The mitochondrial genome and life history of Tomostethus sinofraxini (Hymenoptera: Tenthredinidae), an emerging pest of Fraxinus chinensis

Tomostethus sinofraxini Wang & Wei (a new name is proposed for Tomostethus fraxini Niu & Wei, 2022: Tomostethus sinofraxini Wang & Wei, nom. nov.), an emerging sawfly pest of the Chinese ash, Fraxinus chinensis, is now endemic to Beijing, Tianjin, Hebei, and Shandong provinces. Given the severity of its infestation and the speed of its range expansion, we studied the phylogenetic relationship of T. sinofraxini with other sawfly species and its life history to be better informed for the management strategies. The nearly complete T. sinofraxini mitogenome is 16,169 bp in length and encodes 2 ribosomal RNAs (rrnL and rrnS), 22 transfer RNAs (tRNAs), and 13 protein-coding genes. The nucleotide composition is biased toward adenine and thymine (A + T = 81.7%). In comparison to the architecture of the ancestral insect mitogenome, 2 transposition events occur on the IQM tRNA cluster, rearranging it from IQM to MQI. Our phylogenetic analysis suggests that T. sinofraxini belongs to a group composed of paraphyletic subfamilies Blennocampinae and Heterarthrinae. In addition, to document its life history, we observed T. sinofraxini development at 2 geographical locations in Beijing, China, with different altitudes. At Jiulong Mountain, with a higher altitude and a lower average temperature, the developmental time of egg, larval, and adult stages was 19%-31% longer than that observed at the Chinese Academy of Forestry. A basic understanding of biological traits and molecular signatures is the critical first step to develop an integrated pest management framework for this emerging pest of the Chinese ash.

Cypress terpenes in sawfly larva of Susana cupressi (Hymenoptera: Symphyta: Tenthredinoidea)

Several sawfly species (Hymenoptera: Symphyta) possess larval stages with oesophageal diverticula in which plant compounds are sequestered and used for defence against predators. These organs are present in the larvae of Susana (Tenthredinidae) but remain poorly studied. Here, the aim was to analyse the diverticula extract of Susana cupressi by gas chromatography-mass spectrometry to better understand the ecology of this species. The foliage of the hostplant (Cupressus sempervirens), as well as the larval foregut, midgut, and haemolymph were also analysed. Complementary data were gathered by morphological observations, bioassays using ants, and genetic analyses to identify the studied Susana species. Altogether, 48 terpenes were identified, 30 being sesquiterpenes. The terpenes were generally detected in the foliage, but also in the diverticula, foregut, and midgut, whereas none of them in the haemolymph. The main compounds were alpha-cedrene, alpha-fenchene, alpha-pinene, alpha-terpinyl acetate, beta-myrcene, beta-pinene, cedrol, delta 3-carene, epi-bicyclosesquiphellandrene, germacrene D, limonene, sabinene, and terpinolene. The chemical profiles of these 13 compounds were significantly correlated between foliage-diverticula, diverticula-foregut and foregut-midgut, but not correlated for the three remaining possible comparisons. Alpha-pinene decreased and germacrene D increased from the foliage to the diverticula, which may reflect a specific sequestration of the latter terpene and its known deleterious effects on insects. We conclude that larvae of S. cupressi, similarly to those of diprionids, are well defended against predatory attacks by sequestering and regurgitating hostplant terpenes, including germacrene D.

