Mechano- and chemoreceptors and their possible role in host location behavior of Sympiesis sericeicornis (hymenoptera: eulophidae)

Abstract

Observations of behavioral interactions between the parasitoid Sympiesis sericeicornis Nees (Hymenoptera: Eulophidae) and the leafmining host Phyllonorycter malella (Gerasimov) (Lepidoptera: Gracillariidae) show that the parasitoid reacts to vibrational signals emitted by the moving larva. In this study we used electron microscopy to investigate the sensilla morphology of the parasitoid S. sericeicornis. Classification of the sensilla allowed us to discuss functional aspects in the wider framework of vibrational communication in this system. The antennae of the female parasitoid has 4 types of sensilla. Two are chemoreceptive, mechanoreceptive, and thermohygroreceptive. Several types of trichoid sensilla are found at the antennal tip. Male and female parasitoid are dimorphic for the antennal tip. Of the tarsus structures, only the pretarsus and the last tarsomeres of female and male parasitoids were in contact with the leaf surface. The tarsomeres were covered by 3 types of mechanoreceptors. At the pretarsus, sensilla were found on the manubrium and claws. The claws had contact chemoreceptors and mechanoreceptors, and the manubrium had only mechanoreceptors, a trichoid sensillum, and campaniform sensilla. The membranous arolium had no sensilla, but could be invaginated and evaginated. This evagination process influenced the position of all sensilla on the pretarsus. The sensilla inventory was compared with other parasitoid species. Eulophid parasitoid species share the same basic inventory of sensillae. The role of different sensilla is discussed in detail with respect to functional aspects for host location behavior of S. sericeicornis and other parasitoid species.