Efficacy of Commercially Available Entomopathogenic Agents against the Polyphagous Shot Hole Borer in South Africa

SIMPLE SUMMARY: The accidental introduction of the ambrosia beetle Euwallacea fornicatus and its fungal symbiont, Fusarium euwallaceae, into Israel, the United States and South Africa has had a devastating impact on many economically and ornamentally important tree species. Currently, there is no effective control measure in place to control this beetle pest and its symbiont. As a first step towards controlling this beetle in South Africa, this study investigated the efficacy of commercialized entomopathogenic products against the beetle. Results showed that although effective under lab conditions, currently recommended field application methods of these products to the outer bark of trees have limited effects on beetle survival and reproduction. ABSTRACT: The invasive ambrosia beetle, Euwallacea fornicatus, was first reported in South Africa in 2018. The beetle has now spread to eight provinces of the country and has had a devastating impact on both native and non-native tree species. This is especially true for trees located in urban and peri-urban environments. Recent predictions are that the South African E. fornicatus invasion will cost an estimated ZAR 275 billion (approx. USD 16 billion) if it continues to spread uncontrollably, justifying an urgent need for its effective management in the country. One option is biological control, which is preferred over the use of chemicals due to its lower environmental impact. We tested two broad-spectrum fungal entomopathogenic agents, Eco-Bb(®) and Bio-Insek, which are commercially available in South Africa, for efficacy against E. fornicatus. Initial laboratory assays yielded promising results. However, beetle infestation trials using treated pieces of woody castor bean stems showed little effect on beetle survival and reproduction.