Cynipidae Research Articles

Host Gall Size and Temperature Influence Voltinism in an Exotic Parasitoid

Insect phenology is highly temperature-dependent. Higher temperatures can lead to earlier emergence and lengthening of the active period, which enable many insect groups to complete more generations. Studies on the effects of climate change on insect populations are providing concerning evidence supporting this relationship. These kind of shifts in phenology and voltinism also occur in agricultural and forest insect pests and their natural enemies, with potential implications for biological control. The consequences derived from changing temperature regimes on tritrophic interactions remain poorly studied, particularly in gall-inducing insects and their parasitoids. Here we detail the occurrence of bivoltinism in the exotic parasitoid Torymus sinensis, previously categorized as univoltine, a widely introduced species to fight against the invasive Asian chestnut gall wasp Dryocosmus kuriphilus wherever this pest spread. This plasticity in voltinism has been observed in the southernmost European distribution of D. kuriphilus, and appears to be mediated by both temperature and gall traits, namely size or the number of gall chambers. Bivoltinism was most common at annual mean temperatures around 13.5°C and in galls with more chambers. Through this work, we intend to unravel the factors behind this phenomenon and discern the possible consequences on host-parasitoid interactions.

Andricus cydoniae Giraud, 1859 Junior Synonym of Cynips conifica Hartig, 1843, as Experimentally Demonstrated (Hymenoptera: Cynipidae: Cynipini).

Simple SummaryPhytophagous members of the family Cynipidae induce a spectacular diversity of plant galls that are often complex in structure. Knowledge of the biology, life cycle, and life history of known cynipid species is largely fragmentary; gall wasps can exhibit an alternation of generations known as heterogony in which an all-female alternates with a bisexual generation. The unisexual generation produces eggs parthenogenetically, and these are usually inserted into a specific plant part. At the site of oviposition, galls are induced, within which a bisexual generation develops and later emerges. Emergent males and females mate, and females in turn induce galls from which the unisexual generation emerges. Females of the two generations may be morphologically dissimilar and may induce galls that differ greatly morphologically. Differences in the morphology of both wasps and galls between generations of the same species, coupled with incomplete knowledge of life cycles, have led to considerable taxonomic confusion. Alternating generations of numerous species have been described as separate species or even genera. Here, we demonstrate experimentally that two cynipid species, Cynips conifica (presently Andricus conificus) and Andricus cydoniae, which are morphologically different and produce very different galls on different host oaks, represent alternate generations of a single species.We demonstrated the life cycle closure of Cynips conifica Hartig, 1843 (presently Andricus conificus), previously supposed on the basis of molecular data, and the identity of the sexual generation, through laboratory experiments. As a consequence, Andricus cydoniae Giraud, 1859 became a junior synonym of A. conificus (Hartig, 1843). We provide illustrations and a diagnosis for adults and galls, observations on biology, and information on distribution. Moreover, as sexual galls of A. conificus cannot be distinguished from those of Andricus multiplicatus, a detailed comparison between sexual galls and adults of these two species is reported.

Global phylogeny of the inquilinous gall wasp tribe Synergini (Hymenoptera: Cynipoidea: Cynipidae): first insights and establishment of a new cynipid tribe

Abstract Previous phylogenetic studies of the tribe Synergini were focused on Palaearctic material, in which the genus Synergus was recovered as monophyletic, despite evidence of non-monophyly when global sampling is considered. A global molecular phylogeny of Synergini, including sequenced material from Nearctic and Neotropical realms, is presented herein for the first time. We assembled DNA data for 120 specimens: 104 representing all genera belonging to Synergini, except for the rare monospecific genus Agastoroxenia (ingroup), and 16 belonging to five other tribes of Cynipidae (outgroup). We obtained sequences for four genes: cytochrome c oxidase subunit I (COI), cytochrome b (Cytb), 28S region D2 (28S D2) and 28S region D3 (28S D3). The evaluated analyses support the non-monophyly of both Saphonecrus and Synergus (with Nearctic and Neotropical Synergus resolved into three clades separated from the Palaearctic species), as well as the monophyly of the rest of the genera in Synergini. Furthermore, the results suggest that neither Saphonecrus s.s. nor Synergus s.s. are present in the New World. The future challenges to separate the clades of Saphonecrus and Synergus into new taxa are discussed. Lastly, Rhoophilus was shown to belong to a new tribe, Rhoophilini trib. nov., on the basis of molecular, morphological and biological data.

