Comparative analyses of the venom components in the salivary gland transcriptomes and saliva proteomes of some heteropteran insects

Functional analysis of serine protease EfSP1 in Eocanthecona furcellata Wolff (Hemiptera: Pentatomidae)

BACKGROUND

Serine protease is an important digestive enzyme involved in many physiological and biochemical reactions, including digestion of insect food protein, blood coagulation, signal transduction, immune response, and hormone activation. The physiological functionality of salivary gland serine protease EfSP1 in the predatory natural enemy Eocanthecona furcellata is unknown. As a salivary gland protein, EfSP1 may have insecticidal activity against the prey Spodoptera frugiperda.

RESULTS

The expression of the EfSP1 gene was interfered with microinjection. After RNAi, the molting of the 5th instar nymphs of E. furcellata was blocked, and the survival rate and daily predation of male and female adults were reduced. The prokaryotic expression of EfSP1 protein was injected into the 4th instar larvae of S. frugiperda, causing difficulty in molting to death of the 4th instar larvae, and the dead larvae showed melanization, softening, and liquefaction. The development duration of the 4th instar larvae was prolonged, the survival rate was decreased, the pupal weight was decreased, the pupal period was prolonged, and the pupal eclosion rate was decreased. This inhibited the chitin and trehalose metabolism of S. frugiperda larvae, hemolymph melanization, and phenoloxidase activity, affecting the transcription of antimicrobial peptide genes.

CONCLUSION

These findings indicate that EfSP1 is involved in the growth, development, and predation of E. furcellata. As a salivary gland protein, EfSP1 also has insecticidal activity, affecting the growth and development, chitin metabolism, trehalose metabolism, and humoral immunity of S. frugiperda. These findings reveal the physiological function of EfSP1. © 2025 Society of Chemical Industry.

A venom serpin from the assassin bug Sycanus croceovittatus exhibiting inhibitory effects on melanization, development, and insecticidal activity towards its prey

Serine protease inhibitors (SPIs) have been identified as main common components in the venom of the predatory bugs, while their functional roles remain unexplored. In this study, we identified 35 SPI genes belonging to three subfamilies of serpin, canonical SPI, and A2M in genome of the assassin bug, Sycanus croceovittatus. The amino acid sequences of these SPI genes reveal conserved functional regions, albeit with mutations or deletions at certain active site residues. Transcriptomic and qPCR analyses of gene expression patterns in various tissues across developmental stages indicate that most SPI genes exhibit high expression levels in venom apparatus, suggesting their role as venom proteins. Notably, the ScSPI5 gene from the serpin class was found to be most abundantly expressed in all three distinct venom glands, indicating its significant role as a venomous protein. Functional characterization demonstrated that this venom serpin effectively inhibits trypsin activity in vitro and suppresses phenoloxidase activity, thereby blocking hemolymph melanization in preys, including Spodoptera frugiperda, Achelura yunnanensis, and Tenebrio molitor. When ingested, it reduces the larval and pupal weight of the fall armyworm by impeding trypsin activity in the midgut. Upon injection, ScSPI5 exhibits a dose-dependent insecticidal effect against T. molitor, with an LD50 of 5.6 ± 1.1 μg/g. These findings elucidate the specific functions of SPIs in the venom of predatory bugs, enhancing our understanding of their predation efficiency, and highlighting the potential application of venomous SPIs as protease inhibitors in pest management strategies.

Insecticidal activities of three recombinant venom proteins of the predatory stink bug, Arma custos

BACKGROUND

Widespread resistance of insect pests to insecticides and transgenic crops in the field is a significant challenge for sustainable agriculture, and calls for the development of novel alternative strategies to control insect pests. One potential resource for the discovery of novel insecticidal molecules is natural toxins, particularly those derived from the venoms of insect predators.

RESULTS

In this study, we identified three insecticidal proteinaceous toxins from the venom glands (VGs) of the predatory stink bug, Arma custos (Hemiptera: Asopinae). Transcriptomic analysis of A. custos VGs revealed 151 potentially secreted VG-rich venom proteins. Three VG-rich venom proteins (designated AcVP1 ~ 3) were produced by overexpression in Escherichia coli. Injection of the recombinant proteins into tobacco cutworm (Spodoptera litura) larvae showed that all of the three recombinant proteins caused paralysis, liquefaction and death. Injection of recombinant proteins into rice brown planthopper (Nilaparvata lugens) nymphs showed higher insecticidal activities, among which a trypsin (AcVP2) caused 100% mortality postinjection at 1.27 pmol mg-1 body weight.

CONCLUSION

A natural toolkit for the discovery of insecticidal toxins from predatory insects has been revealed by the present study. © 2024 Society of Chemical Industry.

