Genetic variation in target-site resistance to pyrethroids and pirimicarb in Tunisian populations of the peach potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae).

BACKGROUND: We used molecular assays to diagnose resistance to pyrethroids and pirimicarb in samples of Myzus persicae from field crops or an insect suction trap in Tunisia. Genotypes for resistance loci were related to ones for polymorphic microsatellite loci in order to investigate breeding systems and patterns of genetic diversity, and to inform resistance management tactics. RESULTS: The kdr mutation L1014F conferring pyrethroid resistance was found in all samples. The M918T s-kdr mutation also occurred in most samples, but only in conjunction with kdr. We discovered a previously unreported genotype heterozygous for L1014F but homozygous for M918T. Samples with modified acetylcholinesterase (MACE) conferring resistance to pirimicarb were less common but widespread. 16% of samples contained both the kdr and MACE mutations. Many unique microsatellite genotypes were found, suggesting that M. persicae is holocyclic in Tunisia. There were no consistent associations between resistance and microsatellite markers. CONCLUSION: This first study of insecticide resistance in M. persicae in North Africa showed genetic variation in insecticide resistance within microsatellite multilocus genotypes (MLGM s) and the same resistance mechanisms to be present in different MLGM s. This contrasts with variation in northern Europe where M. persicae is fully anholocyclic. Implications for selection and control strategies are discussed. © 2016 Society of Chemical Industry.

Insecticide resistance status of Myzus persicae in Greece: long-term surveys and new diagnostics for resistance mechanisms.

BACKGROUND: Myzus persicae nicotianae is an important pest in Greece, controlled mainly by neonicotinoids. Monitoring of the aphid populations for resistance mechanisms is essential for effective control. RESULTS: Two new RFLP-based diagnostics for the detection of the M918T (super-kdr pyrethroid resistance) and nAChR R81T (neonicotinoid resistance) mutations were applied, along with other established assays, on 131 nicotianae multilocus genotypes (MLGs) collected from tobacco and peach in Greece in 2012-2013. Furthermore, we present resistance data from aphid clones (>500, mainly nicotianae) collected in 2006-2007. About half of the clones tested with a diagnostic dose of imidacloprid were tolerant. The R81T mutation was not found in the 131 MLGs and 152 clones examined. Over half (58.6%) of a subset of 29 clones showed a 9-36-fold overexpression of CYP6CY3. M918T was found at low to moderate frequencies. The kdr and MACE mechanisms and carboxylesterase-based resistance were found at high frequency in all years. CONCLUSION: The aphid retains costly resistance mechanisms even in the absence of pressure from certain insecticides, which could be attributed to factors related to climate and genetic properties of the populations. The indication of build-up of resistance/tolerance to neonicotinoids, related to CYP6CY3 overexpression, is a matter of concern. © 2015 Society of Chemical Industry.

Stopped in its tracks: how λ-cyhalothrin can break the aphid transmission of a potato potyvirus.

BACKGROUND: Pyrethroids are one of the most widespread and commonly used classes of insecticide and are used in multiple roles, including protecting potato crops from virus vector aphids. Resistance in some genotypes of a few species is now widespread, but most species remain susceptible. The rate of virus transmission by two genotypes of the peach potato aphid, Myzus persicae, fed on potato virus Y (PVY)-infected leaves of potato treated with the pyrethroid λ-cyhalothrin was evaluated. RESULTS: The susceptible genotype, type J, was significantly inhibited from transmitting virus to uninfected seedlings. A genotype containing the M918L super knockdown resistance mutation conferring resistance to pyrethroids, type O, showed no inhibition of transmission. However, when survival of the aphids after exposure was compared, the pyrethroid had not killed the type J aphids. CONCLUSIONS: λ-Cyhalothrin in a commercial formulation disrupts PVY transmission by disorienting aphid vectors for a sufficient time for the virus to lose its transmissibility. However, M. persicae genotypes carrying the M918L mutation are not prevented from transmitting.

Vitamin C and the abscisic acid-insensitive 4 transcription factor are important determinants of aphid resistance in Arabidopsis.

