An insulin-like peptide regulates egg maturation and metabolism in the mosquito Aedes aegypti

Endocrine and enzymatic shifts during insect diapause: a review of regulatory mechanisms

Insect diapause is a vital survival strategy that enables insects to enter a state of suspended development, allowing them to withstand unfavorable environmental conditions. During diapause, insects significantly lower their metabolic rate and build up energy reserves, which they gradually utilize throughout this period. The regulation of diapause involves a complex interaction of hormones and enzymes. Juvenile hormones (JHs) affect adults and larvae differently; in adults, the absence of JH typically triggers diapause, while in larvae, the presence of JH encourages this state. Ecdysteroids, which regulate molting and metamorphosis, are carefully controlled to prevent premature development. Reduced signaling of insulin-like peptides enhances stress resistance and promotes energy storage. Several enzymes play crucial roles in the metabolic adjustments necessary for diapause. These adjustments include the degradation of JH, the ecdysteroidogenic pathway, and the metabolism of fatty acids, glycogen, cryoprotectants, and stress responses. Understanding diapause's molecular and biochemical mechanisms is essential for fundamental entomological research and practical applications. Despite recent advances, many aspects of diapause regulation, especially the interactions among hormonal pathways and the role of enzymes, remain poorly understood. This review analyzes approximately 250 papers to consolidate current knowledge on the enzymatic and hormonal regulation of diapause. It offers a comprehensive overview of key processes based on recent studies and suggests future research directions to fill gaps in our understanding of this significant biological phenomenon. The review also lays the groundwork for enhancing pest control strategies and ecological conservation by deepening our understanding of diapause mechanisms.

Diet influence on male sexual maturation through interplay between insulin signaling and juvenile hormone in insects

In animals, sexual maturation coincides with the development of sexual behaviors and reproductive system. These developmental events are influenced by diet and governed by endocrine signals. Here, for the first time in insects, we explored functional links between nutrition and juvenile hormone (JH) in the male reproductive physiology through the insulin signaling pathway (ISP) acting as a transducer of nutritional signals. We turned to the male moth Agrotis ipsilon for which sexual maturation, including accessory sex glands (ASGs) development concomitantly with antennal lobes (ALs) maturation for female sex pheromone processing and display of sexual behavior, is known to be JH- and diet-dependent. Indeed, a diet rich in sugars with sodium was previously shown to accelerate sexual maturation, which was achieved from the third day of adult life. In this study, we demonstrated that such a diet raised i) the expression of JH signaling actors (Methoprene-tolerant, Taiman, and Krüppel homolog 1) in ALs and ASGs, ii) the biosynthesis and circulating levels of JH, and iii) the expression of both insulin receptor (InR) and insulin-like peptides (ILPs) in corpora allata (CAs) and brain respectively. Insulin injection raised JH biosynthesis following increased HMG-CoA reductase expression in CAs; opposite effects were induced in InR-deficient males. Thus, we highlighted that promoting effects of a diet composed of sugars with sodium on male sexual maturation results from an early induction of ISP causing an increase in JH biosynthesis followed by a potentiation of JH actions on the development of ASGs and ALs in A. ipsilon.

Juvenile hormone induces phosphorylation of insulin/insulin-like growth factor signaling proteins in previtellogenic Aedes aegypti mosquitoes

Juvenile hormone (JH) plays a pivotal role in regulating post-emergence development and metabolism in previtellogenic female Aedes aegypti mosquitoes. In contrast, yolk protein precursor production and egg maturation after a blood meal are regulated by the steroid hormone 20-hydroxyecdysone, the insulin-like growth factor (IGF)/insulin signaling (IIS) pathway, and the mammalian target of rapamycin (mTOR) pathway. The role of IIS/mTOR signaling in female adults prior to blood feeding has not been thoroughly investigated. In this study, we identified a significant increase in the phosphorylation of key effector proteins in the IIS/mTOR signaling pathway, including eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), ribosomal protein S6 kinase (S6K) and forkhead box protein O1 (FoxO1), in previtellogenic females. In vitro fat body culture experiments suggest that JH induces these phosphorylations through rapid nongenomic signaling mediated by the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mTOR network. RNA interference experiments demonstrated that activation of IIS/mTOR signaling in previtellogenic females modulate metabolic gene expression, promoting the accumulation of energy reserves (glycogen and triglycerides), which influence mosquito fecundity. Additionally, depletion of either the insulin receptor (InR) or the JH receptor Methoprene-tolerant (Met) in adult mosquitoes abolished the phosphorylation of these proteins, indicating that both receptors are involved in JH-induced membrane-initiated signal transduction. Although the precise mechanisms remain unclear, this study uncovers a novel function of the IIS/mTOR pathway in adult mosquitoes before blood feeding, as well as a new mode of JH action through its crosstalk with the IIS pathway.

Functional characterization of CCHamides and deorphanization of their receptors in the yellow fever mosquito, Aedes aegypti

As a widely distributed anthropophilic mosquito species and vector of various arboviruses, Aedes aegypti poses a significant threat to human health on a global scale. Investigating mosquito neuropeptides allows us to better understand their physiology. The neuropeptides CCHamide1 (CCHa1) and CCHamide2 (CCHa2) along with their associated G protein-coupled receptors (CCHa1R and CCHa2R) were recently identified and studied across insects. However, expression profiles and physiological roles of CCHamides and their receptors in many other insects, including A. aegypti, remain unclear. This research aimed to quantify and localize the expression of CCHamides along with their receptors and gain insight on their physiological function in the yellow fever mosquito. RT-qPCR analysis revealed transcript abundance of CCHamides and receptors changes over development. Differential expression was also observed in tissues/organs of adult mosquitoes indicating CCHa1 and CCHa2 transcripts are enriched in the midgut, while receptors are expressed across various tissues. CCHamide immunoreactivity was observed in neurons in the brain and ventral nerve cord along with enteroendocrine cells in the posterior midgut adjacent to the midgut-hindgut junction, corroborating their transcript expression profiles. Using different mass spectrometrical approaches, presence of CCHamides were confirmed in the brain of both sexes, including the pars intercerebralis of female mosquitoes, as well as in the gut of adult mosquitoes. For chemical identification of predicted CCHamides, we analyzed brain and gut extracts by ESI-Q Exactive Orbitrap MS and resulting fragmentations confirmed CCHa1 and CCHa2 in brain and midgut samples of both male and female mosquitoes. A heterologous functional assay was used to confirm the specificity and sensitivity of the two CCHamide receptors by assessing their activation in response to diverse mosquito peptides, which confirmed CCHa1 and CCHa2 as natural ligands. Finally, using a capillary feeder (CAFE) bioassay, our results suggest that CCHa2 modulates feeding behaviour in female mosquitoes.

Identification and Characterization of a Novel Insulin-like Receptor (LvRTK2) Involved in Regulating Growth and Glucose Metabolism of the Pacific White Shrimp Litopenaeus vannamei

The insulin receptor (IR) plays a crucial role in the growth and metabolism of animals. However, there are still many questions regarding the IR in crustaceans, particularly their role in shrimp growth and glucose metabolism. In this study, we identified a novel insulin-like receptor gene in Litopenaeus vannamei and cloned its full length of 6439 bp. This gene exhibited a highly conserved sequence and structural characteristics. Phylogenetic analysis confirmed it as an unreported RTK2-type IR, namely, LvRTK2. Expression pattern analysis showed that LvRTK2 is primarily expressed in female reproductive and digestive organs. Through a series of in vivo and in vitro experiments, including glucose treatment, exogenous insulin treatment, and starvation treatment, LvRTK2 was confirmed to be involved in the endogenous glucose metabolic pathway of shrimp under different glucose variations. Moreover, long-term and short-term interference experiments with LvRTK2 revealed that the interference significantly reduced the shrimp growth rate and serum glucose clearance rate. Further studies indicated that LvRTK2 may regulate shrimp growth by modulating the downstream PI3K/AKT signaling pathway and a series of glucose metabolism events, such as glycolysis, gluconeogenesis, glycogen synthesis, and glycogenolysis. This report on the characteristics and functions of LvRTK2 confirms the important role of RTK2-type IRs in regulating shrimp growth and glucose metabolism.

Visualization of Apoptotic Ovarian Follicles during Aedes aegypti Mosquito Egg Maturation by Fluorescent Imaging Studies

In insects, oocyte resorption (oosorption) or follicular atresia is one of the key physiological processes and evolutionary strategies used to optimize reproductive fitness. Mosquitoes are ideal model organisms for studying egg maturation in arthropods, as their follicle development is initiated only following the ingestion of a blood meal, followed by a carefully orchestrated series of hormonally regulated events leading to egg maturation. A cohort of approximately 100 follicles per mosquito ovary begin developing synchronously. However, a significant fraction of follicles ultimately undergo apoptosis and oosorption, especially when available resources from the blood meal are limited. Therefore, simple, rapid, and reliable techniques to accurately evaluate follicular atresia are necessary to understand mechanisms underlying follicle development in insects. This protocol describes how to detect apoptotic follicle cells within the Aedes aegypti mosquito ovaries using a commercially available fluorescent-labeled inhibitor of caspases (FLICA). Caspases are key players in animal apoptosis. In this assay, the FLICA reagent enters the intracellular compartment of follicles in dissected mosquito ovaries and covalently binds to active caspases. The bound reagent remains within the cell and its fluorescent signal can be observed by confocal microscopy. Although this method was specifically developed for visualizing apoptotic ovarian follicles during Ae. aegypti mosquito egg development, it should be applicable to other mosquito tissues that undergo caspase-mediated program cell death in a time-dependent manner.

