INTRODUCTION

In September 2021, a small wood boring beetle was detected in Western Australia when a resident of the Perth suburb of East Fremantle reported signs of dieback and dead branches in their box elder maple tree, Acer negundo L. (Pest and Disease Information Service, 2021). It has since been identified as a member of the Euwallacea fornicatus species complex, E. fornicatus Eichhoff, commonly referred to as the Polyphagous Shot Hole Borer (PSHB). This invasive ambrosia beetle attacks both healthy and dead or dying trees, introducing fungal infections through associations with different fungi, including Fusarium euwallaceae sp. nov. (Freeman et al., 2013) which invades tree vascular tissue, causing localized tissue damage in a wide range of trees (Mendel et al., 2016; Mendel et al., 2017). At the time of writing, the full extent of the outbreak is not known. In this paper, we discuss what it could mean for the Western Australian economy if the beetle does spread over the coming decades and estimate the likely benefits of eradication should it prove technically feasible.

International movement of PSHB has been facilitated by anthropogenic dispersal, and in the last 20 years it has become invasive in the United States of America (U.S.A.) (California, 2003), Israel (2009), South Africa (2017) and Palestine (2019) (Centre for Agricultural Bioscience Information, 2021). It has caused serious damage to urban trees in California (Coleman et al., 2019) and South Africa (de Wit et al., 2021; van den Berg et al., 2019), and minor damage to ornamental trees in Israel (Eskalen, 2012). Generally, the agricultural impact has been small, although damage to avocado production in Israel has been severe (Mendel et al., 2017). Here, damage has been exacerbated by a reluctance to use pesticides in order to preserve export markets in Europe (Eskalen, 2012). Minor agricultural impacts have also recently been reported in neighbouring Palestine (Salman et al., 2019). Fusarium euwallaceae does not spread systemically far from beetle attack points and branch dieback tends not to occur in trees when beetle density is kept in check (Mendel et al., 2016; Mendel et al., 2017). Hence, tree damage in infested areas can be minimized by removing heavily infested trees, pruning infested branches and applying systemic insecticides to healthy or newly infested trees (Grosman et al., 2019; O'Donnell et al., 2016).

Using a simulation model, we estimated the spread and impact of PSHB in Western Australia over several decades in nil management and eradication policy scenarios, calculating resultant costs to urban forests and agricultural production. The rate of spread to expect in Western Australia is unclear. It is possible the beetle has been present for several years without spreading outside the Perth Metropolitan Area. Only females are capable of flight but prefer to remain in colonized branches rather than seeking out new hosts (Mendel et al., 2017). Furthermore, average flight distances observed in another member of the Euwallacea fornicatus species complex, E. perbrevis Schedl, are relatively short at 30–35 m (Owens et al., 2019). However, it is also possible that natural dispersal will lead to rapid colonization. Euwallacea perbrevis can achieve flight distances as long as 400 m (Owens et al., 2019), and PSHB females can produce >30 offspring within 6–7 weeks in laboratory conditions, >90% of which are female (Cooperband et al., 2016). Given this uncertainty, we considered general spread scenarios in this first attempt to simulate PSHB spread in Western Australia and did not attempt detailed population modelling.

Impact is also uncertain as it depends on response actions taken by government. Urban tree damage was estimated in the model as local government costs incurred using insecticide injections and aggressive pruning of susceptible trees in the Perth Metropolitan Area. We assumed this would be the most cost-effective management option rather than tree removal in a nil management scenario. Agricultural costs were estimated as yield losses in avocado trees plus pruning costs associated with the removal of necrotic tree limbs. In the eradication scenario, we evaluate a proposal involving an investment of $43.0–45.0 million over a period of 3 years, which the Western Australian Department of Primary Industries and Regional Development deems sufficient to achieve eradication. This scenario involves the removal and replacement of affected urban trees.

The paper contributes to the literature by quantifying economic damage associated with this pest as it spreads and estimating benefits associated with a specific response policy. To our knowledge, only de Wit et al. (2021) provide a comparable analysis, estimating costs in a nil management scenario assuming exponential spread through combined tree hosts in South Africa. All monetary values are stated in Australian dollars unless otherwise indicated.

