Volatile chemical release by bethylid wasps: identity, phylogeny, anatomy and behaviour MARLÈNE GOUBAULT 1† , TIM P. BATCHELOR 1‡ , ROBERTO ROMANI 2 , ROBERT S. T. LINFORTH 1 , MATTHIAS FRITZSCHE 3 , WITTKO FRANCKE 3 and IAN C. W. HARDY 1 * 1 School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK 2 Dipartimento di Scienze Agrarie e Ambientali, Facoltà di Agraria, Università degli Studi di Perugia, Borgo XX Giugno 74, 06121 Perugia, Italy 3 University of Hamburg, Organic Chemistry, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany Received 20 November 2007; accepted for publication 5 December 2007 The structures of volatile chemicals released by parasitic wasps in the family Bethylidae are shown to correspond to the subfamily to which the species belong. Species in the Epyrinae release skatole (3-methylindole) and species in the Bethylinae release a spiroacetal (2-methyl-1,7-dioxaspiro [5.5]undecane): these compounds are chemically very different. The enantiomeric composition of the spiroacetal differs between congeneric species. Chemical release is a discrete event under the active control of both male and female wasps. Structural differences between the mandibular glands and intramandibular glands suggest the mandibular glands to be the source of released volatiles. Real-time mass spectrometry shows that the spiroacetal is released by Goniozus nephantidis females during dyadic resource contests, with release more common during more aggressive interactions. Chemical tagging with deuterium further shows that the volatile is released by the loser of an agonistic interaction and not the winner. The function of spiroacetal and skatole release by bethylids is discussed. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 837–852. ADDITIONAL KEYWORDS: contest behaviour – mandibular gland – mass spectrometry – parasitoid – skatole – spiroacetal. INTRODUCTION A broad array of animal species, ranging from large vertebrates to small invertebrates, employs chemicals in behavioural interactions with conspecifics. The function of these chemicals may relate to sexual attraction, social organization, territorial marking or signals and weapons used during contests for resources (see Wyatt, 2003 for a review). The array of animal species engaging in contests, particularly dyadic intra-specific contests, also ranges from large vertebrates (e.g. Kokko, López-Sepulcre & Morrell, 2006) to small invertebrates, including some species of parasitoid hymenopterans (e.g. Field & Calbert, 1999; Goubault et al., 2007a). Studies on parasitoid behaviour and ecology asso- ciated with or determined by semiochemicals have mainly focused on tritrophic interactions, particularly the ability of parasitoids to locate hosts using vola- tiles emitted by plants fed on by these hosts (e.g. Gohole et al., 2003). Chemicals have also been shown to play a role in communication between conspecific parasitoids: females may chemically mark hosts after oviposition in order to deter superparasitism (e.g. Rosi et al., 2001) and females may emit sex phero- mones that attract males (reviewed by Godfray [1994]) or repel females (Micha, Stammel & Höller, *Corresponding author. E-mail: ian.hardy@nottingham.ac.uk †Current address: Institute de Recherche sur la Biologie de I’Insecte, UMR CNRS 6035, Université de Tours, 37200, Tours, France ‡Current address: School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK Biological Journal of the Linnean Society, 2008, 94, 837–852. With 8 figures © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 837–852 837