Abstract: To understand mechanisms underlying Galinsoga parviflora invasion and its responses to simulated insect herbivory, individuals of Galinsoga parviflora were treated with different concentrations of methyl jasmonate (MeJA) before blooming. We measued plant height, abundance of leaves and inflorescences, biomass, specific leaf area, trichome density, condensed tannins, total polyphenols, and flavonoids in leaves and inflorescences. The growth and reproduction parameters of G. parviflora treated with 5 mmol·L^-1 MeJA were not significantly different from those of control, higher than those of control when treated with 10 mmol·L^-1 MeJA, with significant difference except plant height, and declined when treated with 20 mmol·L^-1 MeJA. The trichome density of leaf upper epidermis increased and specific leaf area decreased with increasing MeJA concentration, with both being significantly different from that of control. The contents of flavonoids, total polyphenols, and condensed tannins in leaves treated with 5 mmol·L^-1MeJA were not significantly different from those of control. These defensive substances in leaves and inflorescences were highest under 10 mmol·L^-1MeJA treatment. The contents of flavonoids and total polyphenols in inflorescences being higher than those of leaves, while condensed tannins was opposite. The defensive substances in leaves declined under 20 mmol·L^-1MeJA treatment. The results suggested that G. parviflora could use tolerance and resistance strategies comprehensively, and adopted a variety of defense strategies such as compensatory growth, physical defense, and chemical defense, which was conducive to its success in invasion.

Key words: invasive plant, Galinsoga parviflora, simulated insect herbivory, defense trait