Phacusa Walker

This genus and Ephemeroidea Hampson contain narrow-winged blackish species where the spaces between the veins are transparent; this is partial in Phacusa but more extensive except at the margins in Ephemeroidea. The forewing venation in Phacusa has only R3 and R4 sharing a stalk. The forewing facies is generally as in the Bornean species illustrated, with a transparent patch in the cell split by the M-stem, and a subapical patch split by R5. There is also a series of submarginal patches separated by veins M3, CuA1 and CuA2, and a long sub-dorsal transparent area split by CuP. The hindwing has subapical and dorsal patches crossed by dark veins.

The male genitalia are uniform through the genus, with: a distally narrow, but broadly based uncus with a distinct apical spine; a tongue-like valve with the costa and sacculus more strongly sclerotised, the latter terminating in a ventrally directed thorn-like spine on the margin just subapically; an aedeagus vesica with two large, reflexed cornuti set close together opposite a single smaller one, also reflexed, and with a spiny ovate sclerite in between. The species are distinguished mostly on the structure of the ventral margin of the valve and on variations on the general theme of ornamentation of the vesica. The type species (slide 1541; holotype) has the saccular thorn apically slender and relatively long. The more basal cornutus of the pair is robust, shorter than the distal one and apically rounded, and the third cornutus is about two-thirds the size of the distal member of the pair and the same shape.

The female genitalia have a strongly sclerotised praebursa with some irregular interior spining. The corpus bursae is flimsy, unornamented. Specific differences are found particularly in the spining of the praebursa.

About fifteen species are found through the Oriental tropics. The genus has been studied extensively by G.M. Tarmann, studies well advanced to the point of revision and the assessment of the Sundanian species described below is based on his work.

Tarmann (1992b) recorded members of the genus feeding as larvae on Dillenia (Dilleniaceae) and Vitis (Vitaceae). The first was originally from a manuscript by Bell, but this has not been relocated and was not picked up by Robinson et al. (2001).