Fine structure of tarsal sensilla of male and female Simulium vittatum (Diptera: Simuliidae).

Scanning and transmission electron microscopic examination of the general and sensillar anatomy of the prothoracic tarsus of male and female Simulium vittatum reveals four kinds of hair-type sensilla: (1) generally distributed, mechanosensitive type 1 sensilla trichodea; (2) type 2 sensilla trichodea similar to type 1 though smaller and restricted to the ventral surfaces of tarsomeres 1-4; (3) triply-innervated, taste-sensitive peg sensilla of the ventral surfaces of tarsomeres 1-4; and (4) mid-laterally and terminally distributed type 1 sensilla chaetica that possess one mechanosensitive and four chemosensitive neurons. In addition, wholly internal chordotonal sensilla associated with the tarsal tendon are described. Regions of presumed was-secreting epithelial cells were found to line much of the inner ventral tarsal surface. Anatomical findings are discussed in terms of behavioral and/or physiological significance.