Environmental impact classification for alien insects: a review of mechanisms and their biodiversity outcomes

There is strong incentive to identify and prioritise invasive alien species according to their biodiversity and ecosystem impacts. Invasive alien insects and their environmental impacts are poorly represented in much invasion biology literature and many invasive species databases, and the appropriateness of proposed impact classification has not been assessed for insects. We examine standardised impact mechanisms and their outcomes for their relevance and sufficiency to describe the environmental impacts of alien insects. Mechanisms of direct impact, such as competition and herbivory, are well represented. Indirect and higher-order interactions and their impacts are less so. We recommend specific interpretation of mechanisms of impact for insects, and explicit consideration of indirect interactions as key mechanisms by which alien insects impact the environment.