Understanding PSHB

The Polyphagous Shot Hole Borer Beetle (PSHB), Euwallacea whitfordiodendrus, was incorrectly identified as E. fornicatus when it was first discovered within South African borders in the National Botanical Garden of Pietermaritzburg in 2017. This species, originally from South-East Asia, has now spread to 8 out of the 9 provinces. This beetle is one of four species of beetle in a species complex which has strong associations with Fusarium fungi. In its native habitats, the PSHB bore through the bark, into the sapwood of stressed trees, creating tunnel systems called galleries, within the vascular system of the trees. When outside their native range, the PSHB has been observed to attack healthy trees without much discrimination. The PSHB does not feed on the sapwood itself, but adult females carry spores of the fungus Fusarium euwallacea, which are inoculated into the galleries to grow as a food source for the beetle larvae. Adult, female beetles measure around 2 mm in length and are bigger and darker than males. Males are flightless. These beetles have an extremely large diversity of host trees but only reproduce in certain native and exotic species. The exotic species are at higher risk of being infected than native trees, although the beetle seems to be much more aggressive outside of its native habitat. Infected trees can contain more than 100 000 individuals, with the females being able to fly up to 1 km from their original tree. Due to the damage in the vascular systems of affected trees, branch dieback soon starts, followed by higher levels of vulnerability and ultimately death. Even after the host tree has died, PSHB can survive in the wood for up to 12 months. Thus far, the spread of PSHB in South Africa has been random and without clear patterns It has been noted that the most important vector for the spread of PSHB is humans and their movements between regions. This complicates containment and management strategies.  

This making it the largest current outbreak of this pest globally.