Genome of the webworm Hyphantria cunea unveils genetic adaptations supporting its rapid invasion and spread

Molecular Basis of CO2 Sensing in Hyphantria cunea

Carbon dioxide (CO2) released by plants can serve as a cue for regulating insect behaviors. Hyphantria cunea is a widely distributed forestry pest that may use CO2 as a cue for foraging and oviposition. However, the molecular mechanism underlying its ability to sense CO2 has not been elucidated. Our initial study showed that CO2 is significantly attractive to H. cunea adults. Subsequently, 44 H. cunea gustatory receptors (GRs) were identified using transcriptome data, and 3 candidate CO2 receptors that are specifically expressed in the labial palps were identified. In vivo electrophysiological assays revealed that the labial palp is the primary organ for CO2 perception in H. cunea, which is similar to findings in other lepidopteran species. By using the Xenopus oocyte expression system, we showed that the HcunGR1 and HcunGR3 co-expressions produced a robust response to CO2, but HcunGR2 had an inhibitory effect on CO2 perception. Finally, immunohistochemical staining revealed sexual dimorphism in the CO2-sensitive labial pit organ glomerulus (LPOG). Taken together, our results clarified the mechanism by which H. cunea sense CO2, laying the foundation for further investigations into the role of CO2 in the rapid spread of H. cunea.

Can ecological niche models be used to accurately predict the distribution of invasive insects? A case study of Hyphantria cunea in China

In recent decades, ecological niche models (ENMs) have been widely used to predict suitable habitats for species. However, for invasive organisms, the prediction accuracy is unclear. In this study, we employed the most widely used maximum entropy (MaxEnt) model and ensemble model (EM) Biomod2 and verified the practical effectiveness of the ENM in predicting the distribution areas of invasive insects based on the true occurrence of Hyphantria cunea in China. The results showed that when only limited data of invasive areas were used, the two ENMs could not effectively predict the distribution of suitable habitats of H. cunea, although the use of global data can greatly improve the prediction accuracy of ENMs. When analyzing the same data, Biomod2's prediction accuracy was significantly better than that of MaxEnt. For long-term predictions, the area of suitable habitat predicted by the ENMs was much greater than the occurrence area; for short-term predictions, the accuracy of the predicted area was significantly improved. Under the current conditions, the area of suitable habitat for H. cunea in China is 118 × 104 km2, of which 59.32% is moderately or highly suitable habitat. Future climate change could significantly increase the suitable habitat area of H. cunea in China, and the predicted area of suitable habitats in all climate scenarios exceeded 355 × 104 km2, accounting for 36.98% of the total land area in China. This study demonstrates the use of ENMs to study invasive insects and provides a reference for the management of H. cunea in China.

Gut microbiota facilitate adaptation of invasive moths to new host plants

Gut microbiota are important in the adaptation of phytophagous insects to their plant hosts. However, the interaction between gut microbiomes and pioneering populations of invasive insects during their adaptation to new hosts, particularly in the initial phases of invasion, has been less studied. We studied the contribution of the gut microbiome to host adaptation in the globally recognized invasive pest, Hyphantria cunea, as it expands its range into southern China. The southern population of H. cunea shows effective adaptation to Metasequoia glyptostroboides and exhibits greater larval survival on Metasequoia than the original population. Genome resequencing revealed no significant differences in functions related to host adaptation between the two populations. The compatibility between southern H. cunea populations and M. glyptostroboides revealed a correlation between the abundance of several gut bacteria genera (Bacteroides, Blautia, and Coprococcus) and H. cunea survival. Transplanting the larval gut microbiome from southern to northern populations enhanced the adaptability of the latter to the previously unsuitable plant M. glyptostroboides. This research provides evidence that the gut microbiome of pioneering populations can enhance the compatibility of invasive pests to new hosts and enable more rapid adaptation to new habitats.

Caterpillars Detoxify Diterpenoid from Nepeta stewartiana by the Molting Hormone Gene CYP306A1

Herbivorous insects are well known for detoxifying a broad range of the defense compounds produced by the plants that they feed on, but knowledge of the mechanisms of detoxification is still very limited. Here, we describe a system in which two species of lepidopteran caterpillars metabolize an abietane diterpene from the plants of Nepeta stewartiana Diels to an oxygenated derivative that is less active biologically. We found that this transformation could be catalyzed by a cytochrome P450 enzyme in caterpillars, which are associated with molting. Most interestingly, abietane diterpene targets the molting-associated gene CYP306A1 to alter the content of molting hormones in the insect at specific developmental stages and competitively inhibit molting hormone metabolism. These findings identify the mechanism by which caterpillars are able to detoxify abietane diterpenoid through hydroxylation at the C-19 position, which may be opening up exciting research questions into the mechanisms of interaction between plants and insects.

