Phenotypic impacts of PBAN RNA interference in an ant, Solenopsis invicta, and a moth, Helicoverpa zea

Establishment of RNAi-Mediated Pest Control Method for Red Imported Fire Ant, Solenopsis invicta

RNAi plays a crucial role in insect gene function research and pest control field. Nonetheless, the variable efficiency of RNAi across diverse insects and off-target effects also limited its further application. In this study, we cloned six essential housekeeping genes from Solenopsis invicta and conducted RNAi experiments by orally administering dsRNA. Then, we found that mixing with liposomes significantly enhanced the RNAi efficiency by targeting for SiV-ATPaseE. Additionally, we observed a certain lethal effect of this dsRNA on queens by our established RNAi system. Furthermore, no strict sequence-related off-target effects were detected. Finally, the RNAi effect of large-scale bacteria expressing dsRNA was successfully confirmed for controlling S. invicta. In summary, this study established an RNAi system for S. invicta and provided a research template for the future development of nucleic acid drugs based on RNAi.

Pheromone biosynthesis activating neuropeptide family in insects: a review

Neuropeptides are involved in almost all physiological activities of insects. Their classification is based on physiological function and the primary amino acid sequence. The pyrokinin (PK)/pheromone biosynthesis activating neuropeptides (PBAN) are one of the largest neuropeptide families in insects, with a conserved C-terminal domain of FXPRLamide. The peptide family is divided into two groups, PK1/diapause hormone (DH) with a WFGPRLa C-terminal ending and PK2/PBAN with FXPRLamide C-terminal ending. Since the development of cutting-edge technology, an increasing number of peptides have been sequenced primarily through genomic, transcriptomics, and proteomics, and their functions discovered using gene editing tools. In this review, we discussed newly discovered functions, and analyzed the distribution of genes encoding these peptides throughout different insect orders. In addition, the location of the peptides that were confirmed by PCR or immunocytochemistry is also described. A phylogenetic tree was constructed according to the sequences of the receptors of most insect orders. This review offers an understanding of the significance of this conserved peptide family in insects.

Using machine learning to predict protein-protein interactions between a zombie ant fungus and its carpenter ant host

Parasitic fungi produce proteins that modulate virulence, alter host physiology, and trigger host responses. These proteins, classified as a type of "effector," often act via protein-protein interactions (PPIs). The fungal parasite Ophiocordyceps camponoti-floridani (zombie ant fungus) manipulates Camponotus floridanus (carpenter ant) behavior to promote transmission. The most striking aspect of this behavioral change is a summit disease phenotype where infected hosts ascend and attach to an elevated position. Plausibly, interspecific PPIs drive aspects of Ophiocordyceps infection and host manipulation. Machine learning PPI predictions offer high-throughput methods to produce mechanistic hypotheses on how this behavioral manipulation occurs. Using D-SCRIPT to predict host-parasite PPIs, we found ca. 6000 interactions involving 2083 host proteins and 129 parasite proteins, which are encoded by genes upregulated during manipulated behavior. We identified multiple overrepresentations of functional annotations among these proteins. The strongest signals in the host highlighted neuromodulatory G-protein coupled receptors and oxidation-reduction processes. We also detected Camponotus structural and gene-regulatory proteins. In the parasite, we found enrichment of Ophiocordyceps proteases and frequent involvement of novel small secreted proteins with unknown functions. From these results, we provide new hypotheses on potential parasite effectors and host targets underlying zombie ant behavioral manipulation.

Differential Gene Expression of Innate Immune Response Genes Consequent to Solenopsis invicta Virus-3 Infection

The red imported fire ant Solenopsis invicta Buren (fire ant hereafter) is a global pest that inflicts billions of dollars in damages to the United States economy and poses a major threat on a global scale. Concerns with the broad-spectrum application of insecticides have facilitated the hunt for natural enemy-mediated controls. One of these, the virus Solenopsis invicta virus-3 (SINV-3 hereafter) is exceptionally virulent in laboratory settings. However, despite high mortality rates in the laboratory and documented widespread SINV-3 prevalence in the southern United States, the fire ant remains a major pest. To explore this paradox, we document the immune response elicited by the fire ant when infected with SINV-3. We sequence the fire ant transcriptome prior to and following infection with SINV-3, and identify and discuss in detail genes in immune response pathways differentially expressed following infection with SINV-3. This information provides insights into genes and pathways involved in the SINV-3 infection response in the fire ant and offers avenues to pursue, to suppress key immune response genes and force the fire ant to succumb to SINV-3 infection in the field.

