Seasonal flight and genetic distinction among Xylosandrus crassiusculus populations invasive in Australia

ABSTRACT Xylosandrus crassiusculus is an invasive Asian-origin ambrosia beetle that has spread across many regions of the world, including first records in Queensland, Australia, in 2011 and New Zealand in 2019. To determine the seasonal flight activity of this species in Australia, panel traps using quercivorol + ethanol lures were placed at three study sites in New South Wales. This trapping yielded 1173 beetles, consisting of 21 species from three tribes (Xyleborini, Cryphalini and Hylurgini). Xylosandrus crassiusculus contributed almost half the total number of beetles captured over a period of 12 months, mainly driven by catches at one site. The trapping showed a seasonal peak of X. crassiusculus in late March and early April. The genetic relationships between the Australian and New Zealand specimens of X. crassiusculus were compared with other populations across the world. Phylogenetic analysis of the Australian X. crassiusculus populations showed that the beetle population in Queensland was similar to those found in New Zealand and countries in the Americas (Clade I), while the New South Wales population was closely related to Southeast Asian populations (Clade II). This divergence of genetic populations in Australia infers independent introductions of X. crassiusculus into Australia.