The complete mitochondrial genome of Scambus vesicarius Ratzeburg (Hymenoptera: ichneumonidae: pimplinae)

The genomic-level characteristics play a pivotal role as genetic assets for the identification of species and phylogenetic analysis. Here, we sequenced and analyzed the mitochondrial genome of Scambus vesicarius (Ratzeburg), which was first morphologically described in "Die Ichneumonen der Forstinsecten in forstlicher und entomologischer Beziehung." The motivation for this research arises from the necessity to comprehend the genetic composition and evolutionary history of S. vesicarius, a genus of parasitic wasps with potential agricultural significance, which. The circular genome is 26,103bp in length with an overall base composition of 42.02% for A, 43.71% for T, 8.64% for C, and 5.63% for G. The mitochondrial genome of S. vesicarius contained 13 protein-coding genes that initiated by the ATN codon, 22 transfer RNA genes, two ribosomal RNA genes (rRNAs), and a control region (CR). Phylogenetic analyses using Maximum-likelihood methods supported that S. vesicarius is closely related to Pimpla luctuosa, both of which belong to the subfamily Pimplinae, forming a clade that is sister to other subfamilies of Ichneumonidae. This study provides value not only into the genetic diversity and evolutionary history of S. vesicarius at the mitochondrial level but basic research on parasitic wasp biology and applied efforts in biological control.

Parasitoid speciation and diversification

Parasitoid wasps may well be the most species-rich animal group on Earth, and host-parasitoid interactions may thereby be one of the most common types of species interactions. Understanding the major mechanisms underlying diversification in parasitoids should be a high priority, not the least in order to predict consequences from high extinction rates currently observed. The two major hypotheses explaining host-associated diversification are the escape-and-radiate hypothesis and the oscillation hypothesis, where the former assumes that key innovations are major drivers of radiation bursts, whereas the latter rather assumes that diversification depends on processes acting on the standing genetic variation that influences host use. This paper reviews the recent literature on parasitoid speciation in light of these major hypotheses to identify potential key innovations and host use variability underlying diversification. The paper also calls upon recent theoretical advances from a similar system, plant-butterfly interactions, to provide shortcuts in the development of theories explaining the high diversity of parasitoid wasps.

External insect gall morphology influences the functional guilds of natural enemy communities

The evolution of diverse and novel morphological traits is poorly understood, especially how symbiotic interactions can drive these adaptations. The extreme diversity of external traits in insect-induced galls is currently explained by the Enemy Hypothesis, in which these traits have selective advantage in deterring parasitism. While previous tests of this hypothesis used only taxonomic identity, we argue that ecologically functional traits of enemies (i.e. mode of parasitism, larval development strategy) are a crucial addition. Here, we characterize parasitoid guild composition across four disparate gall systems and find consistent patterns of association between enemy guild and gall morphology. Specifically, galls with a longer average larva-to-surface distance host a significantly higher proportion of enemies with a distinct combination of functional traits (i.e. ectoparasitic, idiobiont, elongate ovipositor). Our results support the Enemy Hypothesis and highlight the importance of species ecology in examining insect communities and the evolution of novel defensive characters.

Genomic evidence for contrasting patterns of host-associated genetic differentiation across shared host-plant species in leaf- and bud-galling sawflies

Resource specialization and ecological speciation arising through host-associated genetic differentiation (HAD) are frequently invoked as an explanation for the high diversity of plant-feeding insects and other organisms with a parasitic lifestyle. While genetic studies have demonstrated numerous examples of HAD in insect herbivores, the rarity of comparative studies means that we still lack an understanding of how deterministic HAD is, and whether patterns of host shifts can be predicted over evolutionary timescales. We applied genome-wide single nucleotide polymorphism and mitochondrial DNA sequence data obtained through genome resequencing to define species limits and to compare host-plant use in population samples of leaf- and bud-galling sawflies (Hymenoptera: Tenthredinidae: Nematinae) collected from seven shared willow (Salicaceae: Salix) host species. To infer the repeatability of long-term cophylogenetic patterns, we also contrasted the phylogenies of the two galler groups with each other as well as with the phylogeny of their Salix hosts estimated based on RADseq data. We found clear evidence for host specialization and HAD in both of the focal galler groups, but also that leaf gallers are more specialized to single host species compared with most bud gallers. In contrast to bud gallers, leaf gallers also exhibited statistically significant cophylogenetic signal with their Salix hosts. The observed discordant patterns of resource specialization and host shifts in two related galler groups that have radiated in parallel across a shared resource base indicate a lack of evolutionary repeatability in the focal system, and suggest that short- and long-term host use and ecological diversification in plant-feeding insects are dominated by stochasticity and/or lineage-specific effects.

