Persicae Clones Research Articles

P450-mediated resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae) reduces the efficacy of neonicotinoid seed treatments in Brassica napus.

The prophylactic use of seeds treated with neonicotinoid insecticides remains an important means of controlling aphid pests in canola (Brassica napus) crops in many countries. Yet, one of the most economically important aphid species worldwide, the peach potato aphid (Myzus persicae), has evolved mechanisms which confer resistance to neonicotinoids, including amplification of the cytochrome P450 gene, CYP6CY3. While CYP6CY3 amplification has been associated with low-level resistance to several neonicotinoids in laboratory acute toxicity bioassays, its impact on insecticide efficacy in the field remains unresolved. In this study, we investigated the impact of CYP6CY3 amplification on the ability of M. persicae to survive neonicotinoid exposure under laboratory and semi-field conditions. Three M. persicae clones, possessing different copy numbers of CYP6CY3, were shown to respond differently when exposed to the neonicotinoids, imidacloprid and thiamethoxam, in laboratory bioassays. Two clones, EastNaernup209 and Osborne171, displayed low levels of resistance (3-20-fold), which is consistent with previous studies. However, in a large-scale semi-field trial, both clones showed a surprising ability to survive and reproduce on B. napus seedlings grown from commercial rates of neonicotinoid-treated seed. In contrast, an insecticide-susceptible clone, of wild-type CYP6CY3 copy number, was unable to survive on seedlings treated in the same manner. Our findings suggest that amplification of CYP6CY3 in M. persicae clones substantially impairs the efficacy of neonicotinoid seed treatments when applied to B.napus. These findings highlight the potentially important real-world implications of resistances typically considered to be 'low level' as defined through laboratory bioassays. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Differential regulation of the Tor gene homolog drives the red/green pigmentation phenotype in the aphid Myzuspersicae

In some aphid species, intraspecific variation in body colour is caused by differential carotenoid content: whilst green aphids contain only yellow carotenoids (β-, γ-, and β,γ-carotenes), red aphids additionally possess red carotenoids (torulene and 3,4-didehydrolycopene). Unusually, within animals who typically obtain carotenoids from their diet, ancestral horizontal gene transfer of carotenoid biosynthetic genes from fungi (followed by gene duplication), have imbued aphids with the intrinsic gene repertoire necessary to biosynthesise carotenoids. In the pea aphid, Acyrthosiphon pisum a lycopene (phytoene) desaturase gene (Tor) underpins the red/green phenotype, with this locus present in heterozygous form in red individuals but absent in green aphids, resulting in them being unable to convert lycopene into the red compounds 3,4-didehydrolycopene and torulene. The green peach aphid, Myzus persicae, separated from the pea aphid for ≈45MY also exists as distinct colour variable morphs, with both red and green individuals present. Here, we examined genomic data for both red and green morphs of M. persicae and identified an enlarged (compared to A. pisum) repertoire of 16 carotenoid biosynthetic genes (11 carotenoid desaturases and five carotenoid cyclase/synthase genes). From these, we identify the homolog of A. pisum Tor (here called carotene desaturase 2 or CDE-2) and show through 3D modelling that this homolog can accommodate the torulene precursor lycopene and, through RNA knockdown feeding experiments, demonstrate that disabling CDE-2 expression in red M. persicae clones results in green-coloured offspring. Unlike in A. pisum, we show that functional CDE-2 is present in the genomes of both red and green aphids. However, expression differences between the two colour morphs (350–700 fold CDE-2 overexpression in red clones), potentially driven by variants identified in upstream putative regulatory elements, underpin this phenotype. Thus, whilst aphids have a common origin of their carotenoid biosynthetic pathway, two aphid species separated for over 40MY have evolved very different drivers of intraspecific colour variation.

