The interactive effects of heat stress, parasitism, and hostplant quality in a host-parasitoid system

Species interactions are expected to change in myriad ways as the frequency and magnitude of extreme temperature events increase with anthropogenic climate change. The relationships between endosymbionts, parasites, and their hosts are particularly sensitive to thermal stress, which can have cascading effects to other trophic levels. We investigate the interactive effects of heat stress and parasitism on a terrestrial tritrophic system consisting of two hostplants (one common, high-quality plant and one novel, low-quality plant), a caterpillar herbivore, and a specialist parasitoid wasp. We used a fully-factorial experiment to determine the bottom-up effects of the novel hostplant on both the caterpillars’ life history traits and the wasps’ survival, and the top-down effects of parasitism and heat shock on caterpillar developmental outcomes and herbivory levels. Hostplant identity interacted with thermal stress to affect wasp success, with wasps performing better on the low-quality hostplant under constant temperatures but worse under heat shock conditions. Surprisingly, caterpillars consumed less leaf material of the low-quality hostplant to reach the same final mass across developmental outcomes. In parasitized caterpillars, heat shock reduced parasitoid survival and increased both caterpillar final mass and development time on both hostplants. These findings highlight the importance of studying community-level responses to climate change from a holistic and integrative perspective and provide insight into potential substantial interactions between thermal stress and diet quality in plant-insect systems.

Methods
The corresponding author collected this dataset at UNC-Chapel Hill facilities in 2020. It has been processed through Google Sheets, and then R.