| Plants are central to most community interaction webs and thus the ability to coordinate responses to many simultaneous interactions is an essential adaptation. Interaction with one organism may make the plant more vulnerable or more resistant to attacks by very different organisms. Microorganisms can form intimate associations with plants with direct effects ranging from beneficial to antagonistic, but indirect effects of plant-microbe relationships on plant interactions with other organisms are not well understood. Here, we explore the influences of microorganisms and microbial products on herbivory and resulting plant defenses. We use the legume-rhizobia mutualism as a model-system to explore herbivore-plant interactions by first characterizing the effects of rhizobial inoculation on herbivore feeding and subsequent accumulation of plant defense signaling hormones. We found interactive effects of the legume-rhizobia mutualism on plant-herbivore interactions which were dependent on both the stage of the mutualism and on the feeding style of the herbivore. Next, we explored the effects of association with different sources of rhizobia of soybean on specialist aphid populations in an agricultural setting. We found that particular rhizobia strains can confer greater resistance to their mutualist partners than others. In order to explore the effects of a rhizobia strain-specific trait on herbivory, we focused on the rhizobial product, rhizobitoxine, which can be found in host plant tissues. We found that the presumed presence of this compound decreased herbivore feeding and damage, which could be useful in pest management of legumes. Finally, we utilize genetically modified maize to further explore the application of a microbial product used for insect resistance and its effects on herbivore feeding and induction of plant defenses. Our results contribute to understanding of the evolution of host plant defenses and could facilitate the development of more sustainable management techniques for agriculture that are informed by an understanding of the chemical ecology of plants, microbes, and insects. |
