237 INTRODUCTION Homopteran insects, including aphids, excrete copious amounts of honeydew comprised of substances derived from both the host plant and the insect itself (i.e. specifc sugars and amino acids) (Heidari & Copland, 1993; Leroy et al., 2011). Many studies have shown that this excretory product acts as an attractant for the adult stage of preda- tors and parasitoids, such as Chrysopidae (McEwen et al., 1993; Petersen & Hunter, 2002), Coccinellidae (Evans & Dixon, 1986; Evans & Richard, 1997), Syrphidae (Buden- berg & Powell, 1992; Shonouda, 1996; Bargen et al., 1998; Shonouda et al., 1998a, b; Sutherland et al., 2001) or Aphi- diidae (Budenberg, 1990; Budenberg et al., 1992; Du et al., 1997). These studies demonstrated that aphid honey- dew induces oviposition and increases localisation of hosts or prey. Many predators and parasitoids use this excretory product as a food complement rich in sugars (mono-, di- and trisaccharides), and essential amino acids, also con- taining minerals, vitamins and organic acids (Wäckers, 2000). It is well known that the aphidophagous syrphid Episyr- phus balteatus (De Geer) (Diptera: Syrphidae) is an eff- cient predator of many aphid species in agro-ecosystems and in natural habitats (Tenhumberg & Poehling, 1995). Females generally oviposit near aphid colonies to provide a food source for the emerging larvae which are unable to move any great distance (< 1 m) to search for prey (Chan- dler, 1968a, b; Scholz & Poehling, 2000; Sadeghi & Gil- bert, 2000). Interestingly, Gries (1986) noted that newly emerged syrphid larvae stretch their papillae for better per- ception of prey-associated odours which induce a search behaviour: after fxing its anal end to the surface, the larva raises the rest of its body: it touches the surface with its mouthparts before choosing a new direction (Bhatia, 1939). Previous studies have been focused on the potential odorant cues that enable E. balteatus females to locate and select suitable oviposition sites (Almohamad et al., 2007, 2008a, b; Verheggen et al., 2008, 2009), taking into consid- eration that the quality of an oviposition site can depend not only on the presence of aphids and their numbers, but also on the presence of inter- or intraspecifc competitors (Almohamad et al., 2009, 2010). Nevertheless, little infor- mation is available about the role of honeydew-derived chemical cues in foraging behaviour by predatory hoverfy E. balteatus larvae, a crucial aspect of their effective use in strategies for the biological control of aphids. The presence of aphids is always associated with the presence of large amount of honeydew on the host plant, contaminating peripheral plant parts such as leaves and stems (Buckley, 1987). This strongly suggests that syrphid larvae are often in contact with aphid honeydew. To com- plete our knowledge and to understand the role of aphid honeydew semiochemicals in the foraging behaviour of syrphids (larva or adult), we note that the behaviour of aphid predators on honeydew-contaminated plants sug- gests that honeydew could acts as an arrestant as well as a searching stimulant. An arrestant may be defned as a Eur. J. Entomol. 111(2): 237–242, 2014 doi: 10.14411/eje.2014.028 ISSN 1210-5759 (print), 1802-8829 (online) Aphid honeydew: An arrestant and a contact kairomone for Episyrphus balteatus (Diptera: Syrphidae) larvae and adults Pascal D. Leroy  1 , Raki ALmohAmAD  1 *, sabRine AttiA  2 , Quentin CApeLLA  1 , FRançois J. VerheGGen  1 , eRic hAubruGe  1 and FRéDéRic FrAnCiS  1 1 Department of Functional and Evolutionary Entomology, University of Liège, Gembloux Agro-Bio Tech, Passage des Déportés 2, 5030 Gembloux, Belgium; e-mails: almohamad75@yahoo.fr; leroy.pl@gmail.com; capella.quentin@gmail.com; fverheggen@ulg.ac.be; E.haubruge@ulg.ac.be; Frederic.francis@ulg.ac.be 2 Department of Analytical Chemistry, University of Liège, Gembloux Agro-Bio Tech, Passage des Déportés 2, 5030 Gembloux, Belgium; e-mail: sabine_bios5@yahoo.fr Key words. Diptera, Syrphidae, Episyrphus balteatus, Acyrthosiphon pisum, searching behaviour, adults, honeydew, kairomone, larvae Abstract. predator searching effciency increases in response to a variety of environmental cues associated with its prey. the sugary excretion of aphids (honeydew) has been found to act as a prey-associated cue for many aphid natural enemies. In the present study, the honeydew excreted by Acyrthosiphon pisum (harris) was identifed as an arrestant and a contact kairomone for young larvae and adults of a common predatory hoverfy, Episyrphus balteatus (De Geer) (Diptera: Syrphidae). First and second instar larvae increased their foraging behaviour in the honeydew-treated area. When plants were sprayed with crude honeydew, the speed of movement of female E. balteatus was signifcantly higher than in controls, resulting in a longer period of time spent on treated plants and laying eggs. We conclude that the honeydew excreted by A. pisum induces searching behaviour and acts as and arrestant not only for adults but also for young E. balteatus larvae. * Corresponding author.