Mosquito Egg Development and Eggshell Formation

Anautogenous female mosquitoes, which ingest a blood meal from warm-blooded vertebrates to produce eggs, have become a valuable model organism for investigating signaling pathways and physiological processes that occur during egg development. Different molecular pathways tightly regulate the initiation of egg development and are governed by a balance among different insect hormones. Gravid (mature egg-carrying) females deposit fully developed eggs at the end of each gonotrophic cycle, which is defined as the time interval between the ingestion of a blood meal to oviposition. An intact eggshell protects the oocyte and embryo inside from external factors such as desiccation, physical damage, etc., and the various eggshell proteins are spatially and temporary deposited during oogenesis. Additionally, follicle resorption (oosorption) during blood meal-induced mosquito ovarian follicle development is an adapted physiological process that optimizes reproductive fitness. Mosquito oocytes grow and mature synchronously throughout oogenesis; however, during the later stages of oogenesis, some oocytes may undergo oosorption if sufficient nutrients are unavailable. This introduction highlights how mosquito egg development can be used to investigate follicular resorption and identify proteins involved in eggshell formation in Aedes aegypti mosquitoes.

The complexities of blood-feeding patterns in mosquitoes and sandflies and the burden of disease: A minireview

Mosquitoes and sandflies exhibit a wide range of blood feeding patterns, targeting a wide range of vertebrate species, including birds, mammals, reptiles, and amphibians, for proteins vital for egg development. This broad host range increases the opportunity for them to acquire pathogens of numerous debilitating-and-fatal diseases from various animal reservoirs, playing a significant role in disease crossover between animals and humans, also known as zoonotic transmission. This review focuses on the intricate blood-feeding habits of these dipteran vectors, their sensory systems and the complex dance between host and pathogen during disease transmission. We delve into the influence of blood sources on pathogen spread by examining the insect immune response and its intricate interplay with pathogens. The remarkable sense of smell guiding them towards food sources and hosts is explored, highlighting the interplay of multiple sensory cues in their navigation. Finally, we examine the challenges in mosquito control strategies and explore innovations in this field, emphasizing the need for sustainable solutions to combat this global health threat. By understanding the biology and behaviour of these insects, we can develop more effective strategies to protect ourselves and mitigate the burden of vector-borne diseases.

Effect of nanoformulation Azadirachta indica on some factors associated with the vectorial capacity and competence of Anopheles aquasalis experimentally infected with Plasmodium vivax

Malaria remains a highly prevalent infectious disease worldwide, particularly in tropical and subtropical regions. Effectively controlling of mosquitoes transmitting of Plasmodium spp. is crucial in to control this disease. A promising strategy involves utilizing plant-derived products, such as the Neem tree (Azadirachta indica), known for its secondary metabolites with biological activity against various insect groups of agricultural and public health importance. This study investigated the effects of a nanoformulation prototype Neem on factors linked to the vector competence of Anopheles aquasalis, a malaria vector in Latin America. Different concentrations of the nanoformulation were supplied through sugar solution and blood feeding, assessing impacts on longevity, fecundity, fertility, and transgenerational survival from larvae to adults. Additionally, the effects of the Neem nanoformulation and NeemAZAL® formulation on the sporogonic cycle of P. vivax were evaluated. Overall, significant impacts were observed at 100 ppm and 1,000 ppm concentrations on adult survival patterns and on survival of the F1 generation. A trend of reduced oviposition and hatching rates was also noted in nanoformulation-consuming groups, with fertility and fecundity declining proportionally to the concentration. Additionally, a significant decrease in the infection rate and intensity of P. vivax was observed in the 1,000 ppm group, with a mean of 3 oocysts per female compared to the control's 27 oocysts per female. In the commercial formulation, the highest tested concentration of 3 ppm yielded 5.36 oocysts per female. Concerning sporozoite numbers, there was a reduction of 52 % and 87 % at the highest concentrations compared to the control group. In conclusion, these findings suggest that the A. indica nanoformulation is a potential as a tool for malaria control through reduction in the vector longevity and reproductive capacity, possibly leading to decreased vector population densities. Moreover, the nanoformulation interfered with the sporogonic development of P. vivax. However, further basic research on Neem formulations, their effects, and mechanisms of action is imperative to gain a more specific perspective for safe field implementation.

Lipids in Insect Reproduction: Where, How, and Why

Modern insects have inhabited the earth for hundreds of millions of years, and part of their successful adaptation lies in their many reproductive strategies. Insect reproduction is linked to a high metabolic rate that provides viable eggs in a relatively short time. In this context, an accurate interplay between the endocrine system and the nutrients synthetized and metabolized is essential to produce healthy offspring. Lipids guarantee the metabolic energy needed for egg formation and represent the main energy source consumed during embryogenesis. Lipids availability is tightly regulated by a complex network of endocrine signals primarily controlled by the central nervous system (CNS) and associated endocrine glands, the corpora allata (CA) and corpora cardiaca (CC). This endocrine axis provides hormones and neuropeptides that significatively affect tissues closely involved in successful reproduction: the fat body, which is the metabolic center supplying the lipid resources and energy demanded in egg formation, and the ovaries, where the developing oocytes recruit lipids that will be used for optimal embryogenesis. The post-genomic era and the availability of modern experimental approaches have advanced our understanding of many processes involved in lipid homeostasis; therefore, it is crucial to integrate the findings of recent years into the knowledge already acquired in the last decades. The present chapter is devoted to reviewing major recent contributions made in elucidating the impact of the CNS/CA/CC-fat body-ovary axis on lipid metabolism in the context of insect reproduction, highlighting areas of fruitful research.

Endocrine Control of Lipid Metabolism

Lipids are essential in insects and play pleiotropic roles in energy storage, serving as a fuel for energy-driven processes such as reproduction, growth, development, locomotion, flight, starvation response, and diapause induction, maintenance, and termination. Lipids also play fundamental roles in signal transduction, hormone synthesis, forming components of the cell membrane, and thus are essential for maintenance of normal life functions. In insects, the neuroendocrine system serves as a master regulator of most life activities, including growth and development. It is thus important to pay particular attention to the regulation of lipid metabolism through the endocrine system, especially when considering the involvement of peptide hormones in the processes of lipogenesis and lipolysis. In insects, there are several lipogenic and lipolytic hormones that are involved in lipid metabolism such as insulin-like peptides (ILPs), adipokinetic hormone (AKH), 20-hydroxyecdysone (20-HE), juvenile hormone (JH), and serotonin. Other neuropeptides such as diapause hormone-pheromone biosynthesis activating neuropeptide (DH-PBAN), CCHamide-2, short neuropeptide F, and the cytokines Unpaired 1 and 2 may play a role in inducing lipogenesis. On the other hand, neuropeptides such as neuropeptide F, allatostatin-A, corazonin, leukokinin, tachykinins, limostatins, and insulin-like growth factor (ILP6) stimulate lipolysis. This chapter briefly discusses the current knowledge of the endocrine regulation of lipid metabolism in insects that could be utilized to reveal differences between insects and mammalian lipid metabolism which may help understand human diseases associated with dysregulation of lipid metabolism. Physiological similarities of insects to mammals make them valuable model systems for studying human diseases characterized by disrupted lipid metabolism, including conditions like diabetes, obesity, arteriosclerosis, and various metabolic syndromes.

The diverse roles of insulin signaling in insect behavior

In insects and other animals, nutrition-mediated behaviors are modulated by communication between the brain and peripheral systems, a process that relies heavily on the insulin/insulin-like growth factor signaling pathway (IIS). Previous studies have focused on the mechanistic and physiological functions of insulin-like peptides (ILPs) in critical developmental and adult milestones like pupation or vitellogenesis. Less work has detailed the mechanisms connecting ILPs to adult nutrient-mediated behaviors related to survival and reproductive success. Here we briefly review the range of behaviors linked to IIS in insects, from conserved regulation of feeding behavior to evolutionarily derived polyphenisms. Where possible, we incorporate information from Drosophila melanogaster and other model species to describe molecular and neural mechanisms that connect nutritional status to behavioral expression via IIS. We identify knowledge gaps which include the diverse functional roles of peripheral ILPs, how ILPs modulate neural function and behavior across the lifespan, and the lack of detailed mechanistic research in a broad range of taxa. Addressing these gaps would enable a better understanding of the evolution of this conserved and widely deployed tool kit pathway.

Precise coordination between nutrient transporters ensures fertility in the malaria mosquito Anopheles gambiae

Females from many mosquito species feed on blood to acquire nutrients for egg development. The oogenetic cycle has been characterized in the arboviral vector Aedes aegypti, where after a bloodmeal, the lipid transporter lipophorin (Lp) shuttles lipids from the midgut and fat body to the ovaries, and a yolk precursor protein, vitellogenin (Vg), is deposited into the oocyte by receptor-mediated endocytosis. Our understanding of how the roles of these two nutrient transporters are mutually coordinated is however limited in this and other mosquito species. Here, we demonstrate that in the malaria mosquito Anopheles gambiae, Lp and Vg are reciprocally regulated in a timely manner to optimize egg development and ensure fertility. Defective lipid transport via Lp knockdown triggers abortive ovarian follicle development, leading to misregulation of Vg and aberrant yolk granules. Conversely, depletion of Vg causes an upregulation of Lp in the fat body in a manner that appears to be at least partially dependent on target of rapamycin (TOR) signaling, resulting in excess lipid accumulation in the developing follicles. Embryos deposited by Vg-depleted mothers are completely inviable, and are arrested early during development, likely due to severely reduced amino acid levels and protein synthesis. Our findings demonstrate that the mutual regulation of these two nutrient transporters is essential to safeguard fertility by ensuring correct nutrient balance in the developing oocyte, and validate Vg and Lp as two potential candidates for mosquito control.