A molecular-based identification resource for the arthropods of Finland

To associate specimens identified by molecular characters to other biological knowledge, we need reference sequences annotated by Linnaean taxonomy. In this study, we (1) report the creation of a comprehensive reference library of DNA barcodes for the arthropods of an entire country (Finland), (2) publish this library, and (3) deliver a new identification tool for insects and spiders, as based on this resource. The reference library contains mtDNA COI barcodes for 11,275 (43%) of 26,437 arthropod species known from Finland, including 10,811 (45%) of 23,956 insect species. To quantify the improvement in identification accuracy enabled by the current reference library, we ran 1000 Finnish insect and spider species through the Barcode of Life Data system (BOLD) identification engine. Of these, 91% were correctly assigned to a unique species when compared to the new reference library alone, 85% were correctly identified when compared to BOLD with the new material included, and 75% with the new material excluded. To capitalize on this resource, we used the new reference material to train a probabilistic taxonomic assignment tool, FinPROTAX, scoring high success. For the full-length barcode region, the accuracy of taxonomic assignments at the level of classes, orders, families, subfamilies, tribes, genera, and species reached 99.9%, 99.9%, 99.8%, 99.7%, 99.4%, 96.8%, and 88.5%, respectively. The FinBOL arthropod reference library and FinPROTAX are available through the Finnish Biodiversity Information Facility (www.laji.fi) at https://laji.fi/en/theme/protax. Overall, the FinBOL investment represents a massive capacity-transfer from the taxonomic community of Finland to all sectors of society.

A phylogenetic perspective on parasitoid host ranges with implications for biological control

Interactions that shape parasitoid host ranges occur within the context of both host and parasitoid phylogenetic history. While host-associated speciation of parasitoids can lead to increased host specificity, it can also lead to a broadening of host range through radiation onto a new group of host species. In both cases, sister-species of parasitoids may have widely divergent host ranges. But how should host range be estimated? Traditional views of host ranges as simple lists of species have given way to analyses that can detect host phylogenetic signal. Host relatedness can also be codified into useful indices that reflect the phylogenetic breadth of host range. All of these considerations have important implications for biological control, particularly in the realm of risk assessment.

Dissecting host-associated communities with DNA barcodes

DNA barcoding and metabarcoding methods have been invaluable in the study of interactions between host organisms and their symbiotic communities. Barcodes can help identify individual symbionts that are difficult to distinguish using morphological characters, and provide a way to classify undescribed species. Entire symbiont communities can be characterized rapidly using barcoding and especially metabarcoding methods, which is often crucial for isolating ecological signal from the substantial variation among individual hosts. Furthermore, barcodes allow the evolutionary histories of symbionts and their hosts to be assessed simultaneously and in reference to one another. Here, we describe three projects illustrating the utility of barcodes for studying symbiotic interactions: first, we consider communities of arthropods found in the ant-occupied domatia of the East African ant-plant Vachellia (Acacia) drepanolobium; second, we examine communities of arthropod and protozoan inquilines in three species of Nepenthes pitcher plant in South East Asia; third, we investigate communities of gut bacteria of South American ants in the genus Cephalotes. Advances in sequencing and computation, and greater database connectivity, will continue to expand the utility of barcoding methods for the study of species interactions, especially if barcoding can be approached flexibly by making use of alternative genetic loci, metagenomes and whole-genome data.

This article is part of the themed issue ‘From DNA barcodes to biomes’.

