Polyandry Depends on Postmating Time Interval in the Dengue Vector Aedes aegypti

Juvenile Hormone as a contributing factor in establishing midgut microbiota for fecundity and fitness enhancement in adult female Aedes aegypti

Understanding the factors influencing mosquitoes' fecundity and longevity is important for designing better and more sustainable vector control strategies, as these parameters can impact their vectorial capacity. Here, we address how mating affects midgut growth in Aedes aegypti, what role Juvenile Hormone (JH) plays in this process, and how it impacts the mosquito's immune response and microbiota. Our findings reveal that mating and JH induce midgut growth. Additionally, the establishment of a native bacterial population in the midgut due to JH-dependent suppression of the immune response has important reproductive outcomes. Specific downregulation of AMPs with an increase in bacteria abundance in the gut results in increased egg counts and longer lifespans. Overall, these findings provide evidence of a cross-talk between JH response, gut epithelial tissue, cell cycle regulation, and the mechanisms governing the trade-offs between nutrition, immunity, and reproduction at the cellular level in the mosquito gut.

Sex peptide receptor is not required for refractoriness to remating or induction of egg laying in Aedes aegypti

Across diverse insect taxa, the behavior and physiology of females dramatically changes after mating-processes largely triggered by the transfer of seminal proteins from their mates. In the vinegar fly Drosophila melanogaster, the seminal protein sex peptide (SP) decreases the likelihood of female flies remating and causes additional behavioral and physiological changes that promote fertility including increasing egg production. Although SP is only found in the Drosophila genus, its receptor, sex peptide receptor (SPR), is the widely conserved myoinhibitory peptide (MIP) receptor. To test the functional role of SPR in mediating postmating responses in a non-Drosophila dipteran, we generated 2 independent Spr-knockout alleles in the yellow fever mosquito, Aedes aegypti. Although SPR is needed for postmating responses in Drosophila and the cotton bollworm Helicoverpa armigera, Spr mutant Ae. aegypti show completely normal postmating decreases in remating propensity and increases in egg laying. In addition, injection of synthetic SP or accessory gland homogenate from D. melanogaster into virgin female mosquitoes did not elicit these postmating responses. Our results demonstrate that Spr is not required for these canonical postmating responses in Ae. aegypti, indicating that other, as yet unknown, signaling pathways are likely responsible for these behavioral switches in this disease vector.

The effects of female age on blood-feeding, insemination, sperm storage, and fertility in the dengue vector mosquito Aedes aegypti (Diptera: Culicidae)

Mating induces behavioral and physiological changes in female insects-collectively referred to as the female post-mating response (PMR)-that facilitate the production of progeny. PMRs are elicited by transfer of male-derived seminal components during mating, but are altered by other factors, including adult age. Increased female age is often accompanied by declines in fertility. However, mating shortly after emergence also impacts fertility in the insect model Drosophila melanogaster. Here, we determined the age post-emergence when females of the vector mosquito Aedes aegypti can be inseminated and blood-feed. We next examined fecundity, fertility, and the storage of sperm in the female reproductive tract in "young" (30-41 hours-old) and "old" (2- and 3-week-old) females, finding that blood-feeding began at 14 hours, and mating at ∼24 hours post-emergence. Although young females consumed smaller blood quantities and stored fewer sperm, they were similarly fertile to 4-day-old controls. Old females, however, suffered significant declines in fecundity by 2 weeks of age. Our results show that female Ae. aegypti start to become sexually receptive 1 day after their emergence, but can ingest blood much sooner, suggesting that mating is not a prerequisite to blood-feeding, and that females can ingest an arbovirus infected blood-meal shortly after emergence.

wMel Wolbachia alters female post-mating behaviors and physiology in the dengue vector mosquito Aedes aegypti

Globally invasive Aedes aegypti disseminate numerous arboviruses that impact human health. One promising method to control Ae. aegypti populations is transinfection with Wolbachia pipientis, which naturally infects ~40-52% of insects but not Ae. aegypti. Transinfection of Ae. aegypti with the wMel Wolbachia strain induces cytoplasmic incompatibility (CI), allows infected individuals to invade native populations, and inhibits transmission of medically relevant arboviruses by females. Female insects undergo post-mating physiological and behavioral changes-referred to as the female post-mating response (PMR)-required for optimal fertility. PMRs are typically elicited by male seminal fluid proteins (SFPs) transferred with sperm during mating but can be modified by other factors, including microbiome composition. Wolbachia has modest effects on Ae. aegypti fertility, but its influence on other PMRs is unknown. Here, we show that Wolbachia influences female fecundity, fertility, and re-mating incidence and significantly extends the longevity of virgin females. Using proteomic methods to examine the seminal proteome of infected males, we found that Wolbachia moderately affects SFP composition. However, we identified 125 paternally transferred Wolbachia proteins, but the CI factor proteins (Cifs) were not among them. Our findings indicate that Wolbachia infection of Ae. aegypti alters female PMRs, potentially influencing control programs that utilize Wolbachia-infected individuals.

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.

DMKPs provide a generalizable strategy for studying genes required for reproduction or viability in nontraditional model organisms

The advent of CRISPR/Cas9-mediated genome editing has expanded the range of animals amenable to targeted genetic analysis. This has accelerated research in animals not traditionally studied using molecular genetics. However, studying genes essential for reproduction or survival in such animals remains challenging, as they lack the tools that aid genetic analysis in traditional genetic model organisms. We recently introduced the use of distinguishably marked knock-in pairs (DMKPs) as a strategy for rapid and reliable genotyping in such species. Here we show that DMKPs also facilitate the maintenance and study of mutations that cannot be maintained in a homozygous state, a group which includes recessive lethal and sterile mutations. Using DMKPs, we disrupt the zero population growth locus in Drosophila melanogaster and in the dengue vector mosquito Aedes aegypti. In both species, DMKPs enable the maintenance of zero population growth mutant strains and the reliable recovery of zero population growth mutant animals. Male and female gonad development is disrupted in fly and mosquito zero population growth mutants, rendering both sexes sterile. In Ae. aegypti, zero population growth mutant males remain capable of inducing a mating refractory period in wild-type females and of competing with wild-type males for mates, properties compatible with zero population growth serving as a target in mosquito population suppression strategies. DMKP is readily generalizable to other species amenable to CRISPR/Cas9-mediated gene targeting, and should facilitate the study of sterile and lethal mutations in multiple organisms not traditionally studied using molecular genetics.

