ORIGINAL PAPER Marcus C. Stensmyr á Mattias C. Larsson Shannon Bice á Bill S. Hansson Detection of fruit- and ¯ower-emitted volatiles by olfactory receptor neurons in the polyphagous fruit chafer Pachnoda marginata Coleoptera: Cetoniinae) Accepted: 19 June 2001 / Published online: 8 August 2001 Ó Springer-Verlag 2001 Abstract Olfactory receptor neurons on the antennae of the African fruit chafer species Pachnoda marginata Coleoptera: Scarabaeidae) were examined through ex- tensive use of gas chromatography linked with electro- physiological recordings from single olfactory receptor neurons. Contacted neurons were stimulated with a large number of extracted volatiles from 22 dierent fruits and with 64 synthetic plant compounds. Extracted fruit volatiles were identi®ed using linked gas chroma- tography-mass spectrometry. In total, 48 dierent odor compounds were found to elicit responses. Analysis of the response spectra of the contacted neurons n=232) revealed the presence of 28 classes of receptor neurons. The neurons exhibited strong selectivity as well as high sensitivity. Eleven of the identi®ed classes were selec- tively activated by single compounds, while the re- maining were activated by 2±6 compounds. Several receptor neurons that were activated by more than one compound responded to compounds sharing basic structural similarities. The results support the growing hypothesis that a signi®cant proportion of plant-odor receptor neurons in insects are highly sensitive and selective for single odors. Keywords Electrophysiology á Single cell á Gas-chromatography á Scarab beetle á Plant volatiles Abbreviations FID ¯ame ionization detector á GC gas chromatography á ORN olfactory receptor neuron á SC single cell á SEM scanning electron microscopy Introduction Food specialization is highly divergent in dierent phytophagous insect species, from single species spe- cialists to very broad generalists. In most insect species food location is heavily dependent on olfactory cues. How is the olfactory system of polyphagous insects organized? Are antennal olfactory receptor neurons ORNs) broadly tuned, or is there a range of dierent ORN types that are each speci®c for single odors emitted by dierent food sources? In early investiga- tions, plant odor-speci®c ORNs were considered to be of low sensitivity and speci®city, responding to a wide array of compounds Schneider et al. 1964; Ma and Visser 1978; Den Otter et al. 1980; Selzer 1981; Dick- ens et al. 1984; Kafka 1987). This notion was, how- ever, most likely conceived due to more or less randomly chosen stimulus batteries, where key odor- ants for the ORNs investigated were missing. More recent investigations have indeed demonstrated highly speci®c plant-odor-speci®c ORNs, neurons responding selectively to single odors at minute concentrations Dickens 1990; Todd and Baker 1993; Anderson et al. 1995; Blight et al. 1995; Wibe et al. 1997; Hansson et al. 1999; JoÈnsson and Anderson 1999). In verte- brates dierent levels of speci®city have been demon- strated Malnic et al. 1999; Araneda et al. 2000). A problem is generally that very few key stimuli are known. In the mouse, single odors of known phero- monal signi®cance were tested on vomeronasal recep- tor neurons. In this case an extremely high sensitivity and speci®city could be demonstrated Leinders-Zufall et al. 2000). A key to the characterization of many ORNs has been the use of linked gas chromatography GC) and J Comp Physiol A 2001) 187: 509±519 DOI 10.1007/s003590100222 M.C. Stensmyr á M.C. Larsson á S. Bice á B.S. Hansson &) Department of Ecology, Lund University, 223 62 Lund, Sweden Present address: B.S. Hansson Department of Crop Science Chemical Ecology), Swedish Agricultural University. Box 44, SE-23053 Alnarp, Sweden, e-mail: bill.hansson@ekol.lu.se Tel.: +46-462-23773 or +46-708-793305, Fax: +46-462-224716 Present address: S. Bice Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA e-mail: sbb23@cornell.edu Tel.: +1-607-2544340, Fax: +1-607-2544308