Silencing the triacylglycerol lipase (TGL) gene decreases the number of apyrene sperm and inhibits oviposition in Sitotroga cerealella

Lipid surface droplet 2 (LSD2) regulates lipid metabolism and male reproductive physiology in adult Sitotroga cerealella

Insect metabolism plays a critical role in shaping reproductive physiology, offering valuable insight for pest management strategies and ecological understanding. In this study, we investigated the regulation of the lipid surface droplet protein LSD2 and its impact on lipid metabolism and male reproductive events in Sitotroga cerealella. Using ScLSD2 RNAi, we assessed it effects on energy metabolism, sperm count, motility, oviposition, and hatchability in S. cerealella adults. Our results reveal tissue-specific expression of ScLSD2, predominantly in the fat body. Silencing ScLSD2 led to reduced mating rates, sperm motility parameters, oviposition, and hatchability, alongside alteration in energy metabolites, including decreased in lipid droplets, triglyceride and glycerol levels and increased diglyceride content. Additionally, sperm quantification revealed significant reductions in eupyrene sperm count following ScLSD2 silencing, indicating impaired reproductive function. These results show the pivotal role of LSD2 in linking lipid metabolism and reproductive physiology in S. cerealella, positioning it as a promising target for pest management strategies.

Stage-specific transcriptomic analysis reveals insights into the development, reproduction and biological function of allergens in the European house dust mite Dermatophagoides pteronyssinus

BACKGROUND

House dust mites (HDMs) such as Dermatophagoides pteronyssinus are major allergy elicitors worldwide, yet their gene expression across developmental stages remains underexplored. Herein, we report a comprehensive RNAseq analysis of larvae, nymphs, and adult males and females, mapped to a recently published high-quality genome with extended functional annotations.

RESULTS

Analysis of differentially expressed genes (DEG) revealed that female-biased expression was the most prevalent profile (16% of genes), while males exhibited the highest fold-change differences. DEG data, combined with network clustering and functional enrichment analysis, highlighted distinct genes and biological processes for each stage and sex: females showed upregulation of genes related to cell division and oogenesis, with vitellogenins among the most abundant transcripts; males exhibited increased expression of genes encoding putative seminal fluid proteins (e.g. endopeptidases, serpins, antimicrobial peptides), and those involved in reproductive regulation (e.g. testis-specific serine kinases); while juveniles displayed enhanced expression of genes related to energy metabolism and growth. Further analysis of endocrine pathways revealed non-canonic mechanisms compared to insect models, particularly in ecdysteroid and sesquiterpenoid biosynthesis and regulation. Expression patterns in genes involved in cuticle formation were also identified, reflecting their role in developmental transitions and sexual differentiation. Allergen and allergen-related gene expression showed an overall increase in feeding juveniles, as well as sex-biased expression, with Der p 27 upregulated in females. These findings provide insight into the physiological roles of allergens in digestion, immunity, and muscle formation, among other functions. Additionally, seven new horizontally transferred genes, including a DNA-repair photolyase linked to females, and novel multigene families (e.g. 119 male-specific beta-propeller proteins, 70 hypothetical cuticular proteins, 23 tetraspanin-like proteins, 5 female-associated putative odorant-binding proteins) were identified.

CONCLUSIONS

This study provides the first genome-wide transcriptomic analysis of a HDM across life stages and sexes, expanding our understanding of the molecular mechanisms underlying mite development, sexual reproduction, and allergen expression. The generated data, fully available via supplementary spreadsheet and the ORCAE online platform, provide a valuable foundation for future allergy research and the development of new mite control strategies.

Diallyl Trisulfide, an Active Substance from Garlic, Inhibits Female Oviposition by Decreasing the Expression of the OCT Gene, which is Highly Expressed in the Spermathecal Gland of Sitotroga cerealella (Oliver)

Diallyl trisulfide (DAT) effectively inhibits the fecundity of Sitotroga cerealella. Organic cation transporter (OCT) was most highly expressed in the spermathecal gland of female moths and was significantly decreased after DAT fumigation. However, the function of OCT in insect reproduction has been rarely reported. In this study, after silencing OCT in female adults, the mating rate, oviposition, and number of sperm transferred to females were decreased significantly, and transfer time of sperm in the female was delayed. Meanwhile, the long and short waves formed during sperm movement became longer, which lead sperm to take a longer time to complete a movement cycle. Finally, 5-hydroxytryptamine (5-HT) was significantly increased. Conversely, triacylglycerol (TG) decreased significantly. The expression of the 5-HT 2A receptor gene, which is highly expressed in the abdomen, was significantly decreased. The findings have provided a theoretical basis for explaining the inhibitory effect of garlic essential oil on the reproduction of S. cerealella.

