Temporal and species-specific resistance of sugar beet to green peach aphid and black bean aphid: mechanisms and implications for breeding.

BACKGROUND: Sugar beet (Beta vulgaris ssp. vulgaris), a key crop for sugar production, faces significant yield losses caused by the black bean aphid Aphis fabae (Scop.) and the green peach aphid Myzus persicae (Sulzer), which also transmits viruses. The restriction on neonicotinoid usage in Europe has intensified this problem, emphasizing the urgent need for breeding resistant crop varieties. This study evaluated 26 sugar beet germplasms for resistance against both aphid species by using performance and feeding behavior assays. Additionally, whole plant bioassays and semi-field experiments were carried out with Myzus persicae. RESULTS: Our findings demonstrate the presence of temporal resistance against both aphid species in the primary sugar beet gene pool. Beet yellows virus (BYV) carrying aphids showed enhanced performance. Different levels of plant defense mechanisms were involved including resistance against Myzus persicae before reaching the phloem, particularly in sugar beet line G3. In contrast, resistance against Aphis fabae turned out to be predominately phloem-located. Furthermore, a high incidence of black inclusion bodies inside the stomach of Myzus persicae was observed for approximately 85% of the plant genotypes tested, indicating a general and strong incompatibility between sugar beet and Myzus persicae in an initial phase of interaction. CONCLUSION: Sugar beet resistance against aphids involved different mechanisms and is species-specific. The identification of these mechanisms and interactions represents a crucial milestone in advancing the breeding of sugar beet varieties with improved resistance. © 2023 Julius Kühn-Institut and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The Temporal and Geographical Dynamics of Potato Virus Y Diversity in Russia.

Potato virus Y, an important viral pathogen of potato, has several genetic variants and geographic distributions which could be affected by environmental factors, aphid vectors, and reservoir plants. PVY is transmitted to virus-free potato plants by aphids and passed on to the next vegetative generations through tubers, but the effects of tuber transmission in PVY is largely unknown. By using high-throughput sequencing, we investigated PVY populations transmitted to potato plants by aphids in different climate zones of Russia, namely the Moscow and Astrakhan regions. We analyzed sprouts from the tubers produced by field-infected plants to investigate the impact of tuber transmission on PVY genetics. We found a significantly higher diversity of PVY isolates in the Astrakhan region, where winters are shorter and milder and summers are warmer compared to the Moscow region. While five PVY types, NTNa, NTNb, N:O, N-Wi, and SYR-I, were present in both regions, SYRI-II, SYRI-III, and 261-4 were only found in the Astrakhan region. All these recombinants were composed of the genome sections derived from PVY types O and N, but no full-length sequences of such types were present. The composition of the PVY variants in the tuber sprouts was not always the same as in their parental plants, suggesting that tuber transmission impacts PVY genetics.

Cryptic community structure and metabolic interactions among the heritable facultative symbionts of the pea aphid.

Most insects harbour influential, yet non-essential heritable microbes in their hemocoel. Communities of these symbionts exhibit low diversity. But their frequent multi-species nature raises intriguing questions on roles for symbiont-symbiont synergies in host adaptation, and on the stability of the symbiont communities, themselves. In this study, we build on knowledge of species-defined symbiont community structure across US populations of the pea aphid, Acyrthosiphon pisum. Through extensive symbiont genotyping, we show that pea aphids' microbiomes can be more precisely defined at the symbiont strain level, with strain variability shaping five out of nine previously reported co-infection trends. Field data provide a mixture of evidence for synergistic fitness effects and symbiont hitchhiking, revealing causes and consequences of these co-infection trends. To test whether within-host metabolic interactions predict common versus rare strain-defined communities, we leveraged the high relatedness of our dominant, community-defined symbiont strains vs. 12 pea aphid-derived Gammaproteobacteria with sequenced genomes. Genomic inference, using metabolic complementarity indices, revealed high potential for cooperation among one pair of symbionts-Serratia symbiotica and Rickettsiella viridis. Applying the expansion network algorithm, through additional use of pea aphid and obligate Buchnera symbiont genomes, Serratia and Rickettsiella emerged as the only symbiont community requiring both parties to expand holobiont metabolism. Through their joint expansion of the biotin biosynthesis pathway, these symbionts may span missing gaps, creating a multi-party mutualism within their nutrient-limited, phloem-feeding hosts. Recent, complementary gene inactivation, within the biotin pathways of Serratia and Rickettsiella, raises further questions on the origins of mutualisms and host-symbiont interdependencies.

