Gall-forming Aphid Research Articles

A chromosome-level genome assembly of the Rhus gall aphid Schlechtendalia chinensis provides insight into the endogenization of Parvovirus-like DNA sequences

The Rhus gall aphid, Schlechtendalia chinensis, feeds on its primary host plant Rhus chinensis to induce galls, which have economic importance in medicines and the food industry. Rhus gall aphids have a unique life cycle and are economically beneficial but there is huge gap in genomic information about this group of aphids. Schlechtendalia chinensis induces rich-tannin galls on its host plant and is emerging as a model organism for both commercial applications and applied research in the context of gall production by insects. Here, we generated a high-quality chromosome-level assembly for the S. chinensis genome, enabling the comparison between S. chinensis and non-galling aphids. The final genome assembly is 344.59 Mb with 91.71% of the assembled sequences anchored into 13 chromosomes. We predicted 15,013 genes, of which 14,582 (97.13%) coding genes were annotated, and 99% of the predicted genes were anchored to the 13 chromosomes. This assembly reveals the endogenization of parvovirus-related DNA sequences (PRDs) in the S. chinensis genome, which could play a role in environmental adaptations. We demonstrated the characterization and classification of cytochrome P450s in the genome assembly, which are functionally crucial for sap-feeding insects and have roles in detoxification and insecticide resistance. This genome assembly also revealed the whole genome duplication events in S. chinensis, which can be considered in comparative evolutionary analysis. Our work represents a reference genome for gall-forming aphids that could be used for comparative genomic studies between galling and non-galling aphids and provides the first insight into the endogenization of PRDs in the genome of galling aphids. It also provides novel genetic information for future research on gall-formation and insect-plant interactions.

A new perspective on plant defense against foliar gall-forming aphids through activation of the fruit abscission pathway

The peach aphid Tuberocephalus momonis seriously damages leaves and forms galls in the peach species Prunus persica f. rubro-plena, P. persica, and P. davidiana. Leaves bearing galls formed by these aphids will be abscised at least two months earlier than the healthy leaves on the same tree. Thus, we hypothesize that gall development is likely to be governed by phytohormones involved in normal organogenesis. The soluble sugar content was positively correlated between gall tissues and fruits, suggesting that the galls are sink organs. The results of UPLC-MS/MS analysis showed that higher concentrations of 6-benzylaminopurine (BAP) accumulated in both the gall-forming aphids, the galls themselves and the fruits of peach species than in healthy leaves, suggesting that BAP was being synthesized by the insects to stimulate the establishment of a gall. A significant increase in the concentrations of abscisic acid (ABA) in fruits and jasmonic acid (JA) in gall tissues indicated that these plants are defending from the galls. The concentrations of 1-amino-cyclopropane-1-carboxylic acid (ACC) significantly increased in gall tissues compared with healthy leaves, and were positively correlated with both fruit and gall development. In addition, transcriptome sequencing analysis revealed that during gall abscission, differentially expressed genes in both 'ETR-SIMKK-ERE1' and 'ABA-PYR/PYL/RCAR-PP2C-SnRK2' were significantly enriched during gall abscission. Our results showed that ethylene pathway was involved in the abscission of gall, and this gall abscission allowed the host plants to protect themselves from the gall-forming insects, at least partially.

Discovery of the bicycle gene family provides new insights into insect manipulation of plant development during gall induction.

Galls are complex structures that develop from plant tissue, providing protection and food for gall-forming organisms, such as insects or mites. However, the molecules used by insects or mites to manipulate plant development have proved elusive. A landmark study has tracked down a gene in a gall-forming aphid that controls whether galls on witch hazel are green or red. The 'green allele' is strongly expressed in aphid salivary glands and represses plant genes used for red color formation. Excitingly, the gene product is part of a large suite of proteins that aphids may use to interact with plant biology.

A New Genus and Species of Gall-Forming Fordini (Hemiptera: Aphididae) on Rhus wilsonii Hemsl. from Yunnan, China.

