Invasional meltdown: invasive exotic plants facilitate light brown apple moth (Epiphyas postvittana) invasion

Ecosystems worldwide are increasingly being invaded by organisms from exotic origin. Factors contributing to the success of exotic species have often been sought in species characteristics and interactions with native species in the new region. However, the higher frequency of biological invasions makes interactions between exotic species more likely, where they at one point may facilitate one or the other (invasional meltdown). These novel interactions could accelerate the invasion process of exotic herbivores, thereby increasing their population abundance and dispersal, further degrading native plant and insect communities. The light brown apple moth (Epiphyas postvittana) is a highly polyphagous leaf roller originating from south-east Australia and currently invades agricultural crops and natural ecosystems in California. In order to investigate the potential facilitation of the E. postvittana invasion by exotic host plants we conducted a phylogenetically controlled experiment. We compared the performance of Epiphyas postvittana on six invasive exotic plants and their native congeners. We show that pupal wet weight of E. postvittana was larger, and overall survival was higher on exotic hosts relative to native hosts. In addition, development of E. postvittana larvae was shorter on exotic hosts, although this depended on plant genus. These results suggest that E. postvittana has a greater performance when using exotic plants as host, which may facilitate population abundance and spread in the newly invaded range. We conclude that ongoing introductions of exotic plants and exotic herbivores could lead to an invasional meltdown, contributing to the invasion of exotic herbivores influencing ecosystem dynamics and stability.