Genome-wide identification and characterization of the chemosensory relative protein genes in Rhus gall aphid Schlechtendalia chinensis.

BACKGROUND: The Rhus gall aphid Schlechtendalia chinensis specially uses the only species Rhus chinensis and certain moss species (Mniaceae) as its primary host plant and secondary host plants, respectively. Rhus galls are formed on the primary host by the sucking of aphids, and used in traditional medicine as well as other various areas due to their high tannin contents. Chemoreception is critical for insect behaviors such as host searching, location and identification of mates and reproductive behavior. The process of chemoreception is mediated by a series of protein gene families, including odorant-binding proteins (OBPs), chemosensory proteins (CSPs), olfactory receptors (ORs), gustatory receptors (GRs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs). However, there have been no reports on the analysis of molecular components related to the chemoreception system of S. chinensis at the genome level. RESULTS: We examined the genes of eight OBPs, nine CSPs, 24 ORs, 16 GRs, 22 IRs, and five SNMPs in the S. chinensis genome using homological searches, and these chemosensory genes appeared mostly on chromosome 1. Phylogenetic and gene number analysis revealed that the gene families, e.g., ORs, GRs, CSPs and SNMPs in S. chinensis, have experienced major contractions by comparing to Myzus persicae, while the two gene families OBPs and IRs had slight expansion. The current results might be related to the broader host range of M. persicae versus the specialization of S. chinensis on only a host plant. There were 28 gene pairs between genomes of S. chinensis and Acyrthosiphon pisum in the chemoreceptor gene families by collinear comparison. Ka/Ks ratios (< 1) indicated that the genes of S. chinensis were mainly affected by purification selection during evolution. We also found the lower number and expression level of chemoreception genes in S. chinensis than in other 11 aphid species, such as ORs, GRs and IRs, which play an important role in host search. CONCLUSION: Our study firstly identified the genes of the different chemosensory protein gene families in the S. chinensis genome, and analyzed their general features and expression profile, demonstrating the importance of chemoreception in the aphid and providing new information for further functional research.

Silencing a Myzus persicae Macrophage Inhibitory Factor by Plant-Mediated RNAi Induces Enhanced Aphid Mortality Coupled with Boosted RNAi Efficacy in Transgenic Potato Lines.

Myzus persicae causes considerable losses to crops as a major pest. The damage is direct by feeding and also partly indirect because it vectors plant viruses. The currently available control strategies rely on unsafe and nonecofriendly chemical pesticide applications. Plant-mediated RNA interference (RNAi) has emerged as a powerful tool in crop protection from insect pests. Aphid salivary proteins are essential for phloem feeding and act as mediators of the complex interactions between aphids and their host plants. We documented the efficacy of dsRNA directed against macrophage inhibitory factor (MIF1) of M. persicae to induce aphid mortality and gene silencing through the generation of transgenic potato lines. A binary construct harbouring dsMIF1 driven by the CaMV35S promoter was introduced into the local potato variety 'AGB-white' by Agrobacterium-mediated transformation. PCR and Southern blotting validated the transgene presence and genomic integration in seven transgenic potato lines. An in vitro detached leaf assay revealed a significantly high aphid mortality of 65% in the transgenic potato line sDW-2, while the aphid mortality was 77% in the sDW-2 transgenic line during the in planta bioassay in comparison with 19% aphid mortality in the control nontransgenic potato line. A significantly high silencing effect was observed in the mRNA expression of MIF1, which was reduced to 21% in aphids fed on the transgenic potato line sDW-2. However, variable knockdown effects were found among six other transgenic potato lines, ranging from 30 to 62%. The study concluded that plant-mediated silencing of aphid RNA induces significant RNAi in M. persicae, along with enhanced aphid mortality.

Functional characterization of two different decaprenyl diphosphate synthases in the vetch aphid Megoura viciae.

