Letrasilta, Huang & Volynkin & Yin & Zhang & Fan & Pan & Wang, 2023

Huang, Si-Yao, Volynkin, Anton V., Yin, Xiong-Yan, Zhang, Yu-Long, Fan, Xiao-Ling, Pan, Zhao-Hui & Wang, Min, 2023, Letrasilta, a new genus for the Striatella cernyi Volynkin species-group with description of a new species from Xizang, China, and a replacement name for the genus group name Striatella Volynkin & S. - Y. Huang, 2019 (Lepidoptera: Erebidae: Arctiinae: Lithosiini), Zootaxa 5315 (3), pp. 251-263 : 255-256

Genus Letrasilta S.-Y. Huang & Volynkin, gen. n.

urn:lsid:zoobank.org:act:44960BB3-E0E8-4320-B92E-7FA37E7FD42F

Type species: Letrasilta ratnasambhava (described below), by present designation.

Diagnosis. The new genus is characterised by the combination of the following characters in the male genitalia. (1) The uncus has a dentate dorsal margin (a feature characteristic of the genus). (2) The dorsal margin of the valva is strongly convex medially. (3) The costa is strongly dilated distally and the distal membranous lobe of the valva is situated right below its dilated section. (4) The medial costal process is broad but very short. (5) The vesica bears four compact clusters of slender spine-like cornuti (a feature characteristic of the genus). In the female genitalia, the appendix bursae is vestigial.

Adults of the new genus are externally reminiscent of certain species of Striatochrista nom. n. (type species: Lithosia hypoprepioides Walker, 1862 , figs. 7–9, 19, 25), for example, S. hypoprepioides ( Walker, 1862) , S. nemea ( Volynkin & Černý, 2019) and S. visaya ( Volynkin & Černý, 2019) (illustrated by Volynkin et al. 2019a), and the diagnostic features are found only in the genitalia structures. The male genital capsule of Letrasilta gen. n. is distinguished from Striatochrista nom. n. by the dentate dorsal margin of uncus (it is smooth in Striatochrista nom. n.), the strongly medially convex dorsal margin of the valva (it is flat or somewhat gently convex in the similar genus), the more dilated distal section of the costa, and the distal membranous lobe situated right below the dilated section of the costa whereas it is situated at the distal end of the valva in Striatochrista nom. n.. The vesica of the new genus is bearing four compact clusters of slender spine-like cornuti whereas it is bearing broad clusters of much smaller, shorter and denser cornuti or fields if graniculi. In the female genitalia of Letrasilta gen. n., the appendix bursae is vestigial whereas it is well-developed in Striatochrista nom. n.

The male genitalia structure of Letrasilta gen. n. is also similar to the genus Aberrasine (type species: Miltochrista aberrans Butler, 1877 , figs. 10, 11, 20, 26) by sharing such characters as the medially strongly convex dorsal margin of the valva, the distal membranous lobe connected to the distal end of the costa, and the vesica bearing relatively long and slender cornuti. However, the new genus is externally distinguished from Aberrasine by its yellow ground colour (it is reddish or ochreous in the similar genus), and the smooth and medially curved postmedial line of the forewing, which is zigzagged in Aberrasine . In the male genitalia, unlike Aberrasine , the new genus has a dentate dorsal margin of the uncus, and its vesica is bearing four compact clusters of cornuti whereas Aberrasine has only two clusters, one of which is compact and situated dorsally-distally, while the other one is band-like elongate and situated latero-ventrally. The female genitalia of Letrasilta gen. n. have a vestigial appendix bursae whereas it is well-developed in Aberrasine .

