The genetic adaptations of Toxoptera aurantii facilitated its rapid multiple plant hosts dispersal and invasion.

Toxoptera aurantii Boyer de Fonscolombe (Hemiptera: Aphididae) can attack many plant hosts, including tea (Camellia sinensis L.), citrus (Citrus spp.), lychee (Litchi chinensis Sonn.), banana (Musa spp.), and pineapple (Ananas comasus L.) among others. It is a widely distributed hexapod and one of the most destructive pests in tea plantations, causing enormous economic losses in tea production each year. A high-quality reference genome is important to study the phylogenetics and evolution of T. aurantii because its genome is highly heterozygous and repetitive. We obtained a de novo genome assembly of T. aurantii at the chromosome level using a combination of long Nanopore reads from sequencing with high-throughput chromosome conformation capture technology. When finally assembled, the genome was 318.95 Mb on four chromosomes with a 15.19 Mb scaffold N50. A total of 12,162 genes encoded proteins, while there were 22.01% repetitive sequences that totaled 67.73 Mb. Phylogenetic analyses revealed that T. aurantii and Aphis gossypii parted ways approximately 7.6 million years ago (Mya). We used a combination of long-read single-molecule sequencing with Hi-C-based chromatin interaction maps that resulted in a reference chromosomal level reference genome of T. aurantii that was high quality. Our results will enable the exploration of the genetics behind the special biological features of T. aurantii and also provide a source of data that should be useful to compare the compare genome among the Hemiptera.

The dynamics and the timeline of speciation in the gall-forming aphid Geoica spp. within and among Pistacia host tree species.

Trees of the genus Pistacia serve as obligate hosts for gall-forming aphids (Hemiptera, Aphididae, Fordini). Each aphid species induces a characteristic gall on a single Pistacia host species. The genus Geoica (Fordini) induce similar spherical closed galls on the lower side of the leaflet's midvein, on different Pistacia species. Two species of Pistacia trees that harbor Geoica galls grow naturally in Israel: P. palaestina and P. atlantica. We analyzed the phylogeny and the genetic structure of the Geoica species complex in Israel, and assessed the genetic differentiation and the level of host plant specificity of the aphids between P. atlantica and P. palaestina. We found that the splitting of the genus between P. atlantica and P. palaestina is estimated to have occurred 24-25 Ma (the Oligocene/Miocene boundary). Five different haplotypes suggesting five different species have been further speciating among Geoica spp., galling on P. atlantica, and an additional three species, on P. palaestina.

High Incidence of Strawberry Polerovirus 1 in the Czech Republic and Its Vectors, Genetic Variability and Recombination.

In total, 332 strawberry plants from 33 different locations in the Czech Republic with or without disease symptoms were screened by RT-PCR for the presence of strawberry polerovirus 1 (SPV1) and five other viruses: strawberry mottle virus, strawberry crinkle virus, strawberry mild yellow edge virus, strawberry vein banding virus, and strawberry virus 1. SPV1 was detected in 115 tested strawberry plants (35%), including 89 mixed infections. No correlation between symptoms and the detected viruses was found. To identify potential invertebrate SPV1 vectors, strawberry-associated invertebrate species were screened by RT-PCR, and the virus was found in the aphids Aphis forbesi, A. gossypii, A. ruborum, A.sanquisorbae, Aulacorthum solani, Chaetosiphon fragaefolii, Myzus ascalonicus, and several other non-aphid invertebrate species. SPV1 was also detected in aphid honeydew. Subsequent tests of C. fragaefolii and A.gossypii virus transmission ability showed that at least 4 h of acquisition time were needed to acquire the virus. However, 1 day was sufficient for inoculation using C. fragaefolii. In conclusion, being aphid-transmitted like other tested viruses SPV1 was nevertheless the most frequently detected agent. Czech SPV1 isolates belonged to at least two phylogenetic clusters. The sequence analysis also indicated that recombination events influence evolution of SPV1 genomes.

