Metaemene Hampson

Type species: atrigutta Walker, Borneo.

This genus contains numerous small species with narrow, typically weakly bifalcate forewings with a whitish or grey ground. There is a series of black spots around the margins, and often more in transverse arrays that probably represent the antemedial and postmedial fasciae. There are pink patches between these transverse arrays of spots in species with a white ground. The hindwings are uniform in various shades of grey to almost white on the upperside, but may have darker discal and postmedial markings below. The forewing venation has an areole that gives rise to (R2 (R3, R4)) and R5. The hindwing has both Rs and M1, and M3 and CuA1 stalked. The male antennae are ciliate. The labial palps are slender, upcurved close to the head, reaching the commencement of scaling above the naked clypeofrons. Most of this length consists of the second segment; the very short third segment may be directed slightly forwards from this. The phragma lobes are broad but shallow.

The male abdomen has the eighth segment unmodified except for tergal apodemes. The genitalia have a rather ovate capsule, with the tegumen straight on each side, convergent on the uncus, and usually with dorsally and ventrally directed spines on the exterior. The uncus is long, slender, flexed strongly downwards over the basal zone. The vinculum is ventrally concave. The valves are broad and robust basally, but narrow sharply at an interior angle. Distal to this the saccular portion terminates in a robustly sclerotised apical knob or bifurcated process. The dorsal part of the valve, probably the cucullus, is flimsy, narrow, tongue-like, invested with a number of setae that are at least twice as long as the apex of the valve is wide. The aedeagus is straight and terminates in a complex array of sclerotised plates and spines that probably interact specifically with sclerites in the area where the ductus bursae joins the corpus bursae in the female.

The female genitalia have a complex sterigma that consists of pockets and flaps that flank the ductus bursae symmetrically and probably receive the distal saccular process of the male. The apodemes of the eighth segment are not evident. The distal part of the ductus (or neck of the corpus) bursae is swollen, and gives rise to the ductus seminalis. Within the swelling is a prominent sclerite that terminates in a spine or hook that may interact with the apical plates of the aedeagus. This structure is accompanied by a small number of additional spines in a few species. The corpus bursae is elongate, sausage-like, without ornament.

The forms of the male valves and of the female sterigma are suggestive of modification of the aventiine features of these structures, hence the genus is tentatively included in this subfamily. The structure of the corpus bursae could represent a modification of the features seen in Obana, Arasada, Hyposada and Aroana Bethune-Baker, including the subbasal ring of spines.

Most species in the genus are discussed below; indeed the centre of richness is in Sundaland, possibly even Borneo, though exploration of Sumatra might alter this. Only atrigutta Walker is wide-ranging, and the genus appears to be absent from the Indian Subregion. In addition to those mentioned below, the species atropunctata Pagenstecher and baliochraspedus Rothschild occur in Java and Sumatra respectively, and are closely related, possibly conspecific. The taxon alba Snellen (Java), originally described as a form of atropunctata, may be a distinct species though has maculation as in the typical form. Two further undescribed species occur in Peninsular Malaysia (slides 21327, 21382).

The larvae and cocoons of a Japanese species, probably atrigutta (see below), were illustrated and described by Hayashi (2006). The larva is elongate, a dirty fawn, with subdorsal and lateral rows of irregularly sized black spots; it has a rather warty appearance, with A 1-4 elongate and centrally swollen. Prolegs are present on only A6 and A7, and relatively long. The larvae were found when approaching maturity in a ground layer of herbs and ferns in woods. They pupated in cylindrical cocoons rolled from dead fern leaves, capped at each end much as in Cerynea (p. 91) and Arasada (see p. 120).