Seasonal genetic structure in Beijing populations of the grain aphid Sitobion miscanthi (Takahashi): An investigation using microsatellites

Abstract

The grain aphid Sitobion miscanthi (Takahashi) is a major pest of cereal crops in China. Sexual reproduction is rarely found in this species, and the reproductive strategy is expected to be reflected in the population genetic structure. Using five microsatellites, we analyzed four populations of S. miscanthi sampled during the 2005-2006 wheat season (from October to May) from a Beijing suburb. Substantial allelic diversity was found, with an average 9.8 alleles per locus, but there were only 45 five-locus genotypes detected among the 143 aphid samples. Of the six commonest five-locus genotypes, four were found in all the seasonal populations, and must have reproduced by continuous parthenogenesis through the seasons (including a winter) because of the big differences between their observed and expected frequencies. All populations showed extremely high heterozygosity and heterozygosity excesses, and significantly deviated from Hardy-Weinberg equilibrium even in data sets including one individual per genotype. Those genetic features occur because S. miscanthi is almost anholocyclic. The population collected immediately after the winter significantly differentiated from the other three populations collected earlier or later (FST=0.059-0.064), while differentiations among the other three populations were not significant (FST=-0.016--0.004). The probable causes of this seasonal variation were discussed.