Border interceptions of forest insects established in Australia: intercepted invaders travel early and often.
Invasive forest insects continue to accumulate in Australia (and worldwide) and cause significant impacts through costs of prevention, eradication and management, and through productivity losses and environmental and biodiversity decline. We used our recent non-native Australian forest insect species inventory to analyse border interception rates (2003-2016) of established species, and link interception frequencies with biological traits, historical establishment patterns, commodities and countries of origin. The strongest predictor of interception frequency was year of establishment. Polyphagous species were more likely to be intercepted, as were more concealed species, although this latter likely reflects the higher interceptions of bostrichid borers and other wood-boring Coleoptera relative to other taxa. Interceptions occurred more often for species native to Asia; in contrast, interceptions from other regions were more likely to be of species invasive there. While interception frequencies did not provide a good overall indicator of contemporaneous species establishments, wood and bark borers were more closely linked for establishments and interceptions. The first fifty forest insect species to establish comprised 85% of all border interceptions of established species between 2003 and 2016, while the most-recent fifty species represented just 6% of interceptions. We suggest that early-establishing species are among the "super-invaders" that continue to move globally, while more recent invasive species may be exploiting new trade pathways, new commodity associations, or changes in dynamics in their countries of origin.