Professor University of California, Los Angeles Los Angeles, California, United States
Abstract: Ectotherms are the most vulnerable to climate warming while also being the most abundant group of organisms. The effects of warming will not only affect individual populations of ectotherms, but also species interactions. Predation is one of the most ubiquitous species interaction and the effects of temperature on predation will in turn affect community dynamics. In particular, parasitoids are not only important in natural communities but are also crucial in agricultural settings, where they function as natural enemies of pests. Despite their importance, empirical studies of the effects of temperature on parasitoid-host interactions through the study of their life history traits are rare. Here, we present results from a laboratory experiment using the wasp Anisopterolamus calandrae, a parasitoid of the cowpea seed beetle Callosobruchus maculatus, a cosmopolitan pest of stored products. We measured life history trait responses of A. calandrae at seven temperatures ranging between 18-36 °C. We quantified mortality, maturation, attack rate, and handling time to investigate whether rising temperatures strengthen or weaken the interaction between A. calandrae and its host. Based on previous work, we hypothesize that the parasitoid has lower temperature threshold compared to its host, and that the interaction is altered due to their different temperature responses.
We find that A. calandrae’s temperature responses conform to the qualitative shapes exhibited by other parasitoids. For instance, per capita mortality increases monotonically with temperature, while handling time is U-shaped. Furthermore, A. calandrae is unable to develop at 18 °C, and very few individuals emerged at 36 °C. Therefore, the thermal niche breadth of A. calandrae is narrower than that of its host, which can survive at all experimental temperatures. We are also developing a trait-based model which we will parameterize with experimental data to predict population dynamics in the face of warming. We discuss the implications of these findings on the viability of parasitoid-host interactions and the efficacy of pest control in a warming world. Our experiments also inform the biological control practices that use natural enemies to control agricultural pests.
