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Background The Russian wheat aphid, Diuraphis noxia Kurdjumov, is one of the most important pests of small grains throughout the temperate regions of the world. This phytotoxic aphid causes severe systemic damage symptoms in wheat, barley, and other small grains as a direct result of the salivary proteins it injects into the plant while feeding. Results We sequenced and de novo assembled the genome of D. noxia Biotype 2, the strain most virulent to resistance genes in wheat. The assembled genomic scaffolds span 393 MB, equivalent to 93% of its 421 MB genome, and contains 19,097 genes. D. noxia has the most AT-rich insect genome sequenced to date (70.9%), with a bimodal CpG( O/E ) distribution and a complete set of methylation related genes. The D. noxia genome displays a widespread, extensive reduction in the number of genes per ortholog group, including defensive, detoxification, chemosensory, and sugar transporter groups in comparison to the Acyrthosiphon pisum genome, including a 65% reduction in chemoreceptor genes. Thirty of 34 known D. noxia salivary genes were found in this assembly. These genes exhibited less homology with those salivary genes commonly expressed in insect saliva, such as glucose dehydrogenase and trehalase, yet greater conservation among genes that are expressed in D. noxia saliva but not detected in the saliva of other insects. Genes involved in insecticide activity and endosymbiont-derived genes were also found, as well as genes involved in virus transmission, although D. noxia is not a viral vector. Conclusions This genome is the second sequenced aphid genome, and the first of a phytotoxic insect. D. noxia ’s reduced gene content of may reflect the influence of phytotoxic feeding in shaping the D. noxia genome, and in turn in broadening its host range. The presence of methylation-related genes, including cytosine methylation, is consistent with other parthenogenetic and polyphenic insects. The D. noxia genome will provide an important contrast to the A. pisum genome and advance functional and comparative genomics of insects and other organisms.

The genus Maculolachnus Gaumont, 1920 (Hemiptera: Aphididae: Lachninae) exhibits substantial hidden diversity, yet its life history remains poorly understood. Here, we present an integrative taxonomic study of Maculolachnus in South Korea, revealing a previously unrecognized species closely related to M . submacula and providing the first biological insights into the group. We combined detailed morphological examinations, mitochondrial COI sequence analyses, and field observations of colony structure and phenology to clarify species boundaries and elucidate life history traits. Populations formerly identified as M . submacula exhibited distinct morphological characters and significant COI divergence. Phylogenetic reconstructions (BI, ML, NJ), species delimitation methods (ABGD, ASAP, bPTP), and haplotype network analyses consistently supported four distinct species: M . submacula , M . sijpkensi , M . paiki , and a new species described herein as Maculolachnus koreanus sp. nov. The COI distance between M . koreanus sp. nov. and M . submacula exceeded 2.4%, surpassing the typical aphid barcode gap. We redescribe the rare alate viviparous female of M . paiki , which is endemic to South Korea. Observations on M . koreanus sp. nov. revealed ant attendance and seasonal reproductive strategies. Scanning electron microscopy (SEM) provided the first detailed characterization of sensorial structures. This study highlights the value of integrative taxonomy in revealing hidden diversity within Lachninae. International Commission on Zoological Nomenclature (ICZN). International Code of ZoologicalNomenclature 4th edn, i–xxix, 1–306 (The International Trust for Zoological Nomenclature,1999). urn:lsid:zoobank.org:pub:F4BF9295-FF83-434C-9A29-74FDB7A64A9E

Aphids in the Svalbard archipelago are limited to a few highly specialized species adapted to extreme Arctic conditions. Among them, the endemic species historically identified as Sitobion (Metobion) calvulum remains poorly studied. Its systematic placement has been uncertain due to the lack of fresh material, and key aspects of its reproductive biology and endosymbionts remain unknown. Here, using an integrative approach combining molecular phylogenetics, morphology, and reproductive system analysis, we clarify its taxonomy and biology. Phylogenetic analyses based on mitochondrial COI and nuclear EF-1α sequences reveal its close relationship to Nearctic Macrosiphum species, leading to the establishment of the new taxon combination Macrosiphum calvulum comb. nov. Simultaneously, morphological observations uncover several atypical traits that challenge the established boundaries within Macrosiphini. Ultrastructural studies highlight unique reproductive adaptations, including secretion patterns in male accessory glands and oviparous female spermathecae. The absence of known facultative endosymbionts aligns M. calvulum with other aphids in Svalbard. We used SEM to detail the morphology of the sexual generation and applied TEM and, for the first time in aphids, micro-CT imaging to analyze their reproductive system. Given that Svalbard is among the most climate-threatened regions globally, studying M. calvulum is essential for understanding and conserving Arctic biodiversity.