Biology and Behaviour of Aedes aegypti in the Human Environment: Opportunities for Vector Control of Arbovirus Transmission

Aedes aegypti is a ubiquitous vector of arboviruses mostly in urbanised areas throughout the tropics and subtropics and a growing threat beyond. Control of Ae. aegypti is difficult and costly, and no vaccines are available for most of the viruses it transmits. With practical control solutions our goal, ideally suitable for delivery by householders in affected communities, we reviewed the literature on adult Ae. aegypti biology and behaviour, within and close to the human home, the arena where such interventions must impact. We found that knowledge was vague or important details were missing for multiple events or activities in the mosquito life cycle, such as the duration or location of the many periods when females rest between blood feeding and oviposition. The existing body of literature, though substantial, is not wholly reliable, and evidence for commonly held "facts" range from untraceable to extensive. Source references of some basic information are poor or date back more than 60 years, while other information that today is accepted widely as "fact" is not supported by evidence in the literature. Many topics, e.g., sugar feeding, resting preferences (location and duration), and blood feeding, merit being revisited in new geographical regions and ecological contexts to identify vulnerabilities for exploitation in control.

Evaluating the Mating Competency of Genetically Modified Male Mosquitoes in Laboratory Conditions

Efforts to eradicate mosquito-borne diseases have increased the demand for genetic control strategies, many of which involve the release of genetically modified (GM) mosquito males into natural populations. The first hurdle for GM males is to compete with their wild-type counterparts for access to females. Here, we introduce an eye color-based mating assay, in which both Lvp wild-type and kynurenine 3-monooxygenase (kmo)-null males compete for access to kmo-null females, and therefore the eye color phenotype (black or white) of the progeny is dependent on the parental mating pair. A series of tests addressed that male mating competitiveness between the two strains can significantly be influenced by adult density, light intensity, and mating duration. Interestingly, the mating competitiveness of males was not correlated with body size, which was negatively influenced by a high larval density. Lastly, this eye color-associated assay was applied to characterize GM mosquitoes in their mating competitiveness, establishing this method as a fast and precise way of benchmarking this fitness parameter for laboratory-raised males.

Female mating rates and their fitness consequences in the common house spider Parasteatoda tepidariorum

Mating systems, with varying female mating rates occurring with the same partner (monandry) or with multiple mates (polyandry), can have far reaching consequences for population viability and the rate of gene flow. Here, we investigate the mating rates of the common house spider Parasteatoda tepidariorum (Theridiidae), an emerging model for genetic studies, with yet undescribed reproductive behavior. It is hypothesized that spiders belonging to this family have low re-mating rates. We paired females twice with the same male (monandry) or with different males (polyandry), and recorded behaviors, mating success and fitness resulting from single- and double-matings, either monandrous or polyandrous. Despite the study being explorative in nature, we predict successful matings to be more frequent during first encounters, to reduce female risk of remaining unmated. For re-mating to be adaptive, we expect higher fitness of double-mated females, and polyandrous females to experience highest mating success and fitness if reproductive gains are achieved by mating with multiple partners. We show that the majority of the females did not mate, and those that did mated only once, not necessarily on their first encounter. The likelihood of re-mating did not differ between monandrous and polyandrous encounters and female mating experience (mated once, twice monandrous, twice polyandrous) did not affect fitness, indicated by similar offspring production. Female twanging of the web leads to successful matings suggesting female behavioral receptivity. Cannibalism rates were low and mostly occurred pre-copulatory. We discuss how the species ecology, with potentially high mating costs for males and limited female receptivity, may shape a mating system with low mating rates.

Exploring Conditions for Handling Packing and Shipping Aedes aegypti Males to Support an SIT Field Project in Brazil

The sterile insect technique (SIT) application, as an alternative tool for conventional mosquito control methods, has recently gained prominence. Nevertheless, some SIT components require further development, such as protocols under large-scale conditions, focusing on packing and shipping mosquitoes, and considering transporting time. Immobilization of Aedes aegypti males was tested at temperatures 4, 7, 10, and 14 °C, and each temperature was assessed for 60, 90, and 120 min. The recovery after 24 h was also studied. Chilled and control-reared males had comparable survival rates for all conditions, although 4 °C for 120 min impacted male survival. The male escape rate was affected after 60 min of exposure at 4 °C; this difference was not significant, with 24 h of recovery. First, we defined the successful immobilization at 4 °C for 60 min, thus enabling the evaluation of two transportation intervals: 6 and 24 h, with the assessment of different compaction densities of 100 and 150 mosquitoes/cm³ at 10 °C to optimize the shipment. Compaction during simulated mosquito shipments reduced survival rates significantly after 6 and 24 h. In the mating propensity and insemination experiments, the sterile males managed to inseminate 40 to 66% for all treatments in laboratory conditions. The male insemination propensity was affected only by the highest compaction condition concerning the control. The analysis of the densities (100 and 150 males/cm³) showed that a higher density combined with an extended shipment period (24 h) negatively impacted the percentage of inseminated females. The results are very helpful in developing and improving the SIT packing and shipment protocols. Further studies are required to evaluate all combined parameters' synergetic effects that can combine irradiation to assess sexual competitiveness when sterile males are released into the field.

