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Abstract Insect parasitoids, and the arthropod hosts they consume during development, are important ecological players in almost all environments across the globe. As ectothermic organisms, both parasitoid and host are strongly impacted by environmental temperature. If thermal tolerances differ between host insect and parasitoid, then the outcome of their interaction will be determined by the ambient temperature. As mean temperatures continue to rise and extreme temperatures become more frequent, we must determine the effect of high temperature stress on host–parasitoid systems to predict how they will fare in the face of climate change.The majority of studies conducted on host–parasitoid systems focus on either performance under constant temperature or a fixed metric of thermal tolerance (CTmax) for individual organisms. However, performance at constant temperatures is not predictive of performance under ecologically relevant, fluctuating temperatures and measurements of thermal thresholds provide little information regarding the effects of temperature throughout development. We address this by testing the effects of increasing mean temperature in both constant and fluctuating (±10°C) environments throughout development on the performance of the parasitoid waspCotesia congregataand its lepidopteran larval host,Manduca sexta.The growth ofM. sextawas influenced by mean temperature, diurnal fluctuations and parasitization status. Caterpillar growth rate increased with increasing mean temperature, but decreased in response to diurnal fluctuations and parasitization byC. congregatawasps.Wasp survival decreased with increasing mean temperature and with diurnal fluctuations. The effect of diurnal fluctuations was stronger at higher mean temperatures. Diurnal fluctuations at our highest mean temperature treatment (30 ± 10°C) resulted in complete wasp mortality, and parasitized hosts displayed abnormal physiology, wherein they failed to exhibit wasp emergence, did not enter the prepupal stage, continued to feed and grew up to twofold larger than a normal, unparasitized caterpillar.Our results indicate hosts and parasitoids in this system have different thermal tolerances during development; the parasitoid wasp suffered complete mortality at a temperature regime that is mildly stressful for the unparasitized caterpillar host species. Our findings suggestC. congregatawill suffer more severely under increasing temperatures thanM. sexta, with cascading trophic and ecological effects. A freePlain Language Summarycan be found within the Supporting Information of this article.
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The interactive effects of heat stress, parasitism and host plant quality in a host–parasitoid system
Abstract 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 on other trophic levels.We investigate the interactive effects of heat stress and parasitism on a terrestrial tritrophic system consisting of two host plants (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 host plant 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.Host plant identity interacted with thermal stress to affect wasp success, with wasps performing better on the low‐quality host plant under constant temperatures but worse under heat‐shock conditions.Surprisingly, caterpillars consumed less leaf material from the low‐quality host plant 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 host plants.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. Read the freePlain Language Summaryfor this article on the Journal blog.
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- Award ID(s):
- 2029156
- PAR ID:
- 10486918
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 38
- Issue:
- 3
- ISSN:
- 0269-8463
- Format(s):
- Medium: X Size: p. 642-653
- Size(s):
- p. 642-653
- Sponsoring Org:
- National Science Foundation
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