AIMS: Aphids, like other insects, are probably unable to synthesize vitamin C (ascorbic acid), which is therefore an essential dietary nutrient that has to be obtained from the host plant. Plant responses to aphids involve hormones such as salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA), but hormone/redox interactions remain poorly characterized. We therefore investigated hormone/redox signaling in the response of Arabidopsis thaliana to infestation by the aphid Myzus persicae, focusing on the interactions between ascorbic acid and ABA, together with the influence of altered ascorbate and ABA signaling on the SA- and JA-dependent pathways. RESULTS: Whole-genome microarray analysis revealed highly dynamic transcriptional responses to aphid infestation with extensive differences between transcript profiles of infested and systemic leaves, revealing aphid-dependent effects on the suites of transcripts involved in the redox, SA, and ABA responses. Central roles for ascorbate, ABA-insensitive 4 (ABI4), and oxidative signal-inducible 1 in plant resistance to aphids were demonstrated by altered fecundity on respective mutants. However, ABA had a negative effect on aphid resistance, as did ABI4 or redox-responsive transcription factor 1. The decrease in aphid fecundity observed in mutants defective in ascorbate accumulation (vtc2) was absent from abi4vtc2 double mutants that are also deficient in ABA signaling (abi4). Aphid-dependent transcriptome responses reveal a role for ascorbate-regulated receptor-like kinases in plant defenses against aphids. INNOVATION: Vitamin C deficiency enhances plant resistance to aphids through redox signaling pathways rather than dietary requirements. CONCLUSION: ABI4 is a linchpin of redox regulation of the innate immune response to aphids.

Insecticide resistance profiles can be misleading in predicting the survival of Myzus persicae genotypes on potato crops following the application of different insecticide classes.

BACKGROUND: The accuracy of predicting the survival of insecticide-resistant aphids following the application of commonly used insecticides from the carbamate, the pyrethroid, a mix of the two or the neonicotinoid chemical classes was evaluated in a potato field in Scotland. Equal proportions of five genotypes of the peach-potato aphid, Myzus persicae (Sulzer), with none, resistance to dimethyl-carbamates, resistance to pyrethroids or combinations conferring resistance to both chemical classes were released into potato field plots. The insecticides were sprayed separately onto these plots, the aphid populations were analysed after 6-8 days and the process repeated. RESULTS: For each assessment after the three separate spray events, plots treated with the carbamate had 48, 147 and 28%, those treated with pyrethroid 53, 210 and 89%, those treated with carbamate/pyrethroid 28, 108 and 64% and those treated with neonicotinoid 43, 55 and 11% of the numbers of M. persicae by comparison with untreated controls. Only the proportions of surviving aphids from the genotype containing no insecticide resistance traits and the genotype containing elevated carboxylesterases matched ratios predicted from the selective advantage afforded by the resistance traits alone. Survival of aphids from the other three genotypes that carried 1-3 of the insecticide resistance traits differed from expectations in all cases, possibly owing to physiological differences, including their vulnerability to predators and hymenopterous parasitoids present at the site and/or their carrying unknown insecticide resistance mechanisms. CONCLUSION: Control strategies based on knowledge of the genetically determined insecticide resistance profile of an M. persicae population alone are insufficient. Hence, other important factors contributing to aphid survival under insecticide pressure need to be considered.

Plant responses to insect herbivory: interactions between photosynthesis, reactive oxygen species and hormonal signalling pathways.

Under herbivore attack plants mount a defence response characterized by the accumulation of secondary metabolites and inhibitory proteins. Significant changes are observed in the transcriptional profiles of genes encoding enzymes of primary metabolism. Such changes have often been interpreted in terms of a requirement for an increased investment of resources to 'fuel' the synthesis of secondary metabolites. While enhanced secondary metabolism undoubtedly exerts an influence on primary metabolism, accumulating evidence suggests that rather than stimulating photosynthesis insect herbivory reduces photosynthetic carbon fixation and this response occurs by a re-programming of gene expression. Within this context, reactive oxygen species (ROS) and reductant/oxidant (redox) signalling play a central role. Accumulating evidence suggests that ROS signalling pathways are closely interwoven with hormone-signalling pathways in plant-insect interactions. Here we consider how insect infestation impacts on the stress signalling network through effects on ROS and cellular redox metabolism with particular emphasis on the roles of ROS in the plant responses to phloem-feeding insects.

Infestation of potato (Solanum tuberosum L.) by the peach-potato aphid (Myzus persicae Sulzer) alters cellular redox status and is influenced by ascorbate.

