Background: The green peach aphid, Myzus persicae (Sulzer), is a world-wide insect pest capable of infesting more than 40 plant families, including many crop species. However, despite the significant damage inflicted by M. persicae in agricultural systems through direct feeding damage and by its ability to transmit plant viruses, limited genomic information is available for this species.

Clones of the peach-potato aphid, Myzus persicae (Sulzer), mostly from Scotland, UK were examined using an rDNA fingerprinting technique. Eighty patterns (genotypes) were found amongst the 276 clones. A large number of clones (30%) from all sample areas in Scotland exhibited the same simple pattern, suggesting the presence of a single M. persicae clone. There was no difference in genotype distributions between M. persicae collected from brassica or potato crops, suggesting that host-adapted genotypes have no advantage in the field. Different fingerprints were randomly distributed in the environment, although clones taken from the same leaf were more often the same fingerprint. Highly distinctive fingerprints, which were more widely distributed, suggest that this technique could be used to follow individual clones. In addition to the common clonal type, multiple fingerprint bands were found over successive years, implying that, in Scotland, local overwintering asexual populations are the most common source of M. persicae in the following year.

Abstract. 1. Phenotypic diversity is the fuel that powers evolution.2. Asexual organisms rely on mutation whereas sexual organisms combine mutation with recombination.3. Few organisms provide examples of species that are both sexual and asexual, but aphids do.4. To examine evolution on perceptible timescales requires strong evolutionary forces and, as Darwin noted, agricultural practices provide strong selection. In the case of aphids, insecticides provide a considerable force in the elimination of genotypes.5. Insecticide resistance in Myzus persicae (Sulzer) has arisen independently through point mutation and gene amplification on a number of occasions and at different times. Resistance to organophosphates, pyrethroids, and pirimicarb (a dimethyl carbamate) is now widespread.6. In this paper, we examine these three elements: sexual recombination, clonal expansion, and insecticide selection in the peach-potato aphid M. persicae in relation to the evolution of insecticide resistance and survival of the fittest clone.

Myzus persicae (Sulzer) collected in Scotland were characterized for four microsatellite loci, intergenic spacer fingerprints and the resistance mechanisms modified acetylcholinesterase (MACE), overproduced carboxylesterase and knockdown resistance (kdr). Microsatellite polymorphisms were used to define a limited number of clones that were either fully susceptible to insecticides or possessed characteristic combinations of resistance mechanisms. Within these clones, intergenic spacer fingerprints could either be very consistent or variable, with the latter indicating ongoing evolution within lineages, most likely derived from the same zygote. Two clones (termed A and B) possessed all three resistance mechanisms and predominated at sites treated with insecticides. Their appearance on seed potatoes and oilseed rape in Scotland in 2001 coincided with extensive insecticide use and severe control failures. Clones C, I and J, with no or fewer resistance mechanisms, were found in samples from 1995 and were dominant at untreated sites in 2001. A comparison of Scottish collections with those from other UK and non-UK sites provides insight into the likely origins, distribution and dynamics of M. persicae clones in a region where asexual (anholocyclic) reproduction predominates, but is vulnerable to migration by novel genotypes from areas of Europe where sexual (holocyclic) reproduction occurs.

1 The population of peach-potato aphid Myzus persicae in Scotland is comprised almost entirely of long-term asexual clones. 2 Over a ten year period, M. persicae from Scottish fields and suction traps were analysed with six microsatellite markers. 3 Out of 1497 individuals analysed, 14 clones (denoted A -N) comprised over 98% of the collection. 4 Some clones were particularly abundant but most clones had a widespread distribution on all available plants. 5 Clones E and L had distinct features in their distributions as clone L was geographically totally restricted to the north east of Scotland and clone E showed a marked preference for brassica crops. 6 Clones E and L provide direct evidence of a role for local adaptations in the distribution of M. persicae clones.

