Physiological Entomology (2007) 32, 313–321 DOI: 10.1111/j.1365-3032.2007.00575.x © 2007 The Authors Journal compilation © 2007 The Royal Entomological Society 313 Introduction Microhabitat location describes the behaviour of a parasitoid, flying through the host habitat, perceiving a landing site, fly- ing towards this site and landing on it, or rejecting it. During this process, parasitoids are known to respond to visual and volatile infochemicals (Vinson, 1991). These volatiles may be emitted by the plant, the host population, the host, or their interaction (Quicke, 1997; Vinson, 1998). The accurate char- acterization of these infochemicals is important for applied parasitoid research because they play a large part in deter- mining the insect behaviour and ecology. The subject of the present investigation is Fopius arisanus (Sonan, 1932) (Braconidae: Opiinae), a solitary egg-pupal parasitoid of Tephritidae. After its introduction in Hawaii in 1946, this species became the predominant parasitoid of tephritid flies there (Haramoto & Bess, 1970; Wong et al., 1984), and con- tributed significantly to the regulation of Bactrocera dorsalis and Ceratitis capitata populations (Bess et al., 1961; Vargas et al., 1993). To date, this parasitoid is known to develop on approximately 40 tephritid species and, moreover, to oviposit even in nonhost tephritid species such as Bactrocera cucur- bitae (Coquillett) (Snowball & Lukins, 1964; Wharton & Gilstrap, 1983; Harris & Bautista, 1996; Chinajariyawong et al., 2000; Lawrence et al., 2000; Quimio & Walter, 2001; Calvitti et al., 2002; Zenil et al., 2004; Carmichael et al., 2005; Rousse et al., 2006). Wang & Messing (2003) describe the behaviour of F. arisanus when foraging for host eggs after landing on the fruit (i.e. the host location). In two studies on colour attrac- tion for B. dorsalis, Vargas et al. (1991) and Cornelius et al. (1999) show that F. arisanus responds to coloured sticky traps. Furthermore, Liquido (1991), Harris & Bautista (1996), Bautista & Harris (1996), and Bautista et al. (2004) investi- gate the relationships between host plant odour and parasit- ism rate, and Altuzar et al. (2004) describe its response to fruit odours using a wind tunnel. The host- and microhabitat olfactory location by Fopius arisanus suggests a broad potential host range P. ROUSSE, F. CHIROLEU, J. VESLOT and S. QUILICI UMR PVBMT, CIRAD, St Pierre, France and University Réunion, St Denis, France. Abstract. The identification of infochemicals for parasitoid females is a critical issue in applied and fundamental parasitoid research. The olfactory location of host and its microhabitat by Fopius arisanus (Sonan, 1932) (Hymenoptera: Braconidae), an egg-pupal parasitoid of fruit flies (Diptera: Tephritidae), is investigated. Potential sources of volatiles are placed in opaque traps and tested in field cages, under seminatural conditions. Fopius arisanus females respond positively to synomones from mango leaves and from fruits belonging to many botanical families, including the nonhost plant strawberry. They prefer fruits infested by Tephritidae to uninfested ones but do not discriminate between fresh and old infestations. Fopius arisanus females are attracted by the odours of faeces of the tephritid fly Bactrocera zonata. They exhibit remote detection of a volatile kairomone coating the egg mass of all tested Tephritidae species but absent in the egg mass of the Muscidae Stomoxys calcitrans. All these infochemicals are volatile but only those emanating from fruit and from faeces are attractants perceived before landing. The relationships between this apparent generalist behaviour and the dietary specialization of F. arisanus are discussed, according to its ecology and behaviour in its natural environment. Key words. Behavioural ecology , Braconidae, host selection, infochemicals, insect, polyphagous parasitoid, kairomone, synomone, Tephritidae, tritrophic interactions. Correspondence: Pascal Rousse, CIRAD 3P, 7 chemin de l’IRAT, 97410 St Pierre, France. Tel.: +262 262 499231; fax: +262 262 499293; e-mail: pascal.rousse@cirad.fr