Global patterns in genomic diversity underpinning the evolution of insecticide resistance in the aphid crop pest Myzus persicae.

The aphid Myzus persicae is a destructive agricultural pest that displays an exceptional ability to develop resistance to both natural and synthetic insecticides. To investigate the evolution of resistance in this species we generated a chromosome-scale genome assembly and living panel of >110 fully sequenced globally sampled clonal lines. Our analyses reveal a remarkable diversity of resistance mutations segregating in global populations of M. persicae. We show that the emergence and spread of these mechanisms is influenced by host-plant associations, uncovering the widespread co-option of a host-plant adaptation that also offers resistance against synthetic insecticides. We identify both the repeated evolution of independent resistance mutations at the same locus, and multiple instances of the evolution of novel resistance mechanisms against key insecticides. Our findings provide fundamental insights into the genomic responses of global insect populations to strong selective forces, and hold practical relevance for the control of pests and parasites.

Glyphochaitophorus, a new genus of Chaitophorini (Hemiptera: Aphididae: Chaitophorinae) from China.

Glyphochaitophorus Qiao gen. nov. with one new species Glyphochaitophorus cristaphis Qiao sp. nov. on Acer palmatum from Tibet, China is described and illustrated in the aphid tribe Chaitophorini. A key to Glyphochaitophorus and allied genera is provided.

Intraspecific variation in immune gene expression and heritable symbiont density.

Host genetic variation plays an important role in the structure and function of heritable microbial communities. Recent studies have shown that insects use immune mechanisms to regulate heritable symbionts. Here we test the hypothesis that variation in symbiont density among hosts is linked to intraspecific differences in the immune response to harboring symbionts. We show that pea aphids (Acyrthosiphon pisum) harboring the bacterial endosymbiont Regiella insecticola (but not all other species of symbionts) downregulate expression of key immune genes. We then functionally link immune expression with symbiont density using RNAi. The pea aphid species complex is comprised of multiple reproductively-isolated host plant-adapted populations. These 'biotypes' have distinct patterns of symbiont infections: for example, aphids from the Trifolium biotype are strongly associated with Regiella. Using RNAseq, we compare patterns of gene expression in response to Regiella in aphid genotypes from multiple biotypes, and we show that Trifolium aphids experience no downregulation of immune gene expression while hosting Regiella and harbor symbionts at lower densities. Using F1 hybrids between two biotypes, we find that symbiont density and immune gene expression are both intermediate in hybrids. We propose that in this system, Regiella symbionts are suppressing aphid immune mechanisms to increase their density, but that some hosts have adapted to prevent immune suppression in order to control symbiont numbers. This work therefore suggests that antagonistic coevolution can play a role in host-microbe interactions even when symbionts are transmitted vertically and provide a clear benefit to their hosts. The specific immune mechanisms that we find are downregulated in the presence of Regiella have been previously shown to combat pathogens in aphids, and thus this work also highlights the immune system's complex dual role in interacting with both beneficial and harmful microbes.

emKlimaszewskityrus/em nom. nov., a new replacement name for Klimaszewskia Yin amp; Zhang, 2021.

The genus Klimaszewskia Yin Zhang of the pselaphine tribe Tyrini was recently established to include a single species, viz., K. punctata Yin Zhang, from Indonesia (Yin Zhang 2021). However, the generic name was preoccupied by Klimaszewskia Szelegiewicz, 1979 (Hemiptera, Aphididae). In accordance with the International Code of Zoological Nomenclature (ICZN 1999: Article 60.3), a new replacement is here proposed.

Genetics of wild and mass-reared populations of a generalist aphid parasitoid and improvement of biological control.