Roles of spermary-specific carboxylesterases in Nilaparvata lugens reproduction: Opposite between insecticide-induced upregulation and resistance-associated overexpression

Seminal fluid proteins (SFPs) in insect males are critical for reproduction, being transported into female ovary. In Nilaparvata lugens, a significant rice pest, seven spermary-specific carboxylesterases (CarEs) were found abundantly in SFPs, with over-expression in males of an imidacloprid-resistant (RES) strain compared to a susceptible (SUS) strain. This study aimed to evaluate roles of spermary-specific CarEs in N. lugens reproduction, especially in the reproduction disadvantage in RES. Sublethal doses of three insecticides significantly impacted N. lugens reproduction, concomitant with up-regulation of these CarE genes in males. When RNAi against these CarE genes in SUS males did not affect reproduction, RNAi suppression of insecticide-induced up-regulation worsened the reproductive decline caused by insecticides, indicating a reproduction benefit from the transient up-regulation induced by insecticides. However, constitutive overexpression of these CarEs in RES males did not enhance reproduction and instead imposed a fitness cost. RNAi against part CarE genes in RES males increased reproduction. Collectively, the transient up-regulation and constitutive overexpression of these spermary-expressed CarE genes had the opposite effects on N. lugens reproduction. We need to find a balance between these opposite effects in insect pest control and insecticide resistance management, especially for insecticides targeting reproduction.

E3 Siah ubiquitin ligase regulates dichotomous spermatogenesis in Sitotroga cerealella

Spermatogenesis in Lepidoptera holds significant importance due to its unique process of dichotomous spermatogenesis, yielding eupyrene and apyrene spermatozoa through a complex molecular mechanism. While E3 ubiquitin ligases are known to play vital roles in spermatogenesis across various processes, their functions in dichotomous spermatogenesis remain less known. We utilized the RNAi, biochemical and microscopic procedures to unravel the function of ScE3 Siah in dichotomous spermatogenesis of adult Sitotroga cerealella. In S. cerealella E3 ligase Siah predominantly expressed in adult tissues. Knockdown of ScE3 Siah leads to disruptions in testes and sperm morphology, affecting the structure of eupyrene and apyrene sperm bundles and causing defective ultrastructure in eupyrene sperm. This disruption results in a reduction in the number of dichotomous sperms and significantly reduces their motility. Moreover, ScE3 Siah knockdown inhibits the transfer and motility of dichotomous sperm, impacting spermatophore formation in females and ultimately reducing egg production. Understanding the role of ScE3 Siah is not only crucial for comprehending the complex processes involved in dichotomous spermatogenesis and fertilization but also provides an avenue for sustainable pest control management.

Dual roles of methoprene-tolerant gene TaMet in male molting and female reproduction of the tomato leafminer, Tuta absoluta (meyrick)

The tomato leafminer (Tuta absoluta) is a highly destructive global quarantine pest. The methoprene-tolerant (Met) protein, a member of the bHLH/PAS family of transcription factors, forms complexes with other family members to transduce the juvenile hormone signal, which regulates insect growth and development. However, the functions of the TaMet gene have rarely been studied in T. absoluta. Herein, we investigated the significance of TaMet in T. absoluta. Spatiotemporal expression analysis revealed that TaMet exhibited comparable expression patterns in males and females, with high expression levels during the early pupal and early adult stages. TaMet was predominantly expressed in the female ovary and male wing. TaMet knockdown impaired ovarian development in female adults, causing irregular arrangement and increased spacing of the egg epithelial cells in the ovary. Silencing TaMet also led to a 67.25% reduction in female spawning and a 67.21% decrease in the offspring hatching rate. Furthermore, the vitellogenin content was significantly diminished, and the expression levels of vitellogenin (Vg) and vitellogenin receptor (VgR) genes were significantly downregulated. In contrast, silencing TaMet in 3-day-old male pupae resulted in an 80% mortality rate and various phenotypic abnormalities, including body melanism, molting defects, and wing deformities. Moreover, the expression levels of wing development and chitin metabolism genes decreased significantly after knocking down TaMet. Our results indicate that TaMet plays a significant dual role in male molting and female reproduction of T. absoluta.