The Diversity of Bacteria Associated with the Invasive Gall Wasp Dryocosmus kuriphilus, Its Galls and a Specialist Parasitoid on Chestnuts.

Simple SummaryThe insect Dryocosmus kuriphilus induces galls on chestnut trees. Torymus sinensis is a host-specific parasitoid of D. kuriphilus and phenologically synchronizes with D. kuriphilus. The aim of this research is to investigate the bacterial communities and predominant bacteria of D. kuriphilus, T. sinensis, D. kuriphilus galls and the galled twigs of Castanea mollissima. We provide the first evidence that D. kuriphilus shares most bacterial species with T. sinensis, D. kuriphilus galls and galled twigs. The predominant bacteria of D. kuriphilus are Serratia sp. and Pseudomonas sp. Many species of the Serratia and Pseudomonas genera are plant pathogenic bacteria, and we suggest that D. kuriphilus may be a potential vector of plant pathogens. Furthermore, a total of 111 bacteria are common to D. kuriphilus adults, T. sinensis, D. kuriphilus galls and galled twigs, and we suggest that the bacteria may transmit horizontally among D. kuriphilus, T. sinensis, D. kuriphilus galls and galled twigs on the basis of their ecological associations.Dryocosmus kuriphilus (Hymenoptera: Cynipidae) induces galls on chestnut trees, which results in massive yield losses worldwide. Torymus sinensis (Hymenoptera: Torymidae) is a host-specific parasitoid that phenologically synchronizes with D. kuriphilus. Bacteria play important roles in the life cycle of galling insects. The aim of this research is to investigate the bacterial communities and predominant bacteria of D. kuriphilus, T. sinensis, D. kuriphilus galls and the galled twigs of Castanea mollissima. We sequenced the V5–V7 region of the bacterial 16S ribosomal RNA in D. kuriphilus, T. sinensis, D. kuriphilus galls and galled twigs using high-throughput sequencing for the first time. We provide the first evidence that D. kuriphilus shares most bacterial species with T. sinensis, D. kuriphilus galls and galled twigs. The predominant bacteria of D. kuriphilus are Serratia sp. and Pseudomonas sp. Furthermore, the bacterial community structures of D. kuriphilus and T. sinensis clearly differ from those of the other groups. Many species of the Serratia and Pseudomonas genera are plant pathogenic bacteria, and we suggest that D. kuriphilus may be a potential vector of plant pathogens. Furthermore, a total of 111 bacteria are common to D. kuriphilus adults, T. sinensis, D. kuriphilus galls and galled twigs, and we suggest that the bacteria may transmit horizontally among D. kuriphilus, T. sinensis, D. kuriphilus galls and galled twigs on the basis of their ecological associations.

A new species of oak gall wasp (Hymenoptera: Cynipidae, Cynipini) from Turkey.

A new species of the genus Andricus Hartig, 1840 (Cynipidae: Cynipini) is described from Burdur province in Turkey: Andricus arslani Azmaz Katlm sp. n. sexual generation. The new species induce galls on Quercus cerris L. belonging to section Cerris. SEM images, photos of the host galls, and data on the diagnosis, distribution, and biology of the new species are provided.

The Arthropod Associates of 155 North American Cynipid Oak Galls.

The identities of most arthropod associates of cynipid-induced oak galls in the western Palearctic are generally known. However, a comprehensive accounting of associates has been performed for only a small number of the galls induced by the estimated 700 species of cynipid gall wasps in the Nearctic. This gap in knowledge stymies many potential studies of diversity, coevolution, and community ecology, for which oak gall systems are otherwise ideal models. We report rearing records of insects and other arthropods from more than 527,306 individual galls representing 201 different oak gall types collected from 32 oak tree species in North America. Of the 201 gall types collected, 155 produced one or more arthropods. A total of 151,075 arthropods were found in association with these 155 gall types, and of these 61,044 (40.4%) were gall wasps while 90,031 (59.6%) were other arthropods. We identified all arthropods to superfamily, family, or, where possible, to genus. We provide raw numbers and summaries of collections, alongside notes on natural history, ecology, and previously published associations for each taxon. For eight common gall-associated genera (Synergus, Ceroptres, Euceroptres, Ormyrus, Torymus, Eurytoma, Sycophila, and Euderus), we also connect rearing records to gall wasp phylogeny, geography, and ecology -including host tree and gall location (host organ), and their co-occurrence with other insect genera. Though the diversity of gall wasps and the large size of these communities is such that many Nearctic oak gall-associated insects still remain undescribed, this large collection and identification effort should facilitate the testing of new and varied ecological and evolutionary hypotheses in Nearctic oak galls.

