Mean warming can enhance the resilience to extreme high temperature events in two species of global pests

1. Global warming not only caused increase in mean temperature but also the frequency of heat waves. Mean warming allows ectotherms exposed to mild higher temperatures for multiple generations. Meanwhile these mean-warmed organisms may also encounter extreme high temperature events. However, how short-lived ectotherms that persist in long period of mild mean warming deal with the extreme high temperature events remains largely unknown.2. Here, we investigated this important issue by measuring the acute thermal tolerance (CTmax) and life history traits at high temperatures (30°C) of two aphid species (Sitobion avenae and Rhopalosiphum padi) that had been warmed (at 25°C, 25±6°C) for 14 days or 60 days.3. Our results indicated that mean warming generally improved heat tolerance (CTmax) in both aphid species, and such improvement effects became weaker when warming time became longer. Moreover, mean warming did not deteriorate life history performances at extreme high temperature (30°C).4. Therefore, mean warming helps aphid species to better cope with extreme high temperature events by improving their heat tolerance and demography at high temperatures. Additionally, our findings offer further evidence that the relative dominance shifts of coexisting species under warming conditions may be influenced by differences in their effective acclimation temperatures.