Heat waves reduce variability in milkweed development, simplify arthropod communities, and suppress herbivory.

The frequency and intensity of heat waves are on the rise due to climate change. Heat waves are temporally discrete, and thus occur at different stages of plant development. Yet, compared with mean temperature, little is known about how the timing of extreme heat events interacts with the timing of plant development. In this study, we varied the timing of experimental heat waves applied to common milkweed (Asclepias syriaca) to determine how heat waves timing impacts plant developmental timing and subsequent plant-arthropod interactions. We found that heat waves delay and synchronize plant development, and that these effects are particularly strong for early season heat waves. Heat wave-exposed plants also supported fewer species of arthropods and experienced less chewing herbivory than ambient-temperature controls. Our study reveals that the relationship between extreme event timing and plant developmental timing will shape how increasing prevalence of extreme heat events impacts plant-arthropod communities.