Changes in galling insect community on Caryocar brasiliense trees mediated by soil chemical and physical attributes.

The nutrient stress hypothesis predicts that galling insects prevail on host plants growing in habitats with soils of low nutritional quality. Caryocar brasiliense (Caryocaraceae) is host to four different leaf-galling insects. These insects have the potential to cause a reduction in the production of C. brasiliense fruits, an important source of income for many communities in Brazil. We studied the effects of soil physical and chemical characteristics on the abundance, species richness, and diversity of galling insects and their natural enemies on C. brasiliense trees growing under three different soil conditions. Our data corroborate the hypothesis that in nutritionally poor (e.g., lower phosphorus content) and worse physical textures (e.g., sandy) soils, host plants support higher species richness and diversity of galling insects. However, the abundance of Eurytoma sp. (the most common gall in C. brasiliense), was correlated with a higher phosphorus concentration in the soil (better nutritional condition). The percentage of galled leaflets and the area of leaflets occupied by Eurytoma sp galls were higher in the more fertile soil. In this soil, there was greater abundance, species richness, and diversity of parasitoids of Eurytoma sp. (e.g., Sycophila sp.) and predators (e.g., Zelus armillatus). Our data indicate the importance of habitat quality in the composition of the galling insect community and the impact of soil properties in mediating the distribution of these insects in C. brasiliense.

Review of the inquilinous fauna associated with insect galls in Brazilian restingas.

Several records of associated fauna, including parasitoids, inquilines, predators, and successors, have been reported by insect gall inventories in Brazilian restingas. Although most guilds are well established, inquilines have frequently been misinterpreted. In this paper, the inquilinous fauna of insect galls is revised based on five criteria: food habit; coexistence with the inducer; modification of gall tissues or production of new tissues; phylogenetic relationship with the inducer; and mobility. Gall inventories dated from 1988 to 2019 were examined, totaling 16 publications, eight of them with inquiline records. This guild was reported in 53 gall morphotypes in 44 plant species and four morphospecies distributed among 36 genera of 24 host families for a total of 65 records. Most inquilines were repositioned into the cecidophage guild and others into the kleptoparasite guild, resulting in a large reduction in the frequency of inquilines (from 65 to five records), and in first reports of cecidophages and kleptoparasites, with 46 and 13 records, respectively. Cecidophage was the most diverse guild with insects of five orders (Diptera, Coleoptera, Lepidoptera, Hemiptera, and Thysanoptera) while kleptoparasites were represented only by two orders (Diptera and Hymenoptera) and inquiline solely by Hymenoptera. Other results indicate that Leptothorax sp. (Formicidae) could be a successor and not an inquiline.

Describing biodiversity in the genomics era: A new species of Nearctic Cynipidae gall wasp and its genome

ABSTRACTGall wasps (Hymenoptera: Cynipidae) specializing on live oaks in the genus Quercus (subsection Virentes) are a relatively diverse and well‐studied community with 14 species described to date, albeit with incomplete information on their biology, life history and genetic structure. Incorporating an integrative taxonomic approach, we combine morphology, phenology, behaviour, genetics and genomics to describe a new species, Neuroterus valhalla sp. nov. The alternating generations of this species induce galls on the catkins and stem nodes of Quercus virginiana and Quercus geminata in the southern United States. We describe both generations in the species' life cycle, and primarily use samples from a population in the centre of Houston, Texas, thus serving as an example of the undescribed biodiversity still present in well‐travelled urban centres. In parallel, we present a draft assembly of the N. valhalla genome providing a direct link between the type specimen and reference genome. The genome of N. valhalla is the smallest reported to date within the tribe Cynipini, providing an important comparative contrast to the otherwise large genome size of cynipids. While relatively small, the genome was found to be composed of >64% repetitive elements, including 43% unclassified repeats and 11% retrotransposons. A preliminary ab initio and homology‐based annotation revealed 32,005 genes, and a subsequent orthogroup analysis grouped 18,044 of these to 8186 orthogroups, with some evidence for high levels of gene duplications within Cynipidae. A mitochondrial barcode phylogeny linked each generation of the new species and a phylogenomic ultraconserved element (UCEs) phylogeny indicates that the new species groups with other Nearctic Neuroterus. However, both phylogenies present the genus Neuroterus in North America as polyphyletic.

