LAUSR

BACKGROUND Colorado potato beetle (CPB; Leptinotarsa decemlineata) is a destructive quarantine pest which develops broad physiological adaptations to potato plants. During feeding, CPB deposited copious amount of wet frass on the surface of leaves and stems remaining for long periods of time. Insect behaviors such as feeding, crawling and oviposition are able to mediate plant defenses. However, the specific role of CPB defecation -associated cues in manipulating plant defenses remains unclear. RESULTS CPB larval frass significantly suppressed potato polyphenol oxidase (PPO) activity and enhanced larval growth on treated potato plants. Incorporation of antibiotics (AB) into larval frass triggered higher jasmonic acid (JA) regulated defense responses in potato plants compared to AB-free frass. Four bacterial symbionts belonging to the genera Acinetobacter, Citrobacter, Enterobacter and Pantoea isolated from larval frass suppressed plant defenses. After reinoculation of these bacteria to axenic larvae, Acinetobacter and Citrobacter were found to be highly abundant in the frass, while Enterobacter and Pantoea showed lower portion in the frass probably due to the negative effect of potato steroidal glycoalkaloid (SGA) such as α-solanine. Furthermore, direct application of Acinetobacter and Citrobacter to wounded potato plants significantly inhibited the expression of genes associated with JA-mediated defense signaling pathway and SGA biosynthesis. CONCLUSION Our findings demonstrate that CPB exploits frass-associated bacteria as a deceptive strategy for plant defense suppression, adding an interesting dimension to improve our understanding of how CPB successfully specializes on potato plants.