Phylogenomic Analyses of the Tenthredinoidea Support the Familial Rank of Athaliidae (Insecta, Tenthredinoidea)

The systematic status of the genus Athalia and related genera is a perennial controversy in sawfly taxonomy. Several authors have hypothesized that the placement of Athalia within the Tenthredinidae is artificial, but no studies have focused on this topic. If the hypothesis that Athalia does not belong to Tenthredinidae can be supported, the taxonomic framework of Tenthredinoidea needs revision. We present a comprehensive phylogenomic study of Tenthredinoidae, focusing on the positions of Athalia and related genera by sampling 80 representatives mainly of the Tenthredinoidea, including Heptamelinae and Blasticotomidae. Our phylogenetic reconstructions based on nuclear genes and mitochondrial (mt) sequences support Athalia and related genera as a distinct clade sister to Tenthredinidae + (Cimbicidae + Diprionidae). A comparison of symphytan mitochondrial genomes reveals an innovative gene rearrangement pattern in Athaliidae, in which Dentathalia demonstrates a more ancestral pattern than Athalia and Hypsathalia. The lineage specificity of mt rRNA secondary structures also provides sufficient support to consider Athaliidae as a separate family. In summary, the phylogeny and genomic structural changes unanimously support the taxonomic treatment of Athaliidae as a family and the re-establishment of Dentathalia as a valid genus.

Mitochondrial Phylogenomics of Tenthredinidae (Hymenoptera: Tenthredinoidea) Supports the Monophyly of Megabelesesinae as a Subfamily

Tenthredinidae represents one of the external feeders of the most diverse superfamily, Tenthredinoidea, with diverse host plant utilization. In this study, four complete mitochondrial genomes (mitogenomes), those of Cladiucha punctata, Cladiucha magnoliae, Megabeleses magnoliae, and Megabeleses liriodendrovorax, are newly sequenced and comparatively analyzed with previously reported tenthredinid mitogenomes. The close investigation of mitogenomes and the phylogeny of Tenthredinidae leads us to the following conclusions: The subfamilial relationships and phylogenetic placements within Tenthredinidae are mostly found to be similar to the previously suggested phylogenies. However, the present phylogeny supports the monophyly of Megabelesesinae as a subfamily, with the sister-group placement of Cladiucha and Megabeleses outside of Allantinae. The occurrence of the same type of tRNA rearrangements (MQI and ANS1ERF) in the mitogenomes of Megabelesesinae species and the presence of apomorphic morphological characters also provide robust evidence for this new subfamily. The divergence and diversification times of the subfamilies appear to be directly related to colonization of the flowering plants following the Early Cretaceous. The origin time and diversification patterns of Megabelesesinae were also well matched with the divergence times of their host plants from Magnoliaceae.

From Arge to Zenarge: adult morphology and phylogenetics of argid sawflies (Hymenoptera: Argidae)

The Argidae is the second most diverse family of the ‘Symphyta’ with more than 900 described species. Here we present the first comprehensive phylogenetic study for the family. We compare the adult skeleton anatomy of representatives of 57 described argid genera from different biogeographic regions. We score 223 characters for 117 terminal taxa, and apply maximum parsimony inference to reconstruct the phylogeny, using equal weights and implied weights analyses. The Argidae sensu stricto, i.e. all Argidae except Zenarge, are consistently retrieved as monophyletic. The position of Zenarge changes according to the implied weighting parameters: ((Zenarge+Pergidae)+Argidae) at low (1–3) k-values, (Zenarge+(Pergidae+Argidae)) at high (4–30) k-values. We describe in detail the skeletal anatomy of Zenarge turneri and propose to raise it to family status: Zenargidae stat. revis. We consider the ridge on the teloparameres (=harpes) of the male genitalia to be the main autapomorphy of adults of the Argidae sensu stricto. We recover two main clades within the family and suggest recognizing these as the subfamilies Arginae and Sterictiphorinae. We trace the evolution of characters on the preferred implied weights tree. The genera Arge, Didymia, Pampsilota, Ptenos and Sphacophilus were paraphyletic.