Susceptibility levels of some chestnut cultivars and genotypes to the chestnut gall wasp in Turkey

The Asian chestnut gall wasp (ACGW) is one of the most important pests threatening most Castanea species. The best management strategy against this pest can be establishing new orchards with resistant cultivars along with biocontrol (parasitoid Torymus sinensis Kamijo (Hymenoptera: Torymidae)). In Turkey, ACGW was first detected in 2014 at Gac?k village of Yalova province. Bursa, ?stanbul, Sakarya, Kocaeli, Bal?kesir, Bilecik, D?zce, Giresun, Bart?n, Zonguldak, Sinop and ?zmir provinces are also infected with ACGW. This study was carried out to determine the levels of susceptibility of chestnut cultivars/genotypes to ACGW. The study was carried out in Yalova province between 2016 and 2018. In total, 15 cultivars/genotypes were involved in the study, including European (C. sativa) chestnuts (Albayrak, Alt?nay, ?Erfelek?, ?Osmano?lu?, Sal?pazar?, ?Serdar?, ??nal?), interspecific hybrids (?Marigoule? and BDB-L) and complex hybrids (?Aky?z?, ?Macit 55?, ?Ali Nihat?, A9, A55, A56) were tested in the study. In April 2016, five- to seven-year-old seedlings were ?bark? grafted, and susceptibility to the ACGW was evaluated by recording the ratio of infected buds (%), visual assessment of the damage (severity), and calculations of an infestation index. Among the cultivars and genotypes tested in the study, the ?Aky?z? cultivar was determined to exhibit the highest resistance against the ACGW. To fully understand the resistance mechanism of the ?Aky?z? cultivar, molecular and biochemical studies should be done and compared with other results.

Batı Anadolu’da Yeni Belirlenen Bazı Kestane Genotiplerinin Farklı Aşılama Yöntemleriyle Çoğaltılması

Aim of study: In the study, the most successful grafting method and chestnut genetypes that are best adapted to the Düzce Kaplandağı chestnut population were tried to be determined. Area of study: Chestnut seeds used as rootstock material were collected from natural chestnut forests of Kaplandağı, Cumayeri district of Düzce province. Material and methods: In this study, for the first time identified by us, 20 well-known fruit qualities, two locally known (Serdar and Erfelek), and three foreign (Maraval, Marigoule, and Bethizac) chestnut genotypes were used. It was investigated the success of grafting methods by using 25 different chestnut genotypes and three different grafting methods (budding, the cleft and tongue grafting). The seedlings of the Kaplandağı chestnut population were used as the rootstock chestnut genotype. The genotypes which were grafted on the rootstock were types of Kabalak, İbradı, Paşaormanı, Erfelek, Hacıömer, Serdar, Akçakoca 1, Alaplı 1, Çongara, Fındıklı 1, Gümeli 1, Fındıklı 2, Ereğli-Yazıören, Paşaormanı 2, Gümeli black, Fındıklı 3, Ereğli-Nevzat, Gümeli yellow, Akçakoca yellow, Yığılca-Vedat, Yığılca-Çakır, Ibradı 2. and Maraval, Marigoule, Bouche de Bethizac. Main results: It was determined that stabile temperature and humid conditions affected grafting achievement on chestnut genotypes and grafting techniques. While the lowest grafting success was in the budding, the cleft and tongue grafting methods were the same and have a grafting success rate of 63%. Among the chestnut varieties, the Çongara genotypes (98%) had the highest while the Fındıklı 2 genotypes (20%) had the lowest grafting success. As a result, the most successful grafting methods were cleft and tongue grafting, and the most successful grafting genotypes were found as Çongara, İbradı 2 and Alaplı 1. Also, the sapling obtained from the study were taken under ex-situ protection in Düzce University campus as a chestnut orchard. Highlights: Also, two of them (Pasaormanı and Akçakoca 1) are observed to resist against the gall wasp.

