Interactions of elevated carbon dioxide and temperature with aphid feeding on transgenic oilseed rape: Are <i>Bacillus thuringiensis</i> (Bt) plants more susceptible to nontarget herbivores in future climate?

Abstract

Abstract Climate change factors such as elevated carbon dioxide (CO 2 ) and temperature typically affect carbon (C) and nitrogen (N) dynamics of crop plants and the performance of insect herbivores. Insect‐resistant transgenic plants invest some nutrients to the production of specific toxic proteins [i.e. endotoxins from Bacillus thuringiensis (Bt)], which could alter the C–N balance of these plants, especially under changed abiotic conditions. Aphids are nonsusceptible to Lepidoptera‐targeted Bt Cry1Ac toxin and they typically show response to abiotic conditions, and here we sought to discover whether they might perform differently on compositionally changed Bt oilseed rape. Bt oilseed rape had increased N content in the leaves coupled with reduced total C compared with its nontransgenic counterpart, but in general the C : N responses of both plant types to elevated CO 2 and temperature were similar. Elevated CO 2 decreased N content and increased C : N ratio of both plant types. Elevated temperature increased C and N contents, total chlorophyll and carotenoid concentrations under ambient CO 2 , but decreased these under elevated CO 2 . In addition, soluble sugars were increased and starch decreased by elevated temperature under ambient but not under elevated CO 2 , whereas photosynthesis was decreased in plants grown under elevated temperature in both CO 2 levels. Myzus persicae , a generalist aphid species, responded directly to elevated temperature with reduced developmental time and decreased adult and progeny weights, whereas the development of the Brassica specialist Brevicoryne brassicae was less affected. Feeding by M. persicae resulted in an increase in the N content of oilseed rape leaves under ambient CO 2 , indicating the potential of herbivore feeding itself to cause allocation changes. The aphids performed equally well on both plant types despite the differences between C–N ratios of Bt and non‐Bt oilseed rape, revealing the absence of plant composition‐related effects on these pests under elevated CO 2 , elevated temperature or combined elevated CO 2 and temperature conditions.