Due to their ability to parasitize various insect species, generalist parasitoids are widely used as biological control agents. They can be mass-reared and released in agroecosystems to control several pest species in various crops. However, the existence of genetic differentiation among populations of generalist parasitoid species is increasingly recognized and this can be associated with an adaptation to local conditions or to a reduced range of host species. Moreover, constraints of mass-rearing conditions can alter genetic variation within parasitoid populations released. These features could be associated with a reduced efficiency of the control of targeted pest species. Here, we focused on strawberry greenhouses where the control of aphids with the generalist parasitoid Aphidius ervi appears to be inefficient. We investigated whether this inefficiency may have both genetic and ecological bases comparing wild and commercial populations of A. ervi. We used two complementary genetic approaches: one based on the mitochondrial marker COI and one based on microsatellite markers. COI analysis showed a genetic differentiation within the A. ervi species, but the structure was neither associated with the commercial/wild status nor with host species factors. On the other hand, using microsatellite markers, we showed a genetic differentiation between commercial and wild A. ervi populations associated with a loss of genetic diversity within the mass-reared populations. Our ecological genetics study may potentially explain the weak efficiency of biological control of aphids in protected strawberry crops and enable to provide some insights to improve biological control.

Population dynamics and species composition of maize field parasitoids attacking aphids in northeastern China.

Maize, Zea mays L., is the most abundant field crop in China. Aphids are the most economically damaging pest on maize, particularly in the maize agri-ecosystems of Jilin Province, northeastern China. Parasitic wasps are important natural enemies of aphids, but limited information exists about their species composition, richness and seasonal dynamics in northeastern China. In this study, the population dynamics of maize aphids and parasitoid wasps were assessed in relation to each other during the summer seasons of two consecutive years, 2018 and 2019. We selected maize fields in the Changchun, Songyuan, Huinan and Gongzhuling areas of Jilin Province. Four species of aphids were recorded from these maize fields: Rhopalosiphum padi (L), Rhopalosiphum maidis (Fitch), Aphis gossypii Glover and Macrosiphum miscanthi (Takahashi). The dominant species in each of the four areas were R. maids (Filch) and R. padi in Changchun, R. padi in Songyuan, A. gossypii and R. padi in Huinan, and A.gossypii and R. padi in Gongzhuling. We delineated a species complex made up of primary parasitoids and hyperparasitoids associated with maize aphids. The primary parasitoids Lysiphlebus testaceipes, Binodoxys communis and Aphelinus albipodus together formed approximately 85.3% of the parasitoid complex. Pachyneuron aphidis, Phaenoglyphis villosa, Syrphophagus taeniatus and Asaphes suspensus made up the hyperparasitoids. Of the primary parasitoids, L. testaceipes was the dominant species (81.31%). Of the hyperparasitoid group, P. villosa was the dominant species (68.42%). Parasitism rates followed the fluctuation of the aphid population. The highest parasitic rate was observed during the peak period of cotton aphids. In this paper, the occurrence dynamics and dominant species of aphids and the dynamics of parasitic natural enemies of aphids in maize fields in Jilin Province are, for the first time, systematically reported. This study provides important information for the establishment and promotion of aphid biological control in maize fields.

Seasonal Migration in the Aphid Genus Stomaphis (Hemiptera: Aphididae): Discovery of Host Alternation Between Woody Plants in Subfamily Lachninae.

About 10% of aphid species show host alternation. These aphids migrate between primary and secondary host plant species in spring and autumn. Host alternation has not been observed in subfamily Lachninae, although it has been suggested on the basis of circumstantial evidence that Stomaphis japonica (Takahashi) may alternate its host between Quercus serrata (Murray) and Quercus acutissima (Carruth). However, a molecular phylogenetic study has indicated that the Stomaphis individuals feeding on these two plant species belong to two different lineages and aphids feeding on Q. acutissima and Pinus densiflora (Sieb. & Zucc.) belong to the same lineage. Here, we examined host alternation in Stomaphis species by comparing molecular phylogenetic identities, morphological features, and life cycles. The molecular analysis and morphological examination showed that aphids feeding on Q. acutissima were the same as those feeding on P. densiflora, whereas aphids feeding on Q. serrata were different from those feeding on Q. acutissima or on P. densiflora. Furthermore, winged aphids were observed on both Q. acutissima and P. densiflora in autumn, but we did not observe winged aphids on Q. serrata. These results indicate that Stomaphis (Walker) individuals feeding on Q. serrata and Q. acutissima belong to two species, one that feeds year-round on Q. serrata, and another, heteroecious species that feeds on P. densiflora as a primary host and on Q. acutissima as a secondary host. This study documents host alternation in subfamily Lachninae for the first time and discusses the acquisition of host alternation by Stomaphis from evolutionary and ecological perspectives.

