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Birthama Walker
Type species: obliqua Walker.
Synonyms: Nirma van Eecke (type species: psychidalis van Eecke); Mambarona
Hering (type species: congrua Walker) syn. n.
Typical species of this genus are sexually dimorphic, the females much
larger with heavier and more distinct forewing fasciation. This fasciation is
diagnostic, consisting of an oblique, straight band and a stepped or zig-zag
submarginal. The former is much heavier than the latter, and the latter tends to
be less extremely stepped in the males of the species. The antennae are broadly
bipectinate over the basal half in the male.
The male genitalia are typical of the limacodid ground plan and offer no
generic features, though there are diagnostic characters for the two Bornean
species.
The female genitalia have the ductus unsclerotised, unspiralled, the
ductus seminalis arising from a relatively basal position. The ovipositor lobes
are centrally constricted and shaped in a manner that may be diagnostic though
this character is seen in less extreme form (or in parallel) in Latoia,
Phocoderma, Hydroclada, Susica and Birthamoides. The bursa lacks a
signum.
The larva was described by Bell (MS) for the S. Indian and Sri Lankan
species B. obliquifascia Hampson (=Miresa canescens Hampson, syn.
n.; Bell reared both sexes, which compare with the types of the two taxa
concerned). It is a perfect semiovoid, the surface smooth, dull with minute
frosting and a few small, thinly brown-ringed disc-like tubercles or dots, two
at least to the dorsum of each segment between the subdorsal lines; there are
others more randomly scattered elsewhere. The tubercles produce a fluid when the
larva is disturbed. The colour is a light leaf green matching the underside of
the leaf on which the larva feeds. There is a thin, indistinct white dorsal
line, more indistinct subdorsals and laterals, and a distinct opaque white
subspiracular line.
The pupa is enclosed in a perfectly ovoid fat short cocoon, smooth,
hard, rather soiled chalky white. The surface shows criss-cross silks that are
cemented from the interior by a kind of gum.
The host-plant was Carallia (Rhizophoraceae).
Apart from this Indian species and the two Sundanian ones discussed
below, the genus at present includes B. roseum de Joannis from Tonkin and
B. murex Hering from New Guinea. The illustration of the former by Hering
(1931) suggests it is correctly placed, but the status of the latter requires
further study.
B. nigrina Hering (1931) was described from Borneo but the type must be presumed
destroyed by the bombing of Hamburg in the last war. No specimens could by
located by the Zoological Museum, University of Hamburg. The original
illustration is not clear enough to enable any material at hand to be referred
to this species. Bornethosea nigrina sp. n., (described
on Bornethosea nigrina sp.n.) is the
closest contender but probably too small.
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