Climate change alters species interactions via asymmetric thermal tolerance, mediated by endosymbionts. The phenomenon was investigated here using the emerald ash borer (EAB) and its larval endoparasitoid Tetrastichus planipennisi - a compelling system where the southern range in host insect exceeds distribution of its parasitoid, coinciding with a striking endosymbiont contrast, i.e., while EAB naturally lacks Wolbachia and Rickettsia, its parasitoid maintains both endosymbionts. The study of four T. planipennisi populations (Jilin, Liaoning, Xinjiang, Beijing) revealed the Jilin population exhibited exceptional heat tolerance with 100% endosymbiont infestation. At 40°C, endosymbiont-negative (E-) wasps showed 3-hour shorter survival than endosymbiont-positive (E+) counterparts, with weaker antioxidant capacity. Crucially, rising temperatures impaired endosymbiont transmission to offspring. While beneficial, endosymbionts’ thermal sensitivity creates a trade-off that may disadvantage parasitoids versus E- host insects under climate warming. These findings advance understanding of endosymbiont-mediated climate adaptation and have important implications for biological control strategies in warming environments.

Biological invasions are among the most serious threats to native forest ecosystems worldwide due to ever-increasing global trade and climate change. Understanding invasion processes and the ecology of invasive pests in both newly invaded and native habitats is necessary to effectively mitigate and manage the risks they pose. The effects of exotic ash tree species planted from 1900 to 2019 on distribution, occurrence, and outbreak frequency of a native pest emerald ash borer, Agrilus planipennis Fairmaire, were examined. The frequency and level of pest infestations gradually increased following introduction and widespread plantings of non-native host trees, and the first recorded outbreak occurred after a time lag of 30-50 years. Increased pest populations enhanced its invasion risk to other regions including the native ranges of introduced plants.