Mosquito Lifespan Research Articles

Gene Drive and Symbiont Technologies for Control of Mosquito-Borne Diseases.

Mosquito-borne diseases, such as dengue and malaria, pose a significant burden to global health. Current control strategies with insecticides are only moderately effective. Scalable solutions are needed to reduce the transmission risk of these diseases. Symbionts and genome engineering-based mosquito control strategies have been proposed to address these problems. Bacterial, fungal, and viral symbionts affect mosquito reproduction, reduce mosquito lifespan, and block pathogen transmission. Field tests of endosymbiont Wolbachia-based methods have yielded promising results, but there are hurdles to overcome due to the large-scale rearing and accurate sex sorting required for Wolbachia-based suppression approaches and the ecological impediments to Wolbachia invasion in replacement approaches. Genome engineering-based methods, in which mosquitoes are genetically altered for the modification or suppression of wild populations, offer an additional approach for control of mosquito-borne diseases. In particular, the use of gene drive alleles that bias inheritance in their favor is a potentially powerful approach. Several drives are frequency dependent, potentially giving them broadly similar population dynamics to Wolbachia. However, public acceptance and the behavior of released drives in natural mosquito populations remain challenges. We summarize the latest developments and discuss the knowledge gaps in both symbiont- and gene drive-based methods.

Internal and external drivers interact to create highly dynamic mosquito blood-feeding behaviour.

Blood-feeding, which is necessary for most female mosquitoes to reproduce, provides an opportunity for pathogen transmission. Blood-feeding is influenced by external factors such as light, temperature, humidity and intra- and inter-specific interactions. Physiologically, blood-feeding cycles are linked to nutritional conditions and governed by conserved hormonal signalling pathways that prepare mosquito sensory systems to locate and evaluate hosts. Human activities also alter mosquito blood-feeding behaviour through selection pressures such as insecticide usage, habitat and ecosystem alterations, and climate change. Notably, blood-feeding behaviour changes within a mosquito's lifespan, an underexplored phenomenon from an epidemiological standpoint. A review of the literature indicates that our understanding of mosquito biology and blood-feeding behaviour is predominantly based on studies of a handful of primarily tropical species. This focus likely skews our comprehension of the diversity of critical drivers of blood-feeding behaviour, especially under constraints imposed by harsh conditions. We found evidence of remarkable adaptability in blood-feeding and significant knowledge gaps regarding the determinants of host use. Specifically, epidemiological analyses assume host use is modified by external factors, while neglecting internal physiology. Integrating all significant factors is essential for developing effective models of mosquito-borne disease transmission in a rapidly changing world.

Effect of water salinity on immature performance and lifespan of adult Asian tiger mosquito

BackgroundAedes albopictus (Skuse, 1894) is a vector for pathogens like dengue, chikungunya, and Zika viruses. Its adaptive capacity enables reproduction in temperate climates and development mainly in artificial containers with fresh water in urbanized areas. Nevertheless, breeding in coastal areas may also occur along with its aggressive invasiveness. Global warming and the consequent rise in sea levels will increase saline (> 30 ppt) or brackish (0.5–30 ppt salt) water in coastal regions. To address whether Ae. albopictus can breed in brackish water, we initiated the current study that analyses the survival of immature stages at different salinity concentrations and explores whether carryover effects occur in the resulting adults. This possible adaptation is important when considering the potential for development in new habitats and expansion of one of the world’s most invasive species.MethodsWe investigated the influence of salinity on the survival of Ae. albopictus larvae and adults under laboratory-controlled conditions. First instar larvae were exposed to different salinity concentrations (0 to 30 ppt) and their development time, pupation, adult emergence, and overall survival were monitored daily. We used Kaplan-Meier and Cox regression models to analyze the survival rates at different salinity levels. Furthermore, life tables were constructed under each salinity concentration.ResultsIncreasing salt concentrations significantly increased the mortality risk during immature development, while no significant effect was observed on adult mortality risk. A comparison between distilled and bottled water revealed a notable increase in overall mortality risk for individuals developing in distilled water. However, no significant effects were found when analyzing survival from the first larval stage to adult emergence and adult lifespan. The life expectancy of immature stages decreased with increasing salt concentrations, although salinity concentration did not significantly impact adult life expectancy.ConclusionsOur findings suggest that Ae. albopictus, previously considered freshwater species, can successfully develop and survive in brackish waters, even in the absence of characteristic structures found in euryhaline species. These adaptations may enable Ae. albopictus to establish new breeding sites and colonize unexplored territories. Knowledge of these physiological adaptations of Ae. albopictus to salinity should be pursued to increase the range of control of the species, and to make more accurate predictions of its dispersal and vectoring ability.Graphical