Long-chain polyprenyl diphosphate synthases play a critical role in the formation of the prenyl side-chain of ubiquinones, but up to date, their functions have scarcely been characterized in insects. Here, we first cloned the complementary DNAs encoding the subunits of decaprenyl diphosphate synthase (DPPS) in the vetch aphid Megoura viciae, an important agricultural pest insect. The results showed that there existed three DPPS subunits, designated as MvDPPS1, MvDPPS2a, and MvDPPS2b, with an open reading frame of 1218, 1275, and 1290 bp, and a theoretical isoelectric point of 7.91, 6.63, and 9.62, respectively. The sequences of MvDPPS1s from different aphid species were nearly identical, while the sequences of MvDPPS2a and MvDPPS2b shared only moderate sequence similarity. Phylogenetic analysis clearly separated MvDPPS2a and MvDPPS2b, indicating a functional differentiation between them. Functional coexpression analysis in Escherichia coli showed that MvDPPS1 plus MvDPPS2a and MvDPPS1 plus MvDPPS2b, respectively, catalyzed the formation of the prenyl side-chain of the ubiquinone coenzyme Q10 (CoQ10). Interestingly, MvDPPS1 plus MvDPPS2b catalyzed the formation of the prenyl side-chain of a ubiquinone other than CoQ10. RNA interference-mediated knockdown of MvDPPS2a imposed no significant effect on MvDPPS2b, and vice versa, suggesting no compensatory action between them. In the end, we detected the product CoQ10 in the aphid, the first identification of CoQ10 in an insect species. Taken together, we characterized two functional DPPSs in M. viciae, one of which might be multifunctional. Our study helps to understand the functional plasticity of the terpenoid backbone biosynthesis pathway in insects.

Target site mutations underlying insecticide resistance in Tunisian populations of Myzus persicae (Sulzer) on peach orchards and potato crops.

BACKGROUND: The massive use of synthetic insecticides strongly affects the level of insecticide resistance in populations of Myzus persicae worldwide. The selection of target site insensitivity-mutations is particularly worrying in areas where agro-industrial crops are vulnerable to the attacks of aphids that vector viruses, as in the case of Tunisia. Knowledge of the resistance mechanisms evolved locally in this aphid pest is a prerequisite to improving and retaining the sustainability of integrated pest management strategies. RESULTS: Target site mutations were surveyed in several populations of M. persicae collected from peach and potato crops between 2011 and 2017 in three Tunisian regions using real-time allele-specific PCR. The L1014F mutation (kdr locus) was found at a moderate frequency mostly in the heterozygous state and the homozygous resistant genotype was very uncommon. The M918T mutation (super-kdr locus) was present in a few heterozygous individuals, whereas the M918L mutation was detected for the first time in Tunisia and extreme North Africa. This latter mutation was shown to be widespread and well-established in Tunisia mainly as homozygous individuals, and was more abundant on peach than on potato crops. The S431F mutation (MACE) was found in a few heterozygous individuals. No individuals carrying the R81T mutation linked to neonicotinoid resistance were detected. CONCLUSION: This study points out a critical situation for the efficacy of pyrethroid insecticides to control M. persicae populations in Tunisia. It also confirms the rapid spread of the M918L mutation which has been detected in many different areas of the Mediterranean basin. © 2022 Society of Chemical Industry.

Characterization of carotenoid biosynthetic pathway genes in the pea aphid (Acyrthosiphon pisum) revealed by heterologous complementation and RNA interference assays.

Carotenoids are involved in many essential physiological functions and are produced from geranylgeranyl pyrophosphate through synthase, desaturase, and cyclase activities. In the pea aphid (Acyrthosiphon pisum), the duplication of carotenoid biosynthetic genes, including carotenoid synthases/cyclases (ApCscA-C) and desaturases (ApCdeA-D), through horizontal gene transfer from fungi has been detected, and ApCdeB has known dehydrogenation functions. However, whether other genes contribute to aphid carotenoid biosynthesis, and its specific regulatory pathway, remains unclear. In the current study, functional analyses of seven genes were performed using heterologous complementation and RNA interference assays. The bifunctional enzymes ApCscA-C were responsible for the synthase of phytoene, and ApCscC may also have a cyclase activity. ApCdeA, ApCdeC, and ApCdeD had diverse dehydrogenation functions. ApCdeA catalyzed the enzymatic conversion of phytoene to neurosporene (three-step product), ApCdeC catalyzed the enzymatic conversion of phytoene to ζ-carotene (two-step product), and ApCdeD catalyzed the enzymatic conversion of phytoene to lycopene (four-step product). Silencing of ApCscs reduced the expression levels of ApCdes, and silencing these carotenoid biosynthetic genes reduced the α-, ß-, and γ-carotene levels, as well as the total carotenoid level. The results suggest that these genes were activated and led to carotenoid biosynthesis in the pea aphid.

