Human-mediated plant dispersal changes insect distributions with important evolutionary implications

Human introductions of plant species often lead to secondary invasions by alien insects or range expansions by native ones. For instance, native insects may adopt introduced plants that are closely related to their native host plants. Leptocoris soapberry bugs feeding on plants in the Soapberry family (Sapindaceae) provide prime examples of such host shifts. In Australia and South Africa, the introduction of alien sapinds species, as well as human-mediated changes in the distributions of native sapinds, have the potential to impact the ecology and evolutionary dynamics of native soapberry bugs. We provide observations indicating that in both countries the ranges of some native Leptocoris species have expanded vastly due to the human-mediated movement and introduction of native and alien sapind species, respectively. In Australia, native L. rufomarginatus has established in the Sydney region where native host species have been introduced and naturalised well outside their historical ranges (i.e., extralimital species) and introduced alien L. vicinus was found localised at its initial introduction site in Darwin. In South Africa, native L. mutilatus now occurs ~1000km beyond previous records, feeding on the invasive balloon vine Cardiospermum grandiflorum and the alien tree Alectryon connatus. We provide evidence for differentiation in the proboscis length of L. mutilatus insects feeding on different alien, invasive and native host plants. In Australia, we successfully hybridised and backcrossed native L. tagalicus with alien L . vicinus under laboratory conditions, providing the first report of interspecific hybridisation for the genus. The high eco-evolutionary experience shared between soapberry bugs and their host plants suggest that further changes in these insects’ distributions and adaptive responses to novel host plants are likely to occur. Taken together, our results demonstrate how human-mediated plant dispersal can impact on the ecology, distribution and evolution of insects.