Invasive plants often escape suppression by co-evolved insect natural enemies from their native range and may encounter novel herbivores in the introduced range, therefore, their chemical defence against herbivore may differ between introduced and native ranges. Given that invasive plants often have less damage by herbivores in their introduced ranges, they may reallocate resources from defence against natural enemies to growth and reproduction (the evolution of increased competitive ability hypothesis, or EICA hypothesis). While many previous studies investigated invader trade-offs between defence and growth and some addressed changes in secondary metabolites, little information is available for trade-offs among secondary compounds during plant invasions in an evolutionary context.

To solve this problem, scientists at Wuhan Botanical Garden and Rice University have compared the two different types of anti-herbivore chemicals (including five flavonoids and four tannins) from invasive and native populations of Chinese tallow. They found opposite patterns of change from native to invasive ranges for tannins and flavonoids, suggesting that there is a trade-off in the production of these two types of defences. Furthermore, this study revealed changes in these chemical defences affect specialist and generalist performance accordingly.

The findings on the changes in secondary chemistry from native to introduced populations have implications for biological control. Higher flavonoid concentrations in the introduced Triadica populations may benefit specialists in their host finding and oviposition in addition to the effects we observed on growth, such that the results of these feeding trials may be conservative in terms of the importance of genetic variation in Triadica for biological control success. Therefore, the results may provide insights into the question “why super abundance of some biological control specialists has been found on introduced populations relative to their abundance in the native range”.