Pyrokinin receptor silencing in females of the southern cattle tick Rhipicephalus (Boophilus) microplus is associated with a reproductive fitness cost

Background

Rhipicephalusmicroplus is the vector of deadly cattle pathogens, especially Babesia spp., for which a recombinant vaccine is not available. Therefore, disease control depends on tick vector control. However, R.microplus populations worldwide have developed resistance to available acaricides, prompting the search for novel acaricide targets. G protein-coupled receptors (GPCRs) are involved in the regulation of many physiological processes and have been suggested as druggable targets for the control of arthropod vectors. Arthropod-specific signaling systems of small neuropeptides are being investigated for this purpose. The pyrokinin receptor (PKR) is a GPCR previously characterized in ticks. Myotropic activity of pyrokinins in feeding-related tissues of Rhipicephalussanguineus and Ixodesscapularis was recently reported.

Methods

The R.microplus pyrokinin receptor (Rhimi-PKR) was silenced through RNA interference (RNAi) in female ticks. To optimize RNAi, a dual-luciferase assay was applied to determine the silencing efficiency of two Rhimi-PKR double-stranded RNAs (dsRNA) prior to injecting dsRNA in ticks to be placed on cattle. Phenotypic variables of female ticks obtained at the endpoint of the RNAi experiment were compared to those of control female ticks (non-injected and beta-lactamase dsRNA-injected). Rhimi-PKR silencing was verified by quantitative reverse-transcriptase PCR in whole females and dissected tissues.

Results

The Rhimi-PKR transcript was expressed in all developmental stages. Rhimi-PKR silencing was confirmed in whole ticks 4 days after injection, and in the tick carcass, ovary and synganglion 6 days after injection. Rhimi-PKR silencing was associated with an increased mortality and decreased weight of both surviving females and egg masses (P < 0.05). Delays in repletion, pre-oviposition and incubation periods were observed (P < 0.05).

Conclusions

Rhimi-PKR silencing negatively affected female reproductive fitness. The PKR appears to be directly or indirectly associated with the regulation of female feeding and/or reproductive output in R.microplus. Antagonists of the pyrokinin signaling system could be explored for tick control.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05349-w.

RNA Interference-Based Pesticides and Antiviral Agents: Microbial Overproduction Systems for Double-Stranded RNA for Applications in Agriculture and Aquaculture

RNA interference (RNAi)-based pesticides are pest control agents that use RNAi mechanisms as the basis of their action. They are regarded as environmentally friendly and are a promising alternative to conventional chemical pesticides. The effective substance in RNAi-based pesticides is double-stranded RNA (dsRNA) designed to match the nucleotide sequence of a target essential gene of the pest of concern. When taken up by the pest, this exerts an RNAi effect and inhibits some vital biochemical/biological process in the pest. dsRNA products are also expected to be applied for the control of viral diseases in aquaculture by RNAi, especially in shrimp farming. A critical issue in the practical application of RNAi agents is that production of the dsRNA must be low-cost. Here, we review recent methods for microbial production of dsRNAs using representative microorganisms (Escherichia coli, Pseudomonas syringae, Corynebacterium glutamicum, Chlamydomonas reinhardtii, and others) as host strains. The characteristics of each dsRNA production system are discussed.

Establishing RNAi for basic research and pest control and identification of the most efficient target genes for pest control: a brief guide

RNA interference (RNAi) has emerged as a powerful tool for knocking-down gene function in diverse taxa including arthropods for both basic biological research and application in pest control. The conservation of the RNAi mechanism in eukaryotes suggested that it should-in principle-be applicable to most arthropods. However, practical hurdles have been limiting the application in many taxa. For instance, species differ considerably with respect to efficiency of dsRNA uptake from the hemolymph or the gut. Here, we review some of the most frequently encountered technical obstacles when establishing RNAi and suggest a robust procedure for establishing this technique in insect species with special reference to pests. Finally, we present an approach to identify the most effective target genes for the potential control of agricultural and public health pests by RNAi.

