Cereal aphid performance and feeding behaviour largely unaffected by silicon enrichment of host plants

There is growing interest in using silicon (Si) for pest and disease management in cropping systems, notably in cereals which have the capacity to hyper-accumulate Si from the soil. Si-mediated pest resistance is thought to operate via physical and allelochemical mechanisms, but it is unclear whether phloem-feeders (e.g. aphids) are as adversely affected as chewing pests. To date, the role of Si in wheat (Triticum aestivum) against aphid pests has focussed almost exclusively on one species (Schizaphis graminum). We investigated the impacts of Si supplementation on plant growth and foliar chemistry (concentrations of carbon, nitrogen and Si) and associated changes in performance parameters of two global aphid pests (Rhopalosiphum maidis and Diuraphis noxia). In addition, we used electrical penetration graphs to determine how Si supplementation affected aphid feeding behaviour. Si supplementation increased foliar Si concentrations by 170% and decreased foliar C by c. 5%. Si impacts on aphid performance were only observed for D. noxia. Longevity and intrinsic rates of increase (rm) decreased by c. 8 days and were c. 13.5% lower, respectively, on Si-supplemented plants. The performance of R. maidis was unaffected by Si supplementation, and neither species was affected in terms of feeding behaviour. We conclude that Si enrichment of wheat is unlikely to be an effective pest control strategy for R. maidis and D. noxia. In reporting these findings, we aim to help identify patterns in Si-based crop resistance and inform future directions (e.g. alternative pest species) for research.