Diagnosis. The wings are a relatively rich brown with prominent discal spots and fine, dark, partially interrupted, irregular, crenate fasciae. Males have a conspicuous lens-shaped mass of scales on the foreleg, and the mid-tibia also has a hair pencil.
Taxonomic note. The holotype male of robustalis has lost its abdomen but has facies and foreleg ornamentation identical to that of circumscripta.
Geographical range. India, Sundaland to New Guinea and Queensland.
Habitat preference. This is a frequently encountered species of lowland forest, perhaps more common in disturbed and secondary forest. It is also common in lowland softwood plantations (Chey, 1994).
Biology. Sevastopulo (1948), referring to robustalis of Guenée (nec Walker; see cornicalis Fabricius below), described the life history from eggs laid by a female in Calcutta. The eggs are bun-shaped, a translucent pale grey, unsculptured but with an irregular network of purple-brown streaks.
The first instar is a semi-looper, long, thin, greyish pink on hatching, then pale green with primary setae on small black specks. The prolegs on A3 and A4 are obsolete; in later instars they are described as rudimentary. Later instars have a pale brown head and a dull green body reticulated with purple brown, giving a dull, dark grey impression overall. There are faint dorsal, dorsolateral and lateral lines of the same purple brown, the dorsal one becoming more obvious with age but the others becoming obscured. T1 has a brown dorsal plate, and the intersegmental areas are also tinged brownish.
No really suitable food was established, and the larvae did not reach maturity. Amaranthus (Amaranthaceae) foliage was preferred over Cassia (Leguminosae) and Dalbergia in the same family, recorded previously as a host, was refused, fresh or withered.
