Morphology and Ultrastructure of the Antennal Sensilla of Adult Tetrastichus sp. (Hymenoptera: Eulophidae), a Nymphal Parasitoid Wasp of Agrilus sp. (Coleoptera: Buprestidae)

The olfactory system of parasitoid wasps plays a pivotal role in multiple, essential activities including feeding, mating, oviposition, and host localization. Tetrastichus sp. is a nymphal parasitoid wasp of Agrilus sp. In order to provide morphological basis for further study on behavior of host selection. In the present study, ultrastructure, abundance, distribution and types of the antennal sensilla in both sexes of Tetrastichus sp. were studied using scanning electron microscopy. Antennal sensilla of males and females were compared to those in other hymenopteran parasitoid species and their probable roles were discussed. The antennae of female and male adults of Tetrastichus sp. are similar in shape and belong to geniculate antennae. Antennae consist of radicle, scape, pedicel, anellus, funicle and clava. The female flagellate segment consists of three flagellate subsegments and the male flagellate segment consists of four flagellate subsegments. Six morphologically distinct sensilla types of both sexes of Tetrastichus sp. were observed externally, including Böhm sensilla (BBs), sensilla trichodea (St), sensilla chaetica (SCh), sensilla placodea (Sp), Sensilla mammilliformia (SM), and sensilla styloconicum (Ssty). The phenomenon of sexual dimorphism of antennal sensilla is obvious between the male and female, and the morphological structure, types, number and distribution of the sensilla are different, which could be related to the different functions of the antennal sensilla of male and female. This study is of certain significance to provide the morphological and ultrastructural study of antennal sensilla in Tetrastichus sp. and lays a solid foundation for follow-up functional studies.