Evolutionary modelling indicates that mosquito metabolism shapes the life-history strategies of Plasmodium parasites

Within-host survival and between-host transmission are key life-history traits of single-celled malaria parasites. Understanding the evolutionary forces that shape these traits is crucial to predict malaria epidemiology, drug resistance, and virulence. However, very little is known about how Plasmodium parasites adapt to their mosquito vectors. Here, we examine the evolution of the time Plasmodium parasites require to develop within the vector (extrinsic incubation period) with an individual-based model of malaria transmission that includes mosquito metabolism. Specifically, we model the metabolic cascade of resource allocation induced by blood-feeding, as well as the influence of multiple blood meals on parasite development. Our model predicts that successful vector-to-human transmission events are rare, and are caused by long-lived mosquitoes. Importantly, our results show that the life-history strategies of malaria parasites depend on the mosquito's metabolic status. In our model, additional resources provided by multiple blood meals lead to selection for parasites with slow or intermediate developmental time. These results challenge the current assumption that evolution favors fast developing parasites to maximize their chances to complete their within-mosquito life cycle. We propose that the long sporogonic cycle observed for Plasmodium is not a constraint but rather an adaptation to increase transmission potential.

Insulin-like peptides and ovary ecdysteroidogenic hormone differentially stimulate physiological processes regulating egg formation in the mosquito Aedes aegypti

Mosquitoes including Aedes aegypti are human disease vectors because females must blood feed to produce and lay eggs. Blood feeding triggers insulin-insulin growth factor signaling (IIS) which regulates several physiological processes required for egg development. A. aegypti encodes 8 insulin-like peptides (ILPs) and one insulin-like receptor (IR) plus ovary ecdysteroidogenic hormone (OEH) that also activates IIS through the OEH receptor (OEHR). In this study, we assessed the expression of A. aegypti ILPs and OEH during a gonadotrophic cycle and produced each that were functionally characterized to further understand their roles in regulating egg formation. All A. aegypti ILPs and OEH were expressed during a gonadotrophic cycle. Five ILPs (1, 3, 4, 7, 8) and OEH were specifically expressed in the head, while antibodies to ILP3 and OEH indicated each was released after blood feeding from ventricular axons that terminate on the anterior midgut. A subset of ILP family members and OEH stimulated nutrient storage in previtellogenic females before blood feeding, whereas most IIS-dependent processes after blood feeding were activated by one or more of the brain-specific ILPs and/or OEH. ILPs and OEH with different biological activities also exhibited differences in IIS as measured by phosphorylation of the IR, phosphoinositide 3-kinase/Akt kinase (AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK). Altogether, our results provide the first results that compare the functional activities of all ILP family members and OEH produced by an insect.

Current Status of Omics Studies Elucidating the Features of Reproductive Biology in Blood-Feeding Insects

Female insects belonging to the genera Anopheles, Aedes, Glossina, and Rhodnius account for the majority of global vector-borne disease mortality. In response to mating, these female insects undergo several molecular, physiological, and behavioral changes. Studying the dynamic post-mating molecular responses in these insects that transmit human diseases can lead to the identification of potential targets for the development of novel vector control methods. With the continued advancements in bioinformatics tools, we now have the capability to delve into various physiological processes in these insects. Here, we discuss the availability of multiple datasets describing the reproductive physiology of the common blood-feeding insects at the molecular level. Additionally, we compare the male-derived triggers transferred during mating to females, examining both shared and species-specific factors. These triggers initiate post-mating genetic responses in female vectors, affecting not only their reproductive success but also disease transmission.

Prostaglandin E2 mediates chorion formation of the Asian tiger mosquito, Aedes albopictus, at late oogenesis

Chorion-i.e., the eggshell-is formed during the late stage of oogenesis by follicular epithelium in the ovary. Although the endocrine signal(s) driving choriogenesis remain unclear in mosquitoes, this process in other insects has been suspected to involve the mediation of prostaglandins (PGs). This study tested the role of PG in the choriogenesis of the Asian tiger mosquito, Aedes albopictus, and its influence on controlling the expressions of genes associated with chorion formation by a transcriptome analysis. An immunofluorescence assay showed that PGE2 is localised in follicular epithelium. With the treatment of aspirin, an inhibitor of PG biosynthesis, at mid oogenesis, the PGE2 signal disappeared in the follicular epithelium led to significantly inhibited chorion formation along with a malformed eggshell. Ovary transcriptomes were assessed by RNASeq at the mid and late ovarian developmental stages. Differentially expressed genes (DEGs) exhibiting more than twofold changes in expression levels included 297 genes at mid stage and 500 genes at late stage. These DEGs at these two developmental stages commonly included genes associated with egg and chorion proteins of Ae. albopictus. Most chorion-associated genes were clustered in the 168 Mb region on a chromosome and exhibited significantly induced expressions at both ovarian developmental stages. The inhibition of PG biosynthesis significantly suppressed the expression of the chorion-associated genes while the addition of PGE2 rescued the gene expressions and led to recovery of choriogenesis. These results suggest that PGE2 mediates the choriogenesis of Ae. albopictus.

RNAi-mediated knockdown of two orphan G protein-coupled receptors reduces fecundity in the yellow fever mosquito Aedes aegypti

G protein-coupled receptors (GPCRs) control numerous physiological processes in insects, including reproduction. While many GPCRs have known ligands, orphan GPCRs do not have identified ligands in which they bind. Advances in genomic sequencing and phylogenetics provide the ability to compare orphan receptor protein sequences to sequences of characterized GPCRs, and thus gain a better understanding of the potential functions of orphan GPCRs. Our study sought to investigate the functions of two orphan GPCRs, AAEL003647 and AAEL019988, in the yellow fever mosquito, Aedes aegypti. From our phylogenetic investigation, we found that AAEL003647 is orthologous to the SIFamide-2/SMYamide receptor. We also found that AAEL019988 is orthologous to the Trapped in endoderm (Tre1) receptor of Drosophila melanogaster. Next, we conducted a tissue-specific expression analysis and found that both receptors had highest expression in the ovaries, suggesting they may be important for reproduction. We then used RNA interference (RNAi) to knock down both genes and found a significant reduction in the number of eggs laid per individual female mosquito, suggesting both receptors are important for Ae. aegypti reproduction.

Fertility decline in female mosquitoes is regulated by the orco olfactory co-receptor

Female Aedes aegypti mosquitoes undergo multiple rounds of reproduction, known as gonotrophic cycles. These cycles span the period from blood meal intake to oviposition. Understanding how reproductive success is maintained across gonotrophic cycles allows for the identification of molecular targets to reduce mosquito population growth. Odorant receptor co-receptor (orco) encodes a conserved insect-specific transmembrane ion channel that complexes with tuning odorant receptors (ORs) to form a functional olfactory receptor. orco expression has been identified in the male and female mosquito germline, but its role is unclear. We report an orco-dependent, maternal effect reduction in fertility after the first gonotrophic cycle. This phenotype was removed by CRISPR-Cas9 reversion of the orco mutant locus. Eggs deposited by orco mutant females are fertilized but the embryos reveal developmental defects, reduced hatching, and changes in ion channel signaling gene transcription. We present an unexpected role for an olfactory receptor pathway in mosquito reproduction.

Identification and functional characterization of insulin-like peptides in a pine beetle

Insulin - including insulin-like peptides (ILPs), relaxins and insulin-like growth factors (IGFs) - is an evolutionarily conserved hormone in all metazoans It is involved in various physiological processes, such as metabolism, growth, reproduction, lifespan and stress resistance. However, there are no reports on the functional role of ILPs in the Chinese white pine beetle, Dendroctonus armandi. In this study, we have cloned and identified two ILP cDNAs in D. armandi. The expression levels of DaILP1 and DaILP2 were significantly changed in different developmental stages. Both ILPs were expressed mostly in the head and fat body. Moreover, starvation induces the reduction of ILP1 mRNA level in adults and larvae, while ILP2 only in larvae of D. armandi, respectively. Additionally, RNA-interference (RNAi) using double stranded RNA to knock down ILP1 and ILP2 reduced the mRNA levels of the target genes, and caused a significant reduction in body weight of D. armandi. Moreover, silencing ILP1 led to an increase of trehalose and glycogen and significantly enhanced starvation resistance in both adults and larvae. The results show that the ILP signaling pathway plays a significant role in growth and carbohydrate metabolism of D. armandi and may provide a potential molecular target for pest control.

Chikungunya virus infection in Aedes aegypti is modulated by L-cysteine, taurine, hypotaurine and glutathione metabolism

BACKGROUND

Blood meal and infections cause redox imbalance and oxidative damage in mosquitoes which triggers the mosquito's system to produce antioxidants in response to increased oxidative stress. Important pathways activated owing to redox imbalance include taurine, hypotaurine and glutathione metabolism. The present study was undertaken to evaluate the role of these pathways during chikungunya virus (CHIKV) infection in Aedes aegypti mosquitoes.

METHODOLOGY

Using a dietary L-cysteine supplement system, we upregulated these pathways and evaluated oxidative damage and oxidative stress response upon CHIKV infection using protein carbonylation and GST assays. Further, using a dsRNA based approach, we silenced some of the genes involved in synthesis and transport of taurine and hypotaurine and then evaluated the impact of these genes on CHIKV infection and redox biology in the mosquitoes.

