Ultrastructure of antennal sensilla of a parasitoid fly, Pales pavida Meigen (Diptera: Tachinidae).

Pales pavida Meigen is obligated polyparasitic fly and important natural enemy of some most damaging forest or agricultural pests, and thus could contribute to the biological control of them. The external morphology of main olfactory organs in this tachinid was examined using stereopic microscopy and scanning electron microscopy, and types, distribution and density of sensilla were provided. The first two antennal segments, antennal scape and pedicel, are covered by microtrichiae and several mechanoreceptors. A pedicellar button is detected on antennal pedicel as well, after its separation with antennal funiculus. On antennal funiculus, five types of sensillar structures are observed including trichoid, basiconic, coeloconic, clavate sensilla and sensory pit with subtype II basiconic sensilla and a type of rarely described coeloconic-like sensilla in it, respectively. There are two specific sensillar characteristics of Pales pavida, two types of sensory pit on antennal funiculus and lower densities of all sensilla types than relatively monoparasitic species, which may serve as applicable evidence on their adaption to environment and lifestyle. Besides, the morphology of pedicellar button in tachinids is first addressed, armed with a discussion of their possible function.