The response of Trissolcus basalis to footprint contact kairomones from Nezara viridula females is mediated by leaf epicuticular waxes

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 contamination; whereas approximately 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.

Chemical Ecology of Egg Parasitoids Associated with True Bugs

“…basalis females to significantly reduce their residence time in the arena, similar to the behavior of female wasps in the presence of hexane extracts of male hosts [72]. Parasitoid response to host footprints is mediated by adsorption of the contact kairomone in the epicuticular wax layer of plants walked upon by host bugs [48,73].…”

Behavioral response of the egg parasitoid Ooencyrtus telenomicida to host-related chemical cues in a tritrophic perspective

“…This hypothesis could be extended to N. viridula females which exhibit an analogous tendency to lay egg masses far from sites where adults feed and mate (Colazza et al 1999b). Finally, O. telenomicida females do not respond to by-products of N. viridula adults, as, in open arena bioassays they were not able to detect the footprints contact chemical kairomones left by host adults walking around (Colazza et al 1999b(Colazza et al , 2009. Taking into account that O. kuvanae is attracted to volatiles produced in the accessory gland secretions of the Gypsy Moth, Lymantria dispar L. (Lepidoptera: Lymantriidae) (Hofstetter and Raffa 1998), the possibilities that O. telenomicida females can find host egg masses at short distance spying other host cues than male aggregation pheromone could not be excluded.…”

“…Different host location strategies can have strong effects in shaping extrinsic competition. The host location strategies adopted by T. basalis, have been extensively explored, showing that females are able to exploit chemical cues from adult hosts and/or injured plants in both host finding (Bin et al 1987;Mattiacci et al 1993;Colazza et al 1999bColazza et al , 2004aColazza et al , b, 2007Colazza et al , 2009Peri et al 2006;Laumann et al 2009) and host acceptance (Bin et al 1993;Mattiacci et al 1993;Aldrich et al 1995). On the contrary, no information is available on the host location strategy of O. telenomicida.…”

Plant Volatile Chemicals and Insect Responses

“…It is demonstrated that the detection of oviposition-induced synomones by the parasitoid depends on their adsorption by the epicuticular waxes. Epicuticular waxes of broad bean leaves mediated the foraging behaviour of scelionid egg parasitoid , Trissolcus basalis ( Wollaston ), by absorbing contact kairomones of the host, Nezara viridula (L.) (Colazza et al 2009 ). Wasps displayed the arrestment posture when intact leaves were contaminated by host female footprints, and it was shown earlier that disturbance of plant cuticular layer by adult insect oviposition or chemical footprints stimulate the volatile chemical production which is further used by insect's natural enemies as cues in fi nding their host's environment.…”