Fine Structure of Antennal Sensilla of Paysandisia archon and Electrophysiological Responses to Volatile Compounds Associated with Host Palms

Paysandisia archon (Lepidoptera: Castniidae) is a serious pest of palm trees. A comprehensive knowledge of the insect olfactory system is essential for the development of efficient semiochemical-based control methods. The olfactory sensilla are located particularly on the antennae, and these can detect plant volatiles that provide important cues for the insects in the search for their host plants. To date, the fine structure of P. archon antennal sensilla studies and their role in host-plant perception have not been investigated in great detail. Using light microscopy and scanning and transmission electron microscopy, the antennae of both sexes of P. archon are described here in detail, according to the different types, quantities and distributions of the sensilla. Six types of sensilla were identified. The most widespread are sensilla trichoidea, sensilla basiconica and sensilla auricilica, which are associated with olfactory function. These have cuticular shafts characterised by numerous pores, and they are innervated by two or three sensory neurons. Sensilla coeloconica, sensilla chaetica and sensilla ampullacea are associated with olfactory or olfactory-thermoreception, mechano-gustatory, and thermo-hygroreception functions, respectively. Moreover, the role of P. archon antennae in locating of the host palms was evaluated using electroantennograms, to monitor responses to ester and terpene compounds previously identified as volatiles of damaged/fermenting palm tissues. P. archon showed responses to all of the synthetic chemicals tested, with greater responses in the females, providing a significant sex*dose effect. Among the compounds tested, ethyl isobutyrate elicited the strongest antenna responses. The fine structure of the cuticular and cellular components of the P. archon antenna sensory equipment is described for the first time. The results of this study form an important starting point and complement physiological and behavioural studies, to provide valuable information of practical importance for the development of efficient semiochemical-based control methods.