Data from: Differing thermal sensitivities in a host-parasitoid interaction: high, fluctuating developmental temperatures produce dead wasps and giant caterpillars

1. 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. 2. 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 wasp Cotesia congregata and its lepidopteran larval host, Manduca sexta. 3. The growth of M. sexta was 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 by C. congregata wasps. 4. Wasp survival decreased with increasing mean temperature, and diurnal fluctuations decreased wasp survival, especially at higher mean temperatures. Diurnal fluctuations at our highest mean temperature treatment (30°C±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 two-fold larger than a normal, unparasitized caterpillar. 5. 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 suggest C. congregata will suffer more severely under increasing temperatures than M. sexta, with cascading trophic and ecological effects.

1. 昆虫寄生蜂及其发育过程中取食的节肢动物宿主，是全球几乎所有生境中重要的生态功能类群。作为外温性生物（ectothermic organism），寄生蜂与宿主均受环境温度的显著影响。若宿主昆虫与寄生蜂的热耐受性存在差异，则二者的互作结果将由环境温度决定。随着平均气温持续升高、极端高温事件愈发频繁，我们亟需明确高温胁迫对宿主-寄生蜂系统的影响，以预测二者在气候变化背景下的存续态势。
2. 目前针对宿主-寄生蜂系统的多数研究，要么聚焦于恒定温度下的生长表现，要么仅测定单个生物体的固定热耐受性指标（临界高温，CTmax）。然而，恒定温度下的表现无法预测生态相关的波动温度下的表现，而热阈值的测量结果也难以反映温度在整个发育周期中的影响。为此，我们通过在整个发育过程中设置恒定与波动（±10℃）两种升温模式，检测其对寄生蜂菜蛾盘绒茧蜂（Cotesia congregata）及其鳞翅目幼虫宿主烟草天蛾（Manduca sexta）生长表现的影响。
3. 烟草天蛾的生长受平均温度、昼夜温度波动以及寄生状态的共同调控。幼虫生长速率随平均温度升高而提升，但会因昼夜温度波动以及被菜蛾盘绒茧蜂寄生而下降。
4. 寄生蜂的存活率随平均温度升高而降低，昼夜温度波动进一步降低其存活率，在平均温度较高时这一效应尤为显著。在我们设置的最高平均温度处理组（30℃±10℃）下，昼夜波动模式导致了寄生蜂的全部死亡；被寄生的宿主出现生理异常：无法羽化出寄生蜂、无法进入预蛹期，仍持续取食，体型可达正常未寄生幼虫的两倍之大。
5. 本研究结果表明，该系统中的宿主与寄生蜂在发育过程中具有不同的热耐受性：当温度条件对未寄生的烟草天蛾宿主仅造成轻度胁迫时，菜蛾盘绒茧蜂却已全部死亡。我们的研究结果显示，相较于烟草天蛾，菜蛾盘绒茧蜂在温度持续升高的情境下将受到更严重的影响，进而引发级联营养与生态效应。