Chemical Senses vol. 30 no. 1 © Oxford University Press 2005; all rights reserved.
Volatile Organic Compounds as Signals in a Plant–Herbivore System: Electrophysiological Responses in Olfactory Sensilla of the Moth Cactoblastis cactorum
1 Max-Planck-Institut for Behavioral Physiology, Seewiesen, Germany, 3 Research School of Biological Sciences, Australian National University, Canberra ACT 0200, Australia and 4 Biosphere 2 Chemistry Unit, Columbia University, Oracle, AZ 85623, USA 2 Present address: Federal Office for Radiation Protection, D-85764 Oberschleissheim/Neuherberg, Germany 5 Present address: Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA
Correspondence to be sent to: PD Dr. Blanka Pophof, Bundesamt für Strahlenschutz, Ingolstädter Landstrasse 1, D-85764 Oberschleissheim/Neuherberg, Germany. E-mail: bpophof{at}bfs.de
The morphological sensillum types on the antennae of male and female Cactoblastis cactorum were visualized by scanning electron microscopy. Electrophysiological recordings were performed for the first time on single olfactory sensilla of C. cactorum. The male sensilla trichodea house a receptor cell responding to the putative pheromone component (9Z,12E)-tetradecadienyl acetate. The sensilla trichodea of the females were much shorter than those of the males and contained specialized receptor cells responding to certain terpenoids, the most frequent being the nerolidol-sensitive cell. The sensilla auricillica and sensilla basiconica of both sexes contained cells responding less specifically to terpenoid compounds as well as to green leaf volatiles. Cells of the sensilla coeloconica responded to aliphatic aldehydes and acids. Eight volatile organic compounds emitted by Opuntia stricta, a host plant of C. cactorum, were identified using gas chromatography–mass spectrometry, ß-caryophyllene being the major compound. Five compounds identified by gas chromatography in the headspace of O. stricta elicited responses in olfactory receptor cells of C. cactorum, nonanal being the most active compound and therefore a candidate attractant of C. cactorum.
Key words: Cactoblastis cactorum, gas chromatography–mass spectrometry, Opuntia stricta, pheromones, single sensillum recordings, volatile organic compounds