Sequestration of defensive compounds acquired from the environment can be costly to herbivorous insects. The catalpa sphinx, Ceratomia catalpae Boisduval (Lepidoptera: Sphingidae) sequesters the iridoid glycoside catalpol, which it acquires from Catalpa spp. (Lamiales: Bignoniaceae) host plants, at concentrations above those in host plant leaves. Previous research has shown that C. catalpae larvae are avoided by predatory arthropods; however, catalpol sequestration is negatively associated with the larval immune response, suggesting a cost to sequestration. By measuring the mass of C. catalpae larvae, their frass, and their diet, as well as respiration rate and catalpol sequestration, this study aimed to determine whether sequestration is also associated with reduced growth and nutritional efficiency. I found that respiration rate was negatively correlated with the amount of catalpol sequestered and positively correlated with the concentration, or proportion dry mass of catalpol sequestered, and that the amount of catalpol sequestered was positively correlated with three of four measures of nutritional efficiency. Larger larvae that were closer to pupation sequestered very low proportions dry mass of catalpol and had a reduced respiratory rate per unit mass. These results suggest that sequestration has some costs for expenditure of energy, but is positively correlated with several growth and nutrition‐related processes. Instead, the immunological cost of sequestration measured in previous studies could be due to direct effects on immune system components. Further research on the potential metabolic costs of chemical defense in other specialist species is recommended.

中文翻译：

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梓树狮身人面像、梓楸科（鳞翅目：鞘翅目）的梓醇螯合、代谢和营养效率之间的关系

隔离从环境中获得的防御性化合物对于食草昆虫来说可能是昂贵的。梓树狮身人面像，Ceratomia catalpae Boisduval（鳞翅目：Sphingidae）隔离了环烯醚萜苷梓醇，它从梓属中获得。（Lamiales：Bignoniaceae）寄主植物，浓度高于寄主植物叶子中的浓度。先前的研究表明，捕食性节肢动物会避开 C. catalpae 幼虫；然而，梓醇隔离与幼虫免疫反应呈负相关，表明隔离成本。通过测量 C. catalpae 幼虫的质量、它们的粪便和它们的饮食，以及呼吸速率和梓醇的螯合，本研究旨在确定螯合是否也与生长和营养效率降低有关。我发现呼吸速率与螯合的梓醇量呈负相关，与螯合的梓醇的浓度或干质量比例呈正相关，并且螯合的梓醇量与四种营养效率指标中的三种呈正相关。更接近化蛹的较大幼虫隔离非常低比例的梓醇干质量，并且每单位质量的呼吸频率降低。这些结果表明，封存有一些能量消耗成本，但与几个生长和营养相关的过程呈正相关。相反，先前研究中测量的隔离免疫成本可能是由于对免疫系统成分的直接影响。