Abstract
Plants respond to insect oviposition by emission of oviposition-induced plant volatiles (OIPVs) which can recruit egg parasitoids of the attacking herbivore. To date, studies demonstrating egg parasitoid attraction to OIPVs have been carried out in tritrophic systems consisting of one species each of plant, herbivore host, and the associated egg parasitoid. Less attention has been given to plants experiencing multiple attacks by host and non-host herbivores that potentially could interfere with the recruitment of egg parasitoids as a result of modifications to the OIPV blend. Egg parasitoid attraction could also be influenced by the temporal dynamics of multiple infestations, when the same non-host herbivore damages different organs of the same plant species. In this scenario we investigated the responses of egg parasitoids to feeding and oviposition damage using a model system consisting of Vicia faba, the above-ground insect herbivore Nezara viridula, the above- and below-ground insect herbivore Sitona lineatus, and Trissolcus basalis, a natural enemy of N. viridula. We demonstrated that the non-host S. lineatus disrupts wasp attraction toward plant volatiles induced by the host N. viridula. Interestingly, V. faba damage inflicted by either adults (i.e., leaf-feeding) or larvae (i.e., root-feeding) of S. lineatus, had a similar disruptive effect on T. basalis host location, suggesting that a common interference mechanism might be involved. Neither naïve wasps or wasps with previous oviposition experience were attracted to plant volatiles induced by N. viridula when V. faba plants were concurrently infested with S. lineatus adults or larvae. Analysis of the volatile blends among healthy plants and above-ground treatments show significant differences in terms of whole volatile emissions. Our results demonstrate that induced plant responses caused by a non-host herbivore can disrupt the attraction of an egg parasitoid to a plant that is also infested with its hosts.
Highlights
Parasitoids adopt specialized strategies to efficiently locate and parasitize their herbivorous hosts
In this scenario we investigated the responses of egg parasitoids to feeding and oviposition damage using a model system consisting of Vicia faba, the above-ground insect herbivore Nezara viridula, the above- and below-ground insect herbivore Sitona lineatus, and Trissolcus basalis, a natural enemy of N. viridula
Y-TUBE OLFACTOMETER BIOASSAYS Above-ground treatments Naïve T. basalis females (Figure 2) were significantly attracted to volatiles emitted by plants damaged by N. viridula feeding and oviposition (t = 4.75; df = 33; p < 0.001), and by plants damaged by leaf-feeding by S. lineatus adults (t = −2.13; df = 37; p = 0.040) compared to undamaged control plants
Summary
Parasitoids adopt specialized strategies to efficiently locate and parasitize their herbivorous hosts. Host-seeking females may exploit a plethora of cues, among which volatile organic compounds (VOCs) emitted by the plant as a consequence of herbivore attack, and called herbivore induced plant volatiles (HIPVs), often play a key role (Kessler and Baldwin, 2001; Dicke, 2009). Numerous studies have documented the role of HIPVs as detectable and reliable host location cues for natural enemies of insect herbivores (Dicke and Baldwin, 2010; Kessler and Heil, 2011; Meiners and Peri, 2013). OIPVs can recruit egg parasitoids of insect herbivores in some case studies, a combination of oviposition and feeding activity of the herbivore host is required to trigger attraction (reviewed by Colazza et al, 2010; Conti and Colazza, 2012)
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