Abstract
Plant-associated microbes may induce plant defenses against herbivores. Plants, in turn, can attract natural enemies, such as predators, using herbivore-induced plant volatiles. Intricate communication occurs between microorganisms, plants, and insects. Given that many aspects related to mechanisms involved in this symbiotic system remain unknown, we evaluated how beneficial soil-borne microorganisms can affect the interactions between plants, herbivores, and natural enemies. For this study, we established a multitrophic system composed of the predatory earwig Doru luteipes (Dermaptera: Forficulidae), arugula (Eruca sativa, Brassicaceae) as the host plant, Plutella xylostella (Lepidoptera: Plutellidae) larvae as a specialist herbivore, Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae as a generalist herbivore, and Bacillus amyloliquefaciens as the plant growth-promoting rhizobacteria (PGPR), in a series of nocturnal olfactometry experiments. By assessing earwig preference towards herbivore-induced and PGPR-inoculated plants in different combinations, we showed that the interaction between rhizobacteria, plants, and herbivores can affect the predatory earwig’s behavior. Furthermore, we observed a synergistic effect in which earwigs were attracted by plants that presented as PGPR inoculated and herbivore damaged, for both specialist and generalist herbivores. Our findings help fill the important knowledge gap regarding multitrophic interactions and should provide useful guidelines for their application to agricultural fields.
Highlights
In natural environments, plants are exposed to various types of attacks, including those by herbivorous arthropods
We addressed the following questions: (i) Does the predatory earwig have any preference over odors emitted by arugula plants infested with generalist or specialist herbivores? and (ii) could that behavior be modified by inoculating plants with GB03? As a generalist predator, we hypothesized that D. luteipes (i) would be guided by the plant odors blends produced by the specialist over the generalist herbivore, and (ii) due to the symbiosis between the plant and plant growth-promoting rhizobacteria (PGPR), we expected that earwigs would be attracted mostly to inoculated GB03 plants
Our most relevant result was the synergistic effect of volatiles from inoculated and herbivore-damaged plants, in which the earwigs were attracted by the plants that presented both conditions for both specialist and generalist herbivores
Summary
Plants are exposed to various types of attacks, including those by herbivorous arthropods. To defend themselves, they have developed complex mechanisms, such as constitutive and induced defenses. Plants can affect herbivores through physical barriers, as lignified cell walls, trichomes, and callose deposits [1], or by biochemical pathways as well as the synthesis of secondary metabolites [2]. Plants can be induced to express direct and indirect defenses in response to herbivore attacks. Plants produce toxins or digestion inhibitors [3]. Plants use herbivore-induced plant volatiles (HIPVs), which act as odor cues to attract
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