CONCLUSIONS

We report that CHIKV infection exerts oxidative stress in the A. aegypti, leading to oxidative damage and as a response, an elevated GST activity was observed. It was also observed that dietary L-cysteine treatment restricted CHIKV infection in A. aegypti mosquitoes. This L-cysteine mediated CHIKV inhibition was coincided by enhanced GST activity that further resulted in reduced oxidative damage during the infection. We also report that silencing of genes involved in synthesis of taurine and hypotaurine modulates CHIKV infection and redox biology of Aedes mosquitoes during the infection.

Relaxin-like Gonad-Stimulating Peptides in Asteroidea

Starfish relaxin-like gonad-stimulating peptide (RGP) is the first identified peptide hormone with gonadotropin-like activity in invertebrates. RGP is a heterodimeric peptide, comprising A and B chains with disulfide cross-linkages. Although RGP had been named a gonad-stimulating substance (GSS), the purified peptide is a member of relaxin-type peptide family. Thus, GSS was renamed as RGP. The cDNA of RGP encodes not only the A and B chains, but also signal and C-peptides. After the rgp gene is translated as a precursor, mature RGP is produced by eliminating the signal and C-peptides. Hitherto, twenty-four RGP orthologs have been identified or predicted from starfish in the orders Valvatida, Forcipulatida, Paxillosida, Spinulosida, and Velatida. The molecular evolution of the RGP family is in good accordance with the phylogenetic taxonomy in Asteroidea. Recently, another relaxin-like peptide with gonadotropin-like activity, RLP2, was found in starfish. RGP is mainly present in the radial nerve cords and circumoral nerve rings, but also in the arm tips, the gonoducts, and the coelomocytes. RGP acts on ovarian follicle cells and testicular interstitial cells to induce the production of 1-methyladenine (1-MeAde), a starfish maturation-inducing hormone. RGP-induced 1-MeAde production is accompanied by an increase in intracellular cyclic AMP levels. This suggests that the receptor for RGP (RGPR) is a G protein-coupled receptor (GPCR). Two types of GPCRs, RGPR1 and RGPR2, have been postulated as candidates. Furthermore, 1-MeAde produced by RGP not only induces oocyte maturation, but also induces gamete shedding, possibly by stimulating the secretion of acetylcholine in the ovaries and testes. Thus, RGP plays an important role in starfish reproduction, but its secretion mechanism is still unknown. It has also been revealed that RGP is found in the peripheral adhesive papillae of the brachiolaria arms. However, gonads are not developed in the larvae before metamorphosis. It may be possible to discover new physiological functions of RGP other than gonadotropin-like activity.

Multiple endocrine factors regulate nutrient mobilization and storage in Aedes aegypti during a gonadotrophic cycle

Anautogenous mosquitoes must blood feed on a vertebrate host to produce eggs. Each gonadotrophic cycle is subdivided into a sugar-feeding previtellogenic phase that produces primary follicles and a blood meal-activated vitellogenic phase in which large numbers of eggs synchronously mature and are laid. Multiple endocrine factors including juvenile hormone (JH), insulin-like peptides (ILPs), ovary ecdysteroidogenic hormone (OEH), and 20-hydroxyecdysone (20E) coordinate each gonadotrophic cycle. Egg formation also requires nutrients from feeding that are stored in the fat body. Regulation of egg formation is best understood in Aedes aegypti but the role different endocrine factors play in regulating nutrient mobilization and storage remains unclear. In this study, we report that adult female Ae. aegypti maintained triacylglycerol (TAG) stores during the previtellogenic phase of the first gonadotrophic cycle while glycogen stores declined. In contrast, TAG and glycogen stores were rapidly mobilized during the vitellogenic phase and then replenishment. Several genes encoding enzymes with functions in TAG and glycogen metabolism were differentially expressed in the fat body, which suggested regulation was mediated in part at the transcriptional level. Gain of function assays indicated that stored nutrients were primarily mobilized by adipokinetic hormone (AKH) while juvenoids and OEH regulated replenishment. ILP3 further showed evidence of negatively regulating certain lipolytic enzymes. Loss of function assays indicated AKH depends on the AKH receptor (AKHR) for function. Altogether, our results indicate that the opposing activities of different hormones regulate nutrient stores during a gonadotrophic cycle in Ae. aegypti.

Lipidomic Profiling Reveals Concerted Temporal Patterns of Functionally Related Lipids in Aedes aegypti Females Following Blood Feeding

We conducted a lipidomic analysis of the whole body of female Aedes aegypti mosquitoes at different time points over the course of feeding and reproduction. There were temporal biphasic increases of more than 80% of lipids identified at the time of feeding and from 16 h to 30 h post blood meal (PBM). During these two increases, the abundance of many lipids dropped while body weight remained stable, probably reflecting blood lipid digestion and the synthesis of vitellogenin in this period. A concerted temporal pattern was particularly strong at the second peak for membrane and signalling lipids such as phosphatidylethanolamine (PE), phosphatidylinositol (PI), cardiolipin (CL), hexosylceramide (HexCer) and lyso-phosphatidic acid (LPA). Lyso-glycerophospholipids showed three distinct change patterns that are functionally related: Lyso-PE and Lyso-phosphatidylcholine (LPC), which are membrane lipids, showed little change; LPA, a signalling lipid, showed a significant increase from 16 to 30 h PBM; Lyso-PI, a bioactive lipid, and both lyso-phosphatidylglycerol (LPG) and lyso-phosphatidylserine (LPS), which are bacterial membrane lipids, showed one significant increase from the time of feeding to 16 h post blood meal. The result of our study on the anautogenous insect Ae. aegypti point to specific lipids likely to be important in the reproductive process with a role in the formation and growth of ovarian follicles.

Aedes aegypti exhibits a distinctive mode of late ovarian development

BACKGROUND

Insects live in almost every habitat on earth. To adapt to their diverse environments, insects have developed a myriad of different strategies for reproduction reflected in diverse anatomical and behavioral features that the reproductive systems of females exhibit. Yet, ovarian development remains largely uncharacterized in most species except Drosophila melanogaster (D. melanogaster), a high Diptera model. In this study, we investigated the detailed developmental process of the ovary in Aedes aegypti (Ae. aegypti), a major vector of various disease-causing pathogens that inhabits tropical and subtropical regions.

RESULTS

Compared with Drosophila melanogaster, a model of higher Diptera, the processes of pole cell formation and gonad establishment during embryonic stage are highly conserved in Ae. aegypti. However, Ae. aegypti utilizes a distinct strategy to form functional ovaries during larval/pupal development. First, during larval stage, Ae. aegypti primordial germ cells (PGCs) undergo a cyst-like proliferation with synchronized divisions and incomplete cytokinesis, leading to the formation of one tightly packed "PGC mass" containing several interconnected cysts, different from D. melanogaster PGCs that divide individually. This cyst-like proliferation is regulated by the target of rapamycin (TOR) pathway upon nutritional status. Second, ecdysone-triggered ovariole formation during metamorphosis exhibits distinct events, including "PGC mass" breakdown, terminal filament cell degeneration, and pre-ovariole migration. These unique developmental features might explain the structural and behavioral differences between Aedes and Drosophila ovaries. Importantly, both cyst-like proliferation and distinct ovariole formation are also observed in Culex quinquefasciatus and Anopheles sinensis, suggesting a conserved mode of ovarian development among mosquito species. In comparison with Drosophila, the ovarian development in Aedes and other mosquitoes might represent a primitive mode in the lower Diptera.

CONCLUSIONS

Our study reveals a new mode of ovarian development in mosquitoes, providing insights into a better understanding of the reproductive system and evolutionary relationship among insects.

Insulin-like peptide 8 (Ilp8) regulates female fecundity in flies

Introduction: Insulin-like peptides (Ilps) play crucial roles in nearly all life stages of insects. Ilp8 is involved in developmental stability, stress resistance and female fecundity in several insect species, but the underlying mechanisms are not fully understood. Here we report the functional characterization of Ilp8s in three fly species, including Bactrocera dorsalis, Drosophila mercatorum and Drosophila melanogaster. Methods: Phylogenetic analyses were performed to identify and characterize insect Ilp8s. The amino acid sequences of fly Ilp8s were aligned and the three-dimensional structures of fly Ilp8s were constructed and compared. The tissue specific expression pattern of fly Ilp8s were examined by qRT-PCR. In Bactrocera dorsalis and Drosophila mercatorum, dsRNAs were injected into virgin females to inhibit the expression of Ilp8 and the impacts on female fecundity were examined. In Drosophila melanogaster, the female fecundity of Ilp8 loss-of-function mutant was compared with wild type control flies. The mutant fruit fly strain was also used for sexual behavioral analysis and transcriptomic analysis. Results: Orthologs of Ilp8s are found in major groups of insects except for the lepidopterans and coleopterans, and Ilp8s are found to be well separated from other Ilps in three fly species. The key motif and the predicted three-dimensional structure of fly Ilp8s are well conserved. Ilp8 are specifically expressed in the ovary and are essential for female fecundity in three fly species. Behavior analysis demonstrates that Ilp8 mutation impairs female sexual attractiveness in fruit fly, which results in decreased mating success and is likely the cause of fecundity reduction. Further transcriptomic analysis indicates that Ilp8 might influence metabolism, immune activity, oocyte development as well as hormone homeostasis to collectively regulate female fecundity in the fruit fly. Discussion: Our findings support a universal role of insect Ilp8 in female fecundity, and also provide novel clues for understanding the modes of action of Ilp8.

