INTRODUCTION

Bark beetles are the most damaging pests of conifer forests worldwide (Janes & Batista, 2016), and their impact is predicted to increase in the future due to climate change and the growth of international trade (Avtzis & Lakatos, 2021). These pests are easily moved around and spread to new areas as a result of national and international trade with the main introduction pathways being the movement of wood packaging material, logs, processed woods and containers (Meurisse et al., 2019). Tomicus piniperda L. (Coleoptera, Scolytidae) is the member of its genus with the widest geographic distribution, covering the Palearctic area from western Europe (Portugal) to east Asia (Japan) (Lieutier et al., 2015). It was also found in North America where it is invasive and where it has spread from Ohio (USA) to several other states and to Canada (Lieutier et al., 2015). It is a cold-tolerant species that cannot develop in warm and dry climates (Horn et al., 2012). T. piniperda is a very common and important pest, including in the United Kingdom (UK) where it is responsible for significant economic damage (Lieutier et al., 2015; Wainhouse & Inward, 2016). T. piniperda can attack a variety of conifer species but Scots pine (Pinus sylvestris) is its main host throughout its range (Hanson, 1937; Lieutier et al., 2015). Scots pine is one of only three native conifers in the UK, together with yew and juniper (Taxus baccata and Juniperus communis) and the only native species used for commercial forestry, representing 17% of the trees grown (Edlin, 1970; Forest Research, 2021).

T. piniperda has high dispersal abilities, most likely a result of the rarity of suitable breeding material in the landscape (Kerdelhué et al., 2006), with adults believed to cover several kilometres during their spring flights (Forsse, 1989). Larvae develop in weakened or freshly dead trees as the species cannot survive the defences of healthy conifers (Kerdelhué et al., 2006; Lieutier, 2002). However, T. piniperda can attack and breed in trees that are weakened by other factors such as insect-induced defoliation or drought and so increase tree mortality (Wainhouse & Inward, 2016). In the UK, T. piniperda has contributed to the death of trees that were heavily defoliated by the pine looper moth Bupalus piniaria (Forest Research, 2023; Wainhouse & Inward, 2016). After emerging from breeding galleries within trees, young adult T. piniperda feed on healthy and vigorous pine shoots in order to complete maturation, which can lead to significant tree damage when the beetle population is high (Hanson, 1937; Lieutier et al., 2015; Wainhouse & Inward, 2016). Substantial growth loss is reported when maturation feeding occurs in young plantations or when a large proportion of shoots is destroyed (Hanson, 1937; Lieutier et al., 2015; Wainhouse & Inward, 2016). T. piniperda is also responsible for indirect damage when it vectors other pests, for example, blue stain fungi (Lieutier et al., 2015; Solheim et al., 1993) and the pitch canker disease pathogen (Fusarium circinatum; Bezos et al., 2015). As for other forest pest species, climate change is predicted to increase the damage caused by T. piniperda to Scots pine trees (Wainhouse & Inward, 2016).

Knowledge of pest dispersal is necessary to understand the scale at which to implement management, surveillance plans and to assess the efficacy of management techniques (Mazzi & Dorn, 2012; Miller & Sappington, 2017). Genetic markers are powerful tools that allow the direct and indirect study of dispersal (Broquet & Petit, 2009). Population studies of T. piniperda across continental Europe have revealed high levels of genetic variation, high gene flow across large geographical areas (Horn et al., 2009; Kerdelhué et al., 2006; Ritzerow et al., 2004) and signals of persistence in, and expansion from, multiple glacial refugia (Horn et al., 2009; Ritzerow et al., 2004). None of these studies included samples from the UK, so it is not clear if there is connectivity of T. piniperda populations between continental Europe and the UK. Furthermore, little is known about the dispersal of the beetle between Scots pine stands in the UK (Lieutier et al., 2015) and this information could help control efforts by the British forestry sector. Accordingly, the aim of this study was to evaluate the genetic structure of T. piniperda within the UK as well as connectivity between UK and European conspecific populations. Mitochondrial DNA analysis was employed to permit direct linking of data with that from previous studies (Horn et al., 2009). In addition, nuclear microsatellite DNA markers were employed as they may be more sensitive to recent population processes due to their more rapid rate of evolution. Three specific questions were addressed. Firstly, is the English Channel a barrier to dispersal, as found in other insect species (Minot & Husté, 2022; Thomas et al., 2021)? Secondly, is dispersal in the UK limited by environmental factors such as host distribution or physical barriers or is there long-distance dispersal within the country? Thirdly, is genetic diversity in the UK lower than in European populations in accordance with the classic southern richness northern purity model of post-glacial colonization of northern Europe (Hewitt, 2000)? The results of the present study will inform the management and surveillance of T. piniperda and provide insights on possible patterns of dispersal of other bark beetles with similar dispersal abilities, size and body mass.