The Odorant Binding Protein, SiOBP5, Mediates Alarm Pheromone Olfactory Recognition in the Red Imported Fire Ant, Solenopsis invicta

Olfaction is crucial in mediating various behaviors of social insects such as red imported fire ants, Solenopsis invicta Buren. Olfactory receptor (OR) complexes consist of odor-specific ORs and OR co-receptors (Orco). Orcos are highly conserved across insect taxa and are widely co-expressed with ORs. Odorant binding proteins (OBPs) can transport semiochemicals to ORs as protein carriers and thus constitute the first molecular recognition step in insect olfaction. In this study, three OBP genes highly expressed in S. invicta antenna, OBP1, OBP5, OBP6, and Orco were partially silenced using RNA interference (RNAi). RNAi SiOBP5- and Orco-injected ants showed significantly lower EAG (electroantennography) responses to fire ant alarm pheromones and the alkaloid, 2,4,6-trimethylpyridine than water- or GFP-injected ants 72 h post injection. Subsequent qRT-PCR analysis demonstrated that the transcript level of the OBP1, OBP5, OBP6, and Orco significantly decreased 72 h after ants were injected with dsRNAs; however, there were no transcript level or EAG changes in ants fed dsRNAs. Our results suggest that S. invicta Orco and SiOBP5 are crucial to fire ants for their responses to alarm pheromones. RNAi knocking down SiOBP5 can significantly disrupt alarm pheromone communication, suggesting that disrupting SiOBP5 and Orcos could be potentially useful in the management of red imported fire ants.

A molecular toolkit for superorganisms

Social insects, such as ants, bees, wasps, and termites, draw biologists' attention due to their distinctive lifestyles. As experimental systems, they provide unique opportunities to study organismal differentiation, division of labor, longevity, and the evolution of development. Ants are particularly attractive because several ant species can be propagated in the laboratory. However, the same lifestyle that makes social insects interesting also hampers the use of molecular genetic techniques. Here, we summarize the efforts of the ant research community to surmount these hurdles and obtain novel mechanistic insight into the biology of social insects. We review current approaches and propose novel ones involving genomics, transcriptomics, chromatin and DNA methylation profiling, RNA interference (RNAi), and genome editing in ants and discuss future experimental strategies.

Efficient production of long double-stranded RNAs applicable to agricultural pest control by Corynebacterium glutamicum equipped with coliphage T7-expression system

Abstract

RNA-based pesticides exert their function by suppressing the expression of an essential gene in the target pest through RNA interference caused by double-stranded RNA (dsRNA). Here, we selected target genes for growth suppression of the solanaceous crop pests ladybird beetle (Henosepilachna vigintioctopunctata) and Colorado potato beetle (Leptinotarsa decemlineata)-the death-associated inhibitor of apoptosis protein 1 gene (diap1), and an orthologous gene of the COPI coatomer protein complex (copI), respectively. We constructed a cost-competitive overproduction system for dsRNA using Corynebacterium glutamicum as a host bacterium. The dsRNA expression unit was equipped with two sets of promoters and terminators derived from coliphage T7, and the convergent expression system was designed to be selectively transcribed by T7 RNA polymerase. This expression system efficiently overproduced both target dsRNAs. On culture in a jar fermentor, the yield of diap1-targeting dsRNA (approximately 360 bp) was > 1 g per liter of culture. Long-chain diap1-targeting dsRNAs (up to around 1 kbp) could be produced without a substantial loss of efficiency. dsRNA accumulated in C. glutamicum significantly suppressed larval growth of H. vigintioctopunctata. The dsRNA expression technology developed here is expected to substantially reduce dsRNA production costs. Our method can be applied for a wide range of industrial uses, including agricultural pest control.

Key points

• Overexpression of dsRNA was achieved in C. glutamicum using a coliphage T7 system.

• The best strain produced > 1 g/L of the target dsRNA species, for use as an insecticide.

• The developed system efficiently produced long dsRNA species, up to ~ 1 kbp.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11324-9.

GPCR-Based Bioactive Peptide Screening Using Phage-Displayed Peptides and an Insect Cell System for Insecticide Discovery

The discovery of new insecticides improves integrated pest management (IPM), but is usually a long high-risk process with a low probability of success. For over two decades, insect neuropeptides (NPs) and their G-protein coupled receptors (GPCRs) have been considered as biological targets for insect pest control, because they are involved in almost all physiological processes associated with insect life stages. A key roadblock to success has been the question of how large volume chemical libraries can be efficiently screened for active compounds. New genomic and proteomic tools have advanced and facilitated the development of new approaches to insecticide discovery. In this study, we report a novel GPCR-based screening technology that uses millions of short peptides randomly generated by bacteriophages, and a method using an insect Sf9 cell expression system. The fire ant is a good model system, since bioactive peptides have been identified for a specific GPCR. The novel small peptides could interfere with the target GPCR-ligand functions. Therefore, we refer to this new mechanism as “receptor interference” (RECEPTORi). The GPCR-based bioactive peptide screening method offers multiple advantages. Libraries of phage-displayed peptides (~10⁹ peptides) are inexpensive. An insect cell-based screening system rapidly leads to target specific GPCR agonists or antagonists in weeks. Delivery of bioactive peptides to target pests can be flexible, such as topical, ingestion, and plant-incorporated protectants. A variety of GPCR targets are available, thus minimizing the development of potential insecticide resistance. This report provides the first proof-of-concept for the development of novel arthropod pest management strategies using neuropeptides, and GPCRs.