A new species of gall-forming aphid from China, Qiao jinshaensis gen. et sp. nov., is described from Rhus wilsonii Hemsl. Morphological identification and molecular analyses both support the establishment of a new genus. A diagnosis combining morphological and molecular characters from alate viviparae is provided and specimen metadata are published in an open-access and machine-readable format.

Taxonomic revision of the Tetraneura akinire species group (Insecta, Aphididae, Eriosomatinae), with description of a new species and a correction of a nomenclatural confusion.

Gall-forming aphid species Tetraneura nigriabdominalis and T. fusiformis and its closely related species are taxonomically revised. By referring to the original descriptions, the name T. nigriabdominalis (Sasaki, 1899) is discarded as an erroneous combination, and T. akinire Sasaki, 1904 is adopted as a valid name. The T. akinire species group is defined as having long claws in the first instar nymphs of the root generation. Of the T. akinire species group distributed in Korea and Japan, T. ovaliformis sp. nov., which induces globular galls on the leaves of Ulmus davidiana var. japonica, is described, and T. akinire and T. sorini Hille Ris Lambers, 1970 are redescribed. A molecular phylogeny based on partial sequences of mitochondrial cytochrome c oxidase subunit I (COI) indicates that T. akinire is composed of two clusters, one (type A) which is distributed widely from Europe to East Asia on Ulmus spp., and the other (type B) which is found in Hokkaido, northern Japan on U. davidiana var. japonica and in tropical regions as anholocyclic lineages. Tetraneura fusiformis Matsumura, 1917, which has often been treated as a junior synonym of T. nigriabdominalis, likely corresponds to type B. The taxonomic status of T. fusiformis is discussed and this species is tentatively considered as a junior synonym of T. akinire sensu novo.

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.

Gene Structure-Based Homology Search Identifies Highly Divergent Putative Effector Gene Family.

Homology of highly divergent genes often cannot be determined from sequence similarity alone. For example, we recently identified in the aphid Hormaphis cornu a family of rapidly evolving bicycle genes, which encode novel proteins implicated as plant gall effectors, and sequence similarity search methods yielded few putative bicycle homologs in other species. Coding sequence-independent features of genes, such as intron-exon boundaries, often evolve more slowly than coding sequences, however, and can provide complementary evidence for homology. We found that a linear logistic regression classifier using only structural features of bicycle genes identified many putative bicycle homologs in other species. Independent evidence from sequence features and intron locations supported homology assignments. To test the potential roles of bicycle genes in other aphids, we sequenced the genome of a second gall-forming aphid, Tetraneura nigriabdominalis and found that many bicycle genes are strongly expressed in the salivary glands of the gall forming foundress. In addition, bicycle genes are strongly overexpressed in the salivary glands of a non-gall forming aphid, Acyrthosiphon pisum, and in the non-gall forming generations of H. cornu. These observations suggest that Bicycle proteins may be used by multiple aphid species to manipulate plants in diverse ways. Incorporation of gene structural features into sequence search algorithms may aid identification of deeply divergent homologs, especially of rapidly evolving genes involved in host-parasite interactions.

Linoleic acid as corpse recognition signal in a social aphid

Social insect colonies constantly produce dead insects, which cause sanitary problems and potentially foster deadly pathogens and parasites. Hence, many social insects have evolved a variety of hygienic behaviors to remove cadavers from the colonies. To that end, they have to discriminate dead insects from live ones, where chemical cues should play important roles. In ants, bees and termites, such corpse recognition signals, also referred to as “death pheromones” or “necromones”, have been identified as fatty acids, specifically oleic acid and/or linoleic acid. Meanwhile, there has been no such report on social aphids. Here we attempted to identify the “death pheromone” of a gall-forming social aphid with second instar soldiers, Tuberaphis styraci, by making use of an artificial diet rearing system developed for this species. On the artificial diet plates, soldiers exhibited the typical cleaning behavior, pushing colony wastes with their heads continuously, against dead aphids but not against live aphids. GC-MS and GC-FID analyses revealed a remarkable increase of linoleic acid on the body surface of the dead aphids in comparison with the live aphids. When glass beads coated with either linoleic acid or body surface extract of the dead aphids were placed on the artificial diet plates, soldiers exhibited the cleaning behavior against the glass beads. A series of behavioral assays showed that (i) soldiers exhibit the cleaning behavior more frequently than non-soldiers, (ii) young soldiers perform the cleaning behavior more frequently than old soldiers, and (iii) the higher the concentration of linoleic acid is, the more active cleaning behavior is induced. Analysis of the lipids extracted from the aphids revealed that linoleic acid is mainly derived from phospholipids that constitute the cell membranes. In conclusion, we identified linoleic acid as the corpse recognition factor of the social aphid T. styraci. The commonality of the death pheromones across the divergent social insect groups (Hymenoptera, Blattodea and Hemiptera) highlights that these unsaturated fatty acids are generally produced by enzymatic autolysis of cell membranes after death and therefore amenable to utilization as a reliable signal of dead insects.

