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Under predicted global climate change, species will be gradually exposed to warmer temperatures, and to a more variable climate including more intense and more frequent heatwaves. Increased climatic variability is expected to have different effects on species and ecosystems than gradual warming. A key challenge to predict the impact of climate change is to understand how temperature changes will affect species interactions. Herbivorous insects and their natural enemies belong to some of the largest groups of terrestrial animals, and thus they have a great impact on the functioning of ecosystems and on the services these ecosystems provide. Here we studied the life history traits of the plant-feeding insect Plutella xylostella and its specialist endoparasitoid Diadegma semiclausum, when exposed to a daily heat pulse of 5 or 10°C temperature increase during their entire immature phase. Growth and developmental responses differed with the amplitude of the heat pulse and they were different between host and parasitoid, indicating different thermal sensitivity of the two trophic levels. With a +5°C heat pulse, the adult parasitoids were larger which may result in a higher fitness, whereas a +10°C heat pulse retarded parasitoid development. These results show that the parasitoid is more sensitive than its host to brief intervals of temperature change, and this results in either positive or negative effects on life history traits, depending on the amplitude of the heat pulse. These findings suggest that more extreme fluctuations may disrupt host-parasitoid synchrony, whereas moderate fluctuations may improve parasitoid fitness.

With climate change, the occurrence of extreme weather events such as heatwaves is expected to increase. Extreme temperature events are short periods of high temperature (i.e., >95th percentile of temperature distribution), and their occurrences are difficult to predict. These extreme temperature events pose great challenges to living organisms, especially ectotherms such as insects whose body temperature is greatly influenced by environmental temperature. Temperature is known to play an essential role in driving insect performance as well as inducing behavioral changes. Exposure to extreme temperatures causes physiological damage leading to potential long‐lasting effects on insect performance. We aimed at assessing the impact of direct (i.e., current) and indirect (previously experienced) exposure to extreme temperature on the oviposition success of Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae). Diadegma semiclausum is a larval endoparasitoid of Plutella xylostella L. (Lepidoptera: Plutellidae), a worldwide pest of brassicaceous crops. Oviposition success, measured as the percentage of parasitized P. xylostella, was significantly lower at 33 °C than at 25 °C. However, previous exposure to 33 °C did not significantly impact the egg‐laying performance of D. semiclausum, indicating that, after a heatwave, the egg‐laying performance can recover. Neither the direct nor indirect exposure to extreme temperature altered D. semiclausum host‐instar preference. These results indicate that temperature directly impacts D. semiclausum parasitism performance, although more detailed research is needed to disentangle direct physiological mechanisms from behavioral responses. Overall, these study results confirm others, suggesting that control of P. xylostella by D. semiclausum is likely to be impaired by more frequent heatwaves predicted under climate change scenarios. [ABSTRACT FROM AUTHOR]