Letrasilta gen. n. is externally distinguished from two other genera recovered in the same clade, Indiania Kirti, Joshi & N. Singh, 2014 (type species: Miltochrista eccentropis Meyrick, 1894 , figs. 12, 13, 21, 27) and Idopterum Hampson, 1894 (type species: I. ovale Hampson, 1894 , figs. 14, 15, 22, 28) by the concolourous forewing pattern, whereas in Indiania, the colouration of the medial line is different from the other markings, and the forewing pattern of Idopterum is greatly dissimilar to the new genus and consists of two rounded patches. In the male genitalia, the valvae of the new genus are symmetrical and have relatively short distal processes whereas in Indiania, the valvae are asymmetrical and with more elongate distal processes while the valvae of Idopterum are symmetrical but having strongly elongate and medially downcurved distal processes. Additionally, the valva of Indiania lacks the distal membranous lobe and the medial costal process, which are present in Letrasilta gen. n. In the female genitalia of Indiania and Idopterum , the appendix bursae is well-developed whereas it is vestigial in the new genus.

Description. External morphology of adults. Length of forewing 10 mm in males and 10.5– 11 mm in females. Antenna filiform in both sexes. Head, thorax and abdomen yellow. Patagia yellow. Tegulae yellow with a black dot. Forewing ground colour yellow, pattern consisting of blackish transverse lines and lengthwise streaks. Basal spot present at the costa, connected with short costal streak. Subbasal spot present. Subbasal area with three elongate triangular spots. Antemedial line discontinuous and curved outwards medially in the discal cell. Medial line gently curved medially, sometimes touching the antemedial line in the discal cell. Discal spot present. Postmedial line curved and forming blunt protrusion medially. Blackish lengthwise streaks of different lengths present at all veins. Cilia yellow. Hindwing ground colour pale yellow. Medial line vestigial or absent. Postmedial area with series of diffuse blackish short lines present on veins and connected with each other by blackish suffusion. Cilia yellow. Male genitalia. Uncus long and slender, tapered distally and pointed apically, with dentate dorsal margin. Tuba analis broad. Scaphiun short and weakly sclerotised. Tegumen long triangular. Juxta shield-like. Transtilla tapered medially. Vinculum short. Saccus broad, U-shaped. Valva moderately broad. Costa gently protruding dorsally near the medial part; medial costal process small, long-triangular; distal section of costa dilated with dentate dorsal margin; distal costal process finger-like or spike-like. Distal membranous lobe semicircular, situated right below the distal section of costa. Sacculus sclerotised and gradually tapered distally, with setose dorsal margin. Distal saccular process short, flattened and distally tapered. Phallus elongate, slightly downcurved near the medial section. Vesica broad, sack-like and scattered with four clusters of long and slender cornuti at the subbasal, medial and ventral sections. Female genitalia. Papilla analis broad with rounded corners, weakly setose. Apophyses slender, apophysis anterioris somewhat shorter and thicker than apophysis posterioris. Ostium bursae broad. Posterior section of ductus bursae sclerotised, long and broad, dorso-ventrally flattened. Anterior section of ductus bursae short and membranous. Corpus bursae globular or elliptical. Posterior and medial sections of corpus bursae weakly sclerotised, heavily covered with spinules and scobination. Anterior section of corpus bursae membranous, covered thoroughly with weaker scobination. Signum present, weakly sclerotised and band-like. Appendix bursae vestigial, directed lateroventrally.

Molecular results. The two specimens sampled formed a clade receiving strong support from both methods (UFBS=100, PP=1), corroborating their conspecificity. The systematic position of Letrasilta gen. n. was congruent in the topologies inferred by Bayesian inference and maximum likelihood analyses ( Fig. 1 ), and it is nested in the Miltochrista group (sensu Huang et al. 2021) and sister to the clade ( Aberrasine +(( Indiania + Idopterum )+ Striatoch rista nom. n. )), receiving strong support from both methods (UFBS=100, PP=1).

Distribution. The new genus is distributed in southwestern China (Xizang), northeastern India (Meghalaya) and northern Myanmar (Kachin State).

Etymology. The generic name Letrasilta is an anagram of the genus-group name Striatella . Gender is feminine.

Figures

FIGURE 1. Molecular phylogenetic tree recovered from the Bayesian inference analysis of the combined dataset with the bestfit partitioning strategy. The clades unrelevant to the present study were all collapsed. The Letrasilta clade was marked out by yellow ground colour. The order of the values on the nodes is as follows: ultrafast bootstrap values (UFBS) in IQtree / posterior probabilities (PP) of the Bayesian analysis.