Transcriptome analysis of the moso bamboo pest, Hippotiscus dorsalis, reveals differentially expressed unigenes across various tissues

Hippotiscus dorsalis (Hemiptera: Pentatomidae) is a common pest that feeds on the stems of Moso bamboo. Therefore, investigating the molecular processes related to its fundamental physiology is important. In this study, transcriptome sequencing was employed to compare gene expression in different tissues of male and female adults. A total of 36,238 annotated unigenes were identified through the NR database and compared with those of other known species. Among these, Halyomorpha halys and Nezara viridula showed the highest homology with H. dorsalis, with a total similarity exceeding 86 %. The top significant differentially expressed genes were mainly associated with protein digestion, carbohydrates metabolism, as well as reproduce regulation between sexes. The Gene Ontology enrichment analysis across three different segments of each sex revealed some terms associated with detoxification such like IMP biosynthetic process and acetyl-CoA metabolic process. Additionally, Kyoto Encyclopedia of Genes and Genomes enrichment analysis highlighted significant pathways related to glucose metabolism and pancreatic secretion. Further investigation of these DEGs, particularly in the calcium signaling pathway and glycan biosynthesis and metabolism, is essential for understanding sugar metabolism and transport in phytophagous insects.

The potential use of arginine kinase from the brown tick Rhipicephalus sanguineus as a biomarker for vector exposure in the surveillance of Rocky Mountain spotted fever

The brown dog tick (Rhipicephalus sanguineus) is the vector of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF) in Northern Mexico and Southwestern United States. The immune response to a tick protein in the sera of humans or animals may reveal the zones with a high propensity to acquire RMSF, and vector control strategies may be focused on these zones. Arginine kinase (AK) is a highly antigenic invertebrate protein that may serve as a marker for tick exposure. We used R. sanguineus recombinant AK in an indirect ELISA assay with RMSF-positive patient sera. The response to AK was significantly higher against the sera of RMSF patients than the control sera from healthy participants without contact with dogs. To validate the antigenicity of tick AK, we mutated one predicted conformational epitope to alanine residues, which reduced the recognition by RMSF patients' immunoglobulins. This preliminary result opens a perspective towards the development of a complimentary technique based on RsAK as an antigen biomarker for vector serological surveillance for Rickettsia RMSF prevention.

How to Overcome a Snail? Identification of Putative Neurotoxins of Snail-Feeding Firefly Larvae (Coleoptera: Lampyridae, Lampyris noctiluca)

The larvae of some lampyrid beetles are highly specialized predators of snails. They have been observed to climb on the shells of their prey and use this exposed position to bite and inject secretions potentially originating from the midgut. Besides serving the purpose of extra-oral digestion (EOD), injected compounds also seem to have a paralyzing effect. Up to now, the toxins causing this paralyzing activity have not been identified. In the current study, we provide a first compositional analysis of the midgut secretion from lampyrid larvae, with a focus on identifying putative neurotoxins causing the observed paralyzing effect. For this purpose, we utilized a combined proteo-transcriptomic approach to characterize the compounds present in the midgut secretion of larval stages of Lampyris noctiluca. In terms of the absolute numbers of identified compounds, the midgut secretion is dominated by hydrolyzing enzymes comprising peptidases, carboxylesterases, and glycosidases. However, when considering expression levels, a few rather short cysteine-rich peptides exceed all other compounds. Some of these compounds show moderate similarity to putative neurotoxins identified in the venom of other arthropods and could be responsible for paralyzing effects. In addition to these potential toxins, we provide a list of peptides typical of the midgut secretion of L. noctiluca, supplemented by the corresponding precursor sequences.

Morphological, functional, compositional and transcriptional constraints shape the distinct venom profiles of the assassin bug Sycanus croceovittatus

Predatory bugs employ a salivary venom apparatus to generate complex venoms for capturing and digesting prey. The venom apparatus consists of different glands for the production of distinct venom sets, but the underlying mechanisms behind this process remain poorly understood. Here we present a comprehensive analysis of the morphological, functional, compositional and transcriptional characteristics of venoms derived from posterior main gland (PMG), anterior main gland (AMG), and accessory gland (AG) of the assassin bug Sycanus croceovittatus. Structural observations revealed the intricate constructions of the venom apparatus, enabling the production and storage of three distinct venom sets in anatomically varied glands and allowing them to be modulated in a context-dependent manner upon utilization. There were remarkable differences in the biological activities exhibited by PMG, AMG, and AG venoms. Proteotranscriptomic analysis demonstrated that these venoms displayed compositional heterogeneity at both the quantity and variety levels of proteins. Transcriptional profiles of the identified venom proteins revealed gland-specific or biased expression patterns. These findings indicate that the divergence in venom profiles among different glands arises from morphological, functional, compositional and transcriptional constraints on the venom apparatus, reflecting remarkable morphogenesis and regulatory gene networks responsible for the compartmentalized production of venom proteins in different glands.