Nature's Solution to Aedes Vectors: Toxorhynchites as a Biocontrol Agent.

This review summarizes the predatory potential of Toxorhynchites mosquitoes as biological control agents for Aedes vectors. A single larva can consume hundreds of mosquito larvae during its development, with preference for larger prey and higher consumption rates at higher prey densities. Studies suggest Toxorhynchites can significantly reduce Aedes populations. Beyond direct predation, they may indirectly influence prey behavior and adult mosquito lifespan. Despite the demonstrably positive effects of Toxorhynchites species as biocontrol agents, there are acknowledged limitations that require further investigation. These limitations include potential variations in effectiveness across diverse habitats and mosquito developmental stages. Additionally, long-term ecological sustainability and potential ramifications warrant further research. Future efforts should prioritize optimizing rearing and release strategies to enhance effectiveness. Exploring the potential for combined control methods with other biocontrol agents or traditional methods is also crucial. Finally, investigating the influence of environmental factors on predation rates can further refine and optimize the application of Toxorhynchites in mosquito control programs.

Mechanical transmission of dengue virus by Aedes aegypti may influence disease transmission dynamics during outbreaks.

Dengue virus outbreaks are increasing in number and severity worldwide. Viral transmission is assumed to require a minimum time period of viral replication within the mosquito midgut. It is unknown if alternative transmission periods not requiring replication are possible. We used a mouse model of dengue virus transmission to investigate the potential of mechanical transmission of dengue virus. We investigated minimal viral titres necessary for development of symptoms in bitten mice and used resulting parameters to inform a new model of dengue virus transmission within a susceptible population. Naïve mice bitten by mosquitoes immediately after they took partial blood meals from dengue infected mice showed symptoms of dengue virus, followed by mortality. Incorporation of mechanical transmission into mathematical models of dengue virus transmission suggest that this supplemental transmission route could result in larger outbreaks which peak sooner. The potential of dengue transmission routes independent of midgut viral replication has implications for vector control strategies that target mosquito lifespan and suggest the possibility of similar mechanical transmission routes in other disease-carrying mosquitoes. This study was funded by grants from the National Health Research Institutes, Taiwan (04D2-MMMOST02), the Human Frontier Science Program (RGP0033/2021), the National Institutes of Health (1R01AI143698-01A1, R01AI151004 and DP2AI152071) and the Ministry of Science and Technology, Taiwan (MOST104-2321-B-400-016).