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.

Associations between microbes and animals are ubiquitous and hosts may benefit from harbouring microbial communities through improved resource exploitation or resistance to environmental stress. The pea aphid, Acyrthosiphon pisum, is the host of heritable bacterial symbionts, including the obligate endosymbiont Buchnera aphidicola and several facultative symbionts. While obligate symbionts supply aphids with key nutrients, facultative symbionts influence their hosts in many ways such as protection against natural enemies, heat tolerance, color change and reproduction alteration. The pea aphid also encompasses multiple plant-specialized biotypes, each adapted to one or a few legume species. Facultative symbiont communities differ strongly between biotypes, although bacterial involvement in plant specialization is uncertain. Here, we analyse the diversity of bacterial communities associated with nine biotypes of the pea aphid complex using amplicon pyrosequencing of 16S rRNA genes. Combined clustering and phylogenetic analyses of 16S sequences allowed identifying 21 bacterial OTUs (Operational Taxonomic Unit). More than 98% of the sequencing reads were assigned to known pea aphid symbionts. The presence of Wolbachia was confirmed in A. pisum while Erwinia and Pantoea, two gut associates, were detected in multiple samples. The diversity of bacterial communities harboured by pea aphid biotypes was very low, ranging from 3 to 11 OTUs across samples. Bacterial communities differed more between than within biotypes but this difference did not correlate with the genetic divergence between biotypes. Altogether, these results confirm that the aphid microbiota is dominated by a few heritable symbionts and that plant specialization is an important structuring factor of bacterial communities associated with the pea aphid complex. However, since we examined the microbiota of aphid samples kept a few generations in controlled conditions, it may be that bacterial diversity was underestimated due to the possible loss of environmental or transient taxa.

Many insects engage in symbiotic associations with diverse assemblages of bacterial symbionts that can deeply impact on their ecology and evolution. The intraspecific variation of symbionts remains poorly assessed while phenotypic effects and transmission behaviors, which are key processes for the persistence and evolution of symbioses, may differ widely depending on the symbiont strains. Serratia symbiotica is one of the most frequent symbiont species in aphids and a valuable model to assess this intraspecific variation since it includes both facultative and obligate symbiotic strains. Despite evidence that some facultative S. symbiotica strains exhibit a free-living capacity, the presence of these strains in wild aphid populations, as well as in insects with which they maintain regular contact, has never been demonstrated. Here, we examined the prevalence, diversity, and tissue tropism of S. symbiotica in wild aphids and associated ants. We found a high occurrence of S. symbiotica infection in ant populations, especially when having tended infected aphid colonies. We also found that the S. symbiotica diversity includes strains found located within the gut of aphids and ants. In the latter, this tissue tropism was found restricted to the proventriculus. Altogether, these findings highlight the extraordinary diversity and versatility of an insect symbiont and suggest the existence of novel routes for symbiont acquisition in insects.

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are major phase II detoxification enzymes involved in glycosylation of lipophilic endobiotics and xenobiotics, including phytoalexins. Nicotine, one of the most abundant secondary plant metabolites in tobacco, is highly toxic to herbivorous insects. Plant-herbivore competition is the major impetus for the evolution of large superfamilies of UGTs and other detoxification enzymes. However, UGT functions in green peach aphid (Myzus persicae) adaptation are unknown. In this study, we show that UGT inhibitors (sulfinpyrazone and 5-nitrouracil) significantly increased nicotine toxicity in M. persicae nicotianae, suggesting that UGTs may be involved in nicotine tolerance. In total, 101 UGT transcripts identified in the M. persicae genome/transcriptome were renamed according to the UGT Nomenclature Committee guidelines and grouped into 11 families, UGT329, UGT330, UGT339, UGT341–UGT345, and UGT348–UGT350, with UGT344 containing the most (57). Ten UGTs (UGT330A3, UGT339A2, UGT341A6, UGT342B3, UGT343C3, UGT344D5, UGT344D8, UGT348A3, UGT349A3, and UGT350A3) were highly expressed in M. persicae nicotianae compared to M. persicae sensu stricto. Knockdown of four UGTs (UGT330A3, UGT344D5, UGT348A3, and UGT349A3) significantly increased M. persicae nicotianae sensitivity to nicotine, suggesting that UGT expression in this subspecies may be associated with nicotine tolerance and thus host adaptation. This study reveals possible UGTs relevant to nicotine adaptation in tobacco-consuming M. persicae nicotianae, and the findings will facilitate further validation of the roles of these UGTs in nicotine tolerance.