中文翻译：

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西澳大利亚多食性炮孔虫 Euwallacea fornicatus（鞘翅目：象甲科：Scolytinae）的经济影响

介绍

2021 年 9 月，西澳大利亚州发现了一种小型蛀木甲虫，当时珀斯郊区东弗里曼特尔 (East Fremantle) 的一名居民报告称，他们的黄枫树 Acer negundo L. 出现枯萎和枯枝的迹象（病虫害信息服务，2021年 ））。此后，它被鉴定为Euwallacea fornicatus物种复合体E. fornicatus Eichhoff的成员，通常被称为多食性孔洞蛀虫(PSHB)。这种入侵性的豚草甲虫攻击健康和死亡或垂死的树木，通过与不同的真菌（包括真花镰刀菌）结合引入真菌感染。十一月 （弗里曼等人，  2013）侵入树木维管组织，导致多种树木局部组织损伤（Mendel 等，  2016；Mendel 等，  2017）。截至撰写本文时，尚不清楚疫情爆发的全部范围。在本文中，我们讨论了如果甲虫在未来几十年内确实蔓延，对西澳大利亚经济意味着什么，并估计如果技术上可行的话根除甲虫可能带来的好处。

人为扩散促进了 PSHB 的国际运动，在过去 20 年中，它已成为美国（加利福尼亚州，2003 年）、以色列（2009 年）、南非（2017 年）和巴勒斯坦（2019 年）的入侵者。 ）（农业生物科学信息中心，  2021）。它对加利福尼亚州（Coleman et al., 2019）和南非（de Wit et al.,  2021；van den Berg et al.,  2019 ）的城市树木造成严重损害 ，并对以色列的观赏树木造成轻微损害（Eskalen） ，  2012）。一般来说，尽管以色列鳄梨生产受到严重损害，但农业影响很小（Mendel 等，  2017 ））。在这里，由于不愿使用杀虫剂以保护欧洲出口市场，损害进一步加剧（Eskalen，  2012）。最近邻国巴勒斯坦也报告了轻微的农业影响（Salman 等人，  2019）。当甲虫密度受到控制时，镰刀菌不会系统性地扩散到距甲虫攻击点很远的地方，并且树枝顶枯病往往不会发生（Mendel 等人，2016 年；Mendel 等人，  2017年 ）。因此，通过清除严重受感染的树木、修剪受感染的树枝以及对健康或新受感染的树木施用内吸性杀虫剂，可以最大限度地减少受感染地区的树木损害（Grosman 等人，2019 年；O'Donnell 等 人， 2016）。

使用模拟模型，我们估计了几十年来在零管理和根除政策情景下 PSHB 在西澳大利亚的传播和影响，计算了城市森林和农业生产的最终成本。西澳大利亚州的预期传播速度尚不清楚。这种甲虫可能已经存在好几年了，没有扩散到珀斯大都会区以外的地区。只有雌性才有能力飞行，但更愿意留在定植的树枝上，而不是寻找新的宿主（Mendel et al.,  2017）。此外，在Euwallacea fornicatus物种复合体的另一个成员E. perbrevis Schedl 中观察到的平均飞行距离相对较短，为 30-35 m（Owens 等人， 2019）。然而，自然扩散也有可能导致快速殖民。Euwallacea perbrevis 的飞行距离可达 400 m (Owens et al.,  2019 )，PSHB 雌性在实验室条件下可在 6-7 周内产生 > 30 个后代，其中 > 90% 是雌性 (Cooperband et al., 2019)。  2016）。考虑到这种不确定性，我们在第一次尝试模拟西澳大利亚 PSHB 传播时考虑了一般传播情景，并且没有尝试详细的人口建模。

影响也是不确定的，因为它取决于政府采取的应对行动。该模型估计了城市树木损害，因为当地政府在珀斯大都市区注射杀虫剂和积极修剪易受影响的树木而产生了成本。我们认为这将是最具成本效益的管理选项，而不是在零管理场景中移除树木。农业成本估计为鳄梨树的产量损失加上与去除坏死树枝相关的修剪成本。在根除方案中，我们评估了一项在 3 年内投资 43.0-4500 万澳元的提案，西澳大利亚州第一产业和区域发展部认为这足以实现根除。这种情况涉及拆除和更换受影响的城市树木。

该论文通过量化与这种害虫传播相关的经济损失并估计与特定应对政策相关的效益，为文献做出了贡献。据我们所知，只有 de Wit 等人。（2021）提供了可比较的分析，假设通过南非的组合树宿主呈指数传播，则在零管理场景中估计成本。除非另有说明，所有货币价值均以澳元表示。