The Predatory Stink Bug Arma custos (Hemiptera: Pentatomidae) Produces a Complex Proteinaceous Venom to Overcome Caterpillar Prey

Predatory stink bugs capture prey by injecting salivary venom from their venom glands using specialized stylets. Understanding venom function has been impeded by a scarcity of knowledge of their venom composition. We therefore examined the proteinaceous components of the salivary venom of the predatory stink bug Arma custos (Fabricius, 1794) (Hemiptera: Pentatomidae). We used gland extracts and venoms from fifth-instar nymphs or adult females to perform shotgun proteomics combined with venom gland transcriptomics. We found that the venom of A. custos comprised a complex suite of over a hundred individual proteins, including oxidoreductases, transferases, hydrolases, ligases, protease inhibitors, and recognition, transport and binding proteins. Besides the uncharacterized proteins, hydrolases such as venom serine proteases, cathepsins, phospholipase A₂, phosphatases, nucleases, alpha-amylases, and chitinases constitute the most abundant protein families. However, salivary proteins shared by and unique to other predatory heteropterans were not detected in the A. custos venom. Injection of the proteinaceous (>3 kDa) venom fraction of A. custos gland extracts or venom into its prey, the larvae of the oriental armyworm Mythimna separata (Walker, 1865), revealed insecticidal activity against lepidopterans. Our data expand the knowledge of heteropteran salivary proteins and suggest predatory asopine bugs as a novel source for bioinsecticides.

An Assassin's Secret: Multifunctional Cytotoxic Compounds in the Predation Venom of the Assassin Bug Psytalla horrida (Reduviidae, Hemiptera)

Predatory assassin bugs produce venomous saliva that enables them to overwhelm, kill, and pre-digest large prey animals. Venom from the posterior main gland (PMG) of the African assassin bug Psytalla horrida has strong cytotoxic effects, but the responsible compounds are yet unknown. Using cation-exchange chromatography, we fractionated PMG extracts from P. horrida and screened the fractions for toxicity. Two venom fractions strongly affected insect cell viability, bacterial growth, erythrocyte integrity, and intracellular calcium levels in Drosophila melanogaster olfactory sensory neurons. LC-MS/MS analysis revealed that both fractions contained gelsolin, redulysins, S1 family peptidases, and proteins from the uncharacterized venom protein family 2. Synthetic peptides representing the putative lytic domain of redulysins had strong antimicrobial activity against Escherichia coli and/or Bacillus subtilis but only weak toxicity towards insect or mammalian cells, indicating a primary role in preventing the intake of microbial pathogens. In contrast, a recombinant venom protein family 2 protein significantly reduced insect cell viability but exhibited no antibacterial or hemolytic activity, suggesting that it plays a role in prey overwhelming and killing. The results of our study show that P. horrida secretes multiple cytotoxic compounds targeting different organisms to facilitate predation and antimicrobial defense.

Characterization of anti-microbial peptides and proteins from maggots of Calliphoridae and Sarcophagidae fly species (Diptera)

Removal of infected wounds using maggots has been known for centuries. Early research has shown that the maggot exosecretion, whole body, and fecal waste products of Calliphoridae and Sarcophagidae species contain a variety of alkaline peptides capable of inhibiting bacterial growth. Since the wide application of antibiotics such as penicillin, a number of bacterial infections have become insensitive to antibiotic treatment. In many of these instances, maggot therapy has been successfully applied for the treatment of chronic wounds. To identify and compare the expression patterns of anti-microbial peptides (AMPs) from some dipteran species, transcriptome analyses were conducted for the maggots of 11 Calliphoridae and Sarcophagidae species. Species of the subfamily Calliphorinae showed relatively higher expression levels of AMPs and anti-microbial proteins compared with those of Luciliinae and Sarcophagidae species. Furthermore, among all of the dipteran species examined, Lucilia illustris exhibited the highest transcription levels of AMPs. Cecropin A2 and defensin, whose expression levels were the highest among the anti-microbial peptides, were synthesized to test their biological activity. The synthesized peptides showed anti-microbial activities without hemolytic activities. In particular, cecropin A2 of L. illustris exhibited the highest anti-microbial activity against all of the bacteria and fungi examined, thereby possessing the potential to be developed as a new alternative to antibiotics. This comparative transcriptomic study may provide new insights into anti-microbial compositions of some dipteran species.