Pathogen Profile #2

Hello Robigalia Reader! Welcome back to another week of Robigalia, delivering the latest in plant pathology directly to your inbox!

This latest newsletter is coming to you from Perth, Western Australia where the state government is currently dealing with a Polyphagous Shot-Hole Borer (PSHB) (Euwallacea fornicatus) outbreak.

These tiny (2mm long) beetles have become a significant pest due to its association with fungal symbionts, primarily Fusarium euwallaceae. As the beetle tunnels its way through the wood of the trees, it carries the fungus with it as a food source. This provides the opportunity for the fungus to colonise the xylem of susceptible plants, blocking the flow of water and nutrients to the leaves. The combination of physical damage from the beetle's boring activity and the pathogenic effects of the fungal symbionts it carries disrupts the tree's normal functions, leading to stress, decline, and ultimately, the death of the tree.

PSHB spreads primarily through its ability to fly and disperse to new areas, as well as through human-mediated activities such as the movement of infected wood materials. The wide host range of PSHB facilitates its spread. The beetle can infect and reproduce in a multitude of tree species, both native and introduced, which increases the opportunities for it to establish in diverse environments. While Western Australian native trees are not preferred hosts, infections have been widespread on several native Ficus species with tree removal set for hundreds of trees in the region.

This beetle-fungus duo poses a serious threat to economically valuable plants, impacting agriculture and forestry sectors. PSHB attacks a wide range of host plants, including economically important crops such as avocado and other fruit tress. Beyond agriculture, PSHB also targets a variety of hardwood trees commonly found in urban and forested areas. The spread of PSHB and its associated fungus can lead to a reduction in biodiversity, especially in forested areas where native tree species are susceptible. This loss can alter ecosystems, affecting other plant and animal species dependent on these trees. The economic impact is further compounded by the costs associated with managing and controlling the spread of PSHB. These include the expenses related to pesticide application, removal and disposal of infected trees, and the implementation of quarantine measures to prevent further spread.

While the challenges posed by PSHB are significant, efforts are underway to manage and mitigate its impact. Researchers and government agencies are collaborating on strategies such as the development of resistant tree varieties, enhanced monitoring techniques, and public education campaigns to prevent the spread of this pest.

If you’re interested in reading more about PHSB, I’ve summarised a few articles below. If you’re a subscriber, scroll down to access my online database which includes full summaries of these, and all other Robigalia featured articles.

E. fornicatus papers:

Economic impact of polyphagous shot hole borer Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae) in Western Australia

• This study delves into the economic ramifications of the invasive polyphagous shot hole borer (Euwallacea fornicatus) in Western Australia, revealing the potential for significant financial impact on urban forests and avocado production. They explore scenarios of eradication versus non-action, concluding that while eradication efforts present a high initial cost, they may offer substantial long-term economic benefits.

Pathogenicity of Fusarium euwallaceae, symbiont of the polyphagous shot hole borer beetle, to selected stone fruit trees in South Africa

• This study reveals the pathogenic effects of Fusarium euwallaceae on stone fruit trees in South Africa, particularly nectarines and plums. The findings underscore the urgent need for effective management strategies to protect stone fruit orchards from this PSHB and Euwallacea fornicatus.

Introduction and establishment of Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae) in Brazil

• This paper provides critical insights into the introduction and establishment of Euwallacea fornicatus in Brazil, offering a foundation for developing strategies to manage this invasive pest and protect the country's agriculture with a focus on avocado production.

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Until next week,

Alyssa