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The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South Africa


The polyphagous shot hole borer (PSHB), an ambrosia beetle (Coleoptera: Curculeonidae: Scolytinae) native to Asia, together with its fungal symbiont Fusarium euwallaceae, has emerged as an important invasive pest killing avocado and other trees in Israel and the United States. The PSHB is one of three cryptic species in the Euwallacea fornicatus species complex, the taxonomy of which remains to be resolved. The surge in the global spread of invasive forest pests such as the PSHB has led to the development of programmes utilising sentinel tree plantings to record new host-pest interactions. During routine surveys of tree health in botanical gardens of South Africa undertaken as part of a sentinel project, an ambrosia beetle/fungal associate was detected damaging Platanus x acerifolia (London Plane) in the KwaZulu-Natal National Botanical Gardens, Pietermaritzburg. Identification of the beetle by sequencing part of the mitochondrial cytochrome oxidase c subunit 1 (COI) gene confirmed its identity as PSHB, and specifically one of the invasive haplotypes of the beetle. The associated fungus F. euwallaceae was identified based on phylogenetic analysis of elongation factor (EF 1-α) sequences. Koch’s postulates have confirmed the pathogenicity of fungal isolates to P. x acerifolia. This is the first report of PSHB and its fungal symbiont causing Fusarium dieback in South Africa. This report also represents the first verified case of a damaging invasive forest pest detected in a sentinel planting project, highlighting the importance of such studies. Given the potential impact these species present to urban trees, native biodiversity and agriculture, both the PSHB and its fungal symbiont should be included in invasive species regulations in South Africa.

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This work was supported by the South African National Department of Environment Affairs, through the South African National Biodiversity Institute’s Invasive Species Programme. We thank the KZN National Botanical Gardens for allowing us to undertake the survey and we thank Samantha Bush for photographing the beetle.

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Correspondence to Trudy Paap.

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Supplementary Figure S1:

Maximum Likelihood tree derived from elongation factor 1-α (EF) sequences showing identity of South African Fusarium euwallaceae isolates. The analysis involved 96 nucleotide sequences. There was a total of 688 positions in the final dataset. Isolate numbers of sequences produced in the present study are in bold type. Species numbers for unnamed species are as designated by O’Donnell et al. (2015). Support values above the branches are from 1000 bootstraps. (PDF 101 kb)

Supplementary Figure S2.

Maximum Likelihood tree derived from cytochrome oxidase c subunit 1 (COI) sequences showing phylogenetic placement of South African Euwallacea beetles (in blue) in the E. fornicatus species complex as defined by Stouthamer et al. (2017). Invasive haplotypes are printed in bold type. The analysis involved 76 nucleotide sequences. There was a total of 402 positions in the final dataset. Support values above the branches are from 1000 bootstraps. PSHB: polyphagous shot hole borer; KSHB: Kuroshio shot hole borer; TSHB: tea shot hole borer. (PDF 102 kb)

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Paap, T., de Beer, Z.W., Migliorini, D. et al. The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South Africa. Australasian Plant Pathol. 47, 231–237 (2018).

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  • Invasive pest
  • Fusarium dieback
  • Euwallacea nr. fornicatus
  • International Plant Sentinel Network