The peach-potato aphid (Myzus persicae Sulzer) is a major pest of potato (Solanum tuberosum L.) but the molecular characterization of this interaction particularly with regard to oxidants and antioxidants remains to be undertaken. Aphid colonies reared on potato leaves containing high ascorbate were twice the size of those grown on leaves with low ascorbate. Infestation-dependent decreases in the abundance of key transcripts such as chloroplastic FeSOD, peroxisomal catalase 2, PR1 and JAZ1 preceded detectable leaf H(2)O(2) or polyphenol accumulation. The leaf glutathione pool was increased 48 h after infestation, but the amount of ascorbate was unchanged. The ascorbate/dehydroacorbate (DHA) ratio was lower at 48 h but the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) was unchanged. While DHA reductase and GSSG reductase activities were unaffected by aphid feeding, non-specific peroxidase activities were enhanced 48 h following aphid infestation. Brown ethanol-insoluble deposits were observed close to leaf veins following aphid infestation. Taken together, the results demonstrate that high ascorbate favours aphid colony expansion and that perturbations in the leaf antioxidant system are intrinsic to the potato leaf response to aphids. Moreover, these changes together with the induction of hormone-related transcripts precede the deposition of defence-associated oxidized polyphenols along the stylet track.

Tracking the global dispersal of a cosmopolitan insect pest, the peach potato aphid.

BACKGROUND: Global 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. RESULTS: Bayesian 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. CONCLUSION: The 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.

Genomic resources for Myzus persicae: EST sequencing, SNP identification, and microarray design.

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. RESULTS: Sequencing of 16 M. persicae cDNA libraries generated 26,669 expressed sequence tags (ESTs). Aphids for library construction were raised on Arabidopsis thaliana, Nicotiana benthamiana, Brassica oleracea, B. napus, and Physalis floridana (with and without Potato leafroll virus infection). The M. persicae cDNA libraries include ones made from sexual and asexual whole aphids, guts, heads, and salivary glands. In silico comparison of cDNA libraries identified aphid genes with tissue-specific expression patterns, and gene expression that is induced by feeding on Nicotiana benthamiana. Furthermore, 2423 genes that are novel to science and potentially aphid-specific were identified. Comparison of cDNA data from three aphid lineages identified single nucleotide polymorphisms that can be used as genetic markers and, in some cases, may represent functional differences in the protein products. In particular, non-conservative amino acid substitutions in a highly expressed gut protease may be of adaptive significance for M. persicae feeding on different host plants. The Agilent eArray platform was used to design an M. persicae oligonucleotide microarray representing over 10,000 unique genes. CONCLUSION: New genomic resources have been developed for M. persicae, an agriculturally important insect pest. These include previously unknown sequence data, a collection of expressed genes, molecular markers, and a DNA microarray that can be used to study aphid gene expression. These resources will help elucidate the adaptations that allow M. persicae to develop compatible interactions with its host plants, complementing ongoing work illuminating plant molecular responses to phloem-feeding insects.

Heterogeneity of ITS1 sequences in the biting midge Culicoides impunctatus (Goetghebuer) suggests a population in Argyll, Scotland, may be genetically distinct.

Ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1) is a useful genomic region for understanding evolutionary and genetic relationships. In the current study, variation in ITS1 from eight Culicoides species was analysed by PCR, DNA restriction analysis, cloning, and sequencing. ITS1 variants were essentially homogenized within a species, as sequences were identical or closely related. However, Culicoides impunctatus ITS1 sequences derived from one (Argyll) of five populations contained considerable genomic diversity. The secondary structure of each ITS1 was computed. The structure aided the production of an accurate alignment and the identification of a large indel. A phylogenetic analysis was performed. Some of the sequences from the diverse Argyll C. impunctatus population were more related to Culicoides imicola, a vector of animal pathogens in the Old World, than they were to the other C. impunctatus sequences. Thus, the rDNA ITS1 regions of individuals in the Argyll C. impunctatus population were not conforming to the general theory of rDNA homogenization through molecular drive.

Chromosome size variation occurs in cloned Plasmodium falciparum on in vitro cultivation

Variaçöes de tamanho nos cromossomos de linhagens de parasitos derivados de um clone de Plasmodium falciparum. Tais variaçöes desenvolveram-se durante períodos de muitos meses em parasitos haplóides na fase eritrocitária, mantidos in vitro. As variaçöes foram mais numerosas em populaçöes com resistência à mefloquina, induzida pelo cultivo sob pressäo de droga, do que em parasitas controles mantidos em meio de cultura sem droga. Em alguns casos, as modificaçöes de tamanho foram täo grandes que alteraram a ordem relativa das bandas de DNA cromossômico em separaçöes através de eletroforese em gel de "pulsed-field gradient". As regiöes subteloméricas dos cromossomos säo especialmente ativas, estando envolvidas em rearranjos responsáveis pelas alteraçöes de tamanho. O papel biológico destes rearrranjos näo é conhecido. Entretanto, sua ocorrência em experimentos controles, bem como sua frequente apariçäo em condiçöes de pressäo por mefloquina, sugerem que tais rearranjos reflititiam modificaçöes generalizadas da estrutura genômica em resposta às condiçöes ambientais