Trophobiotic organ and perianal structures in aphid genus Stomaphis WALKER (Aphididae, Lachninae).

Stomaphis Walker is an obligatorily myrmecophilous, tree-trunk feeding aphid genus, having many peculiar features in its morphology. One poorly studied trait is its perianal anatomy, with suspected existence of trophobiotic organ and intriguing tubercles near abdominal segment VIII. Tubercles on rear end of abdomen in Stomaphis were considered to be marginal tubercles, structure typical of aphids. Only after their investigation under scanning electron microscope they revealed to possess a very rough surface, consisting of many protuberant, sclerotic scales with finger-like processes. Analysis and comparison with other aphids suggests, that these structures - perianal tubercles - may be considered remnants of abdominal sternite IX, atrophied in aphids. Due to their similarity to the surface of cauda of non myrmecophilous aphids, they are suspected to serve as sort of auxiliary caudas, protecting from sticky secretions of aphids e. g. honeydew or mucus while giving birth or ovipositing in confined space. A very well developed trophobiotic organ in this genus has been shown to exist for the first time.

Generalized population dynamics model of aphids in wheat based on catastrophe theory.

Wheat aphids are major wheat sap sucking pests found throughout the world. The analysis of wheat aphid population dynamics to develop aphid control strategies is therefore important. Even if all factors that control the size of aphid populations are known, several mathematical tools are needed to help us understand their combined effect. Based on the knowledge of population ecology and catastrophe theory, we proposed a generalized population dynamics model to describe variation of wheat aphid populations and obtained a dynamic threshold function for aphid control. Field survey data from 1997 to 2002 were used to validate this model. The results indicated the model could predict the results of practical measures against a pest if the factors of their immediate effects are known or could be estimated. By explaining and forecasting the size of an aphid outbreak and its probability of occurrence, this catastrophe model can provide a scientific basis for wheat aphid control.

Insights into aphid prey consumption by ladybirds: Optimising field sampling methods and primer design for high throughput sequencing.

Elucidating the diets of insect predators is important in basic and applied ecology, such as for improving the effectiveness of conservation biological control measures to promote natural enemies of crop pests. Here, we investigated the aphid diet of two common aphid predators in Central European agroecosystems, the native Coccinella septempunctata (Linnaeus) and the invasive Harmonia axyridis (Pallas; Coleoptera: Coccinellidae) by means of high throughput sequencing (HTS). For acquiring insights into diets of mobile flying insects at landscape scale minimizing trapping bias is important, which imposes methodological challenges for HTS. We therefore assessed the suitability of three field sampling methods (sticky traps, pan traps and hand-collection) as well as new aphid primers for identifying aphid prey consumption by coccinellids through HTS. The new aphid primers facilitate identification to species level in 75% of the European aphid genera investigated. Aphid primer specificity was high in silico and in vitro but low in environmental samples with the methods used, although this could be improved in future studies. For insect trapping we conclude that sticky traps are a suitable method in terms of minimizing sampling bias, contamination risk and trapping success, but compromise on DNA-recovery rate. The aphid diets of both field-captured ladybird species were dominated by Microlophium carnosum, the common nettle aphid. Another common prey was Sitobion avenae (cereal aphid), which got more often detected in C. septempunctata compared to H. axyridis. Around one third of the recovered aphid taxa were common crop pests. We conclude that sampling methodologies need constant revision but that our improved aphid primers offer currently one of the best solutions for broad screenings of coccinellid predation on aphids.

