Objective Antennae are the most important olfactory organs of insects, and the antennal sensilla are the fundamental morphological units in their olfactory recognitions. To understand the variety and morphology of the antennal sensilla of Sclerodermus pupariae (Hymenoptera: Bethylidae), an important natural enemy of many buprestids and longhorned beetles.

Method The ultrastructures of antennae and sensilla of male and female parasitoid adults were investigated by scanning electron microscope, and the distribution and quantity of sensilla on female and male antennae were analyzed.

Result The antennae of both male and female parasitoids were knee shaped, and they were consistently constituted with scape, pedicel, and 11 flagellomeres. The antennae of male parasitoids were much longer than those of female wasps. There were seven categories with 11 types of sensilla on the antennae of S. pupariae, including two types of sensilla chaetica (Ch1 and Ch2), three types of sensilla trichodea (Tr1, Tr2, and Tr3), one type of sensilla basiconica (Ba), one type of sensilla placodea (Pl), two types of sensilla styloconica (St1 and St2), one type of sensilla coeloconica (Co), and one type of sensilla squamiforma (Sq). Ten types of sensilla were observed on the antennae of female, and the sensilla Tr1, Tr2, and Ba were restrictedly distributed on female′s antennae. There were eight types of sensilla on the antennae of male, and the sensilla Tr3 were only observed in males. There were six types of sensilla showed consistent quantities across individuals of the same sex, including sensilla Tr1, Ba, Pl, St1, St2, and Co. For other five types of sensilla, their numbers varied among individuals in both females and males. The number of sensilla Ch1 and St1 on the antennae of female adults was significantly higher than that on male adults. Nevertheless, the number of sensilla Pl and St2 on the antennae of male adults was significantly higher than that on female adults. The number of sensilla Co was the same between female and male parasitoids. The sensilla Tr1, Tr2, Tr3, Ba, Pl, and Co were six typical chemosensilla because multiple wall pores could be found on their surfaces.

Conclusion We analyzed the ultrastructure of antennal sensilla of S. pupariae, and found that the types, quantities, and distributions of antennal sensilla between female and male parasitoids have typical sexual dimorphism, which will provide fundamental data for the future investigations on the chemoreception mechanism and olfactory behavior differences between the male and female parasitoids.