Suppressing tawny crazy ant (Nylanderia fulva) by RNAi technology

The tawny crazy ant (Nylanderia fulva) is a new invasive pest in the United States. At present, its management mainly relies on the use of synthetic insecticides, which are generally ineffective at producing lasting control of the pest, necessitating alternative environmentally friendly measures. In this study, we evaluated the feasibility of gene silencing to control this ant species. Six housekeeping genes encoding actin (NfActin), coatomer subunit β (NfCOPβ), arginine kinase (NfArgK), and V-type proton ATPase subunits A (NfvATPaseA), B (NfvATPaseB) and E (NfvATPaseE) were cloned. Phylogenetic analysis revealed high sequence similarity to homologs from other ant species, particularly the Florida carpenter ant (Camponotus floridanus). To silence these genes, vector L4440 was used to generate six specific RNAi constructs for bacterial expression. Heat-inactivated, dsRNA-expressing Escherichia coli were incorporated into artificial diet. Worker ants exhibited reduced endogenous gene expression after feeding on such diet for 9 d. However, only ingestion of dsRNAs of NfCOPβ (a gene involved in protein trafficking) and NfArgK (a cellular energy reserve regulatory gene in invertebrates) caused modest but significantly higher ant mortality than the control. These results suggest that bacterially expressed dsRNA can be orally delivered to ant cells as a mean to target its vulnerabilities. Improved efficacy is necessary for the RNAi-based approach to be useful in tawny crazy ant management.

Mapping and identification of potential target genes from short-RNA seq for the control of Pieris rapae larvae

Pieris rapae is a serious pest of brassicas worldwide. We performed de novo assembly of P. rapae transcriptome by next-generation sequencing and assembled approximately 65,727,422 clean paired-end reads into 32,118 unigenes, of which 13,585 were mapped to 255 pathways in the KEGG database. A total of 6173 novel transcripts were identified from reads directly mapped to P. rapae genome. Additionally, 1490 SSRs, 301,377 SNPs, and 29,284 InDels were identified as potential molecular markers to explore polymorphism within P. rapae populations. We screened and mapped 36 transcripts related to OBP, CSP, SNMP, PBAN, and OR. We analyzed the expression profiles of 7 selected genes involved in pheromone transport and degradation by quantitative real-time PCR; these genes are sex-specific and differentially expressed in the developmental stages. Overall, the comprehensive transcriptome resources described in this study could help understand and identify molecular targets particularly reproduction-related genes for developing effective P. rapae management tools.

Overexpression system for recombinant RNA in Corynebacterium glutamicum using a strong promoter derived from corynephage BFK20

In recent years, it has been shown that recombinant RNA molecules have a great potential in mRNA therapy and as novel agricultural pesticides. We developed a fundamental system for efficient production of target RNA molecules in Corynebacterium glutamicum, composed of a strong promoter named F1 and a terminator derived from corynephage BFK20 in a high-copy number plasmid vector. As a target model RNA for overexpression, we designed and used an RNA molecule [designated U1A*-RNA, ∼160 nucleotides (nt) long] containing a stem/loop II (SL-II, hairpin-II) structure from U1 small nuclear RNA (snRNA), which binds to U1A protein, forming a U1 sn-ribonucleoprotein, which is essential in the pre-mRNA splicing process. C. glutamicum strains harboring the U1A*-RNA expression plasmid were cultured and the total RNA was analyzed. We observed prominent expression of RNA corresponding to the U1A*-RNA transcript along with lower expression of a 3'-region-truncated form of the transcript (∼110 nt) in an rnc (encoding RNase III)-deficient strain. We also found that the produced U1A*-RNA bound to the U1A RNA-binding domain protein, which was separately prepared with C. glutamicum. In a batch cultivation using a fermentor, the total accumulated amount of the target RNA reached about 300 mg/L by 24 h. Thus, our results indicated that our system can serve as an efficient platform for large-scale preparation of an RNA of interest.