BackgroundGlobal commerce and human transportation are responsible for the range expansion of various insect pests such as the plant sucking aphids. High resolution DNA markers provide the opportunity to examine the genetic structure of aphid populations, identify aphid genotypes and infer their evolutionary history and routes of expansion which is of value in developing management strategies. One of the most widespread aphid species is the peach-potato aphid Myzus persicae, which is considered as a serious pest on various crops in many parts of the world. The present study examined the genetic variation of this aphid at a world scale and then related this to distribution patterns. In particular, 197 aphid parthenogenetic lineages from around the world were analysed with six microsatellite loci.ResultsBayesian clustering and admixture analysis split the aphid genotypes into three genetic clusters: European M. persicae persicae, New Zealand M. persicae persicae and Global M. persicae nicotianae. This partition was supported by FST and genetic distance analyses. The results showed two further points, a possible connection between genotypes found in the UK and New Zealand and globalization of nicotianae associated with colonisation of regions where tobacco is not cultivated. In addition, we report the presence of geographically widespread clones and for the first time the presence of a nicotianae genotype in the Old and New World. Lastly, heterozygote deficiency was detected in some sexual and asexual populations.ConclusionThe study revealed important genetic variation among the aphid populations we examined and this was partitioned according to region and host-plant. Clonal selection and gene flow between sexual and asexual lineages are important factors shaping the genetic structure of the aphid populations. In addition, the results reflected the globalization of two subspecies of M. persicae with successful clones being spread at various scales throughout the world. A subspecies appears to result from direct selection on tobacco plants. This information highlights the ultimate ability of a polyphagous aphid species to generate and maintain ecologically successful gene combinations through clonal propagation and the role of human transportation and global commerce for expanding their range.

Ribosomal DNA internal transcribed spacers of the eriophyid mites Cecidophyopsis ribis, C. selachodon, C. spicata, C. alpina, C. aurea, C. grossulariae and Phylocoptes gracillis were amplified using PCR, cloned and sequenced. Sequences for the ITS1 of Cecidophyopsids were 92-99% homologous. Cecidophyopsis inter-specific differences were found in seventeen simple sequence repeats (vSSRs), fourteen point mutations and two indels. No intra-specific variation in vSSRs was detected. A hypothetical structure for ITS1 was obtained and vSSRs were mapped onto this. Changes in vSSRs were compensated for by changes in complementary vSSRs or through multiple point mutations. A comparison with vSSRs of other arthropods suggested that the levels of intra-specific variation in Cecidophyopsis mites was less than in organisms which do not use arrhentoky for male determination.

Ribosomal DNA from Cecidophyopsis mites from different Ribes species was amplified using the polymerase chain reaction and the products digested using restriction enzymes. After separating the DNA fragments on gels, it was possible to identify specimens of mites obtained from field samples by comparing the profiles of their DNA banding patterns with those of known Cecidophyopsis species. Using this analysis, a non-gall forming mite found infesting blackcurrant buds in New Zealand was identified as the gooseberry mite (C. grossulariae). On wild red currant (Ribes spicatum) from Finland showing two sizes of galled buds, the red currant gall mite (C. selachodon) was identified in the larger galls located at the tips of branches and a distinct mite in the smaller galls located on the lower parts of the branches. A mite with a DNA banding profile indistinguishable from this latter mite from R. spicatum was also identified in galled buds of blackcurrant genotypes growing in Finland, including those containing the blackcurrant gall mite (C. ribis)-resistance genes P or Ce. The DNA banding profile of this mite resembled most closely that of C. ribis, but was distinct from it. The occurrence of C. grossulariae and this distinct Cecidophyopsis mite on blackcurrant has implications for the genetic control of Cecidophyopsis mites and possibly for the spread of the reversion disease agent in this crop. . 1974. Transference of resistance to blackcurrant gall mite, Cecidophyopsis ribis, from gooseberry to blackcurrant. Annals of Applied Biology 76: 123-130. Navajas M, Gutierrez J, Bonato 0, Bolland H R, Mapangou-Divassa S. 1994. Intraspecific diversity of the Cassava Green Mite Mononychellus progresivus (Acari: Tetranychidae) using comparisons of mitochondria1 and nuclear ribosomal DNA sequences and cross-breeding. Experimental and Applied Acarology 18:351-360. 20:139-168. Ribes. Euphytica 20:422-426. Horticulturae 9587-91. Nuts, pp. 457488. Eds J N Moore and J R Ballinger. Wageningen: ISNS Press. Westwood J 0. 1869a. Currant bud disease. Gardener's Chronicle 32:841. Westwood J 0. 18698. Black currant mite. Gardener's Chronicle 32:1016.