Characterization of the detrimental effects of type IV glandular trichomes on the aphid Macrosiphum euphorbiae in tomato.

BACKGROUND: Glandular trichomes are essential in plants' defence against pests however, the mechanisms of action are not completely understood. While there is considerable evidence of feeding and movement impairment by trichomes, the effect on other traits is less clear. We combined laboratory and greenhouse experiments with molecular analysis to understand how glandular trichomes affect the behavior, population growth, and the expression of biomarkers involved in detoxification, primary metabolism, and developmental pathways of the aphid Macrosiphum euphorbiae. We used two isogenic tomato lines that differ in the presence of type IV glandular trichomes and production of acylsucroses; i.e.,Solanum lycopersicum cv. 'Moneymaker' and an introgressed line from Solanum pimpinellifolium (with trichomes type IV). RESULTS: Type IV glandular trichomes affected host selection and aphid proliferation with aphids avoiding, and showing impaired multiplication on the genotype with trichomes. The exposure to type IV glandular trichomes resulted in the overexpression of detoxication markers (i.e., Hsp70, Hsp17, Hsp10); the repression of the energetic metabolism (GAPDH), and the activation of the ecdysone pathway; all these, underlying the key adaptations and metabolic trade-offs in aphids exposed to glandular trichomes. CONCLUSION: Our results demonstrate the detrimental effect of glandular trichomes (type IV) on the aphid and put forward their mode of action. Given the prevalence of glandular trichomes in wild and cultivated Solanaceae; and of the investigated molecular biomarkers in insects in general, our results provide relevant mechanisms to understand the effect of trichomes not only on herbivorous insects but also on other trophic levels.

Structuration of multilocus genotypes associated with insecticide resistance of the peach potato aphid, Myzus persicae (Sulzer), in potato fields in southern Belgium.

BACKGROUND: The peach potato aphid, Myzus persicae, has developed resistance to many insecticides. In Belgium, M. persicae is one of the most common aphids in potato fields and one of the most effective virus vectors. We monitored resistance mutations to pyrethroids, carbamates and neonicotinoids and related these results to microsatellite genotyping to provide information to support the choice of management tactics. RESULTS: Most of the 254 aphids tested (97.6%) displayed at least one mutation conferring resistance to pyrethroids (L1014F, M918L and M918T) and 36.2% additionally carried the modified acetylcholinesterase (MACE) carbamates resistance making them resistant to two insecticide action modes. Ten mutation combinations were detected, two of which were frequent and a strong linkage was found between MACE and M918L mutations. The R81T mutation conferring resistance to neonicotinoids was not detected. Microsatellites highlighted a moderate genetic diversity [69 multilocus genotypes (MLG) detected], severe deviations from Hardy-Weinberg expectations, a highly significant excess of heterozygotes and linkage disequilibrium between all pairs of loci. A structuration of MLGs in association with the mutation combinations was observed. Genetic differentiation was mainly not significant between sampling locations and most MLGs were geographically widespread. These results suggest the likely coexistence of parthenogenesis (obligatory or facultative) and sexual reproduction, and the existence of 'old' parthenogenetic overwintering asexual lineages. CONCLUSION: The results of this monitoring at a regional scale provide useful information on insecticide resistance, genetic diversity and reproductive modes, and highlight the need to reduce the insecticide selection pressure and to implement mitigating techniques.

First report on molecular basis of potato leaf roll virus (PLRV) aggravation by combined effect of tuber and prevailing aphid.

OBJECTIVE: The Potato Leaf Roll Virus (PLRV) is one of the most devastating virus causing severe yield losses worldwide in potato. The comprehensive observations were made to study the PLRV infestation in major potato growing areas of Bihar (India) and further detailed molecular basis of PLRV aggravation was established. RESULTS: Although aphids population were found comparatively lower with maximum symptomatic plants, our molecular data further confirms the presence of PLRV in all possible symptomatic tissues such as tubers, shoots and leaves. For the first time, we have proposed molecular basis of aggravation of PLRV, where tuber acts as a reservoir during off-season and further transmitted by aphids.

Endosymbionts facilitate rapid evolution in a polyphagous herbivore.