Overexpression of UDP-glucuronosyltransferase and cytochrome P450 enzymes confers resistance to sulfoxaflor in field populations of the aphid, Myzus persicae

The green peach aphid, Myzus persicae, is a highly damaging, globally distributed crop pest that has evolved multiple resistance to numerous insecticides. It is thus imperative that insecticides that are not strongly compromised by pre-existing resistance are carefully managed to maximise their effective life span. Sulfoxaflor is a sulfoximine insecticide that retains efficacy against M. persicae clones that exhibit resistance to older insecticides. In the current study we monitored the efficacy of sulfoxaflor against M. persicae populations collected in Western Australia, following reports of control failures in this region. We identified clones with low (4-23-fold across multiple independent bioassay experiments), but significant, levels of resistance to sulfoxaflor compared with a reference susceptible clone. Furthermore, we demonstrate that sulfoxaflor resistance can persist after many months of culturing in the laboratory in the absence of insecticide exposure. Resistance was not conferred by known mechanisms of resistance to neonicotinoid insecticides, that act on the same target-site as sulfoxaflor, i.e. the R81T mutation or overexpresssion of the P450 gene CYP6CY3. Rather, transcriptome profiling of multiple resistant and susceptible clones identified the P450 CYP380C40 and the UDP-glucuronosyltransferase UGT344P2 as highly overexpressed (21-76-fold and 6-33-fold respectively) in the resistant clones. Transgenic expression of these genes demonstrated that they confer, low, but significant, levels of resistance to sulfoxaflor in vivo. Taken together, our data reveal the presence of low-level resistance to sulfoxaflor in M. persicae populations in Australia and uncover two novel mechanisms conferring resistance to this compound. The findings and tools generated in this study provide a platform for the development of strategies that aim to slow, prevent or overcome the evolution of more potent resistance to sulfoxaflor.

Comparative Analysis of Intra- and Inter-Specific Genomic Variability in the Peach Potato Aphid, Myzus persicae.

The availability of genomic data in the last decade relating to different aphid species has allowed the analysis of the genomic variability occurring among such species, whereas intra-specific variability has hitherto very largely been neglected. In order to analyse the intra-genomic variability in the peach potato aphid, Myzus persicae, comparative analyses were performed revealing several clone-specific gene duplications, together with numerous deletions/rearrangements. Our comparative approach also allowed us to evaluate the synteny existing between the two M. persicae clones tested and between the peach potato aphid and the pea aphid, Acyrthosiphon pisum. Even if part of the observed rearrangements are related to a low quality of some assembled contigs and/or to the high number of contigs present in these aphid genomes, our evidence reveals that aphid clones are genetically more different than expected. These results suggest that the choice of performing genomes sequencing combining different biotypes/populations, as revealed in the case of the soybean aphid, Aphis glycines, is unlikely to be very informative in aphids. Interestingly, it is possible that the holocentric nature of aphid chromosomes favours genome rearrangements that can be successively inherited transgenerationally via the aphid’s apomictic (parthenogenetic) mode of reproduction. Lastly, we evaluated the structure of the cluster of genes coding for the five histones (H1, H2A, H2B, H3 and H4) in order to better understand the quality of the two M. persicae genomes and thereby to improve our knowledge of this functionally important gene family.

Estimating costs of aphid resistance to parasitoids conferred by a protective strain of the bacterial endosymbiont Regiella insecticola