中文翻译：

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遗传变异揭示了英国 Tomicus piniperda L.（鞘翅目、小蠹科）复杂的种群结构：对这种重要害虫管理的启示

介绍

树皮甲虫是全球针叶林最具破坏性的害虫（Janes 和 Batista，  2016），由于气候变化和国际贸易的增长，预计其影响在未来会增加（Avtzis 和 Lakatos，  2021）。由于国内和国际贸易，这些害虫很容易四处移动并传播到新的地区，主要传入途径是木质包装材料、原木、加工木材和容器的移动（Meurisse 等，  2019）。Tomicus piniperda L.（鞘翅目，小蠹科）是其属中地理分布最广的成员，覆盖了从西欧（葡萄牙）到东亚（日本）的古北区（Lieutier et al.,  2015）。在北美也发现了这种病毒，该病毒具有侵入性，并已从俄亥俄州（美国）传播到其他几个州和加拿大（Lieutier 等，  2015）。它是一种耐寒物种，无法在温暖和干燥的气候中生长（Horn et al.,  2012）。T. piniperda是一种非常常见和重要的害虫，包括在英国 (UK)，它造成了重大的经济损失（Lieutier 等，  2015；Wainhouse & Inward，  2016）。T. piniperda可以攻击多种针叶树物种，但欧洲赤松 ( Pinus sylvestris ) 是其整个分布范围的主要宿主（Hanson，  1937；Lieutier 等，  2015）。欧洲赤松是英国仅有的三种本土针叶树之一，另外两个是红豆杉和杜松（红豆杉和杜松），也是唯一用于商业林业的本土树种，占种植树木的 17%（Edlin，  1970 年；森林研究，  2021）。

T. piniperda具有很高的传播能力，很可能是由于该地区缺乏合适的繁殖材料（Kerdelhué 等人，  2006 年），据信成虫在春季飞行期间可以飞行数公里（Forsse，  1989 年）。幼虫在衰弱或刚死的树木中发育，因为该物种无法在健康针叶树的防御下生存（Kerdelhué 等人，  2006 年；Lieutier，  2002 年）。然而，T. piniperda可以攻击因昆虫引起的落叶或干旱等其他因素而削弱的树木并在其中繁殖，从而增加树木死亡率（Wainhouse & Inward,  2016）。在英国，T. piniperda导致了被松尺蛾Bupalus piniaria严重落叶的树木死亡（Forest Research，  2023；Wainhouse & Inward，  2016）。从树内的繁殖区出来后，年轻的松树幼虫会以健康而有活力的松枝为食以完成成熟，当甲虫数量较多时，这可能会导致严重的树木损害（Hanson，  1937；Lieutier 等人，  2015 ） ；Wainhouse & Inward，  2016）。据报道，当年轻种植园发生成熟取食或大部分芽被破坏时，会出现严重的生长损失（Hanson，  1937；Lieutier 等，  2015；Wainhouse 和 Inward，  2016）。T. piniperda在传播其他害虫时也会造成间接损害，例如蓝染真菌（Lieutier et al.,  2015；Solheim et al.,  1993）和沥青溃疡病病原体（Fusarium circinatum；Bezos et al., 2015）。 ，  2015）。至于其他森林害虫物种，预计气候变化将增加T. piniperda对赤松树造成的损害（Wainhouse & Inward，  2016）。

害虫传播知识对于了解实施管理、监测计划的规模以及评估管理技术的有效性是必要的（Mazzi & Dorn，  2012；Miller & Sappington，  2017）。遗传标记是强大的工具，可以直接和间接研究传播（Broquet & Petit，  2009）。对整个欧洲大陆的松柏种群进行的研究揭示了高水平的遗传变异、大范围地理区域的高基因流（Horn 等人，  2009 年；Kerdelhué 等人，  2006 年；Ritzerow 等人，  2004 年）以及持久性信号多个冰川保护区的存在和扩展（Horn 等人，  2009 年；Ritzerow 等人，  2004 年）。这些研究均未包含来自英国的样本，因此尚不清楚欧洲大陆和英国之间的松柏种群是否存在连通性。此外，人们对甲虫在英国赤松林之间的传播知之甚少（Lieutier 等，  2015），这些信息可以帮助控制英国林业部门的工作。因此，本研究的目的是评估英国境内T. piniperda的遗传结构以及英国和欧洲同种种群之间的连通性。采用线粒体 DNA 分析将数据与之前的研究数据直接联系起来（Horn 等，  2009）。此外，还采用了核微卫星 DNA 标记，因为它们的进化速度更快，可能对最近的种群过程更加敏感。讨论了三个具体问题。首先，英吉利海峡是否像其他昆虫物种那样成为传播的障碍（Minot & Husté，  2022；Thomas et al.，  2021）？其次，在英国的传播是否受到宿主分布或物理障碍等环境因素的限制，或者是否存在国内长距离传播？第三，根据北欧冰川后殖民的经典南方丰富北方纯净模型（Hewitt，  2000），英国的遗传多样性是否低于欧洲人群？本研究的结果将为T. piniperda的管理和监测提供信息，并为具有相似扩散能力、大小和体重的其他树皮甲虫的可能扩散模式提供见解。