Heat waves affect an invasive herbivore and its parasitoid differentially with impacts beyond the first generation

Abstract Heat waves are becoming more frequent with climate change, and their impact on lower and higher trophic levels can differ. Higher trophic levels, such as predators and parasitoids, are predicted to be more strongly affected by heat waves than herbivores because they may have smaller thermal windows and because of altered ecological interactions with lower trophic levels. We tested the effects of heat waves of varying intensity (36–42°C), imposed for 4 h during five consecutive days on the egg stage of an invasive herbivore, the brown marmorated stink bug (Halyomorpha halys), and on various developmental stages of its parasitoid, Trissolcus japonicus. Halyomorpha halys eggs had lower hatching success and fewer nymphs emerging with increasing intensity of heat stress, while exposure during the egg and larval stages of T. japonicus did not decrease adult emergence rates. Heat waves increased developmental time of parasitoids and decreased adult emergence when pupal stages were exposed. Adult parasitoids experiencing heat stress had lower survival, but their parasitism success overall was not affected. In addition, we detected transgenerational effects, whereas emergence success and the number of adult parasitoids emerging in the second generation declined when the parental generation was exposed to 42°C. Contrary to expectations, the results suggest that H. halys may be more sensitive to heat stress than T. japonicus, at least during early development. Our findings indicate that biological control services provided by T. japonicus can be maintained in the face of increasing heat wave events and point to the importance of following populations beyond the first generation to better understand the long‐term consequences of heat stress