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.

In order to develop biological control of aphids by a “push-pull” approach, intercropping using repellent emitting plants was developed in different crop and associated plant models. Garlic is one of the potential plant that could be inserted in crops to decrease the pest occurrence in neighboring crop plots. In this study, field works were conducted in wheat fields in Langfang Experimental Station, Hebei Province in China from October 2009 to July 2010 during wheat developmental season. The effect of wheat intercropping with garlic but also the volatiles emission on the incidence of the English grain aphid, Sitobion avenae Fabricius (Homoptera: Aphididae) was assessed. Natural beneficial occurrence and global yields in two winter wheat varieties that were susceptible or resistant to cereal aphid were also determined comparing to control plots without the use of garlic plant intercrop nor semiochemical releaser in the fields. S. avenae was found to be lower in garlic oil blend treatment (GOB), diallyl disulfide treatment (DD) and wheat-garlic intercropping treatment (WGI) when compared to the control plots for both two varieties (P<0.01). Both intercropping and application of volatile chemicals emitted by garlic could improve the population densities of natural enemies of cereal aphid, including ladybeetles and mummified aphids. Ladybeetle population density in WGI, GOB and mummified aphids densities in WGI, DD were significantly higher than those in control fields for both two varieties (P<0.05). There were significant interactions between cultivars and treatments to the population densities of S. avenae. The 1 000-grain weight and yield of wheat were also increased compared to the control. Due to their potential alternatives as a biological control agent against cereal aphid, garlic intercropping and related emitted volatiles are expected to contribute to the further improvement of integrated pest management systems and to potentially reduce the amount of traditional synthetic pesticides applied in wheat fields.

In order to characterize the genetic relationship of the geographic populations of Sitobion avenae (Hemiptera: Aphididae)in China, a 588 bp region of the mitochondrial cytochrome oxidase subunit I (mtDNA-COI) gene was sequenced andanalyzed among the different geographic populations. 269 individuals were collected from 17 localities in different wheatgrowingareas in China that covered most of the range reported for this species. Within the sequence among thesegeographic populations, 15 polymorphic sites defined 16 distinct haplotypes, ranging in sequence divergence from 0.2%(one nucleotide) to 1.7% (10 nucleotides). Of the 15 variable sites, 12 were transitional substitutions, 2 were transversionalsubstitutions and 1 was transitional and transversional substitution. Phylogenetic analysis showed that all haplotypeswere highly interconnected with each other, in absence of phylogeographic structing. Each of 8 haplotypes was foundonly at one locality, and the other haplotypes were the widespread distributed in the different localities. The highergenetic diversity was found in the northern China populations than that in the southern China populations. The lowgenetic differentiation (FST=-0.06945-0.69857) and high migration rate (Nm=0.21575-infinite) of Chinese populations suggestthat dispersal over long distance is a major factor in the demography of S. avenae.