The wheat aphid, Sitobion miscanthi, is one of the most destructive pests of wheat plants in the temperate regions of China.  Little is known about the genetic structure evolution of  the different geographic populations of S. miscanthi with its migration.  In this study, we investigated the population genetic structure and demographic history of S. miscanthi by analysing 18 geographical populations across China using one mitochondrial gene, COI; one nuclear gene, EF-1α; and two endosymbiont Buchnera genes, gnd and trpA.  Analysis of data from the various groups showed high haplotype diversity and low nucleotide variation.  SAMOVA analysis did not find a correlation between genetic distance and geographic distance.  However, areas with high population diversity exhibited high haplotype diversity.  Therefore, we speculate that there are two main natural migration pathways of S. miscanthi in China.  One is from Yunnan to the Sichuan Basin, and the other is from Wuhan, Xinyang and Jiaodong Peninsula areas to the northwest.  Based on this hypothesis, we inferred that these aphid populations appear first in the southwestern and southern regions and spread to the north with the help of the southeastern and southwestern monsoons, which occur in spring and summer.  In autumn, the aphids spread southward with the northeastern and northwestern monsoons.

Cereal aphids are major insect pests of wheat, which cause significant damages to wheat production.  Previous studies mainly focused on the resistance of different wheat varieties to one specific aphid species.  However, reports on the physiology and defense responses of wheat to different cereal aphids are basically lacking.  In this work, we studied the feeding behavior of three cereal aphids: the grain aphid, Sitobion avenae (Fabricius), the greenbugs, Schizaphis graminum (Rondani), and the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) on winter wheat, and the physiology and defense responses of wheat to the infestation of these cereal aphids with focus on how these cereal aphids utilize divergent strategies to optimize their nutrition requirement from wheat leaves.  Our results indicated that S. graminum and R. padi were better adapted to penetrating phloem tissue and to collect more nutrition than S. avenae.  The harm on wheat physiology committed by S. graminum and R. padi was severer than that by S. avenae, through reducing chlorophyll concentration and interfering metabolism genes.  Furthermore, cereal aphids manipulated the plant nutrition metabolism by increasing the relative concentration of major amino acids and percentage of essential amino acids.  In addition, different cereal aphids triggered specific defense response in wheat.  All of these results suggested that different cereal aphids utilize divergent strategies to change the physiological and defense responses of their host plants in order to optimize their nutrition absorption and requirement.  These findings not only extend our current knowledge on the insect–plant interactions but also provide useful clues to develop novel biotechnological strategies for enhancing the resistance and tolerance of crop plants against phloem-feeding insects.