ARL Division of Neurobiology, 611 Gould-Simpson Building, 1040 East Fourth Street, University of Arizona, Tucson, AZ-85721, USA.
To explore the effect of plant volatiles alone in stimulating female moth oviposition responses, we tested the behavioral responses of laboratory-reared female Manduca sexta moths (Lepidoptera: Sphingidae) to hostplant and non-hostplant volatiles. In contrast to other Lepidoptera in which tarsal contact is necessary for ovipositional responses, we have demonstrated that mated, day-3 M. sexta females offered plant volatiles alone can display the abdomen curling response - a pre-cursor to oviposition - without any plant contact by the moth. Female moths responded with abdomen curling both to volatiles released by intact, potted plants and to plant headspace volatiles that were collected and then solvent-desorbed. We also examined the differences in abdomen curling responses between virgin and mated females of comparable ages, and between untreated virgin females, and those that had been pre-treated to up-regulate their sensitivity. To date, we have tested numerous hostplants, both solanaceous and non-solanaceous, and have observed abdomen curling responses ranging from 62 to 96%, depending upon the plant sample and the bioassay arena. In addition, 40% of the female moths challenged with a non-hostplant species, such as cabbage, demonstrated abdomen curling. Ongoing examination of compounds contained within hostplant and non-hostplant headspace volatiles, using GC-MS, suggests that similar compounds are found within headspace samples across all stimulatory plants, whether host or non-host. Moth responses were tested either by exposure within the flight tunnel, or by exposure in a bench-top bioassay. In both cases, we measured the moth's first response to hostplant volatiles.