Insemination in Aedes aegypti and Aedes albopictus

Aedes mosquitoes are the vectors of several arboviruses that cause human disease. A better understanding of their reproduction helps to improve their management and contributes insights into the fundamental biology of mosquitoes. During mating, inseminated mosquito females receive seminal fluids and sperm from males that they then store in the spermathecae. In Aedes aegypti and Aedes albopictus, most mated females become resistant to further insemination within 2 h of initial insemination. Although the male seminal fluids are known to be involved in initiating the resistance of inseminated females to further insemination, the mechanism underlying this resistance is not well-understood. The determination of insemination status is a key step in investigating the behavioral and molecular interactions between males and females and for exploring the proximate influences and evolutionary implications of interspecific copulations. Several methods exist for determining insemination status, as discussed here. The choice of method depends on the research question and the availability of resources.

Putative Degradation of Non-Stored Sperm in the Female Reproductive Tract of the Dengue Vector Mosquito Aedes aegypti

In insect vectors of disease, male and female molecules that mediate reproductive processes are promising targets to suppress fertility of these populations. One process, the storage of sperm in the female reproductive tract, is essential for optimal fertility in all organisms examined to date. In the dengue vector mosquito Aedes aegypti, female sperm storage has not been fully characterized, a requirement to identify sex-specific molecules that mediate this process. Aedes aegypti males deposit the ejaculate into the bursa of the female reproductive tract, and sperm enter the spermathecae—the long-term storage sites—quickly after insemination. However, the proportion of sperm received during mating that are stored in the spermathecae is unclear, and the fate of non-stored sperm unknown. We quantified sperm storage in two Ae. aegypti strains, mated in all combinations, and in two contexts (mass mated and when mating was observed) at 1-, 3- and 5-days post-mating. Sperm quantity in the spermathecae was similar at all timepoints; most females stored ~400 sperm on average. Sperm that did not enter the spermathecae remained in the bursa, where they declined in number and became more fragile to mechanical manipulation at each timepoint. Further, sperm viability in the bursa fell from 91.6% shortly after mating to 12.2% 24 h later. One day after insemination, ~50% of sperm detected in the female reproductive tract was stored in the spermathecae. When we quantified sperm storage in females mated to males that transferred reduced ejaculate quantities (but still able to induce optimal fertility in their mates), sperm detected in the spermathecae similarly declined; females stored ~50% of the sperm received even as sperm quantities transferred at mating declined. Our results suggest that sperm storage in Ae. aegypti females is influenced by ejaculate volume, and that sperm that do not enter the spermathecae remain in the bursa, where they appear to degrade. The consistent presence of sperm in the bursa, even when males transferred low sperm quantities, suggests that the putative degradation of bursa sperm may play a role in Ae. aegypti female fertility, potentially identifying a novel process in this important vector species.

Effects of gamma radiation on the reproductive viability of Aedes aegypti and its descendants (Diptera: Culicidae)

This work evaluated the genetic damage in descendants of male pupae of Aedes (Stegomyia) aegypti (Diptera: Culicidae) separately exposed to 20, 30, and 40 Gy of gamma radiation in the context of Sterile Insect Technique (SIT). Despite the transmission of the dominant lethal mutation, the employed dose levels did not promote a marked reduction in adult mosquito emergence and fertility. This study emphasized that semi-sterilizing doses < 50 Gy for SIT of Aedes aegypti are not recommended.

Seminal fluid proteins induce transcriptome changes in the Aedes aegypti female lower reproductive tract

BACKGROUND

Mating induces behavioral and physiological changes in the arbovirus vector Aedes aegypti, including stimulation of egg development and oviposition, increased survival, and reluctance to re-mate with subsequent males. Transferred seminal fluid proteins and peptides derived from the male accessory glands induce these changes, though the mechanism by which they do this is not known.

RESULTS

To determine transcriptome changes induced by seminal proteins, we injected extract from male accessory glands and seminal vesicles (MAG extract) into females and examined female lower reproductive tract (LRT) transcriptomes 24 h later, relative to non-injected controls. MAG extract induced 87 transcript-level changes, 31 of which were also seen in a previous study of the LRT 24 h after a natural mating, including 15 genes with transcript-level changes similarly observed in the spermathecae of mated females. The differentially-regulated genes are involved in diverse molecular processes, including immunity, proteolysis, neuronal function, transcription control, or contain predicted small-molecule binding and transport domains.

CONCLUSIONS

Our results reveal that seminal fluid proteins, specifically, can induce gene expression responses after mating and identify gene targets to further investigate for roles in post-mating responses and potential use in vector control.

Characterization of the reproductive tract bacterial microbiota of virgin, mated, and blood-fed Aedes aegypti and Aedes albopictus females

Background

Aedes aegypti and Ae. albopictus are vectors of numerous arboviruses that adversely affect human health. In mosquito vectors of disease, the bacterial microbiota influence several physiological processes, including fertility and vector competence, making manipulation of the bacterial community a promising method to control mosquito vectors. In this study, we describe the reproductive tract tissue microbiota of lab-reared virgin Ae. aegypti and Ae. albopictus males, and virgin, mated, and mated + blood-fed females of each species, comparing the bacterial composition found there to the well-described gut microbiota.

Methods

We performed metabarcoding of the 16S rRNA isolated from the gut, upper reproductive tract (URT; testes or ovaries), and lower reproductive tract (LRT; males: seminal vesicles and accessory glands; females: oviduct, spermathecae, and bursa) for each species, and evaluated the influence of host species, tissue, nutritional status, and reproductive status on microbiota composition. Finally, based on the identified taxonomic profiles of the tissues assessed, bacterial metabolic pathway abundance was predicted.

Results

The community structure of the reproductive tract is unique compared to the gut. Asaia is the most prevalent OTU in the LRTs of both Ae. aegypti and Ae. albopictus. In the URT, we observed differences between species, with Wolbachia OTUs being dominant in the Ae. albopictus URT, while Enterobacter and Serratia were dominant in Ae. aegypti URT. Host species and tissue were the best predictors of the community composition compared to reproductive status (i.e., virgin or mated) and nutritional status (i.e., sugar or blood-fed). The predicted functional profile shows changes in the abundance of specific microbial pathways that are associated with mating and blood-feeding, like energy production in mated tissues and siderophore synthesis in blood-fed female tissues.

