Microbes in Helicoverpa armigera oral secretions contribute to increased senescence around plant wounds

1. Plants have long been exposed to insect herbivore attack. Crucial to the plant's ability to defend itself is its ability to identify specific signals associated with attacking insects. Distinctive chemical cues, such as those associated with chewing insect oral secretions (OS), activate targeted defence responses to chewing insect herbivores. 2. Herbivore-associated cues can be complicated by the fact that many herbivores form associations with microbes that produce their own specific signals, which may induce alternative defence processes. 3. Here we report that OS of the global pest, the cotton bollworm (Helicoverpa armigera), induce senescence around wounds in Brachypodium distachyon leaves. Crude OS activate greater levels of senescence than OS with reduced microbial abundance or mechanical wounding alone. Nonetheless, plants closed mechanical wounds more rapidly when treated with H. armigera OS regardless of the microbial component. 4. This study concludes that H. armigera OS can activate senescence and wound closure in plant tissues and that microbes within OS have an important role in shaping plant-herbivore interactions through additional increases in senescence.