Herbivore pressure in the field
To compare herbivore pressures on different non-native and native plant species under natural conditions, we conducted a field survey in abandoned agricultural fields at 28 sites, ranging from 34°00’ to 38°54’ N and 112°55’ to 119°44’ E in northern China in 2018 (Table S1).
At each site, we selected the three tallest plants of each non-native species and co-occurring native species in a 5 x 10 m plot. To determine herbivore pressure, we calculated the percentage of damaged leaves by counting 10-50 leaves starting from the top of each plant and recording the proportion of damaged leaves (Table S2 and S3).
To determine whether herbivore biomass correlated with leaf damage, we recorded the number of each herbivore species on each non-native plant. Native plants were not measured as these measurements were simply to correlate damage with insect biomass. To obtain the mean biomass of each herbivore category, we carried out a field survey at eight sites in 2019. We collected all herbivores on non-native species and determined the fresh weight of individual insects to the nearest 0.01g as described in Supplementary Methods 1.