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).