AbstractHeritable bacterial endosymbionts are common in aphids (Hemiptera: Aphididae), and they can influence ecologically important traits of their hosts. It is generally assumed that their persistence in a population is dependent on a balance between the costs and benefits they confer. A good example is Hamiltonella defensa Moran et al., a facultative symbiont that provides a benefit by strongly increasing aphid resistance to parasitoid wasps, but becomes costly to the host in the absence of parasitoids. Regiella insecticola Moran et al. is another common symbiont of aphids and generally does not influence resistance to parasitoids. In the green peach aphid, Myzus persicae (Sulzer), however, one strain (R5.15) was discovered that behaves like H. defensa in that it provides strong protection against parasitoid wasps. Here we compare R5.15‐infected and uninfected lines of three M. persicae clones to test whether this protective symbiont is costly as well, i.e., whether it has any negative effects on aphid life‐history traits. Furthermore, we transferred R5.15 to two other aphid species, the pea aphid, Acyrthosiphon pisum (Harris), and the black bean aphid, Aphis fabae Scopoli, where this strain is also protective against parasitoids and where we could compare its effects with those of additional, non‐protective strains of R. insecticola. Negative effects of R5.15 on host survival and lifetime reproduction were limited and frequently non‐significant, and these effects were comparable or in one case weaker than those of R. insecticola strains that are not protective against parasitoid wasps. Unless the benefit of protection is counteracted by detrimental effects on traits that were not considered in this study, R. insecticola strain R5.15 should have a high potential to spread in aphid populations.

Assessment of the Dominance Level of the R81T Target Resistance to Two Neonicotinoid Insecticides inMyzus persicae(Hemiptera: Aphididae)

Myzus persicae (Sulzer, 1776), a major crop pest worldwide, displays insecticide resistance to most molecules. The R81T substitution on the β1 subunit of nicotinic receptors of acetylcholine (nAChR) confers target site resistance to neonicotinoids and is widespread in aphid populations colonizing peach tree orchards in Southern Europe. But the impact of this resistance in the field, as well as ways to optimize its management, depends largely on the dominance level of the R81T mutation. In this study, we measured by in vitro assays the response of R81T mutation to two neonicotinoids (imidacloprid and thiacloprid) in 23 M. persicae clones with different resistance genotypes in order to assess the dominance status of this allele. In this study, all homozygous clones for the R81T mutation (genotype 81(TT)) showed a much higher level of resistance to both active substances than other clones. The heterozygous clones 81(RT) displayed a slightly higher level of resistance than wild homozygous, though resistance phenotypes against both neonicotinoids in these two genotypes were overlapping. A great variation of resistance level was found within these two latter clones' categories. The dominance level of insecticide resistance (DLC) strongly suggested that the mutant allele 81T is semirecessive (the wild 81R allele being rather dominant) for both insecticide molecules under test. Mean DLC values were 0.316 for imidacloprid and 0.351 for thiacloprid. Cross-resistance was shown between imidacloprid and thiacloprid. This partial recessivity is valuable information to broaden the knowledge on neonicotinoid resistance, a prerequisite for devising adapted management strategies against insecticide-resistant populations of M. persicae.

Continuous occurrence of intra-individual chromosome rearrangements in the peach potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

Analysis of the holocentric mitotic chromosomes of the peach-potato aphid, Myzus persicae (Sulzer), from clones labelled 50, 51 and 70 revealed different chromosome numbers, ranging from 12 to 14, even within each embryo, in contrast to the standard karyotype of this species (2n=12). Chromosome length measurements, combined with fluorescent in situ hybridization experiments, showed that the observed chromosomal mosaicisms are due to recurrent fragmentations of chromosomes X, 1 and 3. Contrary to what has generally been reported in the literature, X chromosomes were frequently involved in recurrent fragmentations, in particular at their telomeric ends opposite to the nucleolar organizer region. Supernumerary B chromosomes have been also observed in clones 50 and 51. The three aphid clones showed recurrent fissions of the same chromosomes in the same regions, thereby suggesting that the M. persicae genome has fragile sites that are at the basis of the observed changes in chromosome number. Experiments to induce males also revealed that M. persicae clones 50, 51 and 70 are obligately parthenogenetic, arguing that the reproduction by apomictic parthenogenesis favoured the stabilization and inheritance of the observed chromosomal fragments.