Changing temperature profiles and the risk of dengue outbreaks

As temperatures change worldwide, the pattern and competency of disease vectors will change, altering the global distribution of both the burden of infectious disease and the risk of the emergence of those diseases into new regions. To evaluate the risk of potential summer dengue outbreaks triggered by infected travelers under various climate scenarios, we develop an SEIR-type model, run numerical simulations, and conduct sensitivity analyses under a range of temperature profiles. Our model extends existing theoretical frameworks for studying dengue dynamics by introducing temperature dependence of two key parameters: the mosquito extrinsic incubation period and the lifespan of mosquitoes, which empirical data suggests are both highly temperature dependent. We find that changing temperature significantly alters dengue risk in an inverted U-shape, with temperatures in the range 27-31°C producing the highest risk. As temperatures increase beyond 31°C, the determinants of dengue risk begin to shift from mosquito biting rate and carrying capacity to the duration of the human infectious period, suggesting that changing temperatures not only alter dengue risk but also the potential efficacy of control measures. To illustrate the role of spatial and temporal temperature heterogeneity, we select five US cities where the primary dengue vector, the mosquito Aedes aegypti, has been observed, and which have had dengue cases in the past: Los Angeles, Houston, Miami, Brownsville, and Phoenix. Our analysis suggests that an increase of 3°C leads to an approximate doubling of the risk of dengue in Los Angeles and Houston, but a reduction of risk in Miami, Brownsville, and Phoenix due to extreme heat.

Dynamic analysis of a mosquito population model with a stage structure and periodic releases of sterile males

<abstract><p>This paper focuses on the key issues of mosquito population control, particularly exploring the impact of periodic releases of sterile males in the population model with a stage structure. We construct and analyze a model that includes only sexually active sterile mosquitoes in the dynamic interaction system. We focus on the system's dynamical behaviors under two scenarios: when the sexual lifespan $ \bar{T} $ equals the release period $ T $ of sterile mosquitoes, and when $ \bar{T} $ is less than $ T $. In the first scenario, we explore the existence and stability of equilibria, identifying a pivotal threshold $ m^* $ that determines the requisite release amount. In the second scenario, we convert the problem into an impulsive switched system and derive sufficient conditions for the local asymptotic stability of the extinction equilibrium. We also establish the existence of positive periodic solutions using the geometric method of differential equations and the fixed point theorem. Our conclusions show that the relationship between the sexual lifespan and release period of sterile mosquitoes significantly impacts the stability of the mosquito population. Additionally, our numerical simulations not only corroborate but they also complement our theoretical findings.</p></abstract>

Immune gene expression in the mosquito vector Culex quinquefasciatus during an avian malaria infection.

Plasmodium relictum is the most widespread avian malaria parasite in the world. It is listed as one of the 100 most dangerous invasive species, having been responsible for the extinction of several endemic bird species, and the near-demise of several others. Here we present the first transcriptomic study focused on the effect of P. relictum on the immune system of its vector (the mosquito Culex quinquefasciatus) at different times post-infection. We show that over 50% of immune genes identified as being part of the Toll pathway and 30%-40% of the immune genes identified within the Imd pathway are overexpressed during the critical period spanning the parasite's oocyst and sporozoite formation (8-12 days), revealing the crucial role played by both these pathways in this natural mosquito-Plasmodium combination. Comparison of infected mosquitoes with their uninfected counterparts also revealed some unexpected immune RNA expression patterns earlier and later in the infection: significant differences in expression of several immune effectors were observed as early as 30 min after ingestion of the infected blood meal. In addition, in the later stages of the infection (towards the end of the mosquito lifespan), we observed an unexpected increase in immune investment in uninfected, but not in infected, mosquitoes. In conclusion, our work extends the comparative transcriptomic analyses of malaria-infected mosquitoes beyond human and rodent parasites and provides insights into the degree of conservation of immune pathways and into the selective pressures exerted by Plasmodium parasites on their vectors.

Manipulation of pantothenate kinase in Anopheles stephensi suppresses pantothenate levels with minimal impacts on mosquito fitness