Sexually dimorphic galls induced on leaflets of Matayba guianensis (Sapindaceae): a rare phenomenon occurring in Diptera (Cecidomyiidae).

In a general way, galling insects can induce only one gall morphotype on the host plant species. However, some taxa of galling insects such as Eriococcidae can induce sexually dimorphic galls on the same host. In the present study, Lopesia mataybae (Diptera: Cecidomyiidae) induced two gall morphotypes on the leaflets of Matayba guianensis (Sapindaceae), a rare evidence of sexual dimorphism in galls induced by Cecidomyiidae. We investigated the adult emergence of galling insects and the morphological, histological, and histochemical attributes of the gall morphotypes. Both gall morphotypes showed the galling insect in the larval or pupal stage, and the insect adult emergence from different morphotypes was sexually distinct. Galls occupied by females (Globoid) were significantly larger (average height = 4.67mm. S = 0.43/average width = 4.59mm. S = 0.70) than galls occupied by males (cylindrical) (average height = 2.95mm. S = 0.46/average width = 2.34mm. S = 0.45). Both gall types were composed of elongated cells in the inner cortex and rounded cells in the outer cortex of the vessel-like structure. The globoid galls showed 42 cell layers (14 of them cylindrical, S = 3.86; 28 rounded, S = 5.89) and cylindrical galls showed 29 layers. There were no differences between morphotypes in the histochemical compounds detected. We have shown here significant morphological and histological differences between male and female galls possibly due to the different nutritional requirements of Lopesia mataybae sexes. Therefore, the expression of sexual dimorphism in gall morphotypes may be associated with developmental pathway differentiation between the sexes of L. mataybae.

Resistance of subspecies of Eucalyptus camaldulensis to galling by Leptocybe invasa: Could quinic acid derivatives be responsible for leaf abscission and reduced galling?

Abstract Variability in galling caused by Leptocybe invasa Fisher & La Salle has been reported in several species and hybrids of Eucalyptus. Genetic diversity within Eucalyptus camaldulensis Dehnh. could confer resistance to L. invasa via variation in plant specialized metabolites or plant responses detrimental to insect herbivores. Moreover, optimal defence theory proposes that plants will invest more constitutive resistance in parts that are vulnerable to herbivore attack, such as immature leaves and apical buds, which are prone to galling. We investigated constitutive resistance of subspecies and genotypes of E. camaldulensis to L. invasa while controlling for differences among growing conditions characteristic of their autochthonous Australian habitats using common nursery and garden arboreta plantings. Data on galling intensity, gall size, leaf phenolics and leaf physical attributes were used to investigate differences in susceptibility. We show that E. camaldulensis exhibits both constitutive and induced resistance to L. invasa. Intraspecific variability in galling was pronounced and correlated with concentrations of quinic acid derivatives and hypersensitive abscission of leaves. Whether these metabolites directly affect the survival of eggs or larvae remains to be determined. Hypersensitive leaf abscission in subspecies of E. camaldulensis in response to injury by a galling insect has not been reported previously and warrants investigation.

A new genus of Neotropical oak gall wasp, Prokius Nieves-Aldrey, Medianero & Nicholls, gen. nov. (Hymenoptera: Cynipidae: Cynipini), with description of two new species from Panama

A new genus, Prokius Nieves Aldrey, Medianero & Nicholls, gen. nov., and two new species of oak gall wasps (Hymenoptera: Cynipidae: Cynipini), Prokius cambrai Medianero & Nieves-Aldrey sp. nov. and Prokius lisethiae Medianero & Nieves-Aldrey sp. nov., are described from adults reared from galls on Quercus bumelioides Liebm (Fagaceae, sect. Quercus, white oaks) collected in Panama. The new genus is phylogenetically and morphologically close to Dros Kinsey and forms part of a large clade that includes species from several other genera that appear to require revision, including Andricus Hartig and Phylloteras Ashmead. Molecular and morphological data, diagnostic characters, gall descriptions, distribution and biological data of the new genus and the new species are given. This new genus represents the fourth recently described genus of Cynipidae endemic to the Neotropical region.