Phenotypic Effects of PBAN RNAi Using Oral Delivery of dsRNA to Corn Earworm (Lepidoptera: Noctuidae) and Tobacco Budworm Larvae

Insect neuropeptides represent more than 90% of all insect hormones. The pheromone biosynthesis activating neuropeptide (PBAN)/pyrokinin family is a major group of insect neuropeptides. These neuropeptides regulate a variety of biological functions from embryo to adult in moths including, sex pheromone biosynthesis and diapause. Other functions are yet to be determined. The identification of suitable target genes is most important for the successful application of RNA interference (RNAi) for pest insect control. Insect neuropeptide genes including PBAN are known to have multiple functions and could be a good target for RNAi suppression. In this study, we selected the PBAN gene and its neuropeptide products as an RNAi target for two economically important moth species, the corn earworm, Helicoverpa zea (Boddie), and the tobacco budworm, Heliothis virescens (Fabricius). We investigated RNAi effects on immature moths that had ingested the specific double-stranded RNA (dsRNA) starting at the first instar larva through pupation. We report that RNAi treatments resulted in delay of larval growth, interference of pupal development, and mortality in the two pest moths. In addition, we selected small interfering RNAs (siRNAs) to determine if they have negative phenotypic effects similar to their full-length RNAi parents. This is one of the few examples of negative RNAi effects on lepidopteran pests via feeding and suggests possible RNAi-based control of pest moths.

Microbial-Based Double-Stranded RNA Production to Develop Cost-Effective RNA Interference Application for Insect Pest Management

RNA interference (RNAi) is a convenient tool to identify and characterize biological functions in organisms. Recently, it has become an alternative to chemical insecticides as a biologically based control agent. This promising technology has the potential to avoid many problems associated with conventional chemical insecticides. In order for RNAi application to be practical for field use, a major hurdle is the development of a cost-effective system of double-stranded RNA (dsRNA) production for a large quantity of dsRNA. A handful of research reports has demonstrated microbial-based dsRNA production using L4440 vector and HT115 (DE3) Escherichia coli for application to vertebrate and invertebrate systems. However, the dsRNA yield, production efficiency, and biological purity from this in vitro system is still unclear. Thus, our study detailed biochemical and molecular tools for large-scale dsRNA production using the microbial system and investigated the production efficiency and yield of crude and purified dsRNAs. An unrelated insect gene, green fluorescent protein (GFP), and an insect neuropeptide gene, pyrokinin (PK) identified from Drosophila suzukii, were used to construct the recombinant L4440 to be expressed in the HT115 (DE3) cell. A considerable amount of dsRNA, 19.5 µg/mL of liquid culture, was isolated using ultrasonic disruption followed by phenol extraction. The sonication method was further evaluated to extract crude dsRNA without the additional phenol extraction and nuclease treatments and also to reduce potential bacterial viability. The results suggest that the ultrasonic method saved time and costs to isolate crude dsRNA directly from large volumes of cell culture without E coli contamination. We investigated whether the injection of PK dsRNA into flies resulted in increased adult mortality, but it was not statistically significant at 95% confidence level. In this study, the microbial-based dsRNA production has potential for applied RNAi technology to complement current insect pest management practices.

Differential Gene Expression in Red Imported Fire Ant (Solenopsis invicta) (Hymenoptera: Formicidae) Larval and Pupal Stages

Solenopsis invicta Buren is an invasive ant species that has been introduced to multiple continents. One such area, the southern United States, has a history of multiple control projects using chemical pesticides over varying ranges, often resulting in non-target effects across trophic levels. With the advent of next generation sequencing and RNAi technology, novel investigations and new control methods are possible. A robust genome-guided transcriptome assembly was used to investigate gene expression differences between S. invicta larvae and pupae. These life stages differ in many physiological processes; of special importance is the vital role of S. invicta larvae as the colonies' "communal gut". Differentially expressed transcripts were identified related to many important physiological processes, including digestion, development, cell regulation and hormone signaling. This dataset provides essential developmental knowledge that reveals the dramatic changes in gene expression associated with social insect life stage roles, and can be leveraged using RNAi to develop effective control methods.

Rapid Expansion of a Highly Germline-Expressed Mariner Element Acquired by Horizontal Transfer in the Fire Ant Genome

Transposable elements (TEs) are present in almost all organisms and affect the host in various ways. TE activity can increase genomic variation and thereby affect host evolution. Currently active TEs are particularly interesting because they are likely generating new genomic diversity. These active TEs have been poorly studied outside of model organisms. In this study, we aimed to identify currently active TEs of a notorious invasive species, the red imported fire ant Solenopsis invicta. Using RNA profiling of male and female germline tissues, we found that the majority of TE-containing transcripts in the fire ant germline belong to the IS630-Tc1-Mariner superfamily. Subsequent genomic characterization of fire ant mariner content, molecular evolution analysis, and population comparisons revealed a highly expressed and highly polymorphic mariner element that is rapidly expanding in the fire ant genome. Additionally, using comparative genomics of multiple insect species we showed that this mariner has undergone several recent horizontal transfer events (<5.1 My). Our results document a rare case of a currently active TE originating from horizontal transfer.