Pantothenate (Pan) is an essential nutrient required by both the mosquito vector and malaria parasite. We previously demonstrated that increasing pantothenate kinase (PanK) activity and co-enzyme A (CoA) biosynthesis led to significantly decreased parasite infection prevalence and intensity in the malaria mosquito Anopheles stephensi. In this study, we demonstrate that Pan stores in A. stephensi are a limited resource and that manipulation of PanK levels or activity, via small molecule modulators of PanK or transgenic mosquitoes, leads to the conversion of Pan to CoA and an overall reduction in Pan levels with minimal to no effects on mosquito fitness. Transgenic A. stephensi lines with repressed insulin signaling due to PTEN overexpression or repressed c-Jun N-terminal kinase (JNK) signaling due to MAPK phosphatase 4 (MKP4) overexpression exhibited enhanced PanK levels and significant reductions in Pan relative to non-transgenic controls, with the PTEN line also exhibiting significantly increased CoA levels. Provisioning of the PTEN line with the small molecule PanK modulator PZ-2891 increased CoA levels while provisioning Compound 7 decreased CoA levels, affirming chemical manipulation of mosquito PanK. We assessed effects of these small molecules on A. stephensi lifespan, reproduction and metabolism under optimized laboratory conditions. PZ-2891 and Compound 7 had no impact on A. stephensi survival when delivered via bloodmeal throughout mosquito lifespan. Further, PZ-2891 provisioning had no impact on egg production over the first two reproductive cycles. Finally, PanK manipulation with small molecules was associated with minimal impacts on nutritional stores in A. stephensi mosquitoes under optimized rearing conditions. Together with our previous data demonstrating that PanK activation was associated with significantly increased A. stephensi resistance to Plasmodium falciparum infection, the studies herein demonstrate a lack of fitness costs of mosquito Pan depletion as a basis for a feasible, novel strategy to control parasite infection of anopheline mosquitoes.

Assessment of Plasmodium falciparum Infection and Fitness of Genetically Modified Anopheles gambiae Aimed at Mosquito Population Replacement

Genetically modified (GM) mosquitoes expressing anti-plasmodial effectors propagating through wild mosquito populations by means of gene drive is a promising tool to support current malaria control strategies. The process of generating GM mosquitoes involves genetic transformation of mosquitoes from a laboratory colony and, often, interbreeding with other GM lines to cross in auxiliary traits. These mosquito colonies and GM lines thus often have different genetic backgrounds and GM lines are invariably highly inbred, which in conjunction with their independent rearing in the laboratory may translate to differences in their susceptibility to malaria parasite infection and life history traits. Here, we show that laboratory Anopheles gambiae colonies and GM lines expressing Cas9 and Cre recombinase vary greatly in their susceptibility to Plasmodium falciparum NF54 infection. Therefore, the choice of mosquitoes to be used as a reference when conducting infection or life history trait assays requires careful consideration. To address these issues, we established an experimental pipeline involving genetic crosses and genotyping of mosquitoes reared in shared containers throughout their lifecycle. We used this protocol to examine whether GM lines expressing the antimicrobial peptide (AMP) Scorpine in the mosquito midgut interfere with parasite infection and mosquito survival. We demonstrate that Scorpine expression in the Peritrophin 1 (Aper1) genomic locus reduces both P. falciparum sporozoite prevalence and mosquito lifespan; both these phenotypes are likely to be associated with the disturbance of the midgut microbiota homeostasis. These data lead us to conclude that the Aper1-Sco GM line could be used in proof-of-concept experiments aimed at mosquito population replacement, although the impact of its reduced fitness on the spread of the transgene through wild populations requires further investigation.

Modeling and analysis of the transmission dynamics of mosquito-borne disease with environmental temperature fluctuation

Most of the vector-borne diseases show a clear dependence on seasonal variation, including climate change. In this paper, we proposed a nonautonomous mathematical model consisting of a periodic system of nonlinear differential equations. In the proposed model, the realistic functional forms for the different temperature-dependent parameters are considered. The autonomous system of the proposed model is also analyzed. The nontrivial solution of the autonomous model is locally asymptotically stable if [Formula: see text]. It is shown that a unique endemic equilibrium point of the autonomous model exists when [Formula: see text] and proved that endemic solution is linearly stable when [Formula: see text]. The nonautonomous model is shown to have a nontrivial disease-free periodic state, which is globally asymptotically stable whenever temperature-dependent reproduction number is less than unity. It is observed that a unique positive endemic periodic solution of the nonautonomous system exists only when a temperature-dependent reproduction number greater than unity, which makes for the persistence of the disease. Numerical simulation has been carried out to support the analytical results and shows the effects of temperature variability in the life span of mosquitoes as well as the persistence of the disease.

