Temperature affects the outcome of competition between two sympatric endoparasitoids

Temperature is a major driver of species interactions as it determines many physiological and behavioural parameters of ectothermic organisms such as insects. Examining the effects of elevated temperature and extreme temperature events within and between different trophic levels is crucial for understanding their broader implications for community and ecosystem level processes. We compared parasitism success of two hymenopteran parasitoid species, Diadegma semiclausum and Cotesia vestalis, under different temperature regimes when foraging intra- and interspecifically. Both parasitoid species can be found in the same habitat and are important biological control agents of the cosmopolitan lepidopteran pest Plutella xylostella, the host species in this study. Because parasitoid density may influence parasitism success through interference competition, we first investigated the effect of parasitoid density (one to four females of the same species) on parasitism success at 22 & DEG;C. In all assays, parasitoid females were released in cages with a single plant infested with 30 hosts placed in a greenhouse or climate cabinets set at 22, 27 or 33 & DEG;C and removed after 3 h. All cages were returned to 22 & DEG;C until pupation of the parasitoids or hosts, which were then counted. When females of the same species foraged together, parasitism success increased with parasitoid density. However, when both species were foraging together, parasitism success of D. semiclausum decreased with increasing temperature at both tested densities, whereas the opposite was found for C. vestalis. Nevertheless, parasitism success of D. semiclausum was always higher than that of C. vestalis, irrespective of parasitoid density or temperature, but competitive superiority of D. semiclausum decreased with increasing temperature. Increases in the magnitude and frequency of extreme temperature events under climate change are likely to have differential effects on species involved in intimate interactions, depending on community species composition, as species may differ in thermal resilience. & COPY; 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).