Conclusions

Aedes aegypti and Ae. albopictus have distinct differences in the composition of microbiota found in the reproductive tract. The distribution of the bacterial taxonomic groups indicates that some bacteria have tissue-specific tropism for reproductive tract tissue, such as Asaia and Wolbachia. No significant differences in the taxonomic composition were observed in the reproductive tract between virgin, mated, and mated + blood-fed females, but changes in the abundance of specific metabolic pathways were found in the predicted microbial functional profiles in mated and blood-fed females.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05093-7.

Suppressing mosquito populations with precision guided sterile males

The mosquito Aedes aegypti is the principal vector for arboviruses including dengue/yellow fever, chikungunya, and Zika virus, infecting hundreds of millions of people annually. Unfortunately, traditional control methodologies are insufficient, so innovative control methods are needed. To complement existing measures, here we develop a molecular genetic control system termed precision-guided sterile insect technique (pgSIT) in Aedes aegypti. PgSIT uses a simple CRISPR-based approach to generate flightless females and sterile males that are deployable at any life stage. Supported by mathematical models, we empirically demonstrate that released pgSIT males can compete, suppress, and even eliminate mosquito populations. This platform technology could be used in the field, and adapted to many vectors, for controlling wild populations to curtail disease in a safe, confinable, and reversible manner.

A. aegypti is the principal vector for arboviruses that impact on human health and wellbeing. Here the authors use precision guided sterile insect technique—pgSIT—to suppress or eliminate mosquito populations in multigeneration cage experiments.

The impact of mating and sugar feeding on blood-feeding physiology and behavior in the arbovirus vector mosquito Aedes aegypti

BACKGROUND

Aedes aegypti mosquitoes are globally distributed vectors of viruses that impact the health of hundreds of millions of people annually. Mating and blood feeding represent fundamental aspects of mosquito life history that carry important implications for vectorial capacity and for control strategies. Females transmit pathogens to vertebrate hosts and obtain essential nutrients for eggs during blood feeding. Further, because host-seeking Ae. aegypti females mate with males swarming near hosts, biological crosstalk between these behaviors could be important. Although mating influences nutritional intake in other insects, prior studies examining mating effects on mosquito blood feeding have yielded conflicting results.

METHODOLOGY/PRINCIPAL FINDINGS

To resolve these discrepancies, we examined blood-feeding physiology and behavior in virgin and mated females and in virgins injected with male accessory gland extracts (MAG), which induce post-mating changes in female behavior. We controlled adult nutritional status prior to blood feeding by using water- and sugar-fed controls. Our data show that neither mating nor injection with MAG affect Ae. aegypti blood intake, digestion, or feeding avidity for an initial blood meal. However, sugar feeding, a common supplement in laboratory settings but relatively rare in nature, significantly affected all aspects of feeding and may have contributed to conflicting results among previous studies. Further, mating, MAG injection, and sugar intake induced declines in subsequent feedings after an initial blood meal, correlating with egg production and laying. Taking our evaluation to the field, virgin and mated mosquitoes collected in Colombia were equally likely to contain blood at the time of collection.

CONCLUSIONS/SIGNIFICANCE

Mating, MAG, and sugar feeding impact a mosquito's estimated ability to transmit pathogens through both direct and indirect effects on multiple aspects of mosquito biology. Our results highlight the need to consider natural mosquito ecology, including diet, when assessing their physiology and behavior in the laboratory.

Male Age Influences Re-mating Incidence and Sperm Use in Females of the Dengue Vector Aedes aegypti

Diseases transmitted by female Aedes aegypti mosquitoes are public health issues in countries in the tropics and sub-tropics. As in other insects, A. aegypti females undergo behavioral and physiological changes upon mating that principally act to facilitate the production of progeny. The primary effectors of A. aegypti female post-mating responses are male-derived seminal proteins that are transferred to females during mating. Increased male age reduces ejaculate function in numerous taxa and alters seminal protein composition in Drosophila melanogaster, but the impacts of male age on female A. aegypti post-mating responses are unknown. Here, we used "old" (21-22 days old) and "young" (4-5 days old) A. aegypti males to assess the influence of male age on oviposition, fertility, and re-mating incidence in their mates. We also examined how age influenced paternity share in females initially mated to young or old males that subsequently re-mated with a transgenic male that transferred RFP-labeled sperm and whose progeny inherited a larval-expressed GFP marker. We found that increased male age had no effect on female fecundity or fertility but significantly impacted their ability to prevent re-mating in their mates-more than half (54.5%) of the females mated to an old male re-mated, compared to 24% of females initially mated to a young male. Polyandrous A. aegypti females displayed first male precedence regardless of the age of their initial mate. However, young males were better able to compete with rival male sperm, siring significantly more progeny (77%) compared to old males (64%). Young males had significantly more sperm in their seminal vesicles than old males at the time of mating, although males of both age groups transferred similar numbers of sperm to their mates. Our results suggest that male senescence differentially impacts the induction of some post-mating changes in A. aegypti females. As the effect of age may be further exacerbated in the field, age-related declines in male ability to induce sexual refractoriness have implications for A. aegypti population control programs that release adults into the environment.

Suppression gene drive in continuous space can result in unstable persistence of both drive and wild-type alleles

Rapid evolutionary processes can produce drastically different outcomes when studied in panmictic population models vs. spatial models. One such process is gene drive, which describes the spread of "selfish" genetic elements through a population. Engineered gene drives are being considered for the suppression of disease vectors or invasive species. While laboratory experiments and modelling in panmictic populations have shown that such drives can rapidly eliminate a population, it remains unclear if these results translate to natural environments where individuals inhabit a continuous landscape. Using spatially explicit simulations, we show that the release of a suppression drive can result in what we term "chasing" dynamics, in which wild-type individuals recolonize areas where the drive has locally eliminated the population. Despite the drive subsequently reconquering these areas, complete population suppression often fails to occur or is substantially delayed. This increases the likelihood that the drive is lost or that resistance evolves. We analyse how chasing dynamics are influenced by the type of drive, its efficiency, fitness costs, and ecological factors such as the maximal growth rate of the population and levels of dispersal and inbreeding. We find that chasing is more common for lower efficiency drives when dispersal is low and that some drive mechanisms are substantially more prone to chasing behaviour than others. Our results demonstrate that the population dynamics of suppression gene drives are determined by a complex interplay of genetic and ecological factors, highlighting the need for realistic spatial modelling to predict the outcome of drive releases in natural populations.