Comparative transcriptomics of Diuraphis noxia and Schizaphis graminum fed wheat plants containing different aphid-resistance genes.

The molecular bases of aphid virulence to aphid crop plant resistance genes are poorly understood. The Russian wheat aphid, Diuraphis noxia, (Kurdjumov), and the greenbug, Schizaphis graminum (Rondani), are global pest of cereal crops. Each species damages barley, oat, rye and wheat, but S. graminum includes fescue, maize, rice and sorghum in its host range. This study was conducted to compare and contrast the transcriptomes of S. graminum biotype I and D. noxia biotype 1 when each ingested phloem from leaves of varieties of bread wheat, Triticum aestivum L., containing no aphid resistance (Dn0), resistance to D. noxia biotype 1 (Dn4), or resistance to both D. noxia biotype 1 and S. graminum biotype I (Dn7, wheat genotype 94M370). Gene ontology enrichments, k-means analysis and KEGG pathway analysis indicated that 94M370 plants containing the Dn7 D. noxia resistance gene from rye had stronger effects on the global transcriptional profiles of S. graminum and D. noxia relative to those fed Dn4 plants. S. graminum responds to ingestion of phloem sap from 94M370 plants by expression of unigenes coding for proteins involved in DNA and RNA repair, and delayed tissue and structural development. In contrast, D. noxia displays a completely different transcriptome after ingesting phloem sap from Dn4 or 94M370 plants, consisting of unigenes involved primarily in detoxification, nutrient acquisition and structural development. These variations in transcriptional responses of D. noxia and S. graminum suggest that the underlying evolutionary mechanism(s) of virulence in these aphids are likely species specific, even in cases of cross resistance.

Evolutionary diversification of Japanese Stomaphis aphids (Aphididae, Lachninae) in relation to their host plant use and ant association.

Phytophagous insects are among the most diverse of the earth's organisms, and their diversification patterns and the driving forces behind these have attracted considerable research interest. Host shifting to closely related plant species is thought to play an important role in phytophagous insect diversification, but the extent to which other interactions such as mutualistic associations affect diversification is not yet known. In this study, we reconstructed the molecular phylogeny of Japanese Stomaphis aphids and determined whether host shifting or mutualistic association with different ant species could explain diversification in this aphid genus. We analyzed 12 species of Stomaphis and grouped them into ten well-supported DNA lineages. Species in each lineage used a single or a few host plant species, but were mutualistically associated with many ant species of the genus Lasius. This result suggests that Stomaphis evolutionarily diversified primarily through host plant shifts. Interestingly, the reconstructed phylogeny suggests that Stomaphis host shifts occasionally occurred between very distantly related host plant taxa (spanning up to five plant orders). The dependence of Stomaphis on long-lasting Lasius ant colonies situated in temperate deciduous forests where Lasius is the dominant ant genus may have led the aphids to shift to distantly related but spatially adjacent host tree species.

Phylogenomics Identifies an Ancestral Burst of Gene Duplications Predating the Diversification of Aphidomorpha.

Aphids (Aphidoidea) are a diverse group of hemipteran insects that feed on plant phloem sap. A common finding in studies of aphid genomes is the presence of a large number of duplicated genes. However, when these duplications occurred remains unclear, partly due to the high relatedness of sequenced species. To better understand the origin of aphid duplications we sequenced and assembled the genome of Cinara cedri, an early branching lineage (Lachninae) of the Aphididae family. We performed a phylogenomic comparison of this genome with 20 other sequenced genomes, including the available genomes of five other aphids, along with the transcriptomes of two species belonging to Adelgidae (a closely related clade to the aphids) and Coccoidea. We found that gene duplication has been pervasive throughout the evolution of aphids, including many parallel waves of recent, species-specific duplications. Most notably, we identified a consistent set of very ancestral duplications, originating from a large-scale gene duplication predating the diversification of Aphidomorpha (comprising aphids, phylloxerids, and adelgids). Genes duplicated in this ancestral wave are enriched in functions related to traits shared by Aphidomorpha, such as association with endosymbionts, and adaptation to plant defenses and phloem-sap-based diet. The ancestral nature of this duplication wave (106-227 Ma) and the lack of sufficiently conserved synteny make it difficult to conclude whether it originated from a whole-genome duplication event or, alternatively, from a burst of large-scale segmental duplications. Genome sequencing of other aphid species belonging to different Aphidomorpha and related lineages may clarify these findings.