Insulin Receptor Substrate-1 (IRS1) Regulates Oogenesis and Vitellogenesis in Propylea japonica by Mediating the FOXO Transcription Factor Expression, Independent of JH and 20E Signaling Pathways

The insulin receptor substrate (IRS), as the core cytoplasmic adapter protein in the insulin/insulin-like signaling (IIS) pathway, is an important mediator of cellular signaling. However, it is still unknown how IRS crosstalk with hormone signaling regulates insect growth, development, and reproduction. In this study, we demonstrated that knockdown of IRS1 significantly inhibited oogenesis, vitellogenesis, and the development of nurse cells and follicular epithelial cells. In addition, qRT-PCR results showed that FOXO transcription factors significantly responded to silencing of the IRS1 gene. However, IRS1 silencing had no significant effect on the expression of juvenile hormone/20-hydroxyecdysone (JH/20E)-signaling genes, JH synthesis, and degradation enzyme-related genes and the JH/20E titers. Our results suggested that the IIS pathway regulated ovarian development and Vg production through FOXO, independent of JH and 20E signaling pathways. This study revealed the reproductive regulation mechanism in Propylea japonica, which provides a theoretical basis for large-scale expansion of P. japonica as an environment-friendly biological control strategy.

Insulin-like Peptide Receptor (ILPR) in the Cuttlefish Sepiella japonica: Characterization, Expression, and Regulation of Reproduction

Insulin-like peptide receptor (ILPR) can effectively regulate ovarian development in invertebrates, but its effect in cuttlefish has not been reported. We isolated and characterized a ILPR gene from Sepiella japonica, referred to as SjILPR. This gene displayed significant homologies to Octopus bimaculoides ILPR, and contained all typical features of insulin receptors and tyrosine kinase domain structure. SjILPR is expressed in all detected tissues, with the highest expression in the ovary. During ovarian development stages, its expression levels in the ovary, pancreas, and liver were correlated to the female reproductive cycle. After the silencing of SjILPR in vivo, comparative transcriptome analysis identified 4314 differentially expressed genes (DEGs) in the injected group, including 2586 down-regulated genes and 1728 up-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that 832 DEGs were assigned to 222 pathways, many pathways of which were related to gonadal development. Four down-regulated genes relevant to ovarian development (Vitellogenin 1, Vitellogenin 2, Cathepsin L1-like, and Follistatin) were selected to confirm the accuracy of RNA-seq data by qRT-PCR. These results showed that SjILPR might regulate ovarian development to control reproduction by affecting the expression of the relevant genes in female S. japonica.

Reproductive capacity in Adelphocoris suturalis (Hemiptera: Miridae) is regulated by the insulin signaling pathway

The peptide hormone insulin has essential roles in regulating insect metabolism, growth, and reproduction. There are, however, few studies assessing the effects of insulin signaling on reproduction in Miridae (Hemiptera). Here, we used RNA interference (RNAi)-mediated knockdown to examine the role of three critical insulin signaling pathway components (insulin receptor, InR; insulin receptor substrate 1, IRS1; and forkhead box O, FOXO) on reproductive capacity in the mirid Adelphocoris suturalis. Knockdown of AsIRS1 led to a significant reduction in egg maturation in unmated females. To further verify the role of AsIRS1, we examined several reproductive parameters following knockdown. Suppression of AsIRS1 transcript levels throughout the reproductive period resulted in reduced lifetime fecundity, egg hatch rate, and oviposition capacity as well as statistically significant reductions in female survival rate and longevity. These findings demonstrate that the insulin signaling pathway plays a key role in the reproductive development of A. suturalis, and that IRS1 is a key regulatory factor. These findings provide an important theoretical basis for the regulation of insect reproduction by insulin and introduce a new target for potential development is A. suturalis control.

A chromosome-level genome assembly provides insights into the environmental adaptability and outbreaks of Chlorops oryzae

Chlorops oryzae is a pest of rice that has caused severe damage to crops in major rice-growing areas in recent years. We generated a 447.60 Mb high-quality chromosome-level genome with contig and scaffold N50 values of 1.17 Mb and 117.57 Mb, respectively. Hi-C analysis anchored 93.22% scaffolds to 4 chromosomes. The relatively high expression level of Heat Shock Proteins (HSPs) and antioxidant genes in response to thermal stress suggests these genes may play a role in the environmental adaptability of C. oryzae. The identification of multiple pathways that regulate reproductive development (juvenile hormone, 20-hydroxyecdsone, and insulin signaling pathways) provides evidence that these pathways also play an important role in vitellogenesis and thus insect population maintenance. These findings identify possible reasons for the increased frequency of outbreaks of C. oryzae in recent years. Our chromosome-level genome assembly may provide a basis for further genetic studies of C. oryzae, and promote the development of novel, sustainable strategies to control this pest.

A chromosome-level genome assembly for the rice pest, Chlorops oryzae, pinpoints molecular pathways that might contribute toward increased outbreaks for this important crop pest.

Effect of Insulin Receptor on Juvenile Hormone Signal and Fecundity in Spodoptera litura (F.)

Simple Summary

The tobacco cutworm, Spodoptera litura (F.), exemplifies strong reproductive capacities and damages many agricultural crops. The insulin signaling pathway is known as a key determinant of female reproduction in insects. However, the detailed molecular mechanisms in these processes are poorly studied. Here, we injected bovine insulin into the newly emerged moth, resulting in gene expression changes in the insulin pathway, while knockdown of SlInR caused an inverse gene expression change involved in the insulin pathway. Further studies indicated that the content of JH-III, Vg, total proteins and triacylgycerol could be suppressed by SlInR dsRNA injection. Furthermore, stunted ovaries and lower fecundity were observed by RNAi. Our studies indicated that SlInR plays a key role in JH-III synthesis and the ovarian development in S. litura.

Abstract

Insulin signaling can regulate various physiological functions, such as energy metabolism and reproduction and so on, in many insects, including mosquito and locust. However, the molecular mechanism of this physiological process remains elusive. The tobacco cutworm, Spodoptera litura, is one of the most important pests of agricultural crops around the world. In this study, phosphoinositide 3-kinase (SlPI3K), protein kinase B (SlAKT), target of rapamycin (SlTOR), ribosomal protein S6 kinase (SlS6K) and transcription factor cAMP-response element binding protein (SlCREB) genes, except transcription factor forkhead box class O (SlFoxO), can be activated by bovine insulin injection. Then, we studied the influence of the insulin receptor gene (SlInR) on the reproduction of S. litura using RNA interference technology. qRT-PCR analysis revealed that SlInR was most abundant in the head. The SlPI3K, SlAKT, SlTOR, SlS6K and SlCREB genes were decreased, except SlFoxO, after the SlInR gene knockdown. Further studies revealed that the expression of vitellogenin mRNA and protein, Methoprene-tolerant gene (SlMet), could be down-regulated by the injection of dsRNA of SlInR significantly. Furthermore, a depletion in the insulin receptor by RNAi significantly decreased the content of juvenile hormone III (JH-III), total proteins and triacylgycerol. These changes indicated that a lack of SlInR could impair ovarian development and decrease fecundity in S. litura. Our studies contribute to a comprehensive insight into reproduction, regulated by insulin and the juvenile hormone signaling pathway through nutrition, and a provide theoretical basis for the reproduction process in pest insects.

Bidirectional Microbiome-Gut-Brain-Axis Communication Influences Metabolic Switch-Associated Responses in the Mosquito Anopheles culicifacies

The periodic ingestion of a protein-rich blood meal by adult female mosquitoes causes a drastic metabolic change in their innate physiological status, which is referred to as a 'metabolic switch'. While understanding the neural circuits for host-seeking is modestly attended, how the gut 'metabolic switch' modulates brain functions, and resilience to physiological homeostasis, remains unexplored. Here, through a comparative brain RNA-Seq study, we demonstrate that the protein-rich diet induces the expression of brain transcripts related to mitochondrial function and energy metabolism, possibly causing a shift in the brain's engagement to manage organismal homeostasis. A dynamic mRNA expression pattern of neuro-signaling and neuro-modulatory genes in both the gut and brain likely establishes an active gut-brain communication. The disruption of this communication through decapitation does not affect the modulation of the neuro-modulator receptor genes in the gut. In parallel, an unusual and paramount shift in the level of neurotransmitters (NTs), from the brain to the gut after blood feeding, further supports the idea of the gut's ability to serve as a 'second brain'. After blood-feeding, a moderate enrichment of the gut microbial population, and altered immunity in the gut of histamine receptor-silenced mosquitoes, provide initial evidence that the gut-microbiome plays a crucial role in gut-brain-axis communication. Finally, a comparative metagenomics evaluation of the gut microbiome highlighted that blood-feeding enriches the family members of the Morganellaceae and Pseudomonadaceae bacterial communities. The notable observation of a rapid proliferation of Pseudomonas bacterial sp. and tryptophan enrichment in the gut correlates with the suppression of appetite after blood-feeding. Additionally, altered NTs dynamics of naïve and aseptic mosquitoes provide further evidence that gut-endosymbionts are key modulators for the synthesis of major neuroactive molecules. Our data establish a new conceptual understanding of microbiome-gut-brain-axis communication in mosquitoes.

