title: Effects of changes in atmospheric carbon dioxide on the location of hosts by the moth, Cactoblastis cactorum.
abstract: Sensory organs that detect CO2are common in herbivorous moths and butterflies, but their function has been unclear until now. As the CO2gradients in the vicinity of a host plant depend on its physiological condition, CO2could provide a sensory cue for the suitability of the plant as a larval food source. This study investigated whether changing the atmospheric CO2concentration affected oviposition by Cactoblastis cactorum on its host, the cactus Opuntia stricta. On host plants exposed to rapid fluctuations in CO2concentration, the frequency of oviposition was reduced by a factor of 3.2 compared to the control. As the fluctuations mask the much smaller CO2signals generated by the plants, this suggests that those signals constitute an important component of the host identification process. On host plants exposed to a constant background of doubled CO2, oviposition was also reduced, by a factor of 1.8. An increased background reduces host signal detectability, partially as a consequence of a general principle of sensory physiology (Weber-Fechner's law), and partially due to other factors specific to CO2-receptor neurons.
authors.affiliation: Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra ACT 2601, Australia Fax: +61 6 249 3808; e-mail: stange@rsbs-central.anu.edu.au, , , , , , AU.
authors.forename: Gert
authors.initials: G
authors.lastname: Stange
keywords: Key words Insect-plant interactions ;   Host orientation ;  CO2 sensitivity ;  Elevated CO2;  Oviposition 