Spotted lanternfly herbivory activates grapevine defense responses

Plant-insect coevolution has led to the development of both structural and biochemical plant defenses, which may be constitutive or induced, affecting insect growth, survival, and reproduction. The spotted lanternfly (Lycorma delicatula, SLF), an invasive planthopper in the United States, poses a major threat to vineyards, yet little is known about grapevine defenses against SLF feeding. We examined grapevine (Vitis vinifera cultivar Cabernet Franc) defense responses to SLF feeding through density-dependent (0, 5, 10, and 15 insects per vine) and time-course (1, 3, 5, 7, 14, 21, and 29 days) experiments using separate plant sets for each timepoint. We measured total chlorophyll content, polyphenol oxidase (PPO) and peroxidase (POX) activity, condensed tannins, total phenolics, SLF survival, and weight gain. SLF feeding reduced chlorophyll content after 21 and 29 days at a density 15. PPO activity was consistently induced at density 15, except on day 5. POX activity increased at density 15 after 7 days but dropped sharply by days 21 and 29, suggesting potential suppression by SLF. Condensed tannin levels increased at day 21 at density 15, and total phenolics were elevated from day 7 through day 29. When SLF were reintroduced to previously infested plants (density 0, 10, and 15), they had higher mortality and reduced weight gain at density 15 compared to controls. These results suggest that high-density SLF feeding triggers induced grapevine defenses and reduces chlorophyll content, which correlates with low SLF performance, highlighting the detrimental effect of SLF feeding on grapevines and the need to control it.