Characterization of Insulin-like Peptide (ILP) and Its Potential Role in Ovarian Development of the Cuttlefish Sepiella japonica

The insulin-like peptide (ILP) family is well known for regulating reproduction in invertebrates, while its role in mollusks remains largely unknown. In this study, we first isolated and characterized the ILP gene in the cuttlefish Sepiella japonica. The full-length SjILP cDNA obtained was 926 bp and encoded a precursor protein of 161 amino acids. The precursor protein consisted of a signal peptide, a B chain, a C-peptide, and an A chain. It possessed the typical features of ILP proteins, including two cleavage sites (KR) and eight conserved cysteines. To define the function of SjILP, the expression of SjILP in different tissues and ovarian development stages were analyzed using qRT-PCR. SjILP was mainly expressed in the ovary, and its gene expression correlated with ovarian development. Furthermore, silencing SjILP using RNA interference (RNAi) dramatically decreased the expression levels of four ovarian-development-related genes (vitellogenin1, vitellogenin2, cathepsin L1-like, and follistatin). These data suggest the critical role of SjILP in the regulation of ovarian development in S. japonica.

Ad libitum consumption of protein- or peptide-sucrose solutions stimulates egg formation by prolonging the vitellogenic phase of oogenesis in anautogenous mosquitoes

BACKGROUND

Anautogenous mosquitoes commonly consume nectars and other solutions containing sugar but are thought to only produce eggs in discrete gonadotrophic cycles after blood-feeding on a vertebrate host. However, some anautogenous species are known to produce eggs if amino acids in the form of protein are added to a sugar solution. Unclear is how different sources of amino acids in sugar solutions affect the processes that regulate egg formation and whether responses vary among species. In this study, we addressed these questions by focusing on Aedes aegypti and conducting some comparative assays with Aedes albopictus, Anopheles gambiae, Anopheles stephensi and Culex quinquefasciatus.

METHODS

Adult female mosquitoes were fed sugar solutions containing amino acids, peptides or protein. Markers for activation of a gonadotrophic cycle including yolk deposition into oocytes, oviposition, ovary ecdysteroidogenesis, expression of juvenile hormone and 20-hydroxyecdysone-responsive genes, and adult blood-feeding behavior were then measured.

RESULTS

The five anautogenous species we studied produced eggs when fed two proteins (bovine serum albumin, hemoglobin) or a mixture of peptides (tryptone) in 10% sucrose but deposited only small amounts of yolk into oocytes when fed amino acids in 10% sucrose. Focusing on Ae. aegypti, cultures were maintained for multiple generations by feeding adult females protein- or tryptone-sugar meals. Ad libitum access to protein- or tryptone-sugar solutions protracted production of ecdysteroids by the ovaries, vitellogenin by the fat body and protease activity by the midgut albeit at levels that were lower than in blood-fed females. Females also exhibited semi-continual oogenesis and repressed host-seeking behavior.

CONCLUSIONS

Several anautogenous mosquitoes produce eggs when provided ad libitum access to protein- or peptide-sugar meals, but several aspects of oogenesis also differ from females that blood-feed.

Transcriptional Regulation of Reproductive Diapause in the Convergent Lady Beetle, Hippodamia convergens

Simple Summary

Diapause is a dormant period typically controlled by daylength that ensures an insect’s survival through harsh environmental conditions. The convergent lady beetle, Hippodamia convergens, undergoes a reproductive diapause in winter, where female ovaries remain immature and no eggs are laid. This species is an important biological control agent, but during diapause, beetles are less likely to eat pest insects. Thus, knowledge of diapause mechanisms may facilitate manipulation thereof to improve biological control. Further, molecular studies of adult diapause and diapause in Coleoptera are relatively lacking. Here, we assembled and annotated a transcriptome for this species and quantified transcript expression changes during diapause. Female beetles were sampled at three times in diapause (early, mid, and late diapause), which allowed us to characterize the molecular processes occurring at distinct transitions throughout diapause. We found that transcripts involved in flight were consistently upregulated during diapause, which is consistent with dispersal flights at this stage, while transcripts involved in ovarian development were downregulated, which is consistent with the shutdown of reproduction in diapausing females. These findings identify key regulators of diapause in H. convergens and contribute to a growing body of literature on the molecular mechanisms of diapause across the insect phylogeny.

Abstract

Diapause is an alternate development program that synchronizes an insect’s life cycle with seasonally abundant resources and ensures survival in unfavorable conditions. The physiological basis of diapause has been well characterized, but the molecular mechanisms regulating it are still being elucidated. Here, we present a de novo transcriptome and quantify transcript expression during diapause in the convergent lady beetle Hippodamia convergens. H. convergens is used as an augmentative biocontrol agent, and adult females undergo reproductive diapause that is regulated by photoperiod. We sampled females at three stages (early, mid, and late diapause) and compared transcript expression to non-diapausing individuals. Based on principle component analysis, the transcriptomes of diapausing beetles were distinct from non-diapausing beetles, and the three diapausing points tended to cluster together. However, there were still classes of transcripts that differed in expression across distinct phases of diapause. In general, transcripts involved in muscle function and flight were upregulated during diapause, likely to support dispersal flights that occur during diapause, while transcripts involved in ovarian development were downregulated. This information could be used to improve biological control by manipulating diapause. Additionally, our data contribute to a growing understanding of the genetic regulation of diapause across diverse insects.

Insulin-like peptide 3 stimulates hemocytes to proliferate in anautogenous and facultatively autogenous mosquitoes

Most mosquito species are anautogenous, which means they must blood feed on a vertebrate host to produce eggs, while a few are autogenous and can produce eggs without blood feeding. Egg formation is best understood in the anautogenous mosquito Aedes aegypti, where insulin-like peptides (ILPs), ovary ecdysteroidogenic hormone (OEH) and 20-hydroxyecdysone (20E) interact to regulate gonadotrophic cycles. Circulating hemocytes also approximately double in abundance in conjunction with a gonadotrophic cycle, but the factors responsible for stimulating this increase remain unclear. Focusing on Ae. aegypti, we determined that hemocyte abundance similarly increased in intact blood-fed females and decapitated blood-fed females that were injected with ILP3, whereas OEH, 20E or heat-killed bacteria had no stimulatory activity. ILP3 upregulated insulin-insulin growth factor signaling in hemocytes, but few genes - including almost no transcripts for immune factors - were differentially expressed. ILP3 also stimulated circulating hemocytes to increase in two other anautogenous (Anopheles gambiae and Culex quinquefasciatus) and two facultatively autogenous mosquitoes (Aedes atropalpus and Culex pipiens molestus), but had no stimulatory activity in the obligately autogenous mosquito Toxorhynchites amboinensis. Altogether, our results identify ILPs as the primary regulators of hemocyte proliferation in association with egg formation, but also suggest this response has been lost in the evolution of obligate autogeny.

The Peptide Hormone CNMa Influences Egg Production in the Mosquito Aedes aegypti

Mosquito reproduction is regulated by a suite of hormones, many acting through membrane-bound receptor proteins. The Aedes aegypti G protein-coupled receptors AAEL024199 (AeCNMaR-1a) and AAEL018316 (AeCNMaR-1b) were identified as orthologs of the Drosophila melanogaster CNMa receptor (DmCNMaR). The receptor was duplicated early in the evolution of insects, and subsequently in Culicidae, into what we refer to as CNMaR-1a and CNMaR-1b. AeCNMaR-1a is only detected in male mosquito antennae while AeCNMaR-1b is expressed at high levels in mosquito ovaries. Using a heterologous cell assay, we determined that AeCNMa activates AeCNMaR-1a with a ~10-fold lower concentration than it does AeCNMaR-1b, though both receptors displayed half maximal effective concentrations of AeCNMa in the low nanomolar range. Finally, we show that injections of AeCNMa into blood-fed mated female Ae. aegypti resulted in fewer eggs laid.

Evolutionary diversification of insulin-related peptides (IRPs) in aphids and spatiotemporal distribution in Acyrthosiphon pisum

Members of the insulin superfamily activate the evolutionarily highly conserved insulin/insulin-like growth factor signaling pathway, involved in regulation of growth, energy homeostasis, and longevity. In the current study we focus on aphids to gain more insight into the evolution of the IRPs and how they may contribute to regulation of the insulin-signaling pathway. Using the latest annotation of the pea aphid (Acyrthosiphon pisum) genome, and combining sequence alignments and phylogenetic analyses, we identified seven putative IRP encoding-genes, with IRP1-IRP4 resembling the classical insulin and insulin-like protein structures, and IRP5 and IRP6 bearing insulin-like growth factor (IGF) features. We also identified IRP11 as a new and structurally divergent IRP present in at least eight aphid genomes. Globally the ten aphid genomes analyzed in this work contain four to 15 IRPs, while only three IRPs were found in the genome of the grape phylloxera, a hemipteran insect representing an earlier evolutionary branch of the aphid group. Expression analyses revealed spatial and temporal variation in the expression patterns of the different A. pisum IRPs. IRP1 and IRP4 are expressed throughout all developmental stages and morphs in neuroendocrine cells of the brain, while IRP5 and IRP6 are expressed in the fat body. IRP2 is expressed in specific cells of the gut in aphids in non-crowded conditions and in the head of aphids under crowded conditions, IRP3 in salivary glands, and both IRP2 and IRP3 in the male morph. IRP11 expression is enriched in the carcass. This complex spatiotemporal expression pattern suggests functional diversification of the IRPs.

