Leucosigma Druce, 1908

Goldstein, Paul Z., Janzen, Daniel H., Proshek, Benjamin, Dapkey, Tanya & Hallwachs, Winnie, 2018, A review of Leucosigma Druce, 1908: a newly discovered case of fern-feeding and descriptions of three new species (Lepidoptera, Noctuidae), ZooKeys 788, pp. 87-133 : 89-90

Leucosigma Druce, 1908

Chytonidia Schaus, 1914, syn. n.

Type species.

Leucosigma uncifera Druce, 1908, by monotypy.

Etymology.

Leuccosigma was presumably named in reference to the white U-shaped forewing stigma. Chytonidia likely derives from χιτών, a coat, tunic or garment worn under a tunic, possibly in reference to thoracic and abdominal tufts.

Diagnosis.

Species of Leucosigma are diagnosed most readily by the male genitalia, in particular the nature of the highly differentiated clasping architecture, the most striking feature of which is the heavily sclerotized pincer-like cucullus on each valve. In referring to this as a cucullus, we do not interpret it as homologous to the clasper sensu Forbes; although derived from the basal sclerite, it is distinct if not entirely free of the more reduced clasper proper, which appears embedded within the sacculus and free of the basal sclerite. The cucullus bears a swollen, often bulb-like apex with a single heavily sclerotized spine, and a setose usually finger-like dorsal process (swollen apically in L. viridipicta ). These most heavily sclerotized parts of the cucullus may appear simple and pincer-like as in L. uncifera , L. poolei , and L. solisae ; recurved or falcate as in L. albimixta ; asymmetrically distended with sinuate edges as in L. chloe ; or elongate as in L. schausi .

Description.

Head. Labial palpus upturned, densely scaled; second segment usually longer than combined length of the first and third. Eyes smooth or sparsely hairy. Antennae setose-ciliate; bifasciculate in males, scaled above. Thorax. Collar green towards the base, the remainder of the thoracic vestiture more uniformly brown, but scales actually pale at the base. Wings. With the exception of the type species L. uncifera , which exhibits dominantly reddish or russet forewing coloration, the forewings of Leucosigma species are mottled with a mixture of brown and mossy green, particularly in the medial and terminal areas. Reniform and orbicular spots elongate and usually fused ventrally or nearly so, forming a roughly U-shaped stigma. At least four costal striae present. Sexual dimorphism in wing pattern is most conspicuous in the hind wings, which tend to be more uniformly dark gray in the females and paler basally in the males. Legs. Femoral and tibial scales always with an admixture of lime green among the tan and “lilacine” (cf. Schaus 1914: 488); a single pair of striped mid-tibial spurs, two pairs on hind-tibiae; three rows of tibial spines on all legs. Abdomen. Vestiture usually paler than on thorax and concolor ous with hind wing surfaces. Abdomen without coremata, brushes, pockets or levers. Male genitalia. Uncus setose and variously tufted, crested, sinuate, or (in L. viridipicta ) elongate and densely covered with clustered setae throughout. Tegumen hemi-circular to oblong, in some species raised at the base of the uncus. Vinculum shallow U- or V-shaped. Saccus bluntly pointed, rounded, or squared. Valves symmetrical, highly differentiated. For reference, we call attention to four structures numbered 1-4 in Figs 111-118 which account for much of the conspicuous diagnostic variation and which appear throughout the key and descriptions to follow: (1) the sacculus/saccular extension; (2) the cucullus, identified as such by virtue of reëntrant setae sensu Forbes (1954: 13) and what may be interpreted as an anal spine, as well as (3) a finger-like dorsal process which arcs dorso-medially in situ such that the apices of each process flank the uncus; and (4) a smaller finger-like, thorn-like or (in L. viridipicta ) anvil-like clasper. Vesica unadorned, without spines or cornuti; a subbasal diverticulum ranges from rudimentary, as in L. uncifera , to a large recurved torsion in L. albimixta . Female genitalia. Papillae anales blunt, subquadrate. Posterior apophyses usually at least twice as long as anterior apophyses. Lamellae antevaginales robust, ranging from narrowly concave or cup-like to more deeply invaginate, apparently co-developed with colliculum. Colliculum usually well developed but reduced or absent in some species. Ductus bursae otherwise unsclerotized, straight or with minimal torsions, attaching dorso-caudally to the corpus, sometimes with a small pre-collicular lobe. Corpus bursae without signa, oblong, sometimes appearing subtriangular when distended by presence of spermatophore(s). Appendix bursae undifferentiated except as a swollen ventral point of attachment to the ductus seminalis. Spermatophore collum, when visible, appears with a single loop; frenum with a concave face matching the interior surface of appendix bursae at its point of attachment to the ductus seminalis. Paired pad-like sternal sclerotizations on A7 are visible in some specimens.

Distribution.

Mexico, Caribbean, Central and South America.

Biology.

All known caterpillars feed on leaves of ferns ( Pteridophyta).

Remarks.

As is often the case, the type species of Leucosigma is perhaps the most phenotypically atypical of the genus. Known only from adult specimens taken at lights, the life history is unknown, although it may be reasonably suspected that the larva is a fern feeder. Species circumscription and nomenclatural assignment in this work has of necessity involved a combination of recently collected specimens for which DNA barcodes have been generated and historical specimens for which they have not, these latter including (for the present, at least) type specimens, several of which are females.

Key to known species of Leucosigma based on structures of the male genitalia.

Numbers 1-4 refer to structures labeled in figures.