Silba erecta has only 1 strong seta on the katepisternum,
an unusual feature in the genus but shared by three Asian fig-feeding
species: S. ishigaki, S. lashker and S. ischnopda. In external features S.
erecta is most similar to Silba ishigaki, but the key feature which clearly
separates these species is in the shape of the phallus. The phallus of S.
ishigaki is long and thin, serrated for most of its length and with only a
single basal process (MacGowan and Okamoto, 2013, Fig. 7) whilst in S.
erecta it is far more complex
Description. Male. Head. Eyes bare. Frons black, dulled by microsculpture. Orbital plate shining black, bare apart from orbital
seta. Frontal and interfrontal setulae very short, no more than
0.1 × length of orbital seta, longer setulae on anterior margin above
lunule. Lunule black, slightly grey dusted as face and parafacials.
Anterior genal setulae forming single row of 6–7 along mouth margin.
Antennae black; postpedicel with distinct orange medial base, length to
width ratio 2.0:1; arista yellow at base, with short plumosity, at its
greatest extent 0.3 × width of postpedicel.
Thorax. Proepisternum and proepimeron each with 1 seta. Scutum
glittering black, covered with appressed setulae, which approximately
0.4 × length of orbital seta on head. Scutellum shining black on disc,
with 4 marginal setae, with 2 short setulae between lateral and apical
setae, with a single short setula between apical setae. Anepisternum
with 2 anterior and 3 posterior setae; setulae between these rows no
more than 0.5 × length of the setae. Katepisternum with 1 weak
anterior and 1 strong posterior setae near dorsal margin; anterior seta
half as long and strong as posterior seta; 2–3 setulae lying anterior to
these setae along the anterior margin. Wing length 3.0 mm; membrane
covered with long dark microtrichia; veins dark brown. Calypteres
white, with white fringe. Halteres black. Legs entirely black including
ventral row of spicules on fore and hind metatarsi.
Abdomen. Gentalia (Fig. 2). Epandrium higher than long, with semicircular
excavation on anterior margin. Cerci relatively large, rectangular
in shape, bearing numerous short, stiff setulae along posterior
margin and apex. Surstyli not extending the full length of the epandrium;
outer margin with a row of stiff setae (Fig. 2A). Internal view
(Fig. 2B), a small setula located at base of each cercus; prensisetae in
rather uniform single row of 5 running medially from posterior margin
of surstyli; two setulae at dorsal end of the row. Phallus small and
lightly chitinised; intromittent organ long, thin and curving basally;
pair of long antler-like processes each with two strong ventral projections
and a serrated apex (Fig. 2C).
Female. Similar to male except for the usual sexual differences.
Aculeus with apical segment diamond-shaped, in dorsal view twice as
long as wide; basal third embedded in rods of aculeus; with 2 short
setulae on lateral side and long setula on ventral side at apical half.