Abstract
Upon damage by herbivores, plants release herbivory-induced plant volatiles (HIPVs). To find their prey, the pest’s natural enemies need to be fine-tuned to the composition of these volatiles. Whereas standard methods can be used in the identification and quantitation of HIPVs, more recently introduced techniques such as PTR-ToF–MS provide temporal patterns of the volatile release and detect additional compounds. In this study, we compared the volatile profile of apple trees infested with two aphid species, the green apple aphid Aphis pomi, and the rosy apple aphid Dysaphis plantaginea, by CLSA-GC–MS complemented by PTR-ToF–MS. Compounds commonly released in conjunction with both species include nonanal, decanal, methyl salicylate, geranyl acetone, (Z)-3-hexenyl acetate, (Z)-3-hexenyl butanoate, (Z)-3-hexenyl 2-methyl-butanoate, (E)-β-caryophyllene, β-bourbonene and (Z)-3-hexenyl benzoate. In addition, benzaldehyde and (E)-β-farnesene were exclusively associated with A. pomi, whereas linalool, (E)-4,8-dimethyl-1,3,7-nonatriene were exclusively associated with D. plantaginea. PTR-ToF–MS additionally detected acetic acid (AA) and 2-phenylethanol (PET) in the blends of both trees attacked by aphid species. In the wind tunnel, the aphid predator, Chrysoperla carnea (Stephens), responded strongly to a blend of AA and PET, much stronger than to AA or PET alone. The addition of common and species-specific HIPVs did not increase the response to the binary blend of AA and PET. In our setup, two host-associated volatiles AA + PET appeared sufficient in the attraction of C. carnea. Our results also show the importance of combining complementary methods to decipher the odor profile associated with plants under pest attack and identify behaviourally active components for predators.
Highlights
Plants and insects have coexisted on the planet for more than 400 million years
The release of some volatiles increased with rosy apple aphid (RAA) and GAAinfestations, such as (Z)-3-hexenyl acetate (p-values = 0.005 and 0.016, respectively, Fig. 1) and 2-ethyl-1-hexanol, whereas other GLVs were exclusively released upon aphid infestation, sometimes in a species-specific pattern. (Z)-3-hexenyl butyrate and (Z)-3-hexenyl 2-methyl-butanoate were released upon infestation by both species, whereas (Z)-3-hexenyl benzoate was released after RAA infestation and only in one sample after green apple aphid (GAA) infestation
The homoterpene DMNT, and the sesquiterpene (E)-β-caryophyllene were associated with RAA infestation, Fig. 1 Box plot representation of emission of herbivore-induced plant volatiles detected by CLSA-GC–MS in the headspace of undamaged apple trees and infested apple tree with green apple aphid (GAA) and rosy apple aphid (RAA)
Summary
Plants and insects have coexisted on the planet for more than 400 million years. Whereas some of the established interactions are mutualistic, such as pollination, a large number of relationships are antagonistic, such as herbivory (Fürstenberg-Hägg et al 2013). Herbivory may trigger plant responses that can function both as direct and indirect defenses. Whereas the direct ecological effects of plant response that affect the performance of the attacker and/or the susceptibility of the host (Kessler and Baldwin 2002), the indirect ecological effects of plant response function through the attraction of natural enemies, such as predators and parasitoids. Volatiles released under herbivore attack are termed herbivore-induced plant volatiles (HIPVs) and can play an important role in multi-trophic interactions Because natural enemies of pests are often attracted to plants emitting HIPVs, such denovo released compounds can potentially function as synomones, i.e. allelochemicals conveying an advantage to both the emitter and the receiver (Bruinsma & Dicke 2008; Dicke and Baldwin 2010; Gershenzon 2007; Whitfield 2001). Different families of parasitoids and predators, including parasitic wasps (Hymenoptera), hoverflies (Diptera: Syrphidae), predatory bugs (Heteroptera), ladybirds (Coleoptera: Coccinellidae), predatory mites (Mesostigmata), and green lacewings (Neuroptera: Chrysopidae) are attracted to HIPVs in the field (Turlings and Erb 2018)
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