Digestive Characteristics of Hyphantria cunea Larvae on Different Host Plants

Digestive physiology mediates the adaptation of phytophagous insects to host plants. In this study, the digestive characteristics of Hyphantria cunea larvae feeding preferences on different host plants were investigated. The results showed that the body weight, food utilization, and nutrient contents of H. cunea larvae feeding on the high-preference host plants were significantly higher than those feeding on the low-preference host plants. However, the activity of larval digestive enzymes in different host plants presented an opposite trend, as higher α-amylase or trypsin activity was observed in the group feeding on the low-preference host plants than that feeding on the high-preference host plants. Upon treatment of leaves with α-amylase and trypsin inhibitors, the body weight, food intake, food utilization rate, and food conversion rate of H. cunea larvae significantly decreased in all host plant groups. Furthermore, the H. cunea comprised highly adaptable compensatory mechanisms of digestion involving digestive enzymes and nutrient metabolism in response to digestive enzyme inhibitors. Taken together, digestive physiology mediates the adaptation of H. cunea to multiple host plants, and the compensatory effect of digestive physiology is an important counter-defense strategy implemented by H. cunea to resist plant defense factors, especially the insect digestive enzyme inhibitors.

Comparison of gut bacterial communities of Hyphantriacunea Drury (Lepidoptera, Arctiidae), based on 16S rRNA full-length sequencing

There are a large number of microorganisms in the gut of insects, which form a symbiotic relationship with the host during the long-term co-evolution process and have a significant impact on the host's nutrition, physiology, development, immunity, stress tolerance and other aspects. However, the composition of the gut microbes of Hyphantriacunea remains unclear. In order to investigate the difference and diversity of intestinal microbiota of H.cunea larvae feeding on different host plants, we used PacBio sequencing technology for the first time to sequence the 16S rRNA full-length gene of the intestinal microbiota of H.cunea. The species classification, β diversity and function of intestinal microflora of the 5th instar larvae of four species of H.cunea feeding on apricot, plum, redbud and Chinese ash were analysed. The results showed that a total of nine phyla and 65 genera were identified by PacBio sequencing, amongst which Firmicutes was the dominant phylum and Enterococcus was the dominant genus, with an average relative abundance of 59.29% and 52.16%, respectively. PERMANOVA analysis and cluster heat map showed that the intestinal microbiomes of H.cunea larvae, fed on different hosts, were significantly different. LEfSe analysis confirmed the effect of host diet on intestinal community structure and PICRUSt2 analysis showed that most of the predictive functions were closely related to material transport and synthetic, metabolic and cellular processes. The results of this study laid a foundation for revealing the interaction between the intestinal microorganisms of H.cunea and its hosts and provided ideas for exploring new green prevention and control strategies of H.cunea.

Tracking Adaptive Pathways of Invasive Insects: Novel Insight from Genomics

Despite the huge human and economic costs of invasive insects, which are the main group of invasive species, their environmental impacts through various mechanisms remain inadequately explained in databases and much of the invasion biology literature. High-throughput sequencing technology, especially whole-genome sequencing, has been used as a powerful method to study the mechanisms through which insects achieve invasion. In this study, we reviewed whole-genome sequencing-based advances in revealing several important invasion mechanisms of invasive insects, including (1) the rapid genetic variation and evolution of invasive populations, (2) invasion history and dispersal paths, (3) rapid adaptation to different host plant ranges, (4) strong environmental adaptation, (5) the development of insecticide resistance, and (6) the synergistic damage caused by invasive insects and endosymbiotic bacteria. We also discussed prevention and control technologies based on whole-genome sequencing and their prospects.

Comparing the Performance of Hyphantria cunea (Lepidoptera: Arctiidae) on Artificial and Natural Diets: Feasibility of Mass-Rearing on Artificial Diets

In China, Hyphantria cunea (Drury) is an invasive phytophagous pest; it attacks nearly all species of defoliated trees. To develop integrated pest management programs (IPM) for H. cunea, we need to ensure the availability of insects by mass-rearing them on artificial diets under laboratory conditions. This study compared the growth characteristics, nutritional indices, growth indices, and digestive enzyme activity of insects reared on Pterocarya stenoptera C.DC (Fagales: Juglandaceae), the Chinese wingnut, and an artificial diet. We also investigated the correlation between diet components and growth indices using principal components analysis and Pearson correlation analysis. We found that mass-rearing of H. cunea on an artificial diet was feasible. It led to a shorter developmental period, with heavier larvae and pupae than natural diets. The principal components analysis indicated that the growth indices and α-Amylase were significantly positively associated with PC1, which explained 82.45% of the total data variability. Pearson correlation analysis showed a significant correlation between digestion, absorption parameters, and growth. Developing a mass-rearing program to produce H. cunea on an artificial diet will be valuable for improving IPM strategies. Understanding the mechanism of the responses of phytophagous insect populations to anthropogenic diet regulation can provide new ideas and methods for pest control.