Gall-forming aphids are protected (and benefit) from defoliating caterpillars: the role of plant-mediated mechanisms

BackgroundInterspecific interactions among insect herbivores are common and important. Because they are surrounded by plant tissue (endophagy), the interactions between gall-formers and other herbivores are primarily plant-mediated. Gall-forming insects manipulate their host to gain a better nutrient supply, as well as physical and chemical protection form natural enemies and abiotic factors. Although often recognized, the protective role of the galls has rarely been tested.ResultsUsing an experimental approach, we found that the aphid, Smynthurodes betae, that forms galls on Pistacia atlantica leaves, is fully protected from destruction by the folivorous processionary moth, Thaumetopoea solitaria. The moth can skeletonize entire leaves on the tree except for a narrow margin around the galls that remains intact (“trimmed galls”). The fitness of the aphids in trimmed galls is unharmed. Feeding trials revealed that the galls are unpalatable to the moth and reduce its growth. Surprisingly, S. betae benefits from the moth. The compensatory secondary leaf flush following moth defoliation provides new, young leaves suitable for further gall induction that increase overall gall density and reproduction of the aphid.ConclusionsWe provide experimental support for the gall defense hypothesis. The aphids in the galls are protracted by plant-mediated mechanisms that shape the interactions between insect herbivores which feed simultaneously on the same host. The moth increase gall demsity on re-growing defoliated shoots.

A new species of aphid of the genus Nipponaphis (Hemiptera: Aphididae: Hormaphidinae) from China, inducing galls on the trunk of a witch-hazel (Hamamelidaceae)

Plants and insects have co-existed for millions of years. Although research has been conducted on various insect species that induce galls on various plant tissues, information is particularly scarce when it comes to insects that form galls on the tough trunk of their host plants. This contribution describes the gall-inducing aphid Nipponaphis hubeiensis sp. nov. from the Zhushan County, Shiyan City, Hubei Province of China. This aphid induces enclosed galls with woody external layer on the trunk of Sycopsis sinensis (Saxifragales: Hamamelidaceae), an uncommon ecological niche in the aphid-plant interaction system. Morphological features for the identification of new species are provided. In addition, a partial sequence of the nuclear gene EF1α was amplified and sequenced to construct a cluster graph. Based on the clustering graph combined with morphology traits, the gall-forming aphid was classified into Nipponaphis. The unique ecological habits of this new aphid will bring innovative perspectives to the study of the evolution and diversity in aphid-host interaction.

Temporal division of labor in an aphid social system

Temporal division of labor, or age polyethism, in which altruistic caste individuals change their tasks with aging, is widely found in bees and ants (Hymenoptera) and also in other social insects. Here we report the discovery of elaborate age polyethism in a social aphid (Hemiptera). Tuberaphis styraci is a gall-forming aphid in which monomorphic first instar nymphs differentiate into normal nymphs and soldiers upon second instar molt. Soldiers neither grow nor reproduce but perform gall cleaning and colony defense. Using an artificial diet rearing system, we collected age-defined groups of soldiers and monitored their social behaviors. We observed that young soldiers tend to clean whereas old soldiers preferentially attack, thereby verifying age-dependent task switching from housekeeping to defense. Strategic sampling, age estimation and behavioral observation of soldiers from natural galls revealed that (1) young cleaning soldiers tend to inhabit upper gall regions with adult insects, (2) old attacking soldiers tend to be distributed in lower gall regions, particularly around the gall openings, and (3) the gall structure is linked to intra-nest movement, aging and task switching of soldiers in an adaptive manner. These results highlight an evolutionary parallelism comparable to the sophisticated temporal division of labor observed in honeybee colonies.

