Chromosome-level de novo genome assembly of two conifer-parasitic wasps, Megastigmus duclouxiana and Megastigmus sabinae, reveals genomic imprints of adaptation to hosts.

Conifers make up about one third of global forests but are threatened by seed parasitoid wasp species. Many of these wasps belong to the genus Megastigmus, yet little is known about their genomic background. In this study, we provide chromosome-level genome assemblies for two oligophagous conifer parasitoid species of Megastigmus, which represent the first two chromosome-level genomes of the genus. The assembled genomes of Megastigmus duclouxiana and M. sabinae are 878.48 Mb (scaffold N50 of 215.60 Mb) and 812.98 Mb (scaffold N50 of 139.16 Mb), respectively, which are larger than the genome size of most hymenopterans due to the expansion of transposable elements. Expanded gene families highlight the difference in sensory-related genes between the two species, reflecting the difference in their hosts. We further found that these two species have fewer family members but more single-gene duplications than polyphagous congeners in the gene families of ATP-binding cassette transporter (ABC), cytochrome P450 (P450) and olfactory receptors (OR). These findings shed light on the pattern of adaptation to a narrow spectrum of hosts in oligophagous parasitoids. Our findings suggest potential drivers underlying genome evolution and parasitism adaptation, and provide valuable resources for understanding the ecology, genetics and evolution of Megastigmus, as well as for the research and biological control of global conifer forest pests.

A new species of Megastigmus (Hymenoptera, Megastigmidae) from China.

Background: Most species of Megastigmus are considered important economic pests that grow in seeds, especially of conifers. Accurate identification of species is a crucial step for the biological research of parasitic pests and the further application of biological control. However, their large variety, small size, similar morphology and different growth and development stages have brought great challenges to taxonomic research. Traditional morphological identification often takes a long time and this requires us to seek a new method for rapid and accurate identification. Therefore, the better identification of Megastigmus urgently needs to be combined with molecular methods to help taxonomic development. New information: Here, Megastigmusdaduheensis sp. n. (Chalcidoidea: Megastigmidae) was identified, based on morphology and molecular markers, such as COI and Cytb. M.daduheensis sp. n. is distinct from other known species of the same genus in the morphology. The results of the molecular phylogenetic tree, similarity alignment and genetic distance indicate that the COI and Cytb sequences of M.daduheensis sp. n. are highly similar to M.sobinae and M.duclouxiana, but there are some genetic differences. The genetic distances of M.daduheensis sp. nov. with M.duclouxiana and M.sabinae were 0.34 and 0.33 and the percentages of shared base pairs were 76.3% and 76.8%, respectively. Both morphological and molecular data classified M.daduheensis sp. n. as a new species. The obtained COI and Cytb sequences of M.daduheensis sp. n. can be used as DNA barcodes, providing molecular data for rapid and accurate identification of this species in the future.

Mitochondrial genome characterization and phylogeny of Wallacea dactyliferae Maulik 1919 (Coleoptera: Chrysomelidae) from China.

Wallacea dactyliferae Maulik 1919 (Coleoptera: Chrysomelidae) has been reported as a new invasive palm pest in Asia recently. So far, a total of 29 species have been reported in Wallacea. In the present study, the whole mitochondrial genome of W. dactyliferae was identified for the first time (also for the first species of Wallacea) by using high throughput sequencing systems. The entire genome is 16,243 bp in length (ACCN: OK513040) consisting of 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and an A + T-rich region. Phylogenetic analysis revealed that insects from the same subfamily were clustered together, with W. dactyliferae being clustered together with other Cassidinae species. This study can provide essential DNA molecular data for further phylogenetic and evolutionary analyses for Chrysomelidae family of the Coleoptera order.

Corrigendum: Chromosome-Level Genome Assembly Reveals Signifificant Gene Expansion in the Toll and IMD Signaling Pathways of Dendrolimus kikuchii.

[This corrects the article DOI: 10.3389/fgene.2021.728418.].

Chromosome-Level Genome Assembly Reveals Significant Gene Expansion in the Toll and IMD Signaling Pathways of Dendrolimus kikuchii.

A high-quality genome is of significant value when seeking to control forest pests such as Dendrolimus kikuchii, a destructive member of the order Lepidoptera that is widespread in China. Herein, a high quality, chromosome-level reference genome for D. kikuchii based on Nanopore, Pacbio HiFi sequencing and the Hi-C capture system is presented. Overall, a final genome assembly of 705.51 Mb with contig and scaffold N50 values of 20.89 and 24.73 Mb, respectively, was obtained. Of these contigs, 95.89% had unique locations on 29 chromosomes. In silico analysis revealed that the genome contained 15,323 protein-coding genes and 63.44% repetitive sequences. Phylogenetic analyses indicated that D. kikuchii may diverged from the common ancestor of Thaumetopoea. Pityocampa, Thaumetopoea ni, Heliothis virescens, Hyphantria armigera, Spodoptera frugiperda, and Spodoptera litura approximately 122.05 million years ago. Many gene families were expanded in the D. kikuchii genome, particularly those of the Toll and IMD signaling pathway, which included 10 genes in peptidoglycan recognition protein, 19 genes in MODSP, and 11 genes in Toll. The findings from this study will help to elucidate the mechanisms involved in protection of D. kikuchii against foreign substances and pathogens, and may highlight a potential channel to control this pest.

An Ultrasonication-Assisted Cobalt Hydroxide Composite with Enhanced Electrocatalytic Activity toward Oxygen Evolution Reaction.

A catalyst toward oxygen evolution reaction (OER) was synthesized by depositing cobalt hydroxide on carbon black. Ultrasonication was applied during precipitation to improve the performance of the catalyst. The ultrasonic-assisted process resulted in the refinement of the cobalt hydroxide particles from 400 nm to 50 nm, and the thorough incorporation of these particles with carbon black substrate. The resulting product exhibited enhanced OER catalytic activity with an onset potential of 1.54 V (vs. reversible hydrogen electrode), a Tafel slope of 18.18 mV/dec, and a stable OER potential at a current density of 10 mA cm-2, because of the reduced resistance of the catalyst and the electron transfer resistance.

The complete mitochondrial genome of the melon fly Bactrocera cucurbitae (Diptera: Tephritidae).

The mitochondrial genome of Bactrocera cucurbitae, a representative of the Tephritid family, was completely sequenced for the first time. The B. cucurbitae genome is a double-stranded circular molecule of 15,825 bp long, including the entire set of the 37 genes. The 72.9% A+T content and 0.047 AT-skew are within the range of the known dipteran genomes. Comparative analyses showed that dipteran mitochondrial protein-coding genes present complex evolutionary patterns. Some of the codon families were strongly biased towards J-strand. The mitochondrial ATP8 of B. cucurbitae exhibited a faster substitution rate than other genes. Cox1 is the slowest evolving protein and could be considered as a potential phylogenetic marker.