The vanishing clone: karyotypic evidence for extensive intraclonal genetic variation in the peach potato aphid, Myzus persicae (Hemiptera: Aphididae)

Analysis of holocentric mitotic metaphase chromosomes of the peach-potato aphid Myzus persicae (Sulzer) clone 33H revealed different chromosome numbers, ranging from 12 to 17 within each embryo, in contrast to the standard karyotype of this species (2n = 12). Chromosome length measurements revealed that the observed chromosomal mosaicism is the result of recurrent fragmentations of chromosomes X, 1 and 3 because of fragile sites or hot spots of recombination. Fluorescent in situ hybridization experiments showed that X chromosomes were frequently involved in recurrent fragmentations, in particular their telomeric end opposite to the nucleolar organizer region. Experiments to induce males showed that M. persicae clone 33H is obligately parthenogenetic. The reproduction by apomictic parthenogenesis, together with a high telomerase expression that stabilized the chromosomes involved in the fragmentations observed in the M. persicae clone 33H, appears to favour the stabilization of the observed chromosome instability. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 350–358.

Amplification of a Cytochrome P450 Gene Is Associated with Resistance to Neonicotinoid Insecticides in the Aphid Myzus persicae

The aphid Myzus persicae is a globally significant crop pest that has evolved high levels of resistance to almost all classes of insecticide. To date, the neonicotinoids, an economically important class of insecticides that target nicotinic acetylcholine receptors (nAChRs), have remained an effective control measure; however, recent reports of resistance in M. persicae represent a threat to the long-term efficacy of this chemical class. In this study, the mechanisms underlying resistance to the neonicotinoid insecticides were investigated using biological, biochemical, and genomic approaches. Bioassays on a resistant M. persicae clone (5191A) suggested that P450-mediated detoxification plays a primary role in resistance, although additional mechanism(s) may also contribute. Microarray analysis, using an array populated with probes corresponding to all known detoxification genes in M. persicae, revealed constitutive over-expression (22-fold) of a single P450 gene (CYP6CY3); and quantitative PCR showed that the over-expression is due, at least in part, to gene amplification. This is the first report of a P450 gene amplification event associated with insecticide resistance in an agriculturally important insect pest. The microarray analysis also showed over-expression of several gene sequences that encode cuticular proteins (2–16-fold), and artificial feeding assays and in vivo penetration assays using radiolabeled insecticide provided direct evidence of a role for reduced cuticular penetration in neonicotinoid resistance. Conversely, receptor radioligand binding studies and nucleotide sequencing of nAChR subunit genes suggest that target-site changes are unlikely to contribute to resistance to neonicotinoid insecticides in M. persicae.

Metabolic enzyme(s) confer imidacloprid resistance in a clone of Myzus persicae (Sulzer) (Hemiptera: Aphididae) from Greece

Previous studies have reported varying levels of resistance against imidacloprid in several insect species, including populations of the peach-potato aphid, Myzus persicae (Sulzer). These cases of resistance have been attributed to either target-site resistance or enhanced detoxification. In this study, a clone of M. persicae originating from Greece revealed a 60-fold resistance factor to imidacloprid. The Greek clone is compared in terms of metabolic enzyme activity and synergism profiles with other M. persicae clones showing lower imidacloprid resistance. A combination of in vitro biochemical assays and in vivo differential synergism studies using PBO and a close analogue EN 16/5-1 suggests that the mechanism conferring increased resistance in this clone is primarily due to enhanced oxidase activity.

Characterization of the M918T sodium channel gene mutation associated with strong resistance to pyrethroid insecticides in the peach-potato aphid, Myzus persicae (Sulzer)

