Nexosa Diakonoff, 1977

Heppner, John B. & Bae, Yang-Seop, 2015, Review of Nexosa Diakonoff in Vietnam, with a new species and a new subspecies, and transfer to the tribe Archipini (Lepidoptera: Tortricidae: Tortricinae: Archipini), Zootaxa 3999 (1) : -

Nexosa Diakonoff, 1977

Figs. 1–9

Type-species: Mictopsichia marmarastra Meyrick, 1932 , designated by Diakonoff, 1977.

Diagnosis. Adults have three silvery lines (except for Nexosa picturata (Meyrick)) near the forewing apex (two in Mictocommosis ). The wing venation ( Fig. 9 ) is very similar to that of Mictocommosis , but the hindwing discal cell is shorter in Nexosa and veins R and M1 are more approximate at the discal cell, and M2 is closer to M3 than in Mictocommosis . Also, the dorsal margin of the hindwing is very convex. Genital characters differ from those of Mictocommosis , with the male having compact projecting apical spines on the uncus (a broadened anteroventral spine field in Mictocommosis ), the socius with few setae (extensive setae in Mictocommosis ); and the female with a large accessory bursa divergent near the ostium (or lacking in some species, but N. picturata probably belongs to another genus), and no signum in the bursa (more normal archipine-type signum in Mictocommosis , but without a capitulum).

Discussion. This genus appears most related to the Asian and African genus Mictocommosis Diakonoff (1979, 1986 ), although wing maculation differs considerably between the two. Besides describing the new species N. aureola , from Papua New Guinea, Diakonoff (1977) transferred to his new genus Nexosa three other species: N. marmarastra (Meyrick, 1932) from Java ( Indonesia), N. picturata (Meyrick 1912) from Assam ( India), and N. hexaphala (Meyrick 1912) from Sri Lanka. Nexosa picturata likely belongs in a different genus, as the genitalia differ markedly from other Nexosa and Mictocommosis species in both the male and female. Nexosa was first reported from northern Vietnam by Razowski (2008), based on a single male of N. hexaphala captured at Tam Dao, Vinh Phuc Province; but we herein treat that specimen as a new subspecies. The related genus Mictocommosis includes four species: two Asian species (one in Indonesia and one from Japan to Vietnam) and two African species ( Heppner 1977), although the African species need more study.

Whereas Mictocommosis species have a more typical archipine female signum, Nexosa species lack this, yet have virtually the same wing venation and similar male genitalia as Mictocommosis , as well as similar wing maculation and head morphology. Nexosa appears to be a primitive relative of Mictocommosis , and best conforms to characters for the tribe Archipini rather than Hilarographini , based on the tribal characteristics ( Diakonoff 1977, 1986; Horak 1984, 1998). Archipine features of Nexosa and Mictocommosis include the toothed knob at the valval costal base, which is a putative pulvinus that lacks setae (a pulvinus is absent in a few other Archipini ), but the genera also have a complete and flattened or slender transtilla (split in some Archipini ); and the socius is welldeveloped although elongated and with only a few setae in Nexosa . The socius in Nexosa was erroneously labeled as hami by Diakonoff (1977), thereby a further reason the genus may have been described in the Hilarographini .

Razowski (1987) corrected the matter of the socius in Nexosa , but retained the genus in Hilarographini . The male valva is strongly sclerotized both on the dorsal and ventral margins in Nexosa , but mostly membranous on the margins in Mictocommosis (usually sclerotized only on the ventral margin in most Archipini ). The female genitalia in Nexosa have a large accessory bursa in some species and lacking in others, but which varies in presence or absence in many groups; and lacking in Mictocommosis . No signum is present in Nexosa ( Fig. 8 ) (archipine signum in Mictocommosis , but lacking the capitulum).

The correct placement within the Archipini of both Nexosa and Mictocommosis , and possibly related genera, requires further study. Unfortunately, even recent studies, including those using new DNA techniques ( Dombroskie & Sperling 2013, Regier et al. 2012), have not included these genera because they have remained misplaced in Hilarographini (Chlidaontinae) and not specifically studied even as hilarographine genera, or among various exotic genera not included in such studies.

Figures

FIGURE 8. Nexosa tonkinensis, n. sp., female genitalia, with details a) sterigma, ostium, and basal duct of accessory bursa and ductus seminalis (slide JBH 3126).

FIGURE 9. Wing venation of Nexosa marmarastra (Meyrick), Java, Indonesia (redrawn from Diakonoff 1977).

FIGURES 1 – 2. Nexosa species in Vietnam. 1. N. hexaphala tamdaoana, n. subsp., holotype male (13.8 mm wingspan). 2. N. tonkinensis, n. sp., holotype female (12.3 mm wingspan).

FIGURES 3 – 6. Nexosa species head close-ups (lateral and dorsal views). 3 – 4. N. hexaphala tamdaoana, n. subsp., male. 5 – 6. N. tonkinensis, n. sp., female.

FIGURE 7. Nexosa hexaphala tamdaoana, n. subsp., male genitalia, with details a) aedeagus, b) abdominal pregenital sternal plate (slide JBH 2858).