An artificial delay in emergence influences the number but not the fitness of adult emerald ash borer emerging from infested ash wood

Emerald ash borer, Agrilus planipennis Fairmaire (Buprestidae) is the most significant invasive forest pest in North America. Laboratory research on this species requires a source of adult and larval insects that are of the same fitness as those present in the wild. Production of adult emerald ash borer relies on flushing adults from logs which are subject to cold storage for some period prior to use. The effect of this storage on the number of insects emerging or the fitness of those that emerge has not been investigated. We subjected logs of EAB-infested white ash, Fraxinus americana L. to 7–14 month of cold storage and quantified the number of insects that emerged, time to emergence, and the body condition of adults as a measure of fitness. Body condition was evaluated using Soxhlet fat extraction and water weight. No published methods for Soxhlet fat extraction were available for this species so we developed extraction protocols. The number of insects emerging decreased with time, but fitness (i.e., fat content, water content) did not decrease. Time to emergence did increase but only in the longest-storage treatment while a comparison of male versus female emergence provides evidence for protandry in emerald ash borer. Rearing programs for emerald ash borer using wood from cold storage should adjust the amount used to produce a given number of insects but the quality of those individuals emerging will not be affected. We suggest that those insects that perished during storage were of lower quality when entering diapause and thus would serve as poor-quality host in rearing programs for natural enemies of emerald ash borer. These data also provide evidence for one pathway of introduction for emerald ash borer, suggesting that refrigeration in transit was required for EAB to remain viable and establish its beachhead in North America.

翡翠灰螟（Emerald ash borer），学名*Agrilus planipennis* Fairmaire（吉丁甲科Buprestidae），是北美地区危害最为严重的入侵性森林害虫。针对该物种开展实验室研究，需要获取与野生种群健康度一致的成虫与幼虫。翡翠灰螟成虫的繁育需从受侵染原木中诱出成虫，此类原木在使用前需经过一段时间的冷藏储存。目前尚未有研究探讨该冷藏环节对羽化昆虫数量或羽化个体健康度的影响。本研究对受翡翠灰螟侵染的美国白蜡（*Fraxinus americana* L.）原木开展了7至14个月的冷藏处理，并量化统计了羽化昆虫数量、羽化时长以及成虫的身体状况（作为健康度衡量指标）。身体状况通过索氏脂肪提取法（Soxhlet fat extraction）与体重含水率进行评估。由于该物种尚无公开的索氏脂肪提取方法，我们自行开发了适配的提取方案。研究结果显示，羽化昆虫数量随冷藏时长增加而减少，但个体健康度（即脂肪含量、含水率）并未出现下降。羽化时长仅在最长冷藏处理组中有所延长；对比雌雄虫的羽化时间，可为翡翠灰螟的雄性先熟现象提供佐证。采用冷藏原木开展翡翠灰螟饲养的项目，应调整原木使用量以获取固定数量的昆虫，但羽化个体的质量不会受到影响。我们推测，在冷藏过程中死亡的个体，在进入滞育期时健康度本就较低，若将其作为翡翠灰螟天敌饲养的寄主，将难以达到理想的应用效果。本研究数据同时为翡翠灰螟的一条入侵路径提供了佐证，表明运输过程中的冷藏是翡翠灰螟保持存活并在北美建立入侵种群的必要条件。