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Rivula aequalis Walker
     Motina aequalis Walker, 1863, List Specimens lepid. Insects Colln Br. Mus., 27: 12.
    Cholimma leucanioides Walker, [1863] 1864, J. Proc. Linn. Soc. (Zool.), 7: 61, syn. n.
    Cholimma subpunctata Walker, [1863] 1864, J. Proc. Linn. Soc. (Zool.), 7: 61.
    Scopula nexalis Walker, 1865, List Specimens lepid. Insects Colln Br. Mus., 34: 1473.
    Pasira biatomea Moore, 1883, Proc. zool. Soc. Lond., 1883: 29, syn. n.


Rivula aequalis

Rivula aequalis
Figure 10
Figure 26

The forewings of both sexes are slightly narrower than in other species, pale straw except for a transverse, somewhat bipunctate blackish discal mark and an oblique, centrally zigzag, submarginal row of diffuse, dark patches. Distal to the latter there may be a more general darkish suffusion. The hindwings are slightly yellower than the forewings in the female, but the male has this colour obscured by dark greyish scaling except for a band along the costa. There is also a dark discal spot. Males also have dark suffusion in these areas on the underside.

Taxonomic note. All the taxa brought into synonymy above have similar facies and male genitalia; biatomea was listed as a synonym of leucanioides by Sugi in Heppner & Inoue (1992). R. calamina Hampson (= aroa Bethune-Baker, praeocc.) from New Guinea is very similar and may be conspecific. A closely related species, R. ochracea Moore, occurs in India, Singapore and the Philippines, so may prove to occur in Borneo. It has more extreme sexual dimorphism, with males having a pale arcuate structure subdorsally on the brown hindwings. Females of the two species are very similar, as are the genitalia of both sexes.

Geographical range. Indian Subregion to Japan, Sundaland and Philippines, Sulawesi, Seram, ?New Guinea.

Habitat preference. Type material of leucanioides, aequalis and subpunctata was taken by A.R. Wallace in Sarawak, probably in the lowlands, but the species was recorded only in upper montane forest at 2360m on G. Mulu during recent surveys.

Biology. The larva of ochracea was reared by T.R.D. Bell (MS) in India. It is cylindrical, broadest over T3 and A2. The prolegs are all fully developed. The head is brownish yellow, honeycombed by rows of minute brown tubercles, and tinged green in places. The body is glossy, the setae longer than its breadth and minutely plumose, arising from translucent chalazae that are arranged in a belt around each segment. The colour is pale, watery green, whitish dorsally, and with a pinkish transverse band on each side of the setae on each segment. There is a broad, white spiracular band, and there are dorsolateral black spots on T1. The very similar larva of aequalis has been illustrated by Sugi (1987; as leucanioides).

The larva lives actively on a leaf blade, and pupates at the apex of the blade, bending the point over twice and fastening it with silk to form a triangular hollow pyramid, with the point of the leaf as the base, and lined and sealed with silk. The green pupa is held slightly bent, attached by the cremaster, within this.

The host plant is a bamboo, Bambusa (Gramineae), a host genus also recorded for aequalis in Japan (Sugi, 1987: as leucanioides).

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