Genes and genomic processes underpinning the social lives of ants

The >15000 ant species are all highly social and show great variation in colony organization, complexity and behavior. The mechanisms by which such sociality evolved, as well as those underpinning the elaboration of ant societies since their ∼140 million year old common ancestor, have long been pondered. Here, we review recent insights generated using various genomic approaches. This includes understanding the molecular mechanisms underlying caste differentiation and the diversity of social structures, studying the impact of eusociality on genomic evolutionary rates, and investigating gene expression changes associated with differences in lifespan between castes. Furthermore, functional studies involving RNAi and CRISPR have recently been successfully applied to ants, opening the door to exciting research that promises to revolutionize the understanding of the evolution and diversification of social living.

Implementing the sterile insect technique with RNA interference - a review

We review RNA interference (RNAi) of insect pests and its potential for implementing sterile insect technique (SIT)-related control. The molecular mechanisms that support RNAi in pest species are reviewed in detail, drawing on literature from a range of species including Drosophila melanogaster Meigen and Homo sapiens L. The underlying genes that enable RNAi are generally conserved across taxa, although variance exists in both their form and function. RNAi represents a plausible, non-GM system for targeting populations of insects for control purposes, if RNAi effector molecules can be delivered environmentally (eRNAi). We consider studies of eRNAi from across several insect orders and review to what extent taxonomy, genetics, and differing methods of double-stranded (ds) RNA synthesis and delivery can influence the efficiency of gene knockdown. Several factors, including the secondary structure of the target mRNA and the specific nucleotide sequence of dsRNA effector molecules, can affect the potency of eRNAi. However, taxonomic relationships between insects cannot be used to reliably forecast the efficiency of an eRNAi response. The mechanisms by which insects acquire dsRNA from their environment require further research, but the evidence to date suggests that endocytosis and transport channels both play key roles. Delivery of RNA molecules packaged in intermediary carriers such as bacteria or nanoparticles may facilitate their entry into and through the gut, and enable the evasion of host defence systems, such as toxic pH, that would otherwise attenuate the potential for RNAi.

Transcriptomic characterization and curation of candidate neuropeptides regulating reproduction in the eyestalk ganglia of the Australian crayfish, Cherax quadricarinatus

The Australian redclaw crayfish (Cherax quadricarinatus) has recently received attention as an emerging candidate for sustainable aquaculture production in Australia and worldwide. More importantly, C. quadricarinatus serves as a good model organism for the commercially important group of decapod crustaceans as it is distributed worldwide, easy to maintain in the laboratory and its reproductive cycle has been well documented. In order to better understand the key reproduction and development regulating mechanisms in decapod crustaceans, the molecular toolkit available for model organisms such as C. quadricarinatus must be expanded. However, there has been no study undertaken to establish the C. quadricarinatus neuropeptidome. Here we report a comprehensive study of the neuropeptide genes expressed in the eyestalk in the Australian crayfish C. quadricarinatus. We characterised 53 putative neuropeptide-encoding transcripts based on key features of neuropeptides as characterised in other species. Of those, 14 neuropeptides implicated in reproduction regulation were chosen for assessment of their tissue distribution using RT-PCR. Further insights are discussed in relation to current knowledge of neuropeptides in other species and potential follow up studies. Overall, the resulting data lays the foundation for future gene-based neuroendocrinology studies in C. quadricarinatus.

RNA Interference in Moths: Mechanisms, Applications, and Progress

The vast majority of lepidopterans, about 90%, are moths. Some moths, particularly their caterpillars, are major agricultural and forestry pests in many parts of the world. However, some other members of moths, such as the silkworm Bombyx mori, are famous for their economic value. Fire et al. in 1998 initially found that exogenous double-stranded RNA (dsRNA) can silence the homolog endogenous mRNA in organisms, which is called RNA interference (RNAi). Soon after, the RNAi technique proved to be very promising not only in gene function determination but also in pest control. However, later studies demonstrate that performing RNAi in moths is not as straightforward as shown in other insect taxa. Nevertheless, since 2007, especially after 2010, an increasing number of reports have been published that describe successful RNAi experiments in different moth species either on gene function analysis or on pest management exploration. So far, more than 100 peer-reviewed papers have reported successful RNAi experiments in moths, covering 10 families and 25 species. By using classic and novel dsRNA delivery methods, these studies effectively silence the expression of various target genes and determine their function in larval development, reproduction, immunology, resistance against chemicals, and other biological processes. In addition, a number of laboratory and field trials have demonstrated that RNAi is also a potential strategy for moth pest management. In this review, therefore, we summarize and discuss the mechanisms and applications of the RNAi technique in moths by focusing on recent progresses.

