Do non-native plants contribute to insect declines?

Abstract

1. With evidence of significant global insect declines mounting, urgent calls to mitigate such declines are also increasing. Efforts to reverse insect declines will only succeed, however, if we correctly identify and address their major causes. 2. One potential cause that has received little mention is the global spread of non-native plants as invasive species, agroforestry products, and ornamental plants. 3. Here we (a) review the theory predicting that most insect herbivores are evolutionarily constrained to use a fraction of available plant lineages; (b) document the extent to which nonnative plants have displaced native plant communities around the globe; (c) examine the evidence that non-native plants reduce insect abundance and diversity; and (d) suggest guidelines for measuring the impact of non-native plants on insect populations. 4. We conclude that host range expansions to non-natives do occur among many insect herbivores but not at the frequency required to prevent insect declines when non-native plants replace native plant communities. Accordingly, we suggest that curbing the spread and use of non- native plants at local, national, and international scales will be a necessary and effective way to reduce some insect declines.