Maternally transmitted bacterial symbionts can be important mediators of the interactions between insect herbivores and their foodplants. These symbionts are often facultative (present in some host individuals but not others) and can have large effects on their host's phenotype, thus giving rise to heritable variation upon which selection can act. In the cowpea aphid (Aphis craccivora), it has been established that the facultative endosymbiont Arsenophonus improves aphid performance on black locust trees (Robinia pseudoacacia) but not on fava (Vicia faba). Here, we tested whether this fitness differential translated into contemporaneous evolution of aphid populations associated with the different plants. In a laboratory study lasting 16 weeks, we found that the frequency of Arsenophonus-infected individuals significantly increased over time for aphid populations on black locust but declined for aphid populations on fava. By the end of the experiment, Arsenophonus infection was >3× more common on black locust than fava, which is comparable to previously described infection frequencies in natural field populations. Our results clearly demonstrate that aphid populations with mixed facultative symbiont infection status can rapidly evolve in response to the selective environments imposed by different host plants. This selection differential may be a sufficient explanation for the global association between Arsenophonus-infected cowpea aphids and black locust trees, without invoking additional assortative mechanisms. Because the aphid and plant originate from different parts of the world, we further hypothesize that Arsenophonus infection may have acted as a preadaptation that has promoted functional specialization of infected aphids on a novel host plant.

An RNAi supplemented diet as a reverse genetics tool to control bluegreen aphid, a major pest of legumes.

Aphids are important agricultural pests causing major yield losses worldwide. Since aphids can rapidly develop resistance to chemical insecticides there is an urgent need to find alternative aphid pest management strategies. Despite the economic importance of bluegreen aphid (Acyrthosiphon kondoi), very few genetic resources are available to expand our current understanding and help find viable control solutions. An artificial diet is a desirable non-invasive tool to enable the functional characterisation of genes in bluegreen aphid and discover candidate target genes for future use in RNA interference (RNAi) mediated crop protection against aphids. To date no artificial diet has been developed for bluegreen aphid, so we set out to develop a suitable diet by testing and optimising existing diets. Here, we describe an artificial diet for rearing bluegreen aphid and also provide a proof of concept for the supplementation of the diet with RNAi molecules targeting the salivary gland transcript C002 and gap gene hunchback, resulting in bluegreen aphid mortality which has not yet been documented in this species. Managing this pest, for example via RNAi delivery through artificial feeding will be a major improvement to test bluegreen aphid candidate target genes for future pest control and gain significant insights into bluegreen aphid gene function.

RNA interference-mediated knockdown of voltage-gated sodium channel (MpNav) gene causes mortality in peach-potato aphid, Myzus persicae.

Voltage-gated sodium channels (VGSC) are transmembrane proteins that generate an action potential in excitable cells and play an essential role in neuronal signaling. Since VGSCs play a crucial role in nerve transmission they have become primary targets for a broad range of commercial insecticides. RNA interference (RNAi) is a valuable reverse genetics tool used in functional genomics, but recently, it has also shown promise as a novel agent that could be used to control agricultural insect pests. In this study, we targeted the VGSC (MpNav) gene in the peach-potato aphid Myzus persicae, by oral feeding of artificial diets mixed with dsRNAs. Knock-down of MpNav gene expression caused up to 65% mortality in 3rd instar nymphs. Moreover, significantly lower fecundity and longevity was observed in adult aphids that had been fed with dsMpNav solution at the nymphal stage. Analysis of gene expression by qRT-PCR indicated that the aphid mortality rates and the lowered fecundity and longevity were attributable to the down-regulation of MpNav by RNAi. Taken together, our results show that MpNav is a viable candidate target gene for the development of an RNAi-based bio-aphicide.

Repellency, Toxicity, Gene Expression Profiling and In Silico Studies to Explore Insecticidal Potential of Melaleuca alternifolia Essential Oil against Myzus persicae.

In the current study, deterrent assay, contact bioassay, lethal concentration (LC) analysis and gene expression analysis were performed to reveal the repellent or insecticidal potential of M. alternifolia oil against M. persicae. M. alternifolia oil demonstrated an excellent deterrence index (0.8) at 2 g/L after 48 h. The oil demonstrated a pronounced contact mortality rate (72%) at a dose of 4 g/L after 24 h. Probit analysis was performed to estimate LC-values of M. alternifolia oil (40%) against M. persicae (LC30 = 0.115 g/L and LC50 = 0.37 g/L respectively) after 24 h. Furthermore, to probe changes in gene expression due to M. alternifolia oil contact in M. persicae, the expression of HSP 60, FPPS I, OSD, TOL and ANT genes were examined at doses of LC30 and LC50. Four out of the five selected genes-OSD, ANT, HSP 60 and FPPS I-showed upregulation at LC50, whereas, TOL gene showed maximum upregulation expression at LC30. Finally, the major components of M. alternifolia oil (terpinen-4-ol) were docked and MD simulated into the related proteins of the selected genes to explore ligand⁻protein modes of interactions and changes in gene expression. The results show that M. alternifolia oil has remarkable insecticidal and deterrent effects and also has the ability to affect the reproduction and development in M. persicae by binding to proteins.

