Diagnosis. This and the next two species have very similar males. In robustalis postmedial is triarcuate, transverse, and only slightly edged in white. In the next two species the postmedial is more strongly triarcuate, oblique rather than transverse. The area distal to this is only slightly paler in robustalis but distinctly so in the next two species. In robustalis the paleness is restricted to a mauvish suffusion over the basal half of the distal third. In ischyra Prout there is only limited sexual dimorphism, but in robustalis the female has the forewing postmedial straight and usually more strongly lined distad by white (see also Prout (1932)). The subapical lens on the costa is only weakly defined, if at all, in the three species but is much clearer in other Hypena and all Dichromia with a triarcuate postmedial.
Taxonomic note. The synonymy above was etablished by Poole (1989), but indicated by Lödl (1999e) to require further study in relation to mandatalis Walker. This has now been undertaken.
Geographical range. India, Thailand, Sundaland and east to Fiji; the species is not recorded from Australia by Nielsen et al. (1996).
Habitat preference. Two females have been taken, one from Bidi in the lowlands of Sarawak and one from the understorey of secondary forest at 170m on the Bukit Atur road near the Danum Valley Field Centre in Sabah. Two Bornean males seen are both from Sarawak (one from G. Mulu) but without precise data.
Biology. Bell (MS) described the life history under H. mandatalis in India (see the next species). The egg is dome-shaped, much broader than high, the top slightly flattened; there are 30-31 longitudinal ribs, some anastomosing as they extend up from the base to a central circular space. There are finer cross-rays between these ribs. The surface is glossy, smooth, the concave cells between the ribs and rays highly reflective. The colour is delicate green, blotched transversely, linearly by four zones of red.
The larva is elongate, fusiform. The prolegs on A4 are half-size, those on A3 a bit smaller. The anal claspers are outstretched, diverging at right-angles. The head is light yellowish-green, blotched with brown, but the setae are on conical black chalazae. The body is dull, smooth, the primary setae also set on black chalazae. The setae are about the same length as a segment. The colour is a light olive to grassy green with a darker pulsating dorsal line. The spiracles are black.
The larvae lie fully stretched under leaves and on stalks and twigs. They move in a looping manner, feed on the youngest available foliage, and turn pink before pupating in a slight silken cell within a rolled or folded leaf, living or withered, on the ground.
The host plant recorded was Derris (Leguminosae). Robinson et al. (2001; ex IIE records) noted a host plant record for allochroalis in mangrove from an unidentified plant in the Leguminosae.