Host relatedness influences the composition of aphid microbiomes.

Animals are host to a community of microbes, collectively referred to as their microbiome, that can play a key role in their hosts' biology. The bacterial endosymbionts of insects have a particularly strong influence on their hosts, but despite their importance we still know little about the factors that influence the composition of insect microbial communities. Here, we ask: what is the relative importance of host relatedness and host ecology in structuring symbiont communities of diverse aphid species? We used next-generation sequencing to compare the microbiomes of 46 aphid species with known host plant affiliations. We find that relatedness between aphid species is the key factor explaining the microbiome composition, with more closely related aphid species housing more similar bacterial communities. Endosymbionts dominate the microbial communities, and we find a novel bacterium in the genus Sphingopyxis that is associated with numerous aphid species feeding exclusively on trees. The influence of ecology was less pronounced than that of host relatedness. Our results suggest that co-adaptation between insect species and their facultative symbionts is a more important determinant of symbiont species presence in aphids than shared ecology of hosts.

A chromosome-level draft genome of the grain aphid Sitobion miscanthi.

BACKGROUND: Sitobion miscanthi is an ideal model for studying host plant specificity, parthenogenesis-based phenotypic plasticity, and interactions between insects and other species of various trophic levels, such as viruses, bacteria, plants, and natural enemies. However, the genome information for this species has not yet to be sequenced and published. Here, we analyzed the entire genome of a parthenogenetic female aphid colony using Pacific Biosciences long-read sequencing and Hi-C data to generate chromosome-length scaffolds and a highly contiguous genome assembly. RESULTS: The final draft genome assembly from 33.88 Gb of raw data was ∼397.90 Mb in size, with a 2.05 Mb contig N50. Nine chromosomes were further assembled based on Hi-C data to a 377.19 Mb final size with a 36.26 Mb scaffold N50. The identified repeat sequences accounted for 26.41% of the genome, and 16,006 protein-coding genes were annotated. According to the phylogenetic analysis, S. miscanthi is closely related to Acyrthosiphon pisum, with S. miscanthi diverging from their common ancestor ∼25.0-44.9 million years ago. CONCLUSIONS: We generated a high-quality draft of the S. miscanthi genome. This genome assembly should help promote research on the lifestyle and feeding specificity of aphids and their interactions with each other and species at other trophic levels. It can serve as a resource for accelerating genome-assisted improvements in insecticide-resistant management and environmentally safe aphid management.

The composition of the aphid fauna (Insecta, Hemiptera) of the Royal Botanic Gardens, Kew.

At least a dozen species of aphids (Insecta, Hemiptera) of non-native origin have expanded their range in Europe, however the importance of botanic gardens in this phenomenon has not been studied previously in detail. As a case study, investigations on the species composition and host range of Aphidomorpha in the Royal Botanic Gardens, Kew, London, United Kingdom, were conducted over a period of twelve days, in June 2017. The inventory study was carried out in the collection of living plants, both in the gardens and the glasshouses and nurseries. In total, 94 taxa of Aphidomorpha are identified (one phylloxerid, one adelgid and 92 species of aphids). 20 species are regarded as alien to the European aphid fauna and among them nine are believed to be the first published records for Kew. 20 species are regarded as serious pests, capable of virus transmission. The list of host plants includes 155 taxa from 89 genera and 49 families. Ericolophium holsti (Takahashi), species of Asiatic origin associated with Rhododendron spp., was found for the first time in the field in the UK. Changes in the species composition of the aphid fauna in reference to the Eastop's studies in 1960s were discussed.