Whether specialist pests can cause more damage to their host plants than generalist pests is a critical issue in both basic biology and nonnative species management. To date, there is no consensus on how we define “specialist vs. generalist” pests and how we should assess forest damage or impacts (volume loss vs. mortality). Here, we comparatively investigate whether nonnative generalist pests may cause more damage to US forests than nonnative specialist pests using two frameworks: (1) the “binary or dichotomous approach” through a largely arbitrary classification of specialist and generalist pests, and (2) the “specialist-generalist continuum”. We measure damage or impact in two ways, one by the total host volume infested and the other by total host mortality. In the binary comparison, generalists infested more host tree volume per pest species than specialists, but the latter (mostly pathogens) caused higher mortality of host trees. The “specialist-generalist continuum” concept could reveal a different pattern regarding pest invasions and impacts when there is no clear separation between generalists and specialists in a community or region. Therefore, we suggest using the “continuum” approach to address related questions in future studies, thus offering new insights into pest invasions that have deeper implications for forest pest monitoring and management.
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