Despite the relative ease of isolating microsatellites, their development still requires substantial inputs of time, money and expertise. For this reason there is considerable interest in using existing microsatellites on species from which markers were not cloned. We tested cross‐species amplification of 48 existing aphid loci in species of the following genera: Aphidinae: Aphidini: Aphis and Rhopalosiphum; Aphidinae: Macrosiphini: Acyrthosiphum, Brevicoryne, Diuraphis, Illinoia, Macrosiphoniella, Macrosiphum, Metopeurum, Metapolophium, Myzus, Phorodon, Sitobion and Uroleucon and Neuquenaphidinae: Neuquenaphis. Our results show cross‐species application of known microsatellite loci is a highly promising source of codominant markers for population genetic and evolutionary studies in aphids.

Effective pest management is greatly facilitated by knowledge of the genetic structure and host adaptation of the pest species in question. The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) (Homoptera: Aphididae: Macrosiphini), is an important economic pest in many cereal-growing areas of the world, and in this study we investigated these aspects of its populations, using microsatellite markers and host plant response assays. Diuraphis noxia was sampled from 38 locations in Iran and genotyped at four polymorphic microsatellite loci that had been isolated from various Sitobion species. We identified 50 multilocus genotypes in 376 individuals. The overall observed heterozygosity was 0.134. F-statistics showed a regional partitioning in D. noxia populations with overall F ST = 0.231. In addition, there was a significant correlation between genetic and geographic distances. In order to test for the ecological consequences of genetic variability in D. noxia , biotypic variation amongst the isolates collected from wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) was evaluated on a number of resistant and susceptible wheat varieties. The plant variables we measured were damage rating (based on leaf chlorosis, leaf rolling, wilting, and death of the host plant), host plant dry weight, and root length. Damage rating was the best criterion for detecting biotypic variation in D. noxia . Discriminant analysis correctly classified the isolates in respective groups in 80 -91.8% of the cases. The barley isolate showed no differences in performance on resistant and susceptible wheat, indicating a lack of gene-by-gene relationship with wheat plants. In contrast, wheat isolates differentially damaged the resistant and susceptible plants and showed moderate to severe virulence.

The Russian wheat aphid, Diruaphis noxia (Kudjumov) (Hemiptera: Aphididae), is globally one of the most devastating pests of bread wheat, Tritium aestivum L., durum wheat, Triticum turgidum L., and barley, Hordeum vulgare L. Several sources of D. noxia resistance have been incorporated in commercial wheat and barley genotypes, but up to eight virulent biotypes, defined based on their ability to damage different wheat and barley genotypes, now occur across the western United States since the first appearance of D. noxia in North America in 1986. Critical to the study of D. noxia and other invasive species is an understanding of the number and origin of invasions that have occurred, as well as the rate or potential of postinvasion adaptation and geographic range expansion. The goal of this study was to determine whether D. noxia biotypes are by-products of a single invasion or multiple invasions into North America. We used the genome-wide technique of amplified fragment length polymorphisms, in combination with 22 collections of D. noxia from around the world, to assess this question, as well as patterns of genetic divergence. We found multiple lines of evidence that there have been at least two D. noxia invasions of different origin into North America, each resulting in subsequent postinvasion diversification that has since yielded multiple biotypes.

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