Host Sex Discrimination by an Egg Parasitoid on Brassica Leaves

Abstract

Egg parasitoids are able to find their hosts by exploiting their chemical footprints as host location cues. In nature, the apolar epicuticular wax layer of plants that consists of several classes of hydrocarbons serves as the substrate that retains these contact kairomones. However, experiments on chemical footprints generally have used filter paper as substrate to study insect behavior. Here, we explored the ability of Trissolcus basalis (Scelionidae) females to discriminate between footprint cues left by male and female Nezara viridula (Pentatomidae) on leaves of their host plant Brassica oleracea (broccoli). Furthermore, we analyzed the chemical composition of the outermost wax layer of broccoli leaves to evaluate the degree of overlap in insect and plant cuticular hydrocarbons that could lead to masking effects in the detection of footprint cues. Our results showed that B. oleracea epicuticular wax retains the chemical footprints of adult bugs and allows T. basalis females to differentiate hosts of different sex. Traces of female bugs elicited more extensive searching behavior in egg parasitoids than traces of males. The application of n-nonadecane, a compound specific to male N. viridula, on the tarsi of female bugs prevented parasitoid females from distinguishing between host male and host female footprints. Analyses of B. oleracea leaves revealed that epicuticular waxes were mainly composed of linear alkanes, ketones, and secondary alcohols. Alkanes were dominated by n-nonacosane (nC29) and n-hentriacontane (nC31), while male-specific n-nonadecane (nC19) was absent. The ecological significance of these results for parasitoid host location behavior is discussed.

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].…”

“…basalis and Tr. brochymenae are able to discriminate host adult sex and Psyche 5 the physiological conditions of host adults (e.g., virgin versus mated females) [28,31,47,48]. Interestingly, in addition to chemical footprints, Te.…”

Foraging behaviour of an egg parasitoid exploiting plant volatiles induced by pentatomids: the role of adaxial and abaxial leaf surfaces

“…In addition, it is known that footprints left on the substrate by true bugs have kairomonal effect for some Trissolcus and Telenomus species (Hymenoptera: Platygastridae) (Colazza, Salerno & Wajnberg, 1999a; Borges et al, 2003; Conti et al, 2004; Salerno et al, 2006). In particular, footprints left on the substrate by Nezara viridula (L.) (Heteroptera: Pentatomidae) females are perceived by the egg parasitoid Trissolcus basalis (Wollaston) females since they are retained onto the epicuticular waxes (Colazza et al, 2009; Lo Giudice et al, 2010; Lo Giudice et al, 2011). Moreover, the footprints left by Murgantia histrionica Hahn (Heteroptera: Pentatomidae) females on the cabbage leaves are able to induce the emission of contact synomones (Conti et al, 2010; Frati, Salerno & Conti, 2013); in fact, M. histrionica footprints left on leaf surface elicit a behavioural response in the egg parasitoid Trissolcus brochymenae (Ashmead) (Conti et al, 2010).…”

The response of an egg parasitoid to substrate-borne semiochemicals is affected by previous experience

“…This suggests that experience is likely to play an important role in the host location process of egg parasitoids associated with heteropteran hosts after landing on an infested plant. Experience on host-related chemical cues may also have broader relevance, as many herbivores leave chemical residues when moving around on the plant, which can be perceived as host location kairomones by their natural enemies20212930.…”