Fall Armyworm-Associated Gut Bacteria Modulate Plant Defense Responses

Mechanical damage caused by insect feeding along with components present in insect saliva and oral secretions are known to induce jasmonic acid–mediated defense responses in plants. This study investigated the effects of bacteria from oral secretions of the fall armyworm Spodoptera frugiperda on herbivore-induced defenses in tomato and maize plants. Using culture-dependent methods, we identified seven different bacterial isolates belonging to the family Enterobacteriacea from the oral secretions of field-collected caterpillars. Two isolates, Pantoea ananatis and Enterobacteriaceae-1, downregulated the activity of the plant defensive proteins polyphenol oxidase and trypsin proteinase inhibitors (trypsin PI) but upregulated peroxidase (POX) activity in tomato. A Raoultella sp. and a Klebsiella sp. downregulated POX but upregulated trypsin PI in this plant species. Conversely, all of these bacterial isolates upregulated the expression of the herbivore-induced maize proteinase inhibitor (mpi) gene in maize. Plant treatment with P. ananatis and Enterobacteriaceae-1 enhanced caterpillar growth on tomato but diminished their growth on maize plants. Our results highlight the importance of herbivore-associated microbes and their ability to mediate insect plant interactions differently in host plants fed on by the same herbivore.