Journal of Insect Physiology 49 (2003) 845–856 www.elsevier.com/locate/jinsphys Increased EAG responses of tortricid moths after prolonged exposure to plant volatiles: evidence for octopamine-mediated sensitization Lukasz L. Stelinski * , James R. Miller, Noah E. Ressa, Larry J. Gut Department of Entomology, 205 Center for Integrated Plant Systems, Michigan State University, East Lansing, MI 48824, USA Received 11 February 2003; accepted 28 May 2003 Abstract As measured by electroantennograms (EAG), both male and female obliquebanded leafrollers, Choristoneura rosaceana (Harris), and redbanded leafrollers, Argyrotaenia velutinana (Walker), were similarly sensitive to host-related plant volatiles: trans-2-hexenal, benzaldehyde, 1-hexenol, cis-3-hexen-1-ol, geraniol, linalool, (+)-limonene, hexenal and trans-2-hexenol. Females of both species were similarly sensitive to the shared major component of their sex-attractant pheromone ((Z)11-14:Ac). Continuous 60 min pre- exposure of male and female C. rosaceana and A. velutinana to successively higher concentrations of a mixture of the nine plant volatiles in Teflon chambers with continuous air exchange caused a dosage-dependent increase in subsequent responsiveness (sensitization) to green leaf volatiles, as measured by EAGs. In addition, 60 min of pre-exposure of male C. rosaceana to certain individual volatiles ((+)-limonene, geraniol, benzaldehyde) increased EAGs nearly as much as did the mixture of nine volatiles. Pre-exposures to the nine plant-volatile mixture at concentrations achieved by 100 μg and 1 mg loading dosages in 100 μl of mineral oil significantly increased EAG depolarization to pheromone (cross-sensitization) in males but not females of both moth species. Antennae of male C. rosaceana pre-injected with 100 μg of octopamine (OA) without volatile pre-exposure exhibited sensitization nearly identical to that induced by pre-exposing moths to sensitizing concentrations of the plant-volatile mixture. Moreover, injection of the OA antagonist chlorpromazine (CP) blocked sensitization by the plant-volatile pre-exposure. Collectively, these findings suggest that exposures of tortricid moths to certain host-plant related volatiles may modulate subsequent olfactory sensitivity to behaviorally relevant chemical cues and that plant-volatile induced sensitization may be octopamine mediated.  2003 Elsevier Ltd. All rights reserved. Keywords: Cross-sensitization; Green leaf volatiles; Octopamine; Electroantennogram (EAG); Choristoneura rosaceana; Argyrotaenia velutinana 1. Introduction Recently, we reported (Stelinski et al., 2003a) that pre-exposure of male Choristoneura rosaceana (Harris), to the synthetic pheromone ((Z)11-14:Ac and (E)11- 14:Ac) at 36 ± 12 ng/ml air for durations of 15 and 60 min in Teflon chambers with regulated air exchange reduced peripheral sensory responses to these com- pounds by 40–60% in subsequent EAG assays. The EAG responses of male C. rosaceana to their sex-attractant pheromone recover linearly to 70–100% of their pre- * Corresponding author. Tel.: +1-517-432-9514; fax: +1-517-353- 5598. E-mail address: stelinsk@msu.edu (L.L. Stelinski). 0022-1910/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0022-1910(03)00136-7 exposure amplitude within 12.5 min at a rate of 3– 4%/min (Stelinski et al., 2003a). Furthermore, an ident- ical reduction of responsiveness was observed at each effective exposure concentration ranging from 56 to below 1 ng/ml air (Stelinski et al., 2003b). In contrast, no corresponding long-lasting adaptation was found in ident- ically treated Argyrotaenia velutinana (Walker), despite its close taxonomic relatedness and similarity of pheromone blend to C. rosaceana (Stelinski et al., 2003a). The current study originally aimed at determining whether exposure of leafroller moths to EAG-active plant volatiles would induce auto-adaptation of antennal responses to these chemicals and/or reciprocal cross-adaptation to pheromone as meas- ured by EAG. As the study progressed, sensitization rather than adaptation was the predominant phenomenon uncovered and documented herein.