Local-scale dispersal patterns and susceptibility to Dryocosmus kuriphilus in different Castanea species and hybrid clones: insights from a field trial

The chestnut gall wasp Dryocosmus kuriphilus is a major insect pest affecting chestnut trees worldwide. Medium and long-term control of this pest can be improved by using resistant or less susceptible cultivars and hybrid clones. In addition, little is known about the local patterns of dispersal of the pest. We obtained data from trees of 3 chestnut species and 27 hybrid clones in a field trial in NW Spain with the aim of evaluating the susceptibility of the material to the gall wasp and identifying possible drivers of local spatial dispersal. In the first 3 years of the invasion by D. kuriphilus, the number of trees attacked and the number of galls on each tree were spatially clustered. Tree height significantly predicted both variables, suggesting that gall wasps may use visual cues to locate suitable host trees, at least in the early stage of invasion. Assessment of the susceptibility of hybrid clones/pure species must take concurrent indicators of infestation levels into account. We suggest the use of indices involving galls on shoots because these enable good assessment of the damage to chestnut trees. The study findings add to existing knowledge on the susceptibility of hybrid chestnut clones. We report, for the first time, two hybrid clones resistant to the pest and one hybrid clone which exhibited consistently low values for all of the indicators of infestation level. The results have important implications regarding selection of plant material for use in afforestation in Spain, where the current high rate of chestnut planting is expected to continue.

Comparison of Auxin and Cytokinins Concentrations, and the Structure of Bacterial Community between Host Twigs and Lithosaphonecrus arcoverticus Galls.

Simple SummaryInsect galls are characterized by high concentrations of auxins and cytokinins. We calculated the correlation between the concentrations of indoleacetic acid (IAA), trans-zeatin riboside (tZR) and isopentenyladenine (iP) and the bacterial community structure of Lithosaphonecrus arcoverticus galls. Our results indicated the concentrations of IAA, tZR and iP were positively correlated with the bacterial community structure of L. arcoverticus galls. We suggest the high concentrations of IAA, tZR and iP may affect the bacterial community structure of L. arcoverticus galls.Insect galls are the abnormal growth of plant tissues induced by a wide variety of galling insects and characterized by high concentrations of auxins and cytokinins. It remains unclear whether the auxins and cytokinins affect the bacterial community structure of insect galls. We determined the concentrations of indoleacetic acid (IAA) as an example of auxin, trans-zeatin riboside (tZR) and isopentenyladenine (iP) as cytokinins in Lithosaphonecrus arcoverticus (Hymenoptera: Cynipidae) galls and the galled twigs of Lithocarpus glaber (Fagaceae) using liquid chromatography–tandem mass spectrometry. Moreover, for the first time, we compared the bacterial community structure of L. arcoverticus galls and galled twigs by high-throughput sequencing, and calculated the Spearman correlation and associated degree of significance between the IAA, tZR and iP concentrations and the bacterial community structure. Our results indicated the concentrations of IAA, tZR and iP were higher in L. arcoverticus galls than in galled twigs, and positively correlated with the bacterial community structure of L. arcoverticus galls. We suggest the high concentrations of IAA, tZR and iP may affect the bacterial community structure of L. arcoverticus galls.

Tissue-specific gene expression shows a cynipid wasp repurposes oak host gene networks to create a complex and novel parasite-specific organ.

Every organism on Earth depends on interactions with other organisms to survive. In each of these interactions, an organism must utilize the limited toolbox of genes and proteins it possesses to successfully manipulate or cooperate with another species, but it can also co-opt the genome machinery of its partner to expand its available tools. Insect-induced plant galls are an extreme example of this, wherein an insect hijacks the plant's genome to direct the initiation and development of galls consisting of plant tissue. However, previous transcriptomic studies have not evaluated individual tissues within a gall to determine the full extent to which a galling insect manipulates its host plant. Here we demonstrate that the cynipid wasp Dryocosmus quercuspalustris creates a complex parasite-specific organ from red oak tissue via massive changes in host gene expression. Our results show that the gall wasp is not merely modifying oak leaf tissue but creating extensive changes in gene expression between galled and ungalled tissue (differential expression in 28% of genes) and distinct gall tissue types (20% of genes). The outer gall tissue shows increases in various plant defence systems, which is consistent with its predicted functional role of protecting the wasp larva. The inner larval capsule shows suppression of large parts of the plant innate immune system and evidence for the wasp utilizing the plant's RNA interference mechanisms, which may be a potential mechanism for the wasp's control on gall growth.