Ant Genetics: Reproductive Physiology, Worker Morphology, and Behavior

Many exciting studies have begun to elucidate the genetics of the morphological and physiological diversity of ants, but as yet few studies have investigated the genetics of ant behavior directly. Ant genomes are marked by extreme rates of gene turnover, especially in gene families related to olfactory communication, such as the synthesis of cuticular hydrocarbons and the perception of environmental semiochemicals. Transcriptomic and epigenetic differences are apparent between reproductive and sterile females, males and females, and workers that differ in body size. Quantitative genetic approaches suggest heritability of task performance, and population genetic studies indicate a genetic association with reproductive status in some species. Gene expression is associated with behavior including foraging, response to queens attempting to join a colony, circadian patterns of task performance, and age-related changes of task. Ant behavioral genetics needs further investigation of the feedback between individual-level physiological changes and socially mediated responses to environmental conditions.

Identification and expression of a new member of the pyrokinin/pban gene family in the sand fly Phlebotomus papatasi

The major family of neuropeptides (NPs) derived from the pk (pyrokinin)/pban (pheromone biosynthesis activating neuropeptide) gene are defined by a common FXPRL-NH2 or similar sequence at the C-termini. This family of peptides has been found in all insect groups investigated to date and is implicated in regulating various physiological functions, including pheromone biosynthesis and diapause, but other functions are still largely unknown in specific life stages. Here we identify two isoforms of pk/pban cDNA encoding the PBAN domain from the sand fly Phlebotomus papatasi. The two pk/pban isoforms have the same sequence except for a 63 nucleotide difference between the long and short forms, and contain no alternative mRNA splicing site. Two NP homologues, DASGDNGSDSQRTRPPFAPRLamide and SLPFSPRLamide are expected, however, sequence corresponding to the diapause hormone was not found in the P. papatasi pk/pban gene. The PBAN-like amino acid sequence homologue SNKYMTPRL is conserved in the gene, but there is no cleavage site for processing a functional peptide. Characterizing the expression of the isoforms in developmental stages and adults indicates that the short form is differentially transcribed depending on the life stage. The P. papatasi pk/pban gene is the only known pk/pban gene with two transcriptional isoforms and from examination of endoproteolytic cleavage sites is expected to produce fewer peptides than most of the pk/pban genes elucidated to date; only Drosophila melanogaster is simpler with a single NP detected by mass spectroscopy. A phylogenetic analysis showed P. papatasi pk/pban grouped more closely with other nematoceran flies rather than higher flies.

Identification and RNA Interference of the Pheromone Biosynthesis Activating Neuropeptide (PBAN) in the Common Cutworm Moth Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura F. is one of the most destructive insect pests of many agricultural crops and notorious for developing insecticide resistance. Developing environmental friendly control methods such as novel pheromone and RNAi-related control strategies is imperative to control this pest. In the present study, the full-length cDNA encoding the diapause hormone and pheromone biosynthesis activating neuropeptide (DH-PBAN) was identified and characterized in S. litura. This 809-bp transcript contains a 573-nucleotide ORF encoding a 191-amino acid protein, from which five putative neuropeptides, including PBAN, DH, and α-, β-, and γ-subesophageal ganglion neuropeptides, were derived. Phylogenetic analysis showed that both the whole protein and each of the five neuropeptides have high similarities to those of DH-PBANs from other insect orders particularly Lepidoptera. Females treated with TKYFSPRLamide (the active core fragment of PBAN) produced significantly more four types of pheromone compounds (A; B; C; D) than controls. RNA interference by injection of PBAN dsRNA significantly reduced the relative expression levels of this gene in adult females (approximately reduced by 60%). As a consequence, females treated with PBAN dsRNA produced significantly less four types of pheromone compounds (A; B; C; D) than controls. These results suggest that PBAN function in activating sex pheromone biosynthesis and the RNAi of DH-PBAN gene can be induced by the injection of dsRNA into the body cavity in S. litura. This study suggests the possibility of novel pheromone-related pest control strategies based on RNAi techniques.

Did the fire ant supergene evolve selfishly or socially?

The genetic basis for animal social organization is poorly understood. Fire ants provide one of the rare cases where variation in social organization has been demonstrated to be under genetic control, which amazingly, segregates as a single Mendelian locus. A recent genetic, genomic, and cytological analysis revealed that this locus actually consists of over 600 genes locked together in a supergene that possesses many characteristics of sex chromosomes. The fire ant social supergene also behaves selfishly, and an interesting evolutionary question is whether the genes incorporated first into the social supergene were those for social adaptation, selfish genetic drive, or something else. In depth, functional molecular genetic analysis in fire ants and comparative genomics in other closely related socially polymorphic species will be required to resolve this question.