Diversity and distribution of gall-forming aphids of the genus Pemphigus (Sternorrhyncha: Aphididae, Pemphigini) in Eastern Siberia

We reviewed the diversity and distribution of the gall-forming aphids of the genus Pemphigus developing on poplars in Eastern Siberia. As a result, the checklist of this group was compiled comprising 13 species distributed in this macroregion that accounts about 29% of the world's known poplar-feeding Pemphigus species. Biogeographical and host plant data are provided for all listed species. Pemphigus birimatus Ivanovskaja, Pem. laurifoliae Dolgova, and Pem. matsumurai Monzen were documented for the first time in the Republic of Tuva. In addition, the latter two species were also discovered in the Republic of Buryatia and Zabaikalskii Krai, respectively. Two poplars Populus × sibirica and Pop. laurifolia were recorded as novel hosts for 3 Pemphigus species. The origin of Pem. passeki Börner, Pem. spyrothecae Passerini, and Pem. microsetosus Aoki in Eastern Siberia remains unclear. Four species Pem. populi Courchet, Pem. bursarius (Linnaeus), Pem. matsumurai, and Pem. spyrothecae Lichtenstein cause noticeable damage to poplars in man-made plantations.

A Complex Nutrient Exchange Between a Gall-Forming Aphid and Its Plant Host.

It has been a long-standing question as to whether the interaction between gall-forming insects and their host plants is merely parasitic or whether it may also benefit the host. On its host Rhus chinensis, the aphid Schlechtendalia chinensis induces the formation of closed galls, referred to as horned galls. Typically, mature aphid populations comprise thousands of individuals, which is sufficient to cause the accumulation of high CO2 levels in galls (on average 8-fold higher and up to 16 times than atmospheric levels). Large aphid populations also excrete significant amounts of honeydew, a waste product high in sugars. Based on 13C isotope tracing and genomic analyses, we showed that aphid-derived carbon found in CO2 and honeydew was recycled in gall tissues via photosynthesis and glycometabolism. These results indicated that the aphid-gall system evolved in a manner that allowed nutrient recycling, where the gall provides nutrients to the growing aphid population, and in turn, aphid-derived carbon metabolites provide a resource for the growth of the gall. The metabolic efficiency of this self-circulating system indicates that the input needed from the host plant to maintain aphid population growth less than previously thought and possibly minimal. Aside from the recycling of nutrients, we also found that gall metabolites were transported to other parts of the host plant and is particularly beneficial for leaves growing adjacent to the gall. Taken together, galls in the S. chinensis–Rhus chinensis system are highly specialized structures that serve as a metabolic and nutrient exchange hub that benefits both the aphid and its host plant. As such, host plants provide both shelter and nutrients to protect and sustain aphid populations, and in return, aphid-derived metabolites are channeled back to the host plant and thus provide a certain degree of “metabolic compensation” for their caloric and structural needs.

Plant Manipulation by Gall-Forming Social Aphids for Waste Management.

