Bioenergy Crops and Natural Enemies: Host Plant-Mediated Effects of Miscanthus on the Aphid Parasitoid Lysiphlebus testaceipes

Miscanthus spp. are biofuel crops that are triggering growing interest worldwide due to their numerous agronomic advantages. Though breeding programs take into account usual key plant traits of agronomic interest (e.g., biomass production, adaptation to broader climatic range), they generally overlook plant attributes relating to pest and pathogen resistance and even more those that may favor or improve the combined use of biological control agents of pests. A recent study showed that the parental species, Miscanthus sacchariflorus and, to a lesser extent, Miscanthus sinensis, were less suitable and acceptable host plants for the corn leaf aphid Rhopalosiphum maidis, one of the main pests of Miscanthus × giganteus in the USA, than the hybrid M. × giganteus. In the present laboratory study, we investigated the host plant-mediated effects of these three miscanthus species on various life history traits of the aphid parasitoid Lysiphlebus testaceipes. A clear host plant effect was shown on aphid size and, consequently, on parasitoid fitness parameters. High plant resistance to aphids was shown to be more detrimental to the parasitoid than partial resistance, with M. sacchariflorus being the least suitable host plant to both aphid and parasitoid development. Selection of partial resistance, such as the one exhibited by M. sinensis, should then be preferred to support efficient aphid regulation by parasitoids. This study provides the first contribution to the evaluation of bottom-up effects of a biofuel crop on beneficial insects. It also underlines the need to conduct additional research when considering the implementation of new biomass crops.