Lipid Metabolism as a Target Site in Pest Control

Lipid metabolism is essential to insect life as insects use lipids for their development, reproduction, flight, diapause, and a wide range of other functions. The central organ for insect lipid metabolism is the fat body, which is analogous to mammalian adipose tissue and liver, albeit less structured. Various other systems including the midgut, brain, and neural organs also contribute functionally to insect lipid metabolism. Lipid metabolism is under the control of core lipogenic [e.g. acetyl-CoA-carboxylase (ACC), fatty acid synthase (FAS), perilipin 2 (LSD2)], and lipolytic (lipases, perilipin 1) enzymes that are primarily expressed in the fat body, as well as hormones [insulin-like peptides (ILP), adipokinetic hormone (AKH)], transcription factors (SREBPs, foxO, and CREB), secondary messengers (calcium) and post-translational modifications (phosphorylation). Essential roles of the fat body, together with the fact that proper coordination of lipid metabolism is critical for insects, render lipid metabolism an attractive target site in pest control. In the current chapter, we focus on pest control tactics that target insect lipid metabolism. Various classes of traditional chemical insecticides [e.g. organophosphates, pyrethroids, neonicotinoids, and chitin synthesis inhibitors (Sects. 2.1 and 2.2)] have been shown to interfere with lipid metabolism, albeit it is not their primary site of action. However, the discovery of "lipid biosynthesis inhibitors", tetronic and tetramic acid derivatives commonly known as ketoenols (Sect. 2.3), was a milestone in applied entomology as they directly target lipid biosynthesis, particularly in sucking pests. Spirodiclofen, spiromesifen, and spirotetramat targeting ACC act against various insect and mite pests, while spiropidion and spidoxamat have been introduced to the market only recently. Efforts have concentrated on the development of chemical alternatives, such as hormone agonists and antagonists (Sect. 2.4), dsRNA-based pesticides that depend on RNA interference, which have great potential in pest control (Sect. 2.5) and other eco-friendly alternatives (Sect. 2.6).

Diallyl Trisulfide Causes Male Infertility with Oligoasthenoteratospermia in Sitotroga cerealella through the Ubiquitin-Proteasome Pathway

Essential oils extracted from plant sources along with their biologically active components may have negative effects on insects. Diallyl trisulfide (DAT) is an active component of garlic essential oil, and it exhibits multi-targeted activity against many organisms. Previously we reported that DAT induces male infertility and leads to apyrene and eupyrene sperm dysfunction in Sitotroga cerealella. In this study, we conducted an analysis of testis-specific RNA-Seq data and identified 449 downregulated genes and 60 upregulated genes in the DAT group compared to the control group. The downregulated genes were significantly enriched in the ubiquitin-proteasome pathway. Furthermore, DAT caused a significant reduction in mRNA expression of proteasome regulatory subunit particles required for ATP-dependent degradation of ubiquitinated proteins as well as decreased the expression profile of proteasome core particles, including β1, β2, and β5. Sperm physiological analysis showed that DAT decreased the chymotrypsin-like activity of the 20S proteasome and formed aggresomes in spermatozoa. Overall, our findings suggest that DAT impairs the testis proteasome, ultimately causing male infertility characterized by oligoasthenoteratospermia due to disruption in sperm proteasome assembly in S. cerealella.

Dichotomous sperm in Lepidopteran insects: a biorational target for pest management

Lepidoptera are unusual in possessing two distinct kinds of sperm, regular nucleated (eupyrene) sperm and anucleate (apyrene) sperm ('parasperm'). Sperm of both types are transferred to the female and are required for male fertility. Apyrene sperm play 'helper' roles, assisting eupyrene sperm to gain access to unfertilized eggs and influencing the reproductive behavior of mated female moths. Sperm development and behavior are promising targets for environmentally safer, target-specific biorational control strategies in lepidopteran pest insects. Sperm dimorphism provides a wide window in which to manipulate sperm functionality and dynamics, thereby impairing the reproductive fitness of pest species. Opportunities to interfere with spermatozoa are available not only while sperm are still in the male (before copulation), but also in the female (after copulation, when sperm are still in the male-provided spermatophore, or during storage in the female's spermatheca). Biomolecular technologies like RNAi, miRNAs and CRISPR-Cas9 are promising strategies to achieve lepidopteran pest control by targeting genes directly or indirectly involved in dichotomous sperm production, function, or persistence.