Many social aphids form spectacular galls on their host plants, in which hundreds to thousands of aphids thrive for several months or even for over a year. Here, in addition to colony defense against natural enemies, waste disposal is an important task for the gall dwellers to sustain their social life. In open galls, soldier nymphs actively clean colony wastes such as honeydew droplets, cast-off skins, and cadavers by pushing them with their head out of the gall opening. In the gall, the excreted honeydew is coated with aphid-derived powdery wax to form “honeydew balls,” which prevents the aphids from wetting and drowning with their own excretion. How the aphids deal with the accumulated honeydew in closed galls has been a mystery. Here, we report a novel gall-cleaning mechanism: the gall inner surface absorbs and removes the liquid waste through the plant vascular system. Such a plant-mediated water-absorbing property is commonly found in aphids forming closed galls, which must have evolved at least three times independently. By contrast, the inner surface of open galls is wax-coated and water-repelling, and in some cases, the inner surface is covered with dense trichomes, which further enhance the water repellency. In conclusion, gall-forming aphids induce novel plant phenotypes to manage the waste problems by manipulating plant morphogenesis and physiology for their own sake. This review describes our recent studies on waste management strategies by gall-forming social aphids and discusses future directions of this research topic.

The complete mitochondrial genome of Paracolopha morrisoni (Baker, 1919) (Hemiptera: Aphididae)

We have determined the mitochondrial genome of Paracolopha morrisoni (Baker, 1919), a gall-forming aphid collected from Korea. The circular mitogenome of Paracolopha morrisoni is 16,330 bp long including 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNAs, and a single large non-coding region of 932 bp. The base composition was AT-biased (84.9%). Gene order of P. morrisoni is identical to all other aphid mitochondrial genomes. Phylogenetic trees show that P. morrisoni is sister to Eriosoma lanigerum both belonging to tribe. The mitochondrial genome of P. morrisoni will be useful in understanding the genetic backgrounds of the species.

The effect of Tetraneura ulmi L. galling process on the activity of amino acid decarboxylases and the content of biogenic amines in Siberian elm tissues.

Tetraneura ulmi (L.), a member of Eriosomatinae subfamily, is one of the gall-forming aphids occurring on elms. Sap-sucking behaviour of founding mothers results in the formation of new plant organs. This study documents the changes in the content of plant biogenic amines (putrescine, cadaverine, spermidine, tryptamine, spermine and histamine) and key enzymes of their biosynthesis: lysine decarboxylase (LDC), tyrosine decarboxylase and ornithine decarboxylase (ODC) in galls and other parts of Siberian elm (Ulmus pumila L.) leaves during the galling process. The direction and intensity of these changes for particular amines and enzymes were dependent on the stage of gall development and part of the galling leaf. Generally, the amine content tended to increase in gall tissues during the 1st and 2nd period of the galling process and decreased in later phases. LDC and ODC activities were markedly enhanced, especially in gall tissues at the initial stage of the galling process.

Effect of the Galling Aphid of Baizongia pistaciae L. on Composition and Biological Activities of Essential Oils of Pistacia atlantica Desf. Growing Wild in Jordan

Aqueous extract of Pistacia atlantica leaves is widely used in Jordanian traditional medicine for management of diabetes. The genus Pistaciae serves as obligate host for a group of specialized gall-forming aphids. The present study aimed to identify the aphid attacking P. atlantica trees growing wild in Jordan, to determine the composition of the essential oils from leaves and galls (fresh and dry) and to investigate the antiproliferative activities of the traditionally used dry plant on colon and breast cancers. Hydro-distillation of the essential constituents of P. atlantica leaves was performed and their composition determined. The antiproliferative activity of leaf and galls oils, doxorubicin, and six pure components (sabinene, limonene, α-pinene, β-pinene, α-terpinene, and γ-terpinene) were investigated against two colon (Caco-2 and HCT116) and two breast cancer cell lines (MCF7 and T47D) by MTT assay. Fresh leaf showed the greatest variation in the constituents’ composition. Low molecular weight monoterpene hydrocarbons were the major constituents of both tested organs. The highest percentage of sesquiterpenes was observed in fresh leaf oil, with γ-muurolene as the major component. Tested components exhibited differences in their toxicity against the cell lines under experiments. Cytotoxic effect of doxorubicin was enhanced by the addition of P. atlantica leaf oil but not galls oil. Our findings demonstrated qualitative and quantitative diversity in the composition of the P. atlantica oils. The oils exhibited differences in the antiproliferative activity against colon and breast cancer cell lines. Further molecular experiments are needed to explain such differences.

Post-reproductive parthenogenetic pea aphids (Acyrthosiphon pisum) are visually identifiable and disproportionately positioned distally to clonal colonies.

