Genetic diversity and association with bacterial endosymbionts influence phenotype in two important cereal aphid species

Aphids are important pests of cereal crops and cause economically significant damage through direct feeding and the transmission of plant viruses. In Europe, the aphid species of greatest concern are the grain aphid <i>(Sitobion avenae</i> Fabricius) and the bird cherry-oat aphid, (<i>Rhopalosiphum padi</i> Linnaeus). Often, cereal crops are dominated by a small number of prolific clonal populations and these populations can differ in phenotypic traits of agricultural importance. There are two heritable factors that influence aphid phenotype: aphid genetic diversity and the presence of endosymbionts.Here, multiple cereal aphid populations are used to determine how heritable factors influence aphid phenotype. Several agriculturally important phenotypic traits are examined, and both endosymbiont- and genotype-derived phenotypes are identified. For <i>S. avenae</i>, aphid genotype influences all phenotypic traits assessed, and association with the facultative endosymbiont <i>Regiella insecticola</i> influences alate morph production with co-infection of <i>R. insecticola</i> and <i>Fukatsuia symbiotica</i> increasing reproductive output. For <i>R. padi</i>, adult aphid morph (apterous or alate) is the key driver behind reproductive output, with a genotype × morph effect also found to influence development time.Overall, these results provide insight into the biological drivers behind phenotypic diversity in agriculturally important aphid species. Being able to associate heritable factors with key phenotypes can generate biological insights into the processes underpinning the dominance of specific aphid clones and can be used to develop pest and disease management strategies based around the phenotypic risk of the aphid populations present.