Increased insulin signaling in the Anopheles stephensi fat body regulates metabolism and enhances the host response to both bacterial challenge and Plasmodium falciparum infection

In vertebrates and invertebrates, the insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) cascade is highly conserved and plays a vital role in many different physiological processes. Among the many tissues that respond to IIS in mosquitoes, the fat body has a central role in metabolism, lifespan, reproduction, and innate immunity. We previously demonstrated that fat body specific expression of active Akt, a key IIS signaling molecule, in adult Anopheles stephensi and Aedes aegypti activated the IIS cascade and extended lifespan. Additionally, we found that transgenic females produced more vitellogenin (Vg) protein than non-transgenic mosquitoes, although this did not translate into increased fecundity. These results prompted us to further examine how IIS impacts immunity, metabolism, growth and development of these transgenic mosquitoes. We observed significant changes in glycogen, trehalose, triglycerides, glucose, and protein in young (3-5 d) transgenic mosquitoes relative to non-transgenic sibling controls, while only triglycerides were significantly changed in older (18 d) transgenic mosquitoes. More importantly, we demonstrated that enhanced fat body IIS decreased both the prevalence and intensity of Plasmodium falciparum infection in transgenic An. stephensi. Additionally, challenging transgenic An. stephensi with Gram-positive and Gram-negative bacteria altered the expression of several antimicrobial peptides (AMPs) and two anti-Plasmodium genes, nitric oxide synthase (NOS) and thioester complement-like protein (TEP1), relative to non-transgenic controls. Increased IIS in the fat body of adult female An. stephensi had little to no impact on body size, growth or development of progeny from transgenic mosquitoes relative to non-transgenic controls. This study both confirms and expands our understanding of the critical roles insulin signaling plays in regulating the diverse functions of the mosquito fat body.

Insects as a New Complex Model in Hormonal Basis of Obesity

Nowadays, one of the biggest problems in healthcare is an obesity epidemic. Consumption of cheap and low-quality energy-rich diets, low physical activity, and sedentary work favor an increase in the number of obesity cases within many populations/nations. This is a burden on society, public health, and the economy with many deleterious consequences. Thus, studies concerning this disorder are extremely needed, including searching for new, effective, and fitting models. Obesity may be related, among other factors, to disrupting adipocytes activity, disturbance of metabolic homeostasis, dysregulation of hormonal balance, cardiovascular problems, or disorders in nutrition which may lead to death. Because of the high complexity of obesity, it is not easy to find an ideal model for its studies which will be suitable for genetic and physiological analysis including specification of different compounds’ (hormones, neuropeptides) functions, as well as for signaling pathways analysis. In recent times, in search of new models for human diseases there has been more and more attention paid to insects, especially in neuro-endocrine regulation. It seems that this group of animals might also be a new model for human obesity. There are many arguments that insects are a good, multidirectional, and complex model for this disease. For example, insect models can have similar conservative signaling pathways (e.g., JAK-STAT signaling pathway), the presence of similar hormonal axis (e.g., brain–gut axis), or occurrence of structural and functional homologues between neuropeptides (e.g., neuropeptide F and human neuropeptide Y, insulin-like peptides, and human insulin) compared to humans. Here we give a hint to use insects as a model for obesity that can be used in multiple ways: as a source of genetic and peptidomic data about etiology and development correlated with obesity occurrence as well as a model for novel hormonal-based drug activity and their impact on mechanism of disease occurrence.

Glucose metabolomic profile during embryogenesis in the tick Rhipicephalus microplus

INTRODUCTION

Metabolomic approaches can assess the actual state of an organism's energy metabolism during a specific morphological event, providing a more accurate insight into the correlations between physiology and metabolic regulation.

METHODS

The study of the metabolomic profile aim to identify the largest possible number of biomolecules in a certain organism or specific structures. For this purpose, mass spectrometry (MS) and chromatography have been used in the present study.

OBJECTIVES

In this context, the aim of the present work is to evaluate the glucose metabolomic profile during embryogenesis in Rhipicephalus microplus tick, investigating the dynamics of nutrient utilization during tick embryo formation, as well as the control of glucose metabolism.

RESULTS

We show that glycogen reserves are preferentially mobilized to sustain the energy-intensive process of embryogenesis. Subsequently, the increase in concentration of specific amino acids indicates that protein degradation would provide carbons to fuel gluconeogenesis, supplying the embryo with sufficient glucose and glycogen during development.

CONCLUSION

Altogether, these results demonstrated the presence of a very refined catabolic and anabolic control during embryogenesis in R. microplus tick, suggesting the pronounced gluconeogenesis as a strategy to secure embryo development. Moreover, this research contributes to the understanding of the mechanisms that control glucose metabolism during tick embryogenesis and may aid the identification of putative targets for novel chemical or immunological control methods, which are essential to improve the prevention of tick infestations.

E93 confers steroid hormone responsiveness of digestive enzymes to promote blood meal digestion in the midgut of the mosquito Aedes aegypti

Anautogenous female mosquitoes obtain the nutrients needed for egg development from vertebrate blood, and consequently they transmit numerous pathogens of devastating human diseases. Digestion of blood proteins into amino acids that are used for energy production, egg maturation and replenishment of maternal reserves is an essential part of the female mosquito reproductive cycle. However, the regulatory mechanisms underlying this process remain largely unknown. Here, we report that the transcription factor E93 is a critical factor promoting blood meal digestion in adult females of the major arboviral vector Aedes aegypti in response to the steroid hormone 20-hydroxyecdysone (20E). E93 was upregulated in the female mosquito midgut after a blood meal, and RNA interference (RNAi)-mediated knockdown of E93 inhibited midgut blood digestion. E93 RNAi depletion repressed late trypsin (LT), serine protease I (SPI), SPVI and SPVII, and activated early trypsin (ET) expression in the female mosquito midgut after a blood meal. Injection of 20E activated E93, LT, SPI, SPVI and SPVII, and repressed ET expression, whereas RNAi knockdown of the ecdysone receptor (EcR) repressed E93, LT, SPI, SPVI and SPVII, and activated ET expression in the midgut. Furthermore, E93 depletion resulted in a complete loss of 20E responsiveness of LT, SPVI and SPVII. Our findings reveal important mechanisms regulating blood meal digestion in disease-transmitting mosquitoes.

Insulin-Like Peptides and Cross-Talk With Other Factors in the Regulation of Insect Metabolism

The insulin-like peptide (ILP) and insulin-like growth factor (IGF) signalling pathways play a crucial role in the regulation of metabolism, growth and development, fecundity, stress resistance, and lifespan. ILPs are encoded by multigene families that are expressed in nervous and non-nervous organs, including the midgut, salivary glands, and fat body, in a tissue- and stage-specific manner. Thus, more multidirectional and more complex control of insect metabolism can occur. ILPs are not the only factors that regulate metabolism. ILPs interact in many cross-talk interactions of different factors, for example, hormones (peptide and nonpeptide), neurotransmitters and growth factors. These interactions are observed at different levels, and three interactions appear to be the most prominent/significant: (1) coinfluence of ILPs and other factors on the same target cells, (2) influence of ILPs on synthesis/secretion of other factors regulating metabolism, and (3) regulation of activity of cells producing/secreting ILPs by various factors. For example, brain insulin-producing cells co-express sulfakinins (SKs), which are cholecystokinin-like peptides, another key regulator of metabolism, and express receptors for tachykinin-related peptides, the next peptide hormones involved in the control of metabolism. It was also shown that ILPs in Drosophila melanogaster can directly and indirectly regulate AKH. This review presents an overview of the regulatory role of insulin-like peptides in insect metabolism and how these factors interact with other players involved in its regulation.

Fat Body-Multifunctional Insect Tissue

Simple Summary

Efficient and proper functioning of processes within living organisms play key roles in times of climate change and strong human pressure. In insects, the most abundant group of organisms, many important changes occur within their tissues, including the fat body, which plays a key role in the development of insects. Fat body cells undergo numerous metabolic changes in basic energy compounds (i.e., lipids, carbohydrates, and proteins), enabling them to move and nourish themselves. In addition to metabolism, the fat body is involved in the development of insects by determining the time an individual becomes an adult, and creates humoral immunity via the synthesis of bactericidal proteins and polypeptides. As an important tissue that integrates all signals from the body, the processes taking place in the fat body have an impact on the functioning of the entire body.

Abstract

The biodiversity of useful organisms, e.g., insects, decreases due to many environmental factors and increasing anthropopressure. Multifunctional tissues, such as the fat body, are key elements in the proper functioning of invertebrate organisms and resistance factors. The fat body is the center of metabolism, integrating signals, controlling molting and metamorphosis, and synthesizing hormones that control the functioning of the whole body and the synthesis of immune system proteins. In fat body cells, lipids, carbohydrates and proteins are the substrates and products of many pathways that can be used for energy production, accumulate as reserves, and mobilize at the appropriate stage of life (diapause, metamorphosis, flight), determining the survival of an individual. The fat body is the main tissue responsible for innate and acquired humoral immunity. The tissue produces bactericidal proteins and polypeptides, i.e., lysozyme. The fat body is also important in the early stages of an insect’s life due to the production of vitellogenin, the yolk protein needed for the development of oocytes. Although a lot of information is available on its structure and biochemistry, the fat body is an interesting research topic on which much is still to be discovered.

Review: Schistosoma mansoni phosphatidylinositol 3 kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) signaling pathway

Schistosoma mansoni worms are under a milieu of external and internal signaling pathways. The life-cycle stages are exposed to enormous stimuli within the mammalian and the snail hosts and as free-living stages in the fresh water. Furthermore, there is a unique interplay between the male and the female worms involving many stimuli from the male essential for full development of the female. PI3K/Akt/mTOR is an evolutionarily divergent signal transduction pathway universal to nearly every multicellular organism. This work reviews the Schistosoma mansoni PI3K/Akt/mTOR signal pathways and the involvement of the signal in the worms' physiology concerning the uptake of glucose, reproduction and survival. The inhibitors of the signal pathway used against Schistosoma mansoni were summarized. Given the importance of the PI3K/Akt/mTOR signal pathway, its inhibition could be a promising control strategy against schistosomiasis.

