No improved resistance against generalist herbivores found for invasive genotypes: a case study of Senecio vulgaris (Asteraceae) and a generalist snail (Achatina fulica)

Invasive plants escape from some natural enemies as predictions of Enemy Release Hypothesis (ERH). However, in fact they still have to face the pressure of generalist herbivores in introduced ranges resulting in the maintenance or enhancing of resistance ability to generalist herbivores. In this study, we carried out a general feeding bioassay in a laboratory with leaves of Senecio vulgaris to test the difference in resistance between ranges. White jade land snails (WJLD, Achatina fulica) were fed with the leaves of Pakchoi (Brassica chinensis), Lettuce (Lactuca sativa), native and invasive plants of S. vulgaris. The feeding experiment with S. vulgaris leaves was carried out in two waves. We found that both native and invasive S. vulgaris plant were resistant again to WJLD compared to Pakchoi and Lettuce. However, there were no significant differences between native and invasive plants of S. vulgaris in relation to the resistance against WJLD. The results prove the maintenance of chemical defense against generalist herbivores in invasive plants in introduced range. The success of S. vulgaris to invader China could not be explained by releasing from natural enemies but possessing of defense ability against herbivores before it introduced to China.