Effect of Potato virus Y Presence in Solanum tuberosum (Solanales: Solanaceae) and Chenopodium album on Aphid (Hemiptera: Aphididae) Behavior.

This study establishes the effect of Potato Virus Y (PVY; Potyvirus) in potatoes, Solanum tuberosum L. (Solanales: Solanaceae) and in common-lambs' quarter Chenopodium album L. (Amaranthaceae) on Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and Myzus persicae Sulzer (Hemiptera: Aphididae) behavior, host preference, transmission, and fitness under field and laboratory studies. In the field, several weeds, besides C. album, were collected, including: Sisymbrium altissimum L. (Brassicaceae), Erodium cicutarium L., Lactuca serriola L., Solanum sarrachoides Sendtner (Solanaceae), and S. dulcamara L. (Solanaceae). All weeds were serologically tested for the presence of PVY. From all weeds collected, 2.3 and 34% of C. album and S. sarrachoides, respectively, were PVY-positive. From those positive samples, 72% of the PVY found were PVYN; the remaining 28% was PVYO. In addition, several aphid species were collected from those weeds: Ovatus crataegarious Walker, Macrosiphum euphorbiae (Hemiptera: Aphididae), Hyalopterus pruni Geoffroy (Hemiptera: Aphididae), Rophalosiphum madis Fitch, and 'others aphid' species were collected. The highest number of aphids were collected in E. cicutarium, followed by S. dulcamara, L. serriola, S. altissimum, and C. album. In laboratory studies, PVY-infected C. album does not induce the production of aphids. Moreover, M. persicae did not appear to have a strong preference for either healthy or PVY-infected potato plant, but they did develop a preference for infected plants after prolonged feeding. M. persicae and M. euphorbiae transmitted PVY from C. album to S. tuberosum, 44 and 37.5 % of the time. Future research should seek to identify not only other sources and prevalence of PVY in the field but vector relationships. In insect-pathogen complex continues to persist in solanaceous field crops around the world.

A Genetic Survey of Pyrethroid Insecticide Resistance in Aphids in New Brunswick, Canada, with Particular Emphasis on Aphids as Vectors of Potato virus Y.

Aphids are viral vectors in potatoes, most importantly of Potato virus Y (PVY), and insecticides are frequently used to reduce viral spread during the crop season. Aphids collected from the potato belt of New Brunswick, Canada, in 2015 and 2016 were surveyed for known and novel mutations in the Na-channel (para) gene, coding for the target of synthetic pyrethroid insecticides. Specific genetic mutations known to confer resistance (kdr and skdr) were found in great abundance in Myzus persicae (Sulzer) (Hemiptera: Aphididae), which rose from 76% in 2015 to 96% in 2016. Aphids other than M. persicae showed lower frequency of resistance. In 2015, 3% of individuals contained the resistance mutation skdr, rising to 13% in 2016 (of 45 species). Several novel resistance mutations or mutations not before reported in aphids were identified in this gene target. One of these mutations, I936V, is known to confer pyrethroid resistance in another unrelated insect, and three others occur immediately adjacent and prompt similar chemical shifts in the primary protein structure, to previously characterized mutations associated with pyrethroid resistance. Most novel mutations were found in species other than M. persicae or others currently tracked individually by the provincial aphid monitoring program, which were determined by cytochrome C oxidase I (cox1) sequencing. Through our cox1 DNA barcoding survey, at least 45 species of aphids were discovered in NB potato fields in 2015 and 2016, many of which are known carriers of PVY.

Functional characterization of two acetylcholinesterase genes in the brown citrus aphid, Aphis (Toxoptera) citricidus (Kirkaldy), using heterologous expression and RNA interference.

