© 2006 The Authors Journal compilation © 2006 The Royal Entomological Society 73 Insect Molecular Biology (2007) 16(1), 73–81 doi: 10.1111/j.1365-2583.2006.00702.x Blackwell Publishing Ltd Antennal esterase cDNAs from two pest moths, Spodoptera littoralis and Sesamia nonagrioides, potentially involved in odourant degradation C. Merlin*, G. Rosell†, G. Carot-Sans‡, M.-C. François*, F. Bozzolan*, J. Pelletier*, E. Jacquin-Joly*, A. Guerrero‡ and M. Maïbèche-Coisne* *Unité 1272, UPMC–INRA–INA.PG, Physiologie de l’Insecte: Signalisation et Communication, Centre INRA, France; †Unit of Medicinal Chemistry (Associated with CSIC). Faculty of Pharmacy. University of Barcelona, Barcelona, Spain; and ‡Department of Biological Organic Chemistry, IIQAB (CSIC), Barcelona, Spain Abstract Rapid degradation of odours after interaction with olfactory receptors is a critical step of the signal reception process. However, the implied mechanisms are still largely unknown in vertebrates as well as in insects. Involvement of odourant-degrading enzymes in odourant degradation within the antennae has been shown in some insect species and, in particular, esterases could play a key role in degradation of sex pheromones from Lepidoptera. Using a PCR-based strategy, we isolated cDNAs encoding two new esterases from two moths which used acetates as pheromone compounds: the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides . In antennae, both transcripts were clearly restricted to olfactory sensilla, suggesting their involve- ment in the degradation of odourant acetate components. Keywords: odourant-degrading enzymes, antennal esterases, olfaction, Lepidoptera. Introduction Sensitive and specific detection of volatile chemical cues is essential for insects to interpret their environment and communicate with conspecifics. Detection of these chemical signals at the peripheral level takes place in the antennae, where several steps occur successively. While odourant solubilization and delivery by odourant- binding proteins (OBPs) and detection by membrane-bound odourant-receptors (ORs) were intensely studied and, in a large part, deciphered (review in Jacquin-Joly & Lucas, 2005), the last step of odourant degradation is still largely unknown. Efficient degradation of the signal is, however, an integral part of the signal reception and transduction processes. Among the different mechanisms potentially involved in this termination step, enzymatic degradation is certainly the most studied and some odourant-degrading enzymes (ODEs) have been identified in insects, particu- larly in Lepidoptera (Vogt, 2005). These insects are good models for this purpose because males possess a highly specific and sensitive olfactory system, allowing them to detect small amounts of the sex pheromone released by females. During their flight through the discontinuous pheromone trail, rapid deactivation of the pheromone appears to be crucial for males to obtain a spatial and temporal resolution of this intermittent signal (Vickers, 2006), and to allow the olfactory neurones to respond to frequent periodic stimulations (Vogt & Riddiford, 1981; Vogt, 2003). However, involvement of ODEs in fast pheromone deactivation is still debated, because some authors favour a rapid inactivation by OBPs, followed by enzymatic processes (review in Kaissling, 2001). Nevertheless, biochemical approaches have led in the past to the identification of ODEs belonging to different families, such as esterases, aldehyde-oxidases, alcohol- oxidases/dehydrogenases or cytochromes P450 (review in Vogt, 2005), a diversity that could be correlated with the variety of chemical structures of pheromones. In pioneering works, esterases from the silkmoth Antheraea polyphemus were studied two decades ago, and four esterase isozymes were isolated, one from the sensillum lymph (Apol-SE), two from its antennal integument and one from its scales (Vogt & Riddiford, 1981, 1986; Klein, 1987). As the four esterases were able to degrade the ester components of the phero- mone blend, it was proposed that Apol-SE removes the Received 13 June 2006; accepted after revision 1 August 2006; first published online 19 December 2006. Correspondence: Dr Martine Maïbèche-Coisne, Unité 1272, UPMC–INRA–INA.PG, Physiologie de l’Insecte: Signalisation et Communication, Route de Saint-Cyr, Bat A, 78026 Versailles Cedex, France. Tel.: +33 1 30 83 32 12; fax: +33 1 30 83 31 19; e-mail: maibeche@versailles.inra.fr