Chemical and structural effects of invasive plants on herbivore-parasitoid/predator interactions in native communities

The introduction and/or spread of exotic organisms into new habitats is considered a major threat to biodiversity. Invasive plants have been shown to negatively affect native communities, competing with and excluding other plants and disrupting a wide range of trophic interactions associated with them. In spite of this, thus far, few studies have explicitly studied the mechanisms underlying the displacement and potential local extinction of native herbivores and their natural enemies up to the third trophic level and even higher. Here, we formulate hypotheses on how structural and chemical characteristics of invasive plants may affect the plant-finding abilities of herbivores and the host- or prey-finding behavior of predators and parasitoids. The sudden incursion of an invasive plant into a native plant community may fragment native habitats and thus create structural barriers that impede dispersal and plant-finding ability for herbivores and prey- or host-finding ability for predators and parasitoids. At the same time, invasive plants may produce odors that are attractive to native insects and thus interfere with interactions on native plants. If invasive plants are both attractive and toxic to native insects, they may constitute traps that are possibly beneficial against insect pests in agro-ecosystems, but have conservation implications for native herbivores and their natural enemies. However, we also suggest that some herbivores, and by association their parasitoids, may benefit from the establishment and spread of exotic plants because they increase the amount of available resources for them to exploit.