Data from: Influence of mortality factors and host resistance on the population dynamics of emerald ash borer (Coleoptera: Buprestidae) in urban forests

The success of emerald ash borer (Agrilus planipennis Fairmaire) in North America is hypothesized to be due to both the lack of significant natural enemies permitting easy establishment and a population of trees that lack the ability to defend themselves, which allows populations to grow unchecked. Since its discovery in 2002, a number of studies have examined mortality factors of the insect in forests, but none have examined the role of natural enemies and other mortality agents in the urban forest. This is significant because it is in the urban forest where the emerald ash borer has had the most significant economic impacts. We studied populations in urban forests in three municipalities in Ontario, Canada, between 2010 and 2012 using life tables and stage-specific survivorship to analyze data from a split-rearing manipulative experiment. We found that there was little overall mortality caused by natural enemies; most mortality we did observe was caused by disease. Stage-specific survivorship was lowest in small and large larvae, supporting previous observations of high mortality in these two stages. We also used our data to test the hypothesis that mortality and density in emerald ash borer are linked. Our results support the prediction of a negative relationship between mortality and density. However, the relationship varies between insects developing in the crown and those in the trunk of the tree. This relationship was significant because when incorporated with previous findings, it suggests a mechanism and hypothesis to explain the outbreak dynamics of the emerald ash borer.现有假说认为，白蜡窄吉丁（emerald ash borer, Agrilus planipennis Fairmaire）在北美地区的成功定殖，可归因于两大因素：一是缺乏关键天敌，使其得以顺利建立种群；二是宿主树木缺乏防御能力，导致该昆虫种群得以无节制增殖。自2002年被首次发现以来，已有多项研究针对森林生境中该昆虫的致死因子开展分析，但尚无研究关注城市森林生境中天敌与其他致死因子的作用。这一点极具研究价值，因为白蜡窄吉丁所造成的最显著经济影响恰恰出现在城市森林中。本研究于2010至2012年间，以加拿大安大略省三座城市的城市森林中白蜡窄吉丁种群为研究对象，采用生命表法与阶段特异性存活率分析方法，对拆分饲养操控实验获取的数据展开分析。研究结果显示，天敌导致的总体死亡率极低；观测到的绝大多数死亡源于病害。小型与大型幼虫阶段的阶段特异性存活率最低，这一结果佐证了此前关于这两个阶段死亡率偏高的观测结论。本研究同时利用实验数据，检验了"白蜡窄吉丁的死亡率与种群密度存在关联"这一假说，结果支持了"死亡率与密度呈负相关"的预测。不过，这一关联在树冠内与树干内发育的昆虫种群间存在显著差异。该关联具有重要科学意义：结合此前研究成果，它可为解释白蜡窄吉丁的暴发动态提供一套机制与假说。