Hyphantria cunea-mediated inducible defense in low-fitness host plant Tilia amurensis: An arthropod–plant interaction perspective

Inducible defense is an important anti-insect strategy in plants. This study investigated whether larval feeding by Hyphantria cunea at low-density and high-density levels can initiate inducible defense responses in the low-fitness host plant Tilia amurensis on the 7th- and 21th-day post-feeding. The results revealed significant alterations in the nutrient composition (e.g., amino acids, soluble sugars, and total proteins) within T. amurensis, with notable decreases observed on the 7th-day post-feeding, followed by increases on the 21st day, respectively. Specifically, the low-density feeding group prompted significant increases in tannin, total phenols, and total flavonoids on the 7th day, whereas the high-density feeding group induced significant decreases in these compounds. Conversely, total alkaloid levels exhibited an inverse pattern, with lignin contents notably decreasing. By the 21st-day post-feeding, all secondary metabolites demonstrated significant increases. Expression analysis of flavonoid biosynthetic genes mirrors the changes observed in the total flavonoid content. Furthermore, larval feeding activates the α-linoleic acid metabolism pathway consistently across all time points. Subsequent generations of H. cunea larvae in low-density feeding and high-density feeding groups demonstrated decreased growth, along with downregulation of growth regulatory genes and key genes involved in energy metabolism, digestion, and detoxification. Notably, the expression of digestive gene LIP10 and detoxification genes GST18 and CARE14 exhibits adaptive regulation in response to T. amurensis’ inducible defense. Overall, larval feeding by H. cunea elicits a robust and enduring inducible defense response in T. amurensis, ultimately decreasing the fitness of the subsequent generations of H. cunea larvae on T. amabilis.