Key message Being fed on A. artemisiifolia grown under elevated CO 2 and heat wave conditions resulted in the poor performance of O. communa (high mortality, long development period, and low reproduction). Elevated CO 2 and heat waves resulted in the accumulation of secondary metabolites in A. artemisiifolia . After feeding on the secondary metabolites accumulated by A. artemisiifolia , the mortality of O. communa increased. To predict and mitigate the effects of climate change on communities and ecosystems, the joint effects of extreme climatic events on species interactions need to be understood. Using the common ragweed ( Ambrosia artemisiifolia L.)—leaf beetle ( Ophraella communa ) system, we investigated the effects of heat wave and elevated CO 2 on common ragweed growth, secondary metabolism, and the consequent impacts on the beetle. The results showed that elevated CO 2 and heat wave facilitated A. artemisiifolia growth; further, A. artemisiifolia accumulated large amounts of defensive secondary metabolites. Being fed on A. artemisiifolia grown under elevated CO 2 and heat wave conditions resulted in the poor performance of O. communa (high mortality, long development period, and low reproduction). Overall, under elevated CO 2 , heat wave improved the defensive ability of A. artemisiifolia against herbivores. On the other hand, enhanced adaptability to climatic changes may aggravate invasive plant distribution, posing a challenge to the control of invasive plants in the future.