The role of kin-selection in the evolution of post-reproductive life is controversial. While anthropological and demographic studies strongly suggest that humans and a few other species experience kin selection for significant post-reproductive survival, these results are necessarily correlational. Understanding could therefore be advanced by the development of a globally available, field and laboratory tractable experimental model of kin-selected post-reproductive survival. In only one invertebrate (Quadrartus yoshinomiyai, a gall-forming aphid endemic to Japan) have individuals too old to reproduce been shown to be both numerous in natural habitats and able to help close relatives survive or reproduce. Pea aphids, (Acyrthosiphon pisum), common, tractable organisms, frequently outlive their reproductive ages in laboratories, live in tight interacting groups that are often clonal, and therefore should be evaluated as potential model organisms for the study of adaptive post-reproductive life. The first major step in this process is to identify an optimal method for assessing if a parthenogenetic adult is post-reproductive. We evaluated three methods, relying respectively on isolation in clip cages, visual examination for embryonic eyespots, and dissection. In every case each method identified the same individuals as reproductive versus post-reproductive. While the clip-cage method requires a multi-day wait to produce data, and dissection is inevitably fatal, the eyespot method is quick (under one minute per individual) easy, and non-invasive. This method makes it possible to accurately assess the post-reproductive status of a large number of parthenogenetic pea aphids. We demonstrate the usefulness of the eyespot method in showing that while reproductively valuable adults tend to place themselves near the centers of clonal colonies, less valuable post-reproductive adults are more often at or beyond the edges of colonies. These encouraging early results provide both impetuous and aid for further investigations into the post-reproductive lives of pea aphids.

Hereditary effects of radioactive fallout on gall-forming aphids and the subsequent recovery process near the Fukushima Daiichi Nuclear Power Plant.

To evaluate the effects of fallout from the Fukushima Daiichi Nuclear Power Plant (FNPP) accident on organisms, I compared the morphology and viability of gall-forming aphids in a Fukushima population with that of control populations from non-contaminated area. The gall is a part of a tree that aphids have transformed from the leaf tissue, and aphids develop and parthenogenetically produce offspring within the gall. Galls are useful for identifying the aphid species, the survival rate and fecundity. I focused on the morphology of the first-instar gall-formers derived from the first sexual reproduction after the accident. Of 164 instars of Tetraneura sorini galls obtained 32 km from FNPP in spring 2012, 13.2% exhibited morphological abnormalities; 2.4% were conspicuously malformed individuals [1]. In contrast, in seven control areas, the average percentage of the first instars with abnormal morphology was 3.8% (0.0–5.1% in the total range). The frequencies of abnormality and mortality were significantly higher in Fukushima than in control areas. However, only 0.37% of second-generation larvae from Fukushima had abnormalities, suggesting that abnormalities found in the first generation were not inherited by the next generation. It was interesting that radioactive contamination was reported in the bark, but inside the galls (made of new leaves) was not directly affected by the fallout. Furthermore, analysis of the aphids collected in spring 2013 indicated that the viability and healthiness of the aphids were significantly improved compared with those collected in 2012. Thus, the results of this study suggest the possibility that a reduced level of radiation and/or selection for radiation tolerance may have led to improved viability and healthiness of the Fukushima population. These results suggest that radioactive contamination near to the FNPP had deleterious effects on embryogenesis in eggs, but a negligible influence on the second generation (produced in closed galls). I am now undertaking further research, analyzing how the DNA sequences vary over years.

New record and re-description of a gall-forming aphid (Hemiptera: Aphididae), commonly confused in the north of South America, associated with an ant (Hymenoptera: Formicidae)

The gall-forming aphid <em>Tetraneura fusiformis</em> is recorded for the first time for Northern South America. Its identity is clarified, and descriptions of this species and that of <em>T. nigriabdominalis</em>, with which it is commonly confused, are offered. The association of this sap sucking insect with the ant <em>Linepithema angulatum</em> (Hymenoptera: Formicidae) is recorded for the first time as well.