Mosquito Sexual Selection and Reproductive Control Programs

The field of mosquito mating biology has experienced a considerable expansion in the past decade. Recent work has generated many key insights about specific aspects of mating behavior and physiology. Here, we synthesize these findings and classify swarming mosquito systems as polygynous. Male mating success is highly variable in swarms and evidence suggests that it is likely determined by both scramble competition between males and female choice. Incorporating this new understanding will improve both implementation and long-term stability of reproductive control tools.

Mating and blood-feeding induce transcriptome changes in the spermathecae of the yellow fever mosquito Aedes aegypti

Aedes aegypti mosquitoes are the primary vectors of numerous viruses that impact human health. As manipulation of reproduction has been proposed to suppress mosquito populations, elucidation of biological processes that enable males and females to successfully reproduce is necessary. One essential process is female sperm storage in specialized structures called spermathecae. Aedes aegypti females typically mate once, requiring them to maintain sperm viably to fertilize eggs they lay over their lifetime. Spermathecal gene products are required for Drosophila sperm storage and sperm viability, and a spermathecal-derived heme peroxidase is required for long-term Anopheles gambiae fertility. Products of the Ae. aegypti spermathecae, and their response to mating, are largely unknown. Further, although female blood-feeding is essential for anautogenous mosquito reproduction, the transcriptional response to blood-ingestion remains undefined in any reproductive tissue. We conducted an RNAseq analysis of spermathecae from unfed virgins, mated only, and mated and blood-fed females at 6, 24, and 72 h post-mating and identified significant differentially expressed genes in each group at each timepoint. A blood-meal following mating induced a greater transcriptional response in the spermathecae than mating alone. This study provides the first view of elicited mRNA changes in the spermathecae by a blood-meal in mated females.

Using spatial genetics to quantify mosquito dispersal for control programs

Background

Hundreds of millions of people get a mosquito-borne disease every year and nearly one million die. Transmission of these infections is primarily tackled through the control of mosquito vectors. The accurate quantification of mosquito dispersal is critical for the design and optimization of vector control programs, yet the measurement of dispersal using traditional mark-release-recapture (MRR) methods is logistically challenging and often unrepresentative of an insect’s true behavior. Using Aedes aegypti (a major arboviral vector) as a model and two study sites in Singapore, we show how mosquito dispersal can be characterized by the spatial analyses of genetic relatedness among individuals sampled over a short time span without interruption of their natural behaviors.

Results

Using simple oviposition traps, we captured adult female Ae. aegypti across high-rise apartment blocks and genotyped them using genome-wide SNP markers. We developed a methodology that produces a dispersal kernel for distance which results from one generation of successful breeding (effective dispersal), using the distance separating full siblings and 2nd- and 3rd-degree relatives (close kin). The estimated dispersal distance kernel was exponential (Laplacian), with a mean dispersal distance (and dispersal kernel spread σ) of 45.2 m (95% CI 39.7–51.3 m), and 10% probability of a dispersal > 100 m (95% CI 92–117 m). Our genetically derived estimates matched the parametrized dispersal kernels from previous MRR experiments. If few close kin are captured, a conventional genetic isolation-by-distance analysis can be used, as it can produce σ estimates congruent with the close-kin method if effective population density is accurately estimated. Genetic patch size, estimated by spatial autocorrelation analysis, reflects the spatial extent of the dispersal kernel “tail” that influences, for example, the critical radii of release zones and the speed of Wolbachia spread in mosquito replacement programs.

Conclusions

We demonstrate that spatial genetics can provide a robust characterization of mosquito dispersal. With the decreasing cost of next-generation sequencing, the production of spatial genetic data is increasingly accessible. Given the challenges of conventional MRR methods, and the importance of quantified dispersal in operational vector control decisions, we recommend genetic-based dispersal characterization as the more desirable means of parameterization.

Male sexual history influences female fertility and re-mating incidence in the mosquito vector Aedes aegypti (Diptera: Culicidae)

Aedes aegypti is the primary vector of several arboviruses that impact human health including the dengue, Zika, and yellow fever viruses. The potential of Ae. aegypti females to transmit viruses is enhanced by mating-induced behavioral and physiological changes that increase female host-seeking behaviors, blood-feeding frequency and longevity. The mating-induced changes are due to female receipt of male seminal fluid proteins (SFPs) during copulation. SFPs also inhibit female re-mating-re-mating incidence is significantly reduced in the initial hours after mating and nearly absent after 24 h. Males, however, are not limited in the number of females they can inseminate and are able to mate with multiple females in succession. As successive mating depletes SFPs, we examined parameters of fertility and re-mating incidence in females after mating with recently mated males. Males of two Ae. aegypti strains (Colombian and Thai) were mated five consecutive times and fecundity, resulting larvae and hatch percentage in each female of the mating sequence was assessed. In both strains, we found that males can mate three times in succession without impacting fertility in their mates. However, significant declines in fecundity, resulting larvae, and hatch percentage were observed after a third mating. Male size influenced female fecundity and fertility as mates of small males showed further reductions compared to mates of big males after mating consecutively. Seven days after the consecutive mating assays, the re-mating rate of females mated fifth in succession was significantly increased (Colombian strain: 33%; Thai strain: 48%) compared to females mated first (0% in both strains). Re-mating incidence was further increased in small, Thai strain males where 82% of fifth mated females re-mated compared to 0% of first mated females. Finally, we show that regardless of male size, mates of experimental males were similarly fertile to mates of control males when mated for a sixth time 48 h after the consecutive mating assays, showing that males recover fertility after 2 d. Our results show that male sexual history influences fertility and re-mating incidence of Ae. aegypti females.