Identification of sawflies and horntails (Hymenoptera, 'Symphyta') through DNA barcodes: successes and caveats

The 'Symphyta' is a paraphyletic assemblage at the base of the order Hymenoptera, comprising 14 families and about 8750 species. All have phytophagous larvae, except for the Orussidae, which are parasitoids. This study presents and evaluates the results of DNA barcoding of approximately 5360 specimens of 'Symphyta', mainly adults, and 4362 sequences covering 1037 species were deemed of suitable quality for inclusion in the analysis. All extant families are represented, except for the Anaxyelidae. The majority of species and specimens are from Europe, but approximately 38% of the species and 13% of the specimens are of non-European origin. The utility of barcoding for species identification and taxonomy of 'Symphyta' is discussed on the basis of examples from each of the included families. A significant level of cryptic species diversity was apparent in many groups. Other attractive applications include the identification of immature stages without the need to rear them, community analyses based on metabarcoding of bulk samples and association of the sexes of adults.

Tracking the elusive history of diversification in plant-herbivorous insect-parasitoid food webs: insights from figs and fig wasps

The food webs consisting of plants, herbivorous insects and their insect parasitoids are a major component of terrestrial biodiversity. They play a central role in the functioning of all terrestrial ecosystems, and the number of species involved is mind-blowing (Nyman et al. 2015). Nevertheless, our understanding of the evolutionary and ecological determinants of their diversity is still in its infancy. In this issue of Molecular Ecology, Sutton et al. (2016) open a window into the comparative analysis of spatial genetic structuring in a set of comparable multitrophic models, involving highly species-specific interactions: figs and fig wasps. This is the first study to compare genetic structure using population genetics tools in a fig-pollinating wasp (Pleistodontes imperialis sp1) and its main parasitoid (Sycoscapter sp.A). The fig-pollinating wasp has a discontinuous spatial distribution that correlates with genetic differentiation, while the parasitoid bridges the discontinuity by parasitizing other pollinator species on the same host fig tree and presents basically no spatial genetic structure. The full implications of these results for our general understanding of plant-herbivorous insect-insect parasitoids diversification become apparent when envisioned within the framework of recent advances in fig and fig wasp biology.

The use of DNA barcodes in food web construction-terrestrial and aquatic ecologists unite!

By depicting who eats whom, food webs offer descriptions of how groupings in nature (typically species or populations) are linked to each other. For asking questions on how food webs are built and work, we need descriptions of food webs at different levels of resolution. DNA techniques provide opportunities for highly resolved webs. In this paper, we offer an exposé of how DNA-based techniques, and DNA barcodes in particular, have recently been used to construct food web structure in both terrestrial and aquatic systems. We highlight how such techniques can be applied to simultaneously improve the taxonomic resolution of the nodes of the web (i.e., the species), and the links between them (i.e., who eats whom). We end by proposing how DNA barcodes and DNA information may allow new approaches to the construction of larger interaction webs, and overcome some hurdles to achieving adequate sample size. Most importantly, we propose that the joint adoption and development of these techniques may serve to unite approaches to food web studies in aquatic and terrestrial systems-revealing the extent to which food webs in these environments are structured similarly to or differently from each other, and how they are linked by dispersal.

Community ecology of the 'other' parasitoids

The study of parasitoid communities is an active and dynamic field. Most studies, however, are focused primarily on parasitic wasps, despite the thousands of other insect parasitoids distributed across many lineages. Although questions in parasitoid community ecology are much the same for different groups, answers to these questions may not be due to differing biological traits. The ecology of non-hymenopteran ('NH') parasitoid communities is poorly known, but recent work indicates that habitat and host traits have strong impacts on the size and composition of these parasitoid assemblages. Recent food-web analyses indicate that host ranges vary widely within and among taxa and associations are shaped by host ecology and defenses. Evidence is also accumulating for strong 'bottom-up' and 'top-down' multi-trophic interactions between NH-parasitoids and nonadjacent trophic levels, as well as trait-mediated indirect effects on communities. Recent technical and conceptual advances in characterizing and comparing food webs, consideration of phylogenetic history, and increasing anthropogenic impacts provide many new and stimulating areas of research on parasitoid communities.