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Rivula basalis Hampson
     Rivula basalis Hampson, 1891, Illustr. Typical Specimens Lepid. Het. Colln. Br. Mus., 8: 26, 10.


Rivula basalis
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This and the next species are extremely similar in facies, though specimens of simulatrix Hampson from the Asian mainland can be a more ochreous, rufous brown tint, with the males particularly being paler. The basal area of the forewing is much darker than the rest up to the obtusely angled antemedial, and is blackish or dark brown in Sundanian material of both species. There is a pale, subcostally angled postmedial, and the ground distal to this is usually slightly darker than that in the medial area, though not as dark as the basal part. There is often a dark shading around a bipunctate discal mark, this tending to be more intense in basalis. Males of basalis can readily be distinguished by the presence of a subtornal cleft in the distal margin of the hindwings; the genitalia have the slender, tapering valves extending just beyond the apex of the uncus, whereas they extend well beyond it in simulatrix. Dissection of females is necessary to distinguish this sex, however. Both species have unequal signa in the apex of the corpus bursae, one tongue-like, the other trident-like. In basalis the constricted central part of the corpus bursae is shorter and broader, with a distinct basal lobe in addition to an expansion at the basal end.

Geographical range. Indian Subregion to China, Taiwan, Thailand (Kononenko & Pinratana, 2005), Java, Bali, Borneo.

Habitat preference. The only Bornean specimen located is a faded female labelled just 'Sarawak'.

Biology. The species was reared in India by T.R.D. Bell (MS). The body is cylindrical, the segments constricted only shallowly. The head is broader than high, heart-shaped, honey-yellow, marbled with blood-red. The setae of both the head and the body are minutely plumose, mostly white, some on the head being black. The body is greenish, transparent, with a fine subdorsal white line and a broken, irregular, broad yellow spiracular band that extends in places in some segments up to the dorsum. The intersegmental membranes can be reddish.

The larva lies on the underside of a grass blade and pupates in a cocoon at the tip, pulling the sides of the blade together with silk. The pupa is attached inside to the silk by the cremaster.

The host grasses (Gramineae) were not identified.

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