Pyriproxyfen-treated bed nets reduce reproductive fitness and longevity of pyrethroid-resistant Anopheles gambiae under laboratory and field conditions

BackgroundThe efficacy of insecticide-treated nets (ITNs) containing the insect growth regulator pyriproxyfen (PPF) and pyrethroid insecticides (PPF-ITNs) is being assessed in clinical trials to determine whether they provide greater protection from malaria than standard pyrethroid-treated ITNs in areas where mosquitoes are resistant to pyrethroids. Understanding the entomological mode of action of this new ITN class will aide interpretation of the results from these trials.MethodsAnopheles gambiae sensu lato (s.l.) mosquitoes from a susceptible laboratory strain were exposed to PPF-treated netting 24 h, 6 h, and immediately prior to, or 24 h post blood feeding, and the impact on fecundity, fertility and longevity recorded. Pyrethroid-resistant populations were exposed to nets containing permethrin and PPF (PPF-ITNs) in cone bioassays and daily mortality recorded. Mosquitoes were also collected from inside houses pre- and post-distribution of PPF-ITNs in a clinical trial conduced in Burkina Faso; female An. gambiae s.l. were then assessed for fecundity and fertility.ResultsPPF exposure reduced the median adult lifespan of insecticide-susceptible mosquitoes by 4 to 5 days in all exposure times (p < 0.05) other than 6 h pre-blood meal and resulted in almost complete lifelong sterilization. The longevity of pyrethroid-resistant mosquitoes was also reduced by at least 5 days after exposure to PPF-ITNs compared to untreated nets, but was unaffected by exposure to standard pyrethroid only ITNs. A total of 386 blood-fed or gravid An. gambiae s.l. females were collected from five villages between 1 and 12 months before distribution of PPF-ITNs. Of these mosquitoes, 75% laid eggs and the remaining 25% appeared to have normal ovaries upon dissection. In contrast, only 8.6% of the 631 blood-fed or gravid An. gambiae s.l. collected post PPF-ITN distribution successfully oviposited; 276 (43.7%) did not oviposit but had apparently normal ovaries upon dissection, and 301 (47.7%) did not oviposit and had abnormal eggs upon dissection. Egg numbers were also significantly lower (average of 138/female prior distribution vs 85 post distribution, p < 0.05).ConclusionExposure to a mixture of PPF and pyrethroids on netting shortens the lifespan of mosquitoes and reduces reproductive output. Sterilization of vectors lasted at least one year under operational conditions. These findings suggest a longer effective lifespan of PPF-pyrethroid nets than reported previously.

Specific phytochemicals in floral nectar up-regulate genes involved in longevity regulation and xenobiotic metabolism, extending mosquito life span.

During nectar feeding, mosquitoes ingest a plethora of phytochemicals present in nectar. The ecological and physiological impacts of these ingested phytochemicals on the disease vectors are poorly understood. In this study, we evaluated the effects of three nectar phytochemicals‐‐ caffeine, p‐coumaric acid, and quercetin‐‐on longevity, fecundity, and sugar‐feeding behavior of the Asian tiger mosquito (Aedes albopictus). Adult females of Ae. albopictus were provided continuous access to 10% sucrose supplemented with one of the three phytochemicals and their fecundity, longevity, and the amount of sucrose consumed determined. Transcriptome response of Ae. albopictus females to p‐coumaric acid and quercetin was also evaluated. Dietary quercetin and p‐coumaric acid enhanced the longevity of female Ae. albopictus, while caffeine resulted in reduced sugar consumption and enhanced fecundity of gravid females. RNA‐seq analyses identified 237 genes that were differentially expressed (DE) in mosquitoes consuming p‐coumaric acid or quercetin relative to mosquitoes consuming an unamended sucrose solution diet. Among the DE genes, several encoding antioxidant enzymes, cytochrome P450s, and heat shock proteins were upregulated, whereas histones were downregulated. Overall, our findings show that consuming certain nectar phytochemicals can enhance adult longevity of female Asian tiger mosquitoes, apparently by differentially regulating the expression level of genes involved in longevity and xenobiotic metabolism; this has potential impacts not only on life span but also on vectorial capacity and insecticide resistance.

