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Risoba olivens Bethune-Baker
Risoba olivens Bethune-Baker, 1906, Novit. zool., 13: 234.
Risoba olivens Bethune-Baker; Holloway, 1976: 21.


Risoba olivens

Diagnosis and taxonomic note.
This species and R. prominens Moore (Indian Subregion, Japan, Vietnam, Sundaland except Borneo) are very closely related (see under obstructa above) and have the typical asymmetric valve ornamentation of the male genitalia seen in the vialis group. The two have more contrasted grey-green forewings than the previous three, and the hindwings are less of a clear yellow, more obscured with brown than in vialis or avola. In olivens the apical patch is more rounded and clearly defined by the arcuate component of the postmedial immediately basal to it; at its posterior edge the white mark tends to be triangular in olivens and more rectangular in prominens. As indicated under obstructa above, the postmedial meets the dorsum in a more regular and sharper curve in olivens, and there is often a pale lining to the dorsum basal to it. In prominens there is often a dull, ochreous patch at the tornus. The male genitalia are also very similar, but differ in the following features: the right saccular process reaches the valve margin in prominens and extends beyond it in olivens; the left process is more deeply bifid, enclosing a right-angle rather than a distinctly obtuse one; the ventral margin of the valve in prominens has a slight lobe near the base of the saccular process on each side; the aedeagus has a few small spines centrally in prominens but a more conspicuous longitudinal flange in olivens (semicircular in the Bornean male, triangular in males from Sulawesi and New Guinea). The female from Bukit Retak (see below) is somewhat atypical with more irregular patterning.

Geographical range. New Guinea, Seram, Buru, Sulawesi, Borneo, Sumatra.

Habitat preference. Both specimens taken in recent surveys are from montane localities: 1930m on G. Kinabalu; 1465m on Bukit Retak in Brunei.

Biology. Gardner (1948) described the larva of prominens as having a darkly reticulated testaceous head and a mottled purplish body, the latter with an irregular, pale, dorsolateral line on each side. The setae are on white dots, and the prolegs have a dark spot externally.

The host-plant was Pterocarya (Juglandaceae), but Mell (1943) recorded Melastoma (Melastomataceae) in China, and Sugi (1987) noted Myrica (Myricaceae) in Japan, and illustrated a green larva with yellow dorsal and lateral lines, with the setal bases also yellow. There may be confusion over the identity of these larvae. Barlow (1982) recorded Quisqualis (Combretaceae); see also Robinson et al. (2001).

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