Recent advances in the characterisation of insect sodium channel gene sequences have identified a small number of point mutations within the channel protein that are implicated in conferring target-site resistance to pyrethroid insecticides (so-called knockdown resistance or kdr). The L1014F (leucine-to-phenylalanine) mutation located in the centre of segment 6 of the domain II region (IIS6) of the sodium channel (the so-called kdr trait) has been detected in the peach-potato aphid, Myzus persicae (Sulzer), and is considered to be the primary cause of pyrethroid resistance in this species. Here we report on the characterisation of a second mutation, M918T (methione-to-threonine), within the nearby IIS4-S5 intracellular linker (the so-called super-kdr trait) in a field clone also possessing L1014F, with both mutations present in heterozygous form. The resistance phenotype of M. persicae clones possessing various combinations of L1014F and M918T to a wide range of pyrethroids (both Type I and II) was assessed in leaf-dip bioassays and to lambda-cyhalothrin applied at up to ten times the recommended field rate as foliar sprays to aphids feeding on whole plants. Bioassay results demonstrated that presence of both mutations was associated with extreme resistance to all the pyrethroids tested relative to aphids lacking the mutations. Furthermore, this resistance well exceeded that shown by aphids that were homozygous for L1014F but lacking M918T. However, pre-treatment with piperonyl butoxide in the leaf-dip bioassays failed to suppress pyrethroid resistance in aphids carrying one or both of the mutations. The relevance of these findings for monitoring and managing pyrethroid resistance in M. persicae populations in the field is discussed.

Behavioural side-effects of insecticide resistance in aphids increase their vulnerability to parasitoid attack

Previous studies using the aphid Myzus persicae have shown that strong heritable variability in a defence behaviour, response to aphid alarm pheromone, is consistently associated with the possession of two insecticide resistance mechanisms. Insecticide-susceptible and -resistant aphids therefore provide the ideal biological material for testing the hypothesis that interactions with the third trophic level (parasitoids) can play a significant inhibitory role in the evolution of adaptive traits at the second trophic level (aphids), based on a fitness trade-off between resistance to insecticides and avoidance of parasitism through defence behaviour. Eight parthenogenetic M. persicae clones, representing different insecticide resistance genotypes, were exposed to alarm pheromone to confirm their level of response. Observations of these clones during periods of exposure to adult female parasitoids, Diaeretiella rapae, were then made in small-scale arenas in the presence and absence of measured amounts of alarm pheromone. Clones showing a consistently high alarm response (insecticide-susceptible forms) displayed a range of behaviours during and after parasitoid attack that were significantly associated with greater survival (avoidance of parasitism) compared with aphids showing a low alarm response (insecticide-resistant forms). Furthermore, this culminated in the latter suffering significantly higher levels of mummification. These data not only provide important empirical evidence that a normal (wild-type) high aphid alarm response reduces vulnerability to parasitoid attack but also represent the first example of insecticide resistance genes having negative pleiotropic effects on fitness by producing maladaptive behaviours in the context of selection imposed by a higher trophic level.

Insecticide resistance and genetic composition of Myzus persicae (Hemiptera: Aphididae) on field potatoes in New Zealand

The prevalence of insecticide resistance mechanisms in populations of Myzus persicae on potatoes in New Zealand was determined in five parthenogenetic aphid lineages raised from individuals collected from Pukekohe in the North Island, and 66 from Canterbury and one from the West Coast in the South Island during mid-summer (January) to early autumn (March) 2005. For each lineage, the genotypes, determined using four microsatellite loci, were compared with the presence or absence of resistance mechanisms assessed using a combination of biochemical tests, polymerase chain reaction-based allelic discrimination and diagnostic dose bioassays. The 72 lineages comprised 23 genotypes (defined using microsatellite markers), with 60% containing one or more mechanisms that confer resistance to between one and three of any of four insecticide classes. In all, 38% contained high or extreme elevated carboxylesterases (E-Carb-R 2 and -R 3) that confer resistance primarily to organophosphates, and some resistance to carbamates and pyrethroids; 19% contained modified acetylcholinesterase (MACE) that gives strong resistance to the di-methyl carbamates, pirimicarb and triazamate; 54% contained a mutation in a voltage-gated sodium channel gene, called knockdown resistance (kdr), that confers resistance to pyrethroids; and 36% contained a second mutation of the gene (super-kdr) that gives enhanced resistance to pyrethroids. In all, 10% of the lineages also showed low-level resistance to neonicotinoids, as shown in imidacloprid diagnostic dose bioassays. Most of the microsatellite genotypes appeared to disclose cycles of sexual reproduction, the clones of which were susceptible to all classes of insecticide chemistry, except two that had acquired MACE possibly by breeding with an invasive MACE genotype or an individual carrying a locally derived MACE mutation. However, lineages carrying multiple resistance mechanisms belonged to two resistant genotypes that formed widely distributed clones. Behavioural bioassays on selected lineages from New Zealand and Europe showed that M. persicae clones from both regions carried E-Carb R 3, or kdr/s-kdr, and showed consistently low responses to the aphid alarm pheromone ( E)- β-farnesene. Methods are discussed for exploiting such putative fitness costs of resistance traits in M. persicae aphids to minimise the development of resistance and restore efficacy to insecticide programmes.

