Plants and insects interact with a host of microbes found within their tissues, in the atmosphere and in partner tissues, and yet we have rarely examined how these microbial communities influence each other and their hosts. Previously published work from our group and others has demonstrated that the composition of the soil microbiome influences the composition of the microbiome of insects feeding on plants growing with that soil microbiome. However, multiple mechanisms have been proposed for how the soil microbiome influences herbivore microbiomes. Here we present evidence from a new system (tomatoes and tobacco hornworm) supporting the hypothesis that the influence of soil microbiome composition on herbivores is mediated by the plant and not by direct contact with the soil microbiome.
