Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on?

Abstract

We reviewed exotic insect species that are considered threats to Australia’s plantation, amenity, native forests and timber-in-service (“risk species”), comparing them to already-established non-native species. We examined biological and phylogenetic traits, border interceptions, origins and geographic distributions, to identify similarities between groups. Border interceptions of insect species considered an invasion risk were further analysed to identify their likely pathways. The two groups “risk species” and “established species” differed compositionally, with the dissimilarity possibly due to: (1) neither timber pests nor, to a lesser extent, exotic amenity tree host taxa being considered in industry or environmental biosecurity plans (e.g. explaining the under-representation of Bostrichidae in perceived risks compared to establishments and interceptions); (2) the importance of high-profile pests overseas (e.g. Monochamus spp., Lymantria spp.) inflating some groups over others; (3) unpredictability (“known unknowns”) (e.g. establishment of unexpected species such as Marchalina hellenica and Essigella californica); (4) identification of emerging pests or pathways that may differ from historical arrivals; (5) surveillance — for insects at least — traditionally targeting more detectable taxa (possibly explaining the over-representation of moths and cerambycids in risk lists compared to establishments). The under-representation of Hemiptera on risk lists may reflect their low visibility as impact species outside Australia, their lower detectability, and hence, unpredictability. Risk and established species groups could be separated based on body size and geographic distribution, as well as in the frequency (proportion of species intercepted), but not number, of border interceptions. Risk species were often intercepted from their invaded range, and were largely associated with wood products and packaging and non-commercial pathways (mail, baggage, personal effects). Our study highlights common factors that might assist with developing risk lists — e.g. polyphagy, history of invasiveness, body size — and the fallibility of such lists. Improving general surveillance capacity and capability will increase the chance of detecting cryptic or unpredictable pests that are not effectively targeted in specific surveillance.