The polyphagous shot hole borer beetle: Current status of a perfect invader in South Africa

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

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.

Forest Insect Biosecurity: Processes, Patterns, Predictions, Pitfalls

The economic and environmental threats posed by non-native forest insects are ever increasing with the continuing globalization of trade and travel; thus, the need for mitigation through effective biosecurity is greater than ever. However, despite decades of research and implementation of preborder, border, and postborder preventative measures, insect invasions continue to occur, with no evidence of saturation, and are even predicted to accelerate. In this article, we review biosecurity measures used to mitigate the arrival, establishment, spread, and impacts of non-native forest insects and possible impediments to the successful implementation of these measures. Biosecurity successes are likely under-recognized because they are difficult to detect and quantify, whereas failures are more evident in the continued establishment of additional non-native species. There are limitations in existing biosecurity systems at global and country scales (for example, inspecting all imports is impossible, no phytosanitary measures are perfect, knownunknowns cannot be regulated against, and noncompliance is an ongoing problem). Biosecurity should be a shared responsibility across countries, governments, stakeholders, and individuals.

An Assessment of the Potential Economic Impacts of the Invasive Polyphagous Shot Hole Borer (Coleoptera: Curculionidae) in South Africa

Studies addressing the economic impacts of invasive alien species are biased towards ex-post assessments of the costs and benefits of control options, but ex-ante assessments are also required to deal with potentially damaging invaders. The polyphagous shot hole borer Euwallacea fornicatus (Coleoptera: Curculionidae) is a recent and potentially damaging introduction to South Africa. We assessed the potential impact of this beetle by working across economic and biological disciplines and developing a simulation model that included dynamic mutualistic relations between the beetle and its symbiotic fungus. We modeled the potential growth in beetle populations and their effect on the net present cost of damage to natural forests, urban trees, commercial forestry, and the avocado industry over 10 yr. We modeled high, baseline, and low scenarios using discount rates of 8, 6, and 4%, and a plausible range of costs and mortality rates. Models predicted steady growth in the beetle and fungus populations, leading to average declines in tree populations of between 3.5 and 15.5% over 10 yr. The predicted net present cost was 18.45 billion international dollars (Int. $), or about 0.66% of the country's GDP for our baseline scenario ($2.7 billion to $164 billion for low and high scenarios). Most of the costs are for the removal of urban trees that die as a result of the beetle and its fungal symbiont, as has been found in other regions. We conclude that an ex-ante economic assessment system dynamics model can be useful for informing national strategies on invasive alien species management.