Morphological characteristics of the antennal flagellum and its sensilla chaetica with character displacement in the sandfly Phlebotomus argentipes Annandale and Brunetti sensu lato (Diptera: psychodidae).

Using light microscope and scanning electron microscope, the external morphological characteristics of the antennal flagellum and its sensilla are described in the sandfly, Phlebotomus argentipes Annandale and Brunetti sensu lato, a well known vector of visceral leishmaniasis in India. A revised terminology is given for the antennal segments to bring phlebotomine more in line with other subfamilies and families while a description of antennal sensilla is provided for the first time in phlebotomine sandflies. Each flagellum consists of scape, pedicel, flagellomeres I to XIII and apiculus. The antennal segments contain scales and sensilla and the latter consist of sensilla trichodea, s. basiconica, s. auricillica, s. coeloconica and s. chaetica and their putative functions are discussed. The sensilla chaeticum hitherto known as antennal ascoid in the phlebotomine sandflies was used to differentiate within and between species. Differences in its relative size to the flagellomere between the populations of P. argentipes collected from the endemic and non-endemic areas in Tamil Nadu state, southern India were established. These differences are considered to be a character displacement as means of premating reproductive isolating mechanism among the populations/members of species complex.