Population Dynamics and Tree Damage of the Invasive Chestnut Gall Wasp, Dryocosmus kuriphilus, in Its Southernmost European Distributional Range.

Simple SummaryChestnut cultivation makes it possible to invigorate the economy of many rural areas in Europe. The chestnut gall wasp Dryocosmus kuriphilus is a serious invasive pest that causes severe damage to chestnut cultivation worldwide. Its rapid spread across Europe endangers the continuity of the entire chestnut industry. Despite this growing concern, scarce attention has been paid to the status of D. kuriphilus in its southernmost distributional range in continental Europe and limited knowledge on the factors modelling their populations is available. In this study, we assessed spatio-temporal patterns in the population dynamics, phenology and tree damage in southern Spain, and further evaluated the relationship between these variables and thermal trends. Strong variation in the population dynamics and flight phenology was found both among localities and over time, which was influenced by differences in thermal regimes. Similarly, tree damage evolved differently over time in each locality, thus suggesting that local conditions may determine significant differences in damage evolution. Our work contributes to a better understanding of this pest in countries throughout the Mediterranean basin and can be useful for further improvement of control and management strategies.The invasive chestnut gall wasp (CGW), Dryocosmus kuriphilus, the worst pest of chestnut cultivation, has spread worryingly throughout Europe in less than 20 years. Despite the great concern around this pest, little is known about the status in its southernmost distribution in continental Europe. We assessed spatio-temporal patterns in the population dynamics, phenology and tree damage caused by CGW in southern Spain. Likewise, the relationship between these variables and thermal trends was evaluated. We found strong variation in the population dynamics and flight phenology among localities and over time, which were highly influenced by changes in thermal regimes. Specifically, warmer localities and vegetative periods promoted higher population densities, a partial increase in the survival of immature stages, and advanced flight activity. Moreover, tree damage evolved differently over time in each locality, which suggests that local conditions may determine differences in damage evolution. Our findings evidence that great spatio-temporal variability in the CGW populations takes place across invaded areas in its southernmost European distributional range. Although control mechanisms have been introduced, implementation of further control and management measures are critical to cope with this main threat for the chestnut industry and to prevent its spread to nearing chestnut-producing areas.

Fate of carotenoids in the closed living system of gall–gall wasp–parasitoid

Fate of carotenoids in the closed living system of gall–gall wasp–parasitoid

Interactions of gall-formers and leaf-chewers on a tropical tree fern: evidence for non-repulsion and co-occurrence between insect guilds.

Host plant selection by herbivores is driven by a complex array of cues, including leaf traits and previous leaf damage. Herbivore-associated cues to host selection at the plant and leaf scale aid understanding of mechanisms responsible for host preference that might translate into increased performance, as well as processes structuring herbivore populations mediated by interactions. We investigated how changes induced by a galling insect in the tropical fern Cyathea phalerata act as repellent or attractant cues for sawfly feeding and the effects of leaf size on herbivory levels. We recorded gall abundance, damage by chewers, leaf size, plant nutritional quality, phenolic concentration and leaf anatomical traits between galled and non-galled leaf samples. Galled samples contained less N, higher levels of phenolics and higher C/N ratio. However, leaf-chewing damage did not differ between galled and non-galled leaves. The gall structure was avoided by chewers, as it had high concentrations of phenolics, lignification and suberization. Larger leaves sustained higher gall abundance, but leaf size did not have a significant effect on chewer damage. A co-occurrence index calculated for both guilds indicated that galls and chewers exhibited a distribution that did not differ from random, reinforcing that the two guilds on C. phalerata do not show patterns of repulsion such as those maintained by interspecific competition. Sawflies dismissing chemical cues indicate that the increase in phenolics caused by galling insects does not generate increased protection of the galled pinnules. Our results highlight ferns as key resources for herbivores and as a potential plant group to study new research avenues on plant-insect interactions.