SHORT COMMUNICATION The response of Trissolcus basalis to footprint contact kairomones from Nezara viridula females is mediated by leaf epicuticular waxes Stefano Colazza & Mauro Lo Bue & Daniela Lo Giudice & Ezio Peri Received: 26 March 2009 / Revised: 17 April 2009 / Accepted: 18 April 2009 / Published online: 20 May 2009 # Springer-Verlag 2009 Abstract Chemical footprints left behind by true bugs are perceived as contact kairomones by scelionid egg parasitoids. Female wasps encountering a contaminated artificial substrate display a characteristic arrestment posture, holding the body motionless and antennating the surface. In the system Nezara viridula (L.) and its egg parasitoid Trissolcus basalis (Wollaston), previous studies have shown that the kairomone mediating such behavior is part of N. viridula’ s cuticular hydrocarbons (CHC) and furthermore that the wasp’ s ability to discriminate host male and female footprints is mainly based on the presence/absence of nonadecane (nC 19 ). In this study, the effect of epicuticular waxes of leaves of broad bean, Vicia faba, on wasp responses to footprints of N. viridula females were investigated. Approximately 20% of T. basalis females displayed an arrestment posture when released on the adaxial leaf surfaces of broad bean plants with intact wax layer and without host chemical contam- ination; whereas ∼70% of wasps displayed the arrestment posture when intact leaves were contaminated by host female footprints. Adaxial leaf surfaces of broad bean plants dewaxed with an aqueous solution of gum arabic and afterwards contaminated by N. viridula females induced arrestment responses in about 10% of female wasps; the same percentage of arrestment (10%) was observed when the wasps were released on leaves contaminated by host females and subsequently dewaxed. The side of the polymer film that was appressed to the leaf surface, peeled from the contaminated leaves, induced an arrestment posture in about 95% of observed wasps. Scanning electron microscopy (SEM) revealed that the epicuticular waxes occurred as a film densely crystallized as irregularly shaped platelets with spherical granules randomly distributed. These findings demonstrated that epicuticular waxes of broad bean leaves can mediate the foraging behavior of T. basalis females by absorbing contact kairomones of the host. Keywords Insects . Egg parasitoids . Southern green stink bug . Vicia faba . Scanning electron microscopy Introduction Insect parasitoids find their hosts via a series of behavioral steps, which are mainly mediated by chemical cues directly or indirectly related to the host (Vinson 1998). Chemical stimuli lead the wasps in a hierarchical process to the host habitat, to the host plant, and finally to the susceptible host stage (Vinson 1985; Quicke 1997). The fitness of para- sitoids strongly depends upon their ability to find hosts quickly, before hosts become unsuitable as a consequence of their fast development (Vet and Dicke 1992; Godfray 1994). This is particularly true for egg parasitoids, which must oviposit into recently laid eggs before embryo development renders them unsuitable as hosts (Strand 1986; Vinson 1998). To find host eggs quickly, egg parasitoid females can exploit semiochemicals arising from the host eggs, from the interaction of the plant and the eggs, or from stages other than the one attacked (Powell 1999; Fatouros et al. 2008). This last group of semiochemicals, termed indirect host-related cues, does not provide infor- mation on the location or the age of host eggs, but brings Naturwissenschaften (2009) 96:975–981 DOI 10.1007/s00114-009-0548-3 S. Colazza (*) : M. Lo Bue : D. Lo Giudice : E. Peri Department of S.En.Fi.Mi.Zo.—Entomology, Acarology and Zoology, Università degli Studi di Palermo, 13 viale delle Scienze, 90128 Palermo, Italy e-mail: colazza@unipa.it