Specificity and sensitivity of plant odor-detecting olfactory sensory neurons in Ctenarytaina eucalypti (Sternorrhyncha: Psyllidae) Jothi Kumar Yuvaraj a , Martin N. Andersson a , Martin J. Steinbauer b , Kevin Farnier b , Olle Anderbrant a,⇑ a Department of Biology, Lund University, Sölvegatan 37, SE-223 62 Lund, Sweden b Department of Zoology, La Trobe University, Melbourne, VIC 3086, Australia article info Article history: Received 11 December 2012 Received in revised form 11 March 2013 Accepted 12 March 2013 Available online 21 March 2013 Keywords: Ctenarytaina eucalypti Olfactory sensory neuron Single sensillum recordings Headspace volatiles Host finding abstract The blue gum psyllid, Ctenarytaina eucalypti (Sternorrhyncha: Psyllidae), is an economic threat to Euca- lyptus subgenus Symphyomyrtus plantations worldwide. To date, no generally applicable control method is available and the potential for semiochemical-based monitoring or control methods has not yet been investigated. Hence, we conducted the first study on the olfactory sense of C. eucalypti, investigating the specificity and sensitivity of its olfactory sensory neurons (OSNs) to host plant volatiles using single sen- sillum recordings (SSR). Synthetic compounds were selected from published identifications of Eucalyptus volatiles and after analysis of headspace collections from Eucalyptus cordata. The antenna of C. eucalypti carries four cavities containing olfactory sensilla (S1–S4). Our recordings revealed that each of these sen- silla houses three OSNs that could be distinguished electrophysiologically based on spike amplitude dif- ferences (A, B, and C neuron with large, intermediate, and small amplitude, respectively). The A neuron in sensillum S1 responded primarily to b-caryophyllene and weaker to b-ocimene, whereas the accompany- ing B-neuron responded strongly and very specifically to linalool. Furthermore, the B-neuron in both S2 and S3 responded strongly to 1-hexanol, Z3-hexenol, and Z3-hexenyl acetate. OSNs in S4 responded only weakly to a few of the synthetic compounds. Response thresholds in strongly responding OSNs to puta- tive key compounds were close to the 1 ng dose on the filter paper and responses exhibited a phasic-tonic profile irrespective of compound dose. C. eucalypti may use the physiologically active compounds for long-range host finding. Future laboratory and field experiments will reveal whether plant volatiles can be used in the management and monitoring of C. eucalypti. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The genus Eucalyptus contains some of the most commonly cul- tivated hardwood timber species around the world (Santos et al., 2004). In addition to timber production, Eucalyptus trees are used for medicine, ornamental foliage, as landscape trees or wind breaks (Doughty, 2000). In the late 1990s, the commercial usage of Euca- lyptus spp. increased dramatically in range and distribution across Europe, North and South America (Hodkinson, 1999). However, over the past three decades Eucalyptus growing as exotics outside Australia have suffered increased biotic stress caused by a number of Australian and endemic herbivorous insects (Gill et al., 1998; Paine et al., 2011). Among these pests is the small (1.5–2.0 mm) blue gum psyllid, Ctenarytaina eucalypti (Maskell) (Sternorrhyncha: Psyllidae), which feeds preferentially on waxy juvenile Eucalyptus globulus foliage (Burckhardt et al., 1999; Purvis et al., 2002; Hollis, 2004). Extralimitally, this psyllid has been reported attacking more than 25 eucalypts, including Eucalyptus dunnii, Eucalyptus gunnii, Eucalyptus cordata (all subgenus Symphyomyrtus) and even Corymbia citriodora (Burckhardt et al., 1999; Dahlsten et al., 1998a; Hodkinson, 1999; Purvis et al., 2002; Santana, 2005; San- tana and Burckhardt, 2007). C. eucalypti is native to Australia but has been introduced into at least 18 countries across the world (Burckhardt, 1998; Burckhardt et al., 1999; Costanzi et al., 2003; Hodkinson, 2007; Olivares, 2000; Purvis et al., 2002; Taylor, 1997). Female blue gum psyllids can lay 20–100 eggs, normally as a group in the leaf buds and the axils of young leaves of young plants (Cadahia, 1980; Santana and Burckhardt, 2007). The psyllid can produce up to four generations per year, depending on climate and plant suitability. The larval instars and the adults feed on plant sap. While feeding they excrete large amounts of honeydew and waxy secretions that act as a growth medium for sooty molds (Dahlsten et al., 1998b; Santana and Burckhardt, 2007). According to Santana and Burckhardt (2007), damage by C. eucalypti can be induced directly by sucking the sap, or indirectly by injecting toxic substances from the saliva. The direct effects of feeding include 0022-1910/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jinsphys.2013.03.004 ⇑ Corresponding author. Tel.: +46 (0) 46 2224997; fax: +46 (0) 46 2224716. E-mail addresses: jothi_kumar.yuvaraj@biol.lu.se (J.K. Yuvaraj), martin_n. andersson@biol.lu.se (M.N. Andersson), m.steinbauer@latrobe.edu.au (M.J. Stein- bauer), kfarnier@students.latrobe.edu.au (K. Farnier), olle.anderbrant@biol.lu.se (O. Anderbrant). Journal of Insect Physiology 59 (2013) 542–551 Contents lists available at SciVerse ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys