Population structure of the invasive ambrosia beetle, Euwallacea fornicatus, indicates multiple introductions into South Africa

The ambrosia beetle Euwallacea fornicatus (Polyphagous Shot Hole Borer; PSHB), native to Asia, was documented in South Africa for the first time in 2012. Death of susceptible host trees is caused by blocking of xylem tissues by the mutualistic plant-pathogenic fungus, Fusarium euwallaceae and extensive tunnelling by the beetles into the sapwood. Within a few years, PSHB has spread from its putative entrance point in the coastal province of KwaZulu-Natal to nearly every other province in South Africa. This study serves as a preliminary assessment of dispersal pathways and population genetic relationships of PSHB in South Africa. PSHB individuals were collected from five provinces across South Africa. In addition, data on PSHB from three provinces in its native range in China and invasive PSHB from California were also generated here and supplemented by sequence data of PSHB available from GenBank. Comparisons of Cytochrome Oxidase Subunit I (COI) sequences of PSHB in South Africa revealed a nearly homogenous population. The majority of individuals have the same haplotype as is present in California, Israel and Vietnam (H33). A second haplotype was present in only two localities in KwaZulu-Natal and the Western Cape. This haplotype is also present in Vietnam and China (H38). The placement of the two haplotypes identified within South Africa, into different haplogroups suggests more than one invasion event. This pilot project justifies the use of more comprehensive genomic tools to finely map the relationships, global invasion pathways and within-country dispersal patterns of PSHB to better inform management of this invasive species.

Automated summary

This study provides a preliminary assessment of the dispersal pathways and population genetic relationships of the ambrosia beetle Euwallacea fornicatus (PSHB) in South Africa. The results suggest a nearly homogeneous population in South Africa with potential multiple invasion events.