Phloem Alkaloid Tolerance Allows Feeding on Resistant Lupinus angustifolius by the Aphid Myzus persicae

We examined the hypothesis that the polyphagous green peach aphid (Myzus persicae) shows clone-specific adaptation to the narrow-leafed lupin (Lupinus angustifolius) containing toxic quinolizidine alkaloids. We compared the performance of a lupin-feeding clone of M. persicae from Western Australia to that of nine clones of the same species collected from eastern Australian locations, where narrow-leafed lupins rarely occur. Mean relative growth rate (MRGR) and colonization ability varied among the M. persicae clones on one aphid-susceptible and two aphid-resistant lupin varieties. The performance of the lupin-feeding clone was better than that of all other clones on the resistant narrow-leafed lupin varieties "Tanjil" and "Kalya", indicating that successful lupin feeding is not a characteristic of the species. Gas chromatography-mass spectrometry analyses (GC-MS) of phloem from the different lupin varieties detected differences in the quantities of two alkaloid compounds identified as 13-OH-lupanine and lupanine. The lupin-feeding M. persicae clone also showed better performance on artificial diet amended with lupanine. The results suggest that the M. persicae clone collected from Western Australia is adapted to feed successfully on narrow-leafed lupin, and that this adaptation may involve improved tolerance of lupanine in its diet.

The attack of the clones: tracking the movement of insecticide-resistant peach–potato aphids Myzus persicae (Hemiptera: Aphididae)

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.

Resistência de genótipos de batata ao pulgão

Avaliou-se a resistência (e antibiose) de genótipos de batata, comerciais e em fase de melhoramento, ao pulgão Myzus persicae, em ensaios efetuados com plantas em vasos, sem chance de escolha, em Jaboticabal (SP). Foram efetuados seis experimentos, utilizando-se um total de 16 genótipos, a saber: 'Achat', 'Apuã', 'Aracy', 'Aracy Ruiva', 'Bintje', 'Ibitu Açu', 'Itararé', 'N 140-201', 'NYL 235-4', '288.719-13', '288.764-26', '288.776-3', '288.776-6', '288.794-19', '288.801-6' e '288.814-7'. Em cada experimento foram utilizadas combinações variadas dos mesmos. Nos dois primeiros experimentos as plantas foram infestadas com 30 pulgões adultos por planta, distribuídos em três folhas, com três avaliações realizadas em semanas subseqüentes à infestação, contando-se o número de indivíduos por planta. O terceiro experimento foi conduzido aprisionando-se duas fêmeas adultas no interior de pequenas gaiolas fixadas na face abaxial dos folíolos, em número de dez por planta, avaliando-se a reprodução do pulgão após sete dias, em dois plantios. No quarto experimento efetuou-se a infestação da planta com 15 pulgões, avaliando-se o crescimento da população na planta toda durante três semanas consecutivas. No quinto experimento foi avaliada a descendência de uma única fêmea adulta por folíolo e no sexto experimento avaliou-se o peso dos pulgões aos sete dias de vida. Os tricomas glandulares presentes nos folíolos e a funcionalidade dos mesmos também foram avaliados. A cultivar 'Ibitu Açu' apresentou elevado grau de antibiose a M. persicae; os genótipos '288.776-3' e '288.794-19' também apresentaram esse tipo de resistência, em grau moderado; '288.719-13' e '288.764-26' foram resistentes ao pulgão, provavelmente devido à presença de tricomas glandulares funcionais, dos tipos A e B, em seus folíolos (antixenose); entre os mais suscetíveis destacaram-se 'Bintje' e '288.801-6'.

