Ultrastructure and distribution of antennal sensilla of the chilli thrips Scirtothrips dorsalis hood (Thysanoptera: Thripidae).

The chilli thrips, Scirtothrips dorsalis Hood, is a serious pest of numerous important vegetable and ornamental crops. Various signals, especially phytochemical cues, determine the behavior of the phytophagous thrips at host selection. The sensory abilities of S. dorsalis are poorly understood although the antennae of adult are known to possess important sensory structures in orther insects. In this study, the morphology, distribution, and ultrastructure of the antennal sensilla of the S. dorsalis were examined by using scanning and transmission electron microscopy. Microscopy observations revealed that adult male and female S. dorsalis possess filiform antennae. Each antenna comprises a scape, a pedicel, and a flagellum composed of six segments without clear sexual dimorphism in the number and distribution of antennal sensilla. The scape and pedicel exhibit Böhm's bristles, sensilla chaetica, and sensilla campaniform. The external structures of these organs reveal their mechanosensory function. In the flagellum, the most represented sensilla are the multiporous sensilla basiconica, which can be divided into three types of single-walled olfactory sensilla; three types of sensilla chaetica with mechanosensory and gustatory functions; sensilla coeloconica, which possess hollow cuticular spoke channels and represent double-walled olfactory sensilla; sensilla capitula and sensilla cavity with thermo-hygrosensory functions; and aporous sensilla trichodea with smooth cuticula and mechanosensory function. The putative function of described sensilla is discussed in ralation to host plant selection behavior of S. dorsalis.