Acetylcholinesterase (AChE) is the primary target of organophosphate- and carbamate-based insecticides. We sequenced the full-length cDNAs of two AChE genes from the brown citrus aphid Aphis (Toxoptera) citricidus (Kirkaldy). These two genes, Tcace1 and Tcace2, which encode TcAChE1 and TcAChE2, respectively, had a shared amino acid identity of 29% and were highly similar to other insect ace1 and ace2 genes, respectively, having specific functional motifs. Potential differences in enzymatic function were characterized by the heterologous expression of the two genes using a baculovirus system in Sf9 insect cells. Both of the recombinant AChEs had high specific activities for three typical substrates, acetylthiocholine iodide, butyrylthiocholine iodide, and propinylthiocholine iodide. TcAChE1 had a lower Michaelis-Menten constant value and a higher maximal reaction velocity than recombinant TcAChE2, indicating a higher affinity for substrates and greater catalytic efficiency, respectively. Bioassays showed a greater sensitivity of recombinant TcAChE1 to the 10 tested insecticides. Silencing of Tcace1 and Tcace2 by RNA interference significantly increased the susceptibility of A. citricidus to malathion and carbaryl; however, silencing Tcace1 resulted in a higher mortality rate than silencing Tcace2. Additionally, the specific enzyme activity decreased more after silencing Tcace1 than after silencing Tcace2. Thus, TcAChE1 plays a major role in postsynaptic neurotransmission in A. citricidus.

Potato aphid Macrosiphum euphorbiae performance is determined by aphid genotype and not mycorrhizal fungi or water availability.

Intra- and interspecific variation in plant and insect traits can alter the strength and direction of insect-plant interactions, with outcomes modified by soil biotic and abiotic conditions. We used the potato aphid (Macrosiphum euphorbiae Thomas) feeding on cultivated Solanum tuberosum and wild Solanum berthaulti to study the impact of water availability and plant mutualistic arbuscular mycorrhizal (AM) fungi on aphid performance and susceptibility to a parasitoid wasp (Aphidius ervi Haliday). Plants were grown under glass with live or sterile AM fungal spores and supplied with sufficient or reduced water supply. Plants were infested with 1 of 3 genotypes of M. euphorbiae or maintained as aphid-free controls; aphid abundance was scored after 1 week, after which aphid susceptibility to A. ervi was assayed ex planta. Solanum tuberosum accumulated c. 20% more dry mass than S. berthaultii, and root mass of S. berthaultii was smallest under reduced water supply in the presence of AM fungi. Aphid abundance was lowest on S. berthaultii and highest for genotype "2" aphids; genotype "1" aphid density was particularly reduced on S. berthaultii. Aphid genotype "1" exhibited low susceptibility to parasitism and was attacked less frequently than the other two more susceptible aphid genotypes. Neither AM fungi nor water availability affected insect performance. Our study suggests a fitness trade-off in M. euphorbiae between parasitism resistance and aphid performance on poor quality Solanum hosts that warrants further exploration, and indicates the importance of accounting for genotype identity in determining the outcome of multitrophic interactions.

An Aphid Effector Targets Trafficking Protein VPS52 in a Host-Specific Manner to Promote Virulence.

Plant- and animal-feeding insects secrete saliva inside their hosts, containing effectors, which may promote nutrient release and suppress immunity. Although for plant pathogenic microbes it is well established that effectors target host proteins to modulate host cell processes and promote disease, the host cell targets of herbivorous insects remain elusive. Here, we show that the existing plant pathogenic microbe effector paradigm can be extended to herbivorous insects in that effector-target interactions inside host cells modify critical host processes to promote plant susceptibility. We showed that the effector Mp1 from Myzus persicae associates with the host Vacuolar Protein Sorting Associated Protein52 (VPS52). Using natural variants, we provide a strong link between effector virulence activity and association with VPS52, and show that the association is highly specific to Mpersicae-host interactions. Also, coexpression of Mp1, but not Mp1-like variants, specifically with host VPS52s resulted in effector relocalization to vesicle-like structures that associate with prevacuolar compartments. We show that high VPS52 levels negatively impact virulence, and that aphids are able to reduce VPS52 levels during infestation, indicating that VPS52 is an important virulence target. Our work is an important step forward in understanding, at the molecular level, how a major agricultural pest promotes susceptibility during infestation of crop plants. We give evidence that an herbivorous insect employs effectors that interact with host proteins as part of an effective virulence strategy, and that these effectors likely function in a species-specific manner.