Cryo-Electron Microscopy Reveals That Sperm Modification Coincides with Female Fertility in the Mosquito Aedes aegypti

Manipulating mosquito reproduction is a promising approach to reducing mosquito populations and the burden of diseases they carry. A thorough understanding of reproductive processes is necessary to develop such strategies, but little is known about how sperm are processed and prepared for fertilization within female mosquitoes. By employing cryo-electron microscopy for the first time to study sperm of the mosquito Aedes aegypti, we reveal that sperm shed their entire outer coat, the glycocalyx, within 24 hours of being stored in the female. Motility assays demonstrate that as their glycocalyx is shed in the female’s sperm storage organs, sperm transition from a period of dormancy to rapid motility—a critical prerequisite for sperm to reach the egg. We also show that females gradually become fertile as sperm become motile, and that oviposition behavior increases sharply after females reach peak fertility. Together, these experiments demonstrate a striking coincidence of the timelines of several reproductive events in Ae. aegypti, suggesting a direct relationship between sperm modification and female reproductive capacity.

Proteins, Transcripts, and Genetic Architecture of Seminal Fluid and Sperm in the Mosquito Aedes aegypti

The yellow fever mosquito, Aedes aegypti,, transmits several viruses causative of serious diseases, including dengue, Zika, and chikungunya. Some proposed efforts to control this vector involve manipulating reproduction to suppress wild populations or to replace them with disease-resistant mosquitoes. The design of such strategies requires an intimate knowledge of reproductive processes, yet our basic understanding of reproductive genetics in this vector remains largely incomplete. To accelerate future investigations, we have comprehensively catalogued sperm and seminal fluid proteins (SFPs) transferred to females in the ejaculate using tandem mass spectrometry. By excluding female-derived proteins using an isotopic labeling approach, we identified 870 sperm proteins and 280 SFPs. Functional composition analysis revealed parallels with known aspects of sperm biology and SFP function in other insects. To corroborate our proteome characterization, we also generated transcriptomes for testes and the male accessory glands-the primary contributors to Ae. aegypti, sperm and seminal fluid, respectively. Differential gene expression of accessory glands from virgin and mated males suggests that transcripts encoding proteins involved in protein translation are upregulated post-mating. Several SFP transcripts were also modulated after mating, but >90% remained unchanged. Finally, a significant enrichment of SFPs was observed on chromosome 1, which harbors the male sex determining locus in this species. Our study provides a comprehensive proteomic and transcriptomic characterization of ejaculate production and composition and thus provides a foundation for future investigations of Ae. aegypti, reproductive biology, from functional analysis of individual proteins to broader examination of reproductive processes.

Spermathecal Filling in Aedes aegypti and Aedes albopictus: Effects of Female and Male Body Sizes and Species

The mosquitoes Aedes aegypti (L.) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) are ecologically similar species that have evolved independently in their native ranges, Ae. aegypti in Africa and Ae. albopictus in Asia. Where their invasive ranges overlap, interspecific mating is facilitated by both species swarming to mate around bloodmeal hosts during daylight. Here, we test hypotheses to account for variation in spermathecal filling in females of Ae. aegypti and Ae. albopictus, particularly, the effect of mosquito size on the number of spermathecae containing sperm after intraspecific and interspecifc matings of these two species. Results show that significantly more spermathecae contained sperm in large than in small Ae. albopictus females, but there was no effect of Ae. aegypti female body size on the average number of spermathecae filled. Among inseminated females, there was no effect of male size or cross-type on number of spermathecae with sperm. Differences in the effect of female size on the number of spermathecae that store sperm in Ae. aegypti and Ae. albopictus imply differences in the mating biology of these two species.

Female resistance and harmonic convergence influence male mating success in Aedes aegypti

Despite the importance of mosquito mating biology to reproductive control strategies, a mechanistic understanding of individual mating interactions is currently lacking. Using synchronised high-speed video and audio recordings, we quantified behavioural and acoustic features of mating attempts between tethered female and free-flying male Aedes aegypti. In most couplings, males were actively displaced by female kicks in the early phases of the interaction, while flight cessation prior to adoption of the pre-copulatory mating pose also inhibited copulation. Successful males were kicked at a reduced rate and sustained paired contact-flight for longer than those that were rejected. We identified two distinct phases of acoustic interaction. Rapid frequency modulation of flight tones was observed in all interactions up to acceptance of the male. Harmonic convergence (wingbeat frequency matching) was detected more often in successful attempts, coinciding with the transition to stabilised paired flight and subsequent genital contact. Our findings provide a clearer understanding of the relationship between acoustic interactions and mating performance in mosquitoes, offering insights which may be used to target improvements in laboratory reared lines.

Small females prefer small males: size assortative mating in Aedes aegypti mosquitoes

BACKGROUND

With Aedes aegypti mosquitoes now being released in field programmes aimed at disease suppression, there is interest in identifying factors influencing the mating and invasion success of released mosquitoes. One factor that can increase release success is size: released males may benefit competitively from being larger than their field counterparts. However, there could be a risk in releasing only large males if small field females avoid these males and instead prefer small males. Here we investigate this risk by evaluating mating success for mosquitoes differing in size.

RESULTS

We measured mating success indirectly by coupling size with Wolbachia-infected or uninfected mosquitoes and scoring cytoplasmic incompatibility. Large females showed no evidence of a mating preference, whereas small males were relatively more successful than large males when mating with small females, exhibiting an advantage of around 20-25%.

CONCLUSIONS

Because field females typically encompass a wide range of sizes while laboratory reared (and released) males typically fall into a narrow size range of large mosquitoes, these patterns can influence the success of release programmes which rely on cytoplasmic incompatibility to suppress populations and initiate replacement invasions. Releases could include some small males generated under low food or crowded conditions to counter this issue, although this would need to be weighed against issues associated with costs of producing males of various size classes.