Rack-1, GAPDH3, and actin: proteins of Myzus persicae potentially involved in the transcytosis of beet western yellows virus particles in the aphid

Beet western yellows virus (BWYV) is a Polerovirus that relies on the aphid Myzus persicae for its transmission, in a persistent-circulative mode. To be transmitted, the virus must cross the midgut and the accessory salivary glands (ASG) epithelial barriers in a transcytosis mechanism where vector receptors interact with virions. In this paper, we report in vitro interaction experiments between BWYV and aphid components. Using the M. persicae clone from Colmar, we showed that a set of aphid polypeptides, separated by SDS-PAGE or 2D electrophoresis (2DE), can bind in vitro to purified wild type or mutant particles. Using subcellular fractionation, we showed that the 65-kDa polypeptide identified as symbionin is a soluble protein whereas the other polypeptides seem to be associated more or less strongly to the membrane. We hypothesize that three polypeptides, identified by mass spectrometry as Rack-1, GAPDH3, and actin, may be involved in the epithelial transcytosis of virus particles in the aphid vector.

Performance of Myzus persicae (Hemiptera: Aphididae) clones on different host-plants and their host preference.

The performance of eighteen clones of Myzus persicae (Sulzer) on pepper and tobacco plants at 20 degrees C and L16:D8 and the choice of young adult apterae between tobacco and pepper leaf-discs were examined. The clones were collected from weeds and peach in two tobacco-growing regions: Katerini, northern Greece and Karditsa, central Greece (only from weeds) and from Lehonia, central eastern Greece where tobacco is not cultivated. All clones did well on both hosts. However, the analysis of data revealed a significant effect of "region / host plant origin" on aphid performance. The mean values of adult weight, intrinsic rate of increase and fecundity of the clones collected in Lehonia and reared on tobacco were significantly lower than the observed values for clones from Katerini and Karditsa. Aphids from Lehonia had significantly higher mean values for developmental time on tobacco than clones from the other regions whereas the opposite was observed when aphids were reared on pepper. Aphids collected in Lehonia performed better on pepper than those originating from the tobacco-growing regions. A choice test revealed differences among the clones originating from different regions. Fifty three percent and 43% of aphids from weeds and peach from Lehonia, respectively, chose pepper. By comparison 41.5% and 40.0% of aphids from peach and weeds from Katerini, respectively and 49.5% of aphids from Karditsa preferred tobacco. The results are discussed in relation to host specialization in M. persicae.

Bioassay and field-simulator studies of the efficacy of pymetrozine against peach-potato aphids, Myzus persicae (Hemiptera: Aphididae), possessing different mechanisms of insecticide resistance.

Twenty-one clones of the peach-potato aphid, Myzus persicae (Sulzer), carrying various combinations of known mechanisms of insecticide resistance were assessed for their response to the new pyridine azomethine compound, pymetrozine, in leaf-dip bioassays. Pymetrozine was also applied as a foliar spray to populations of four different UK M persicae clones on potato plants in field-simulator chambers. Neither study showed any evidence of cross-resistance to this compound. Pymetrozine, used in conjunction with other effective aphicides, such as pirimicarb and imidacloprid, can therefore play an important role in insecticide resistance-management strategies for M persicae.

Analysis of clonal diversity of the peach-potato aphid, Myzus persicae (Sulzer), in Scotland, UK and evidence for the existence of a predominant clone.

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.