Identification and expression of PBAN/diapause hormone and GPCRs from Aedes aegypti

Neuropeptides control various physiological functions and constitute more than 90% of insect hormones. The pheromone biosynthesis activating neuropeptide (PBAN)/pyrokinin family is a major group of insect neuropeptides and is well conserved in Insecta. This family of peptides has at least two closely related G-protein-coupled receptors (GPCRs) activated by PBAN and a diapause hormone (DH). They have been shown to control several biological activities including pheromone production and diapause induction in moths. However, beyond some moth species, the biological function(s) of PBAN/pyrokinin peptides are largely unknown although these peptides are found in all insects. In this study we identified and characterized PBAN/pyrokinin peptides and corresponding GPCRs from the mosquito, Aedes aegypti. Ae. aegypti PBAN mRNA encodes four putative peptides including PBAN and DH, and is expressed in females and males during all life stages. The PBAN receptor (PBAN-R) and the DH receptor (DH-R) were functionally expressed and confirmed through binding assays with PBAN and DH peptides. These receptors are differentially expressed from eggs to adults with the relative gene expression of the PBAN-R significantly lower during the 4th instar larval (L4) and pupal (P1-P2) stages compared to the 2nd and 3rd instar larval stages (L2 and L3). However, DH-R expression level is consistently 4-10 times higher than the PBAN-R in the same period, suggesting that PBAN-R is downregulated in the late larval and pupal stages, whereas DH-R stays upregulated throughout all developmental stages. PBAN/pyrokinin mRNA expression remains high in all stages since it produces PBAN and DH peptides. This study provides the foundation for determining the function(s) of the PBAN/pyrokinin peptides in mosquitoes and establishes data critical to the development of methods for disruption of these hormone actions as a novel strategy for mosquito control.

Ant genomics sheds light on the molecular regulation of social organization

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.

Neuropeptidergic regulation of reproduction in insects

Successful animal reproduction depends on multiple physiological and behavioral processes that take place in a timely and orderly manner in both mating partners. It is not only necessary that all relevant processes are well coordinated, they also need to be adjusted to external factors of abiotic and biotic nature (e.g. population density, mating partner availability). Therefore, it is not surprising that several hormonal factors play a crucial role in the regulation of animal reproductive physiology. In insects (the largest class of animals on planet Earth), lipophilic hormones, such as ecdysteroids and juvenile hormones, as well as several neuropeptides take part in this complex regulation. While some peptides can affect reproduction via an indirect action (e.g. by influencing secretion of juvenile hormone), others exert their regulatory activity by directly targeting the reproductive system. In addition to insect peptides with proven activities, several others were suggested to also play a role in the regulation of reproductive physiology. Because of the long evolutionary history of many insect orders, it is not always clear to what extent functional data obtained in a given species can be extrapolated to other insect taxa. In this paper, we will review the current knowledge concerning the neuropeptidergic regulation of insect reproduction and situate it in a more general physiological context.

Ant trail pheromone biosynthesis is triggered by a neuropeptide hormone

Our understanding of insect chemical communication including pheromone identification, synthesis, and their role in behavior has advanced tremendously over the last half-century. However, endocrine regulation of pheromone biosynthesis has progressed slowly due to the complexity of direct and/or indirect hormonal activation of the biosynthetic cascades resulting in insect pheromones. Over 20 years ago, a neurohormone, pheromone biosynthesis activating neuropeptide (PBAN) was identified that stimulated sex pheromone biosynthesis in a lepidopteran moth. Since then, the physiological role, target site, and signal transduction of PBAN has become well understood for sex pheromone biosynthesis in moths. Despite that PBAN-like peptides (∼200) have been identified from various insect Orders, their role in pheromone regulation had not expanded to the other insect groups except for Lepidoptera. Here, we report that trail pheromone biosynthesis in the Dufour's gland (DG) of the fire ant, Solenopsis invicta, is regulated by PBAN. RNAi knock down of PBAN gene (in subesophageal ganglia) or PBAN receptor gene (in DG) expression inhibited trail pheromone biosynthesis. Reduced trail pheromone was documented analytically and through a behavioral bioassay. Extension of PBAN's role in pheromone biosynthesis to a new target insect, mode of action, and behavioral function will renew research efforts on the involvement of PBAN in pheromone biosynthesis in Insecta.