Anopheles coluzzii stearoyl-CoA desaturase is essential for adult female survival and reproduction upon blood feeding

Vitellogenesis and oocyte maturation require anautogenous female Anopheles mosquitoes to obtain a bloodmeal from a vertebrate host. The bloodmeal is rich in proteins that are readily broken down into amino acids in the midgut lumen and absorbed by the midgut epithelial cells where they are converted into lipids and then transported to other tissues including ovaries. The stearoyl-CoA desaturase (SCD) plays a pivotal role in this process by converting saturated (SFAs) to unsaturated (UFAs) fatty acids; the latter being essential for maintaining cell membrane fluidity amongst other housekeeping functions. Here, we report the functional and phenotypic characterization of SCD1 in the malaria vector mosquito Anopheles coluzzii. We show that RNA interference (RNAi) silencing of SCD1 and administration of sterculic acid (SA), a small molecule inhibitor of SCD1, significantly impact on the survival and reproduction of female mosquitoes following blood feeding. Microscopic observations reveal that the mosquito thorax is quickly filled with blood, a phenomenon likely caused by the collapse of midgut epithelial cell membranes, and that epithelial cells are depleted of lipid droplets and oocytes fail to mature. Transcriptional profiling shows that genes involved in protein, lipid and carbohydrate metabolism and immunity-related genes are the most affected by SCD1 knock down (KD) in blood-fed mosquitoes. Metabolic profiling reveals that these mosquitoes exhibit increased amounts of saturated fatty acids and TCA cycle intermediates, highlighting the biochemical framework by which the SCD1 KD phenotype manifests as a result of a detrimental metabolic syndrome. Accumulation of SFAs is also the likely cause of the potent immune response observed in the absence of infection, which resembles an auto-inflammatory condition. These data provide insights into mosquito bloodmeal metabolism and lipid homeostasis and could inform efforts to develop novel interventions against mosquito-borne diseases.

Female mosquitoes can become infected with malaria parasites upon ingestion of blood from an infected person and can transmit the disease when they bite another person some days later. The bloodmeal is rich in proteins which female mosquitoes use to develop their eggs after converting them first to saturated and then to unsaturated fatty acids inside their gut cells. Here, we present the characterization of the enzyme that mosquitoes use to convert saturated to unsaturated fatty acids and show that when this enzyme is eliminated or inhibited mosquitoes cannot produce eggs and die soon after they feed on blood. The mosquito death appears to be primarily associated with the collapse of their gut epithelial barrier due to the loss of cell membrane integrity, leading to their inner body cavity being filled with the ingested blood. These mosquitoes also suffer from an acute and detrimental auto-inflammatory condition due to mounting of a potent immune response in the absence of any infection. We conclude that this enzyme and the mechanism of converting blood-derived proteins to unsaturated fatty acids as a whole can be a good target of interventions aiming at limiting the mosquito abundance and blocking malaria transmission.

Differential expression of PEPCK isoforms is correlated to Aedes aegypti oogenesis and embryogenesis

The mosquito Aedes aegypti undertakes a shift in carbohydrate metabolism during embryogenesis, including an increase in the activity of phosphoenolpyruvate carboxykinase (PEPCK), a key gluconeogenic enzyme, at critical steps of embryo development. All eukaryotes studied to date present two PEPCK isoforms, namely PEPCK-M (mitochondrial) and PEPCK-C (cytosolic). In A. aegypti, however, these proteins are so far uncharacterized. In the present work we describe two A. aegypti PEPCK isoforms by sequence alignment, protein modeling, and transcription analysis in different tissues, as well as PEPCK enzymatic activity assays in mitochondrial and cytoplasmic compartments during oogenesis and embryogenesis. First, we characterized the protein sequences compared to other organisms, and identified conserved sites and key amino acids. We also performed structure modeling for AePEPCK(M) and AePEPCK(C), identifying highly conserved structural sites, as well as a signal peptide in AePEPCK(M) localized in a very hydrophobic region. Moreover, after blood meal and during mosquito oogenesis and embryogenesis, both PEPCKs isoforms showed different transcriptional profiles, suggesting that mRNA for the cytosolic form is transmitted maternally, whereas the mitochondrial form is synthesized by the zygote. Collectively, these results improve our understanding of mosquito physiology and may yield putative targets for developing new methods for A. aegypti control.

Non-immune Traits Triggered by Blood Intake Impact Vectorial Competence

Blood-feeding arthropods are considered an enormous public health threat. They are vectors of a plethora of infectious agents that cause potentially fatal diseases like Malaria, Dengue fever, Leishmaniasis, and Lyme disease. These vectors shine due to their own physiological idiosyncrasies, but one biological aspect brings them all together: the requirement of blood intake for development and reproduction. It is through blood-feeding that they acquire pathogens and during blood digestion that they summon a collection of multisystemic events critical for vector competence. The literature is focused on how classical immune pathways (Toll, IMD, and JAK/Stat) are elicited throughout the course of vector infection. Still, they are not the sole determinants of host permissiveness. The dramatic changes that are the hallmark of the insect physiology after a blood meal intake are the landscape where a successful infection takes place. Dominant processes that occur in response to a blood meal are not canonical immunological traits yet are critical in establishing vector competence. These include hormonal circuitries and reproductive physiology, midgut permeability barriers, midgut homeostasis, energy metabolism, and proteolytic activity. On the other hand, the parasites themselves have a role in the outcome of these blood triggered physiological events, consistently using them in their favor. Here, to enlighten the knowledge on vector-pathogen interaction beyond the immune pathways, we will explore different aspects of the vector physiology, discussing how they give support to these long-dated host-parasite relationships.

The involvement of insulin/ToR signaling pathway in reproductive performance of Rhodnius prolixus

Insulins are peptide hormones widely studied for their important regulatory roles in metabolism, growth and development. In insects, insulin signaling along with the target of rapamycin (ToR) are involved in detecting and interpreting nutrient levels. Recently, by transcriptome analysis we reported an up-regulation of transcripts involved in insulin/ToR signaling in unfed Rhodnius prolixus; however, this signaling pathway is only activated in fed insects. Here, continuing with the blood-gorging triatomine R. prolixus as a model, we report the direct effect of insulin/ToR signaling on reproductive performance. By immunofluorescence we identified cells in the brain with positive signal to the R. prolixus ILP (Rhopr-ILP1) and show that the insulin receptor and protein effectors downstream of insulin/ToR signaling activation, are differentially expressed in ovarian follicles dependent on their developmental stage. Using qPCR we find that the expression of transcripts involved in insulin signaling in the central nervous system (CNS), fat body and ovaries increase as the state of starvation progresses, promoting a more highly sensitized state to respond rapidly to ILP/IGF levels. In addition, using dsRNA injection and in vivo and ex vivo assays to promote signaling activation we demonstrate a direct participation of insulin/ToR signaling in coordinating the synthesis of the main yolk protein precursor, vitellogenin, thereby influencing the numbers of eggs laid per female. We thereby show a mechanism by which nutritional signaling regulates reproductive performance in a vector of Chagas disease. As reproduction is responsible for propagation of insect populations, this work is important for the development of innovative biocontrol methods.

Functional characterization of the insulin signaling pathway in the hard tick Ixodes ricinus

Ticks are blood-feeding arachnids transmitting a variety of pathogens to humans and animals. A unique trait in tick physiology is their ability to engorge and digest large amounts of host blood, ensuring their high reproductive potential. Activation of the blood digestive machinery in the tick gut, as well as processes controlling maturation of ovaries, are triggered upon blood meal uptake by still largely unknown mechanisms. Sensing of the nutritional status in metazoan organisms is facilitated by the evolutionarily conserved Insulin Signaling Pathway (ISP) and the interlinked Target of Rapamycin (TOR) pathway. Recently, we have identified three components of these pathways in the hard tick Ixodes ricinus midgut transcriptome, namely a putative insulin receptor (InR), and the downstream intracellular serine/threonine kinases AKT and TOR. In this study, we primarily focus on the molecular and functional characterization of the I. ricinus insulin receptor (IrInR), the first InR characterized in Chelicerates. A phylogenetic analysis across the major Arthropod lineages demonstrated that ticks possess only one gene encoding an InR-related molecule. Tissue expression profiling by quantitative PCR in semi-engorged I. ricinus females revealed that the IrInR, as well as AKT (IrAKT) and TOR (IrTOR) are expressed in various organs, with the highest expression being detected in ovaries. We have further evaluated the impact of RNAi-mediated knock-down (KD) of IrInR, IrAKT, and IrTOR on tick blood-feeding and reproductive capacity. Weights of engorged IrInR KD females and laid egg clutches were reduced compared to the control group, and these quantitative parameters clearly correlated with the efficiency of RNAi-KD achieved in individual ticks. The most striking phenotype was observed for IrAKT KD that impaired tick feeding and completely aborted egg production. A recombinant extracellular fragment of the IrInR α-subunit was used to produce antibodies in experimental rabbits to assess its potential as a protective antigen against tick feeding and reproduction. Our data clearly indicate the functionality of the ISP in ticks and demonstrate the need for further investigation of specific roles played by the endogenous insulin-like peptides in tick physiological processes.