Comparison of Long-Read Methods for Sequencing and Assembly of Lepidopteran Pest Genomes

Lepidopteran species are mostly pests, causing serious annual economic losses. High-quality genome sequencing and assembly uncover the genetic foundation of pest occurrence and provide guidance for pest control measures. Long-read sequencing technology and assembly algorithm advances have improved the ability to timeously produce high-quality genomes. Lepidoptera includes a wide variety of insects with high genetic diversity and heterozygosity. Therefore, the selection of an appropriate sequencing and assembly strategy to obtain high-quality genomic information is urgently needed. This research used silkworm as a model to test genome sequencing and assembly through high-coverage datasets by de novo assemblies. We report the first nearly complete telomere-to-telomere reference genome of silkworm Bombyx mori (P50T strain) produced by Pacific Biosciences (PacBio) HiFi sequencing, and highly contiguous and complete genome assemblies of two other silkworm strains by Oxford Nanopore Technologies (ONT) or PacBio continuous long-reads (CLR) that were unrepresented in the public database. Assembly quality was evaluated by use of BUSCO, Inspector, and EagleC. It is necessary to choose an appropriate assembler for draft genome construction, especially for low-depth datasets. For PacBio CLR and ONT sequencing, NextDenovo is superior. For PacBio HiFi sequencing, hifiasm is better. Quality assessment is essential for genome assembly and can provide better and more accurate results. For chromosome-level high-quality genome construction, we recommend using 3D-DNA with EagleC evaluation. Our study references how to obtain and evaluate high-quality genome assemblies, and is a resource for biological control, comparative genomics, and evolutionary studies of Lepidopteran pests and related species.

Genome sequence and silkomics of the spindle ermine moth, Yponomeuta cagnagella, representing the early diverging lineage of the ditrysian Lepidoptera

Many lepidopteran species produce silk, cocoons, feeding tubes, or nests for protection from predators and parasites for caterpillars and pupae. Yet, the number of lepidopteran species whose silk composition has been studied in detail is very small, because the genes encoding the major structural silk proteins tend to be large and repetitive, making their assembly and sequence analysis difficult. Here we have analyzed the silk of Yponomeuta cagnagella, which represents one of the early diverging lineages of the ditrysian Lepidoptera thus improving the coverage of the order. To obtain a comprehensive list of the Y. cagnagella silk genes, we sequenced and assembled a draft genome using Oxford Nanopore and Illumina technologies. We used a silk-gland transcriptome and a silk proteome to identify major silk components and verified the tissue specificity of expression of individual genes. A detailed annotation of the major genes and their putative products, including their complete sequences and exon-intron structures is provided. The morphology of silk glands and fibers are also shown. This study fills an important gap in our growing understanding of the structure, evolution, and function of silk genes and provides genomic resources for future studies of the chemical ecology of Yponomeuta species.

Evaluation of Optimal Reference Genes for qRT-PCR Analysis in Hyphantria cunea (Drury)

The relative quantification of gene expression is mainly achieved through reverse transcription-quantitative PCR (qRT-PCR); however, its reliability and precision rely on proper data normalization using one or more optimal reference genes. Hyphantria cunea (Drury) has been an invasive pest of forest trees, ornamental plants, and fruit trees in China for many years. Currently, the molecular physiological role of reference genes in H. cunea is unclear, which hinders functional gene study. Therefore, eight common reference genes, RPS26, RPL13, UBI, AK, RPS15, EIF4A, β-actin, α-tub, were selected to evaluate levels of gene expression stability when subjected to varied experimental conditions, including developmental stage and gender, different tissues, larvae reared on different hosts and different larval density. The geNorm, BestKeeper, ΔCt method, and NormFinder statistical algorithms were used to normalize gene transcription data. Furthermore, the stability/suitability of these candidates was ranked overall by RefFinder. This study provides a comprehensive evaluation of reference genes in H. cunea and could help select reference genes for other Lepidoptera species.

RNAi-Mediated Silencing of the Chitinase 5 Gene for Fall Webworm (Hyphantria cunea) Can Inhibit Larval Molting Depending on the Timing of dsRNA Injection

Chitinases, which are crucial enzymes required for chitin degradation and reconstruction, are often selectively considered to be effective molecular targets for pest control due to their critical roles in insect development. Although the Hyphantria cunea chitinase gene has been reported previously, its sequence characteristics, gene function, and feasibility as a potential target for pest management were absent. In the present study, we characterized the H. cunea chitinase gene and designated it HcCht5. Phylogenic and domain structure analysis suggested that HcCht5 contained the typical chitinase features and was clustered into chitinase group I. Tissue-specific and developmental expression pattern analysis with Real-Time Quantitative PCR (RT-qPCR) showed that HcCht5 was mainly expressed in the integument tissues and that the transcript levels peaked during molting. RNA interference (RNAi)-mediated silencing of HcCht5 caused 33.3% (2 ug) and 66.7% (4 ug) mortality rates after double-stranded RNA (dsRNA) injection. Importantly, the interference efficiency of HcCht5 depended on the injection time of double-stranded RNA (dsRNA), as the pre-molting treatment achieved molt arrest more effectively. In addition, transcriptome sequencing (RNA-seq) analysis of RNAi samples demonstrated silencing of the down-regulated HcCht5 genes related to chitin metabolism and molting hormone signaling, as well as genes related to detoxification metabolism. Our results indicate the essential role of HcCht5 in H. cunea development and detail the involvement of its gene function in the larval molting process.