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.