniquely derived characters: costa of valva with a medial projection; cucullus large; and cornuti on vesica fewer and arranged in a crown shape. About 12 species of Thera are known and they occur widely throughout the Holarctic region.

T. firmata has seven autapomorphies: vertex distinct with whitish scales (character #1- 1), discal dot of forewing united to the costal part of antemedial line (#9-1), costa of valva with a distal expansion (#26-1), cornuti on vesica large and spinular and grouped into one-patch (#34-1, #35-1), and ductus bursae sclerotized (#48-1). The species T. firmata is placed at the basal node of Thera in the successive weighting approach ( fig. 61 ), but as a member of Heterothera ( fig. 60 ). The status of this species was first discussed by Pierce ( 1914). He distinguished it from Thera based on structures of the genitalia. Later, Viidalepp ( 1980) moved it to Pennithera , on the basis of two apomorphies: indistinct sacculus and shortly bipectinate male antenna. However, Choi ( 1997) subsequently combined it with Heterothera, using three synapomorphies: apical streak of forewing absent, anellus lobe expanded, and saccus flat and broad. In the present analysis, firmata is again associated with Thera .

Figures

Fig. 61. One cladogram derived from successive weighting approach using NONA. See fig. 60 for generic abbreviations and symbols. Each node number is indicated.

Fig. 60. Strict consensus cladogram derived from unweighted analysis using NONA. Abbreviations: C Cidaria, D Dysstroma, P Plemyria, Pe Pennithera, Pd Paradysstroma, Pr Praethera, Ps Pseudodysstroma, H Heterothera, T Thera, Di Diathera. Plus signs (+) indicate a taxon or node that produces the polytomy in the consensus cladogram; asterisks (*) indicate taxa that have ambiguous taxonomic positions.