Data from: Disentangling the drivers of invasion spread in a vector-borne tree disease

1. Pine wilt disease (PWD) invaded southern Japan in the early 1900’s and has gradually expanded its range to northern Honshu (Japanese mainland). The disease is caused by a pathogenic North American nematode, which is transmitted by native pine sawyer beetles. Recently the disease has invaded other portions of East Asia and Europe where extensive mortality of host pines is anticipated to resemble historical patterns seen in Japan. 2. There is a critical need to identify the main drivers of PWD invasion spread so as to predict future spread and evaluate containment strategies in newly invaded world regions. But the coupling of pathogen and vector population dynamics introduces considerable complexity that is important for understanding this and other plant disease invasions. 3. In this study, we analysed historical (1980-2011) records of PWD infection and vector abundance, which were spatially extensive but recorded at coarse categorical levels (none, low and high) across 403 municipalities in northern Honshu. We employed a multistate occupancy model that accounted both for demographic stochasticity and observation errors in categorical data.
4. Analysis revealed that sparse sawyer populations had lower probabilities of transition to high abundance than did more abundant populations even when regional abundance stayed the same, suggesting the existence of positive density dependence, i.e. an Allee effect, in sawyer dynamics. Climatic conditions (average accumulated degree days) substantially limited invasion spread in northern regions, but this climatic influence on sawyer dynamics was generally weaker than the Allee effect. 5. Our results suggest that tactics (e.g., sanitation logging of infected pines) which strengthen Allee effects in sawyer dynamics may be effective strategies for slowing the spread of PWD.

1. 松材线虫病（Pine wilt disease, PWD）于20世纪初入侵日本南部，随后逐渐扩散至本州北部（日本本土）。该病由一种致病性北美线虫引发，并通过本地松墨天牛（pine sawyer beetles）传播。近年来，该病已入侵东亚及欧洲其他区域，预计当地寄主松树的大规模死亡将复刻日本历史上的发病模式。2. 当前亟需明确松材线虫病入侵扩散的核心驱动因素，以预测未来扩散趋势并评估新入侵区域的防控策略。然而，病原物与媒介种群动态的耦合效应极大增加了研究复杂度，这一问题对于理解松材线虫病及其他植物病害的入侵过程至关重要。3. 本研究分析了1980-2011年松材线虫病感染及媒介种群丰度的历史记录，此类数据空间覆盖范围广泛，但仅按粗略的分类等级（无、低、高）在本州北部403个市镇进行记录。研究采用了多状态占用模型（multistate occupancy model），该模型可同时考量分类数据中的种群统计随机性（demographic stochasticity）与观测误差。4. 分析结果显示，即便区域种群丰度保持恒定，稀疏的松墨天牛种群向高丰度状态转换的概率低于种群丰度更高的群体，这表明松墨天牛种群动态存在正密度依赖效应，即阿利效应（Allee effect）。气候条件（平均累积积温）显著限制了北部区域的入侵扩散，但气候对松墨天牛种群动态的影响总体上弱于阿利效应。5. 本研究结果表明，能够强化松墨天牛种群动态中阿利效应的防控手段（例如对感病松树开展卫生采伐），或可成为减缓松材线虫病扩散的有效策略。