Characterization of neutral lipases revealed the tissue-specific triacylglycerol hydrolytic activity in Nilaparvata lugens

The lipid metabolism plays an essential role in the development and reproduction of insects, and lipases are important enzymes in lipid metabolism. In Nilaparvata lugens, an important insect pest on rice, triacylglycerol hydrolytic activities were different among tissues, with high activity in integument, ovary, and fat body, but low activity in intestine. To figure out the tissue-specific triacylglycerol hydrolytic activity, we identified 43 lipases in N. lugens. Of these 43 lipases, 23 belonged to neutral lipases, so this group was selected to perform further experiments on triacylglycerol hydrolysis. The complete motifs of catalytic triads, β9 loop, and lid motif, are required for the triacylglycerol hydrolytic activity in neutral lipases, which were found in some neutral lipases with high gene expression levels in integument and ovary, but not in intestine. The recombinant proteins of 3 neutral lipases with or without 3 complete motifs were obtained, and the activity determination confirmed the importance of 3 motifs. Silencing XM_022331066.1, which is highly expressed in ovary and with 3 complete motifs, significantly decreased the egg production and hatchability of N. lugens, partially through decline of the lipid metabolism. In summary, at least one-third of important motifs were incomplete in all neutral lipases with high gene expression in intestine, which could partially explain why the lipase activity in intestine was much lower than that in other tissues. The low activity to hydrolyze triacylglycerol in N. lugens intestine might be associated with its food resource and nutrient components, and the ovary-specific neutral lipases were important for N. lugens reproduction.

Lipid class-dependent alterations of Caenorhabditis elegans under harmane exposure

Altered lipid patterns in Caenorhabditis elegans (C. elegans) resulting from exposure to harmane remain to be explored. In this study, untargeted lipidomics was carried out to elucidate the effects of acute exposure to harmane on the lipidome of C. elegans. Exposure to the compound was evaluated based on the reproduction ability of the worms at 0.1 and 1 μg/mL. No significant effects of harmane were observed at these concentrations. Furthermore, we found that the modulatory effects of harmane on the lipidome of C. elegans at 1 μg/mL were lipid class dependent. In particular, harmane-treated worms were enriched in triglycerides and fatty acids, regardless of the degree of saturation. Glycerophospholipids were generally down-regulated. Furthermore, functional analyses suggested that there was a reduction in lipid membrane bilayer-related terms, and in some related to the mitochondria, and endoplasmic reticulum of C. elegans when treated with harmane. Lipid droplets and storage appeared to be up-regulated. In conclusion, our findings suggest that harmane exposure affects the lipidome of C. elegans in a sophisticated manner. Further investigations are required to elucidate the molecular mechanisms underlying these lipid pattern changes.

Diallyl Trisulfide, a Biologically Active Component of Garlic Essential Oil, Decreases Male Fertility in Sitotroga cerealella by Impairing Dimorphic Spermatogenesis, Sperm Motility and Lipid Homeostasis

Diallyl trisulfide (DAT) is a biologically active component of garlic essential oil and exhibits multi-targeted activity against many organisms. The current study tested the capacity of DAT to decrease the male fertility of Sitotroga cerealella. The effects on testis morphology, sperm number, motility, and lipid homeostasis were observed in adult males fumigated with DAT at a dose of 0.01 μL/L in air. The results indicated that the DAT significantly decreased the dimorphic sperm number. Meanwhile, the ultrastructural analysis of the sperm showed that the DAT caused malformed and aberrant structures of mitochondrial derivatives of dimorphic sperm. Additionally, the lipid homeostasis and ATP contents in the male adults were significantly decreased after treatment. Moreover, the total sperm motility was reduced, while the wave-propagation velocity, amplitude, frequency, and wavelength were significantly decreased compared with the controls. Overall, this study reported, for the first time, that DAT impairs energy metabolism, inhibits dimorphic spermatogenesis, and decreases sperm motility, while these abnormalities in sperm lead to adult-male infertility.