This study presents the first record of the spruce shoot aphid, Cinara pilicornis (Hartig, 1841) (Hemiptera: Aphididae: Lachninae), in South Korea. Native to Europe, C . pilicornis has expanded its distribution globally and is recognized as a significant quarantine pest in South Korea, posing substantial ecological and economic risks to native spruce trees and forestry ecosystems. Through detailed morphological and molecular analyses, including scanning electron microscopy (SEM) and mitochondrial COI gene sequencing, the identity of C . pilicornis was confirmed. Phylogenetic analyses (BI and NJ) and species delimitation methods (ABGD, ASAP, and bPTP) further validated the species classification, with all South Korean populations belonging to haplotype 1 a putative ancestral haplotype widely distributed across other regions. Population analyses revealed limited genetic diversity in South Korea, suggesting a recent introduction. Climatic niche modeling indicated that C . pilicornis has the potential to establish populations in temperate and subtropical regions, including Europe, North America, coastal South America, and East Asia. Observations of colony behavior on Picea abies revealed high honeydew production and the formation of black sooty mold, causing visible damage to host plants. This study underscores the importance of strengthening quarantine measures and monitoring native spruce trees in national parks to mitigate the spread and impact of this invasive pest. Effective management strategies are essential to prevent further ecological disruption and economic losses caused by C . pilicornis .

The introduction of alien insect species is increasingly facilitated by global plant trade, particularly through the movement of ornamental plants. Takecallis nigroantennatus, a host-specific aphid associated with cold-hardy Fargesia bamboo, has recently expanded its range in Europe. To examine its invasion dynamics, we conducted a population-level survey across 13 locations in six countries, sampling individuals from botanic and private gardens, specialized bamboo nurseries, garden centers, and urban horticultural environments in the UK, Belgium, The Netherlands, Germany, Poland, and Norway. A total of 117 specimens were analyzed using mitochondrial COI sequences, revealing a single dominant haplotype without geographic structure based on Bayesian and Maximum Likelihood phylogenetic analyses. This striking genetic uniformity indicates a narrow introduction bottleneck, suggesting a single or highly restricted introduction event followed by clonal spread. Despite the species’ ability for sexual reproduction, the data support a founder effect and rapid recent expansion closely linked to the introduction history of Fargesia in Europe. The results are also consistent with a possible time lag between the arrival of ornamental bamboo and the subsequent establishment of its associated herbivore, a scenario that warrants further investigation. Importantly, our study provides a practical framework for applied monitoring and early detection in bamboo nurseries, botanical gardens, and other high-risk introduction sites, illustrating how molecular tools can inform biosecurity and the management of emerging invasive species.

Both genetic and environmental factors underlie phenotypic variation. While research at the interface of evolutionary and developmental biology has made excellent advances in understanding the contribution of genes to morphology, less well understood is the manner in which environmental cues are incorporated during development to influence the phenotype. Also virtually unexplored is how evolutionary transitions between environmental and genetic control of trait variation are achieved. Here, I review investigations into molecular mechanisms underlying phenotypic plasticity in the aphid wing dimorphism system. Among aphids, some species alternate between environmentally sensitive (polyphenic) and genetic (polymorphic) control of wing morph determination in their life cycle. Therefore, a traditional molecular genetic approach into understanding the genetically controlled polymorphism may provide a unique avenue into not only understanding the molecular basis of polyphenic variation in this group, but also the opportunity to compare and contrast the mechanistic basis of environmental and genetic control of similar dimorphisms.