Spatial And Temporal Genetic Variability In Chinese Populations Of The Grain Aphid Macrosiphum Miscanthi (Takahashi)

Macrosiphum miscanthi (Takahashi) (Homoptera: Aphididae), widespread throughout the country, is one of the most common and destructive pests attacking the wheat. Colonies of the aphid not only feed upon the wheat leaves, but also transmit the barley yellow dwarf virus (BYDV) to some small crops. In addition, the long-distance migration of the aphids would cause the crop's damage extension and virus disease spreading. Here we used microsatellite markers and geographic information system (GIS) to discuss migration and population genetics of the grain aphid in relation to the geographic distance and gene flow.Samples of the grain aphid collected from 15 locations in China have been examined at 5 polymorphic microsatellite loci. Overall, genetic diversity displays a relation between the migration and gene flow in the grain aphid: a free and frequent gene flow is found in the eastern populations, and gene isolation occurs in the two western populations, especially Datong population and Guiyang population. The natural barriers may present an insurmountable obstacle preventing gene flow and aphid migration. However, a spatial genetic differentiation between populations is correlated with their geographical separation, indicating the geographic differentiation may play an important role in shaping the genetic structure of M. miscanthi populations. In addition, it seems that the long distance migration of the grain aphid may enhance gene flow and decrease genetic differentiation among different populations.Wolbachia, found in reproductive tissues of arthropods, are transmitted through the cytoplasm of eggs and have evolved various mechanisms for manipulating reproduction of their hosts. Based on the amplification of part of wsp gene encoding the outer membrane protein of Wolbachia, the presence of Wolbachia has been successfully detected in the grain aphid M. miscanthi. Moreover, it is shown that Wolbachia infection rates in different populations of the grain aphid have been obvious dissimilarity. After molecular identification of wsp gene, some factors contributing to this uncongnience are discussed here.Based on VC++ developing platform, we developed Aphid GIS system with many functions such as editing, querying, analysis of space data and attribute data, etc. and using the MapX control as the graphical platform. Anyway geographic differentiation and environment factors (e.g. altitudes, longitude and relative humidity) seem the most adequate explanation for spatial genetic structure of the aphid. Further studies are necessary to clarify the genetic background of M. miscanthi to find genetics correlated with abiotic (e.g. climate and topography) and biotic (e.g. life-cycle) factors by analyzing more populations at more loci for more information. We hope these results could be useful in modeling and forecasting outbreaks of grain aphid and in designing rational control strategies.