Male contributions during mating increase female survival in the disease vector mosquito Aedes aegypti

Aedes aegypti is a vector of medically important viruses including those causing Zika, dengue, and chikungunya. During mating, males transfer a number of proteins and other molecules to the female and these components of the male ejaculate are essential in shifting female post-mating behaviors in a number of insect species. Because these molecules are highly variable by species, and female post-mating behavior by species is also varied, behavioral assays testing the function of the ejaculate are necessary before we can develop control strategies targeting the mating system to reduce mosquito populations. Because increased survival in mosquitoes strongly increases vectorial capacity and can influence population sizes and potential risk we tested the effect of mating on female survival. The ejaculate can either promote or reduce female survival, as both have been shown in multiple insect species, yet this effect has not been directly assessed in mosquitoes. We compared survival of females in four treatment groups: mated females, virgin females, and virgin females injected with either an extract from the male reproductive glands or a saline control. Survival, blood feeding frequency, fecundity and cumulative net reproductive rate (R0) were determined after multiple feedings from a human host. Our results confirm that male reproductive gland substances increase female fecundity and blood feeding frequency, resulting in dramatic increases in fitness (R0). We also demonstrate, for the first time, an effect of male reproductive gland extracts alone on female survival, regardless of whether or not the female ingested a vertebrate blood meal. Thus, the effects of MAG extract on survival are not secondary effects from altered blood feeding. Collectively, we demonstrate a direct role for Ae. aegypti male-derived molecules on increasing female fitness, reproductive success and, ultimately, transmission potential for vector borne pathogens.

Age and Body Size Influence Sperm Quantity in Male Aedes albopictus (Diptera: Culicidae) Mosquitoes

Aedes albopictus (Skuse) (Diptera: Culicidae) is a vector of several arboviruses impacting human health, including dengue, chikungunya, and potentially Zika. Vector control strategies that deploy modified males into the field are in use or under development and require a solid understanding of male biology; unfortunately, there has been limited effort to understand male Ae. albopictus reproductive biology, including sperm production and capacity. We tested whether body size and age affect spermatogenesis in Ae. albopictus. In general, older and larger males produced more sperm than their younger or smaller counterparts. Large males continued spermatogenesis well after 10-d post-eclosion (dpe), augmenting their reserves by 39%. By contrast, small males stopped producing sperm at 10 dpe. These results contribute to a deeper understanding of Ae. albopictus reproductive physiology. We discuss the usefulness of these findings in the context of Ae. albopictus life history and their utility in optimizing male mosquito release strategies.

Mosquito pornoscopy: Observation and interruption of Aedes aegypti copulation to determine female polyandric event and mixed progeny

Ades aegypti is the most important arbovirus vector in the world, and new strategies are under evaluation. Biological studies mentioning the occurrence of a second mate in Aedes aegypti can interfere with vector control program planning, which involves male mosquito release technique. This study presents different experiments to show the occurrence of mixed progeny. Mixed male crosses (using a combination of different type of males in confinement with virgin females) showed no polyandric female. Individual crosses with male substitution in every gonotrophic cycle also did not show any polyandric female. Individual crosses with a 20 minutes interval, with subsequent male change, showed that only a few females presented mixed offspring. The copulation breach in three different moments, group A with full coitus length, group B the coitus was interrupted in 5-7 seconds after the start; and group C, which the copulation was interrupted 3 seconds after started. In summary, group A showed a majority of unique progeny from the first male; group B showed the higher frequency of mixed offspring and group C with the majority of the crosses belonging to the second male. To conclude, the occurrence of a viable second mate and mixed offspring is only possible when the copulation is interrupted; otherwise, the first mate is responsible for mixed progeny.

A mosquito sperm's journey from male ejaculate to egg: Mechanisms, molecules, and methods for exploration

The fate of mosquito sperm in the female reproductive tract has been addressed sporadically and incompletely, resulting in significant gaps in our understanding of sperm-female interactions that ultimately lead to fertilization. As with other Diptera, mosquito sperm have a complex journey to their ultimate destination, the egg. After copulation, sperm spend a short time at the site of insemination where they are hyperactivated and quickly congregate near the entrance of the spermathecal ducts. Within minutes, they travel up the narrow ducts to the spermathecae, likely through the combined efforts of female transport and sperm locomotion. The female nourishes sperm and maintains them in these permanent storage organs for her entire life. When she is ready, the female coordinates the release of sperm with ovulation, and the descending egg is fertilized. Although this process has been well studied via microscopy, many questions remain regarding the molecular processes that coordinate sperm motility, movement through the reproductive tract, maintenance, and usage. In this review, we describe the current understanding of a mosquito sperm's journey to the egg, highlighting gaps in our knowledge of mosquito reproductive biology. Where insufficient information is available in mosquitoes, we describe analogous processes in other organisms, such as Drosophila melanogaster, as a basis for comparison, and we suggest future areas of research that will illuminate how sperm successfully traverse the female reproductive tract. Such studies may yield molecular targets that could be manipulated to control populations of vector species. Mol. Reprod. Dev. 83: 897-911, 2016 © 2016 Wiley Periodicals, Inc.

