Date Published: June 12, 2018
Publisher: Public Library of Science
Author(s): Salvatore J. Agosta, Kanchan A. Joshi, Karen M. Kester, Owain Rhys Edwards.
Understanding how climate change affects host-parasite systems and predicting the consequences for ecosystems, economies, and human health has emerged as an important task for science and society. Some basic insight into this complex problem can be gained by comparing the thermal physiology of interacting host and parasite species. In this study, we compared upper thermal tolerance among three component species in a natural host-parasitoid-hyperparasitoid system from Virginia, USA. To assess the ecological relevance of our results, we also examined a record of maximum daily air temperatures collected near the study site in the last 124 years. We found that the caterpillar host Manduca sexta had a critical thermal maximum (CTmax) about 4°C higher than the parasitic wasp, Cotesia congregata, and the hyperparasitic wasp, Conura sp., had a CTmax about 6°C higher than its host, C. congregata. We also found significant differences in CTmax among instars and between parasitized and non-parasitized M. sexta. The highest maximum daily air temperature recorded near the study in the last 124 years was 42°C, which equals the average CTmax of one species (C. congregata) but is several degrees lower than the average CTmax of the other two species (M. sexta, Conura sp.) in this study. Our results combined with other studies suggest that significant differences in thermal performance within and among interacting host and parasite species are common in nature and that climate change may be largely disruptive to these systems with responses that are highly variable and complex.
Of the many dimensions to climate change, predicting the response of host-parasite systems to warming has received considerable attention (e.g. [1–14]). Parasitism—broadly defined as including traditional parasites, many plant-feeding insects, parasitoids, and pathogens—is perhaps the most common mode of life on the planet involving interactions among a huge number and diversity of organisms [15–18]. In the terrestrial realm, one common type of host-parasite system is the interaction between herbivorous caterpillars (larval Lepidoptera) and their wasp (Hymenoptera) and fly (Diptera) parasitoids. Unlike typical parasites, parasitoids normally kill their host after larval development . Many host-parasitoid systems also involve a third level of hyper-parasitism, with hyperparasitoids that parasitize the original host’s parasitoids.
To our knowledge, this is the first study to test for differences in the upper thermal tolerance of component species in a natural H-P-HP system. Based on our estimates of CTmax, the upper limits to performance differ by several degrees between the caterpillar, M. sexta, and adults of its major parasitoid, C. congregata, and between C. congregata and adults of one of its major hyperparasitoids, Conura sp. The specific average values of CTmax that we estimated for the component species ranged from 42–48°C, which is well within the range of previously measured values for insects .