Assessing the threat of the Polyphagous Shot Hole Borer beetle (PSHB, Euwallacea fornicatus) and its symbiotic fungus (Fusarium euwallaceae) to deciduous fruit trees in the Western Cape Province of South Africa

PSHB and its symbiotic fungus can kill a wide range of trees including deciduous fruit trees. The proposed project investigated differences in the susceptibility of different fruit trees and their most lucrative cultivars to PSHB and its fungus.

We conducted in-field monitoring of infestation levels and in-field pathogenicity trials of the fungus towards various deciduous fruit trees that are of economic importance in the Western Cape Province. We conducted in-field trials and monitoring of the ability of PSHB to breed in various deciduous fruit trees. In addition, in-field and in-laboratory choice assays of PSHB towards various deciduous fruit trees were conducted.

PSHB  infestations were found on two pear cultivars, an apple cultivar, four plum cultivars, and two windbreak tree species (Poplar and Beefwood). ‘African Delight,’ ‘Songold’ and ‘Black Pearl’ plum cultivars were most susceptible to F. euwallaceae. Except for ‘Early Bon Chretien’ pears in the laboratory, PSHB does not easily establish breeding colonies in these in the field or in the laboratory.

PSHB has infested various deciduous fruit tree species and cultivars in Somerset West. Even though the pathogenicity of Fusarium euwallaceae towards all deciduous fruit species and cultivars tested was proven, PSHB does not easily establish breeding colonies in these.

We confirm that PSHB infests various commercial orchards, at low frequency. Most attacks arise from surrounding infested hosts. Managing PSHB will therefore need to focus on the surrounding vegetation.