A Peptide Signaling System that Rapidly Enforces Paternity in the Aedes aegypti Mosquito

Female Aedes aegypti mosquitoes typically mate only once with one male in their lifetime, a behavior known as "monandry" [1]. This single mating event provisions the female with sufficient sperm to fertilize the >500 eggs she will produce during her ∼4- to 6-week lifespan in the laboratory [2]. Successful mating induces lifetime refractoriness to subsequent insemination by other males, enforcing the paternity of the first male [3-5]. Ae. aegypti mate in flight near human hosts [6], and females become refractory to remating within seconds [1, 3, 4], suggesting the existence of a rapid mechanism to prevent female remating. In this study, we implicate HP-I, an Aedes- and male-specific peptide transferred to females [7], and its cognate receptor in the female, NPYLR1 [8], in rapid enforcement of paternity. HP-I mutant males were ineffective in enforcing paternity when a second male was given access to the female within 1 hr. NPYLR1 mutant females produced mixed paternity offspring at high frequency, indicating acceptance of multiple mates. Synthetic HP-I injected into wild-type, but not NPYLR1 mutant, virgins reduced successful matings. Asian tiger mosquito (Ae. albopictus) HP-I peptides potently activated Ae. aegypti NPYLR1. Invasive Ae. albopictus males are known to copulate with and effectively sterilize Ae. aegypti females by causing them to reject future mates [9]. Cross-species transfer of sperm and active seminal fluid proteins including HP-I may contribute to this phenomenon. This signaling system promotes rapid paternity enforcement within Ae. aegypti but may promote local extinction in areas where they compete with Ae. albopictus.

Maintaining Aedes aegypti Mosquitoes Infected with Wolbachia

Aedes aegypti mosquitoes experimentally infected with Wolbachia are being utilized in programs to control the spread of arboviruses such as dengue, chikungunya and Zika. Wolbachia-infected mosquitoes can be released into the field to either reduce population sizes through incompatible matings or to transform populations with mosquitoes that are refractory to virus transmission. For these strategies to succeed, the mosquitoes released into the field from the laboratory must be competitive with native mosquitoes. However, maintaining mosquitoes in the laboratory can result in inbreeding, genetic drift and laboratory adaptation which can reduce their fitness in the field and may confound the results of experiments. To test the suitability of different Wolbachia infections for deployment in the field, it is necessary to maintain mosquitoes in a controlled laboratory environment across multiple generations. We describe a simple protocol for maintaining Ae. aegypti mosquitoes in the laboratory, which is suitable for both Wolbachia-infected and wild-type mosquitoes. The methods minimize laboratory adaptation and implement outcrossing to increase the relevance of experiments to field mosquitoes. Additionally, colonies are maintained under optimal conditions to maximize their fitness for open field releases.

The importance of male body size on sperm uptake and usage, and female fecundity in Aedes aegypti and Aedes albopictus

Background

Adult mosquito density is a critical factor in the transmission of arboviruses by container Aedes spp. mosquitoes. Female fecundity drives population growth, and therefore contributes to adult mosquito density. Previous studies have focused on female body size as the major determinant of fecundity, paying little attention to male condition. In this study, we examined the effects of male body size on the abundance of sperm in spermatheca, depletion of sperm over time, and female fecundity.

Methods

We generated males in two size classes using different larval densities, and allowed them to mate with females generated from a moderately dense larval environment. We counted sperm in female spermatheca in a sample of females immediately after mating, then every week for four weeks post-mating. We provided weekly blood meals to females and determined their fecundity over four weeks after the initial blood meal.

Results

We found significantly more sperm in Aedes albopictus females than in Aedes aegypti, and detected depletion of sperm in Ae. aegypti, but not in Ae. albopictus. We did not see significant differences in number of sperm in spermathecae in relation to male body size in either species over subsequent gonotrophic cycles. We found a significant effect of male body size on fecundity in Ae. albopictus, but not Ae. aegypti, with a 46 % increase in fecundity for female Ae. albopictus offered four blood meals.

Conclusions

Our results suggest substantial differences in the mating biology of these ecologically similar species and the importance of considering males in understanding female fecundity. The substantial increase in fecundity in Ae. albopictus has implications for population growth, estimating vector density, and modeling the transmission of pathogens.

Mating-Induced Transcriptome Changes in the Reproductive Tract of Female Aedes aegypti

The Aedes aegypti mosquito is a significant public health threat, as it is the main vector of dengue and chikungunya viruses. Disease control efforts could be enhanced through reproductive manipulation of these vectors. Previous work has revealed a relationship between male seminal fluid proteins transferred to females during mating and female post-mating physiology and behavior. To better understand this interplay, we used short-read RNA sequencing to identify gene expression changes in the lower reproductive tract of females in response to mating. We characterized mRNA expression in virgin and mated females at 0, 6 and 24 hours post-mating (hpm) and identified 364 differentially abundant transcripts between mating status groups. Surprisingly, 60 transcripts were more abundant at 0hpm compared to virgin females, suggesting transfer from males. Twenty of these encode known Ae. aegypti seminal fluid proteins. Transfer and detection of male accessory gland-derived mRNA in females at 0hpm was confirmed by measurement of eGFP mRNA in females mated to eGFP-expressing males. In addition, 150 transcripts were up-regulated at 6hpm and 24hpm, while 130 transcripts were down-regulated at 6hpm and 24hpm. Gene Ontology (GO) enrichment analysis revealed that proteases, a protein class broadly known to play important roles in reproduction, were among the most enriched protein classes. RNAs associated with immune system and antimicrobial function were also up-regulated at 24hpm. Collectively, our results suggest that copulation initiates broad transcriptome changes across the mosquito female reproductive tract, “priming” her for important subsequent processes of blood feeding, egg development and immune defense. Our transcriptome analysis provides a vital foundation for future studies of the consequences of mating on female biology and will aid studies seeking to identify specific gene families, molecules and pathways that support key reproductive processes in the female mosquito.

Female post-mating behavior has important consequences for mosquito populations and their ability to transmit diseases. Male Aedes aegypti seminal fluid substances transferred during mating cause many important changes to female behavior and physiology, including blood feeding behavior, egg development, and oviposition. In an effort to understand how males induce these responses in Ae. aegypti females, we characterized the transcriptome changes that occur in the female reproductive tract at different time points after mating. We found several RNAs that are apparently transferred by the male, and 280 genes whose mRNA abundance in the female is affected by mating. The nature of the predicted products of many of these genes suggests roles in priming the reproductive tract for egg development, protecting the female against bacterial infections or processing the blood meal. This identification of mating-responsive genes provides information potentially useful for developing tools aimed at preventing disease transmission by manipulating female mosquitoes’ post-mating responses.