Complete mitochondrial genome sequence of Labriocimbex sinicus, a new genus and new species of Cimbicidae (Hymenoptera) from China

Labriocimbex sinicus Yan & Wei gen. et sp. nov. of Cimbicidae is described. The new genus is similar to Praia Andre and Trichiosoma Leach. A key to extant Holarctic genera of Cimbicinae is provided. To identify the phylogenetic placement of Cimbicidae, the mitochondrial genome of L. sinicus was annotated and characterized using high-throughput sequencing data. The complete mitochondrial genome of L. sinicus was obtained with a length of 15,405 bp (GenBank: MH136623; SRA: SRR8270383) and a typical set of 37 genes (22 tRNAs, 13 PCGs, and two rRNAs). The results demonstrated that all PCGs were initiated by ATN codon, and ended with TAA or T stop codons. The study reveals that all tRNA genes have a typical clover-leaf secondary structure, except for trnS1. Remarkably, the secondary structures of the rrnS and rrnL of L. sinicus were much different from those of Corynis lateralis. Phylogenetic analyses verified the monophyly and positions of the three Cimbicidae species within the superfamily Tenthredinoidea and demonstrated a relationship as (Tenthredinidae + Cimbicidae) + (Argidae + Pergidae) with strong nodal supports. Furthermore, we found that the generic relationships of Cimbicidae revealed by the phylogenetic analyses based on COI genes agree quite closely with the systematic arrangement of the genera based on the morphological characters. Phylogenetic tree based on two methods shows that L. sinicus is the sister group of Praia with high support values. We suggest that Labriocimbex belongs to the tribe Trichiosomini of Cimbicinae based on adult morphology and molecular data. Besides, we suggest to promote the subgenus Asitrichiosoma to be a valid genus.

The West Palaearctic genera of Nematinae (Hymenoptera, Tenthredinidae)

Keys to adults and larvae of the genera of West Palaearctic nematine sawflies are presented. Species of some of the smaller genera are keyed, and their taxonomy, distribution, and host plants reviewed, with a geographic focus on north-western Europe, particularly Sweden. Dinematus Lacourt, 2006 is a new junior subjective synonym of Pristiphora Latreille, 1810, resulting in the new combination Pristiphora krausi (Lacourt, 2006) for the type species of Dinematus. Hemichroa monticola Ermolenko, 1960 is a new junior subjective synonym of Hemichroa australis (Serville, 1823). Lectotypes are designated for Tenthredo opaca Fabricius, 1775, Mesoneura opaca var. nigerrima Enslin, 1914, Mesoneura opaca var. obscuriventris Enslin, 1914, Nematus hypogastricus Hartig, 1837, Nematus alnivorus Hartig, 1840, Leptopus rufipes Förster, 1854, Nematus protensus Förster, 1854, and Platycampus luridiventris var. pleuritica Enslin, 1915. A phylogenetic analysis based on four genes (mitochondrial COI and nuclear NaK, POL2, and TPI) supports the current generic classification.

A new xyelotomid (Hymenoptera) from the Middle Jurassic of China displaying enigmatic venational asymmetry

BACKGROUND

Pterygota insects typically have symmetric veins in left and right wings. For studying taxonomy and phylogeny of fossil insects, venational patterns are commonly used as diagnostic characters, in conjunction with preserved body characters. Some examples of asymmetrical venation are known among extant insects, but only a few fossil insects with asymmetric wings have been reported, among which a previously described xyelotomid of Hymenoptera, Xyelocerus diaphanous, displays an unusual, small cell of vein Rs in the left forewing, but not in the right.

RESULTS

Herein we report a new sawfly of the family Xyelotomidae, Aethotoma aninomorpha gen. et sp. nov., from the late Middle Jurassic of China having a simple Sc in the forewing and Sc with two branches in the hind wing. In additional, the new specimen exhibits an enigmatic venational asymmetry. In the right forewing, crossvein 2r-rs of forms a loop, then forks into 2 long branches reaching Rs, while 2r-rs of the left forewing forks into 2 short branches reaching Rs, in contrast to a linear 2r-rs in typical fossil and extant sawflies.

CONCLUSION

Such rare asymmetrical venation found from fossil sawflies provides a glance at early occurrences of venational variability and instability, or possibly aberrational development, for insects in the late Middle Jurassic.