Sensillia twig basiconica
Sensilla twig basiconica (STB) is found only at the apical end of adult
labial palps and consists of four subtypes (STB I, STB II, STB III, and
STB IV). The shape of these sensors varies markedly between subtypes
(Fig. 4): STB I has a smooth surface and a flat and deeply concave
apical part with a distinct chamber and no basal fossa; STB II has a
generally smooth surface and a rounded apical part with
chrysanthemum shaped granules and no
basal fossa; STB III has a smooth surface and a flower-like wrapping
around a finger-like projection at the tip; STB IV has an overall smooth
surface and a rounded apical part with a dome.
The terminal tapered inductor of the labial palpus exhibits external
morphological features that are significantly longer in males than in
females, including STB I (t = -4.00, P < 0.01)
and STB II (t = -4.59, P < 0.01), while the
basal width of STB III (t = -5.76, P < 0.01) in
males is similarly significantly wider than in females; however, the STB
IV basal width (t = 2.15, P < 0.05) in females
was significantly wider than males. Quantitatively, females had
significantly more STB IV than males (Fig. 3).