A non-destructive sugar-feeding assay for parasite detection and estimating the extrinsic incubation period of Plasmodium falciparum in individual mosquito vectors

Despite its epidemiological importance, the time Plasmodium parasites take to achieve development in the vector mosquito (the extrinsic incubation period, EIP) remains poorly characterized. A novel non-destructive assay designed to estimate EIP in single mosquitoes, and more broadly to study Plasmodium–Anopheles vectors interactions, is presented. The assay uses small pieces of cotton wool soaked in sugar solution to collect malaria sporozoites from individual mosquitoes during sugar feeding to monitor infection status over time. This technique has been tested across four natural malaria mosquito species of Africa and Asia, infected with Plasmodium falciparum (six field isolates from gametocyte-infected patients in Burkina Faso and the NF54 strain) and across a range of temperatures relevant to malaria transmission in field conditions. Monitoring individual infectious mosquitoes was feasible. The estimated median EIP of P. falciparum at 27 °C was 11 to 14 days depending on mosquito species and parasite isolate. Long-term individual tracking revealed that sporozoites transfer onto cotton wool can occur at least until day 40 post-infection. Short individual EIP were associated with short mosquito lifespan. Correlations between mosquito/parasite traits often reveal trade-offs and constraints and have important implications for understanding the evolution of parasite transmission strategies.

Linking mosquito surveillance to dengue fever through Bayesian mechanistic modeling.

Our ability to effectively prevent the transmission of the dengue virus through targeted control of its vector, Aedes aegypti, depends critically on our understanding of the link between mosquito abundance and human disease risk. Mosquito and clinical surveillance data are widely collected, but linking them requires a modeling framework that accounts for the complex non-linear mechanisms involved in transmission. Most critical are the bottleneck in transmission imposed by mosquito lifespan relative to the virus’ extrinsic incubation period, and the dynamics of human immunity. We developed a differential equation model of dengue transmission and embedded it in a Bayesian hierarchical framework that allowed us to estimate latent time series of mosquito demographic rates from mosquito trap counts and dengue case reports from the city of Vitória, Brazil. We used the fitted model to explore how the timing of a pulse of adult mosquito control influences its effect on the human disease burden in the following year. We found that control was generally more effective when implemented in periods of relatively low mosquito mortality (when mosquito abundance was also generally low). In particular, control implemented in early September (week 34 of the year) produced the largest reduction in predicted human case reports over the following year. This highlights the potential long-term utility of broad, off-peak-season mosquito control in addition to existing, locally targeted within-season efforts. Further, uncertainty in the effectiveness of control interventions was driven largely by posterior variation in the average mosquito mortality rate (closely tied to total mosquito abundance) with lower mosquito mortality generating systems more vulnerable to control. Broadly, these correlations suggest that mosquito control is most effective in situations in which transmission is already limited by mosquito abundance.

Infection\xa0of highly insecticide-resistant malaria vector Anopheles coluzzii with entomopathogenic bacteria Chromobacterium violaceum reduces its survival, blood feeding propensity and fecundity

BackgroundThis is now a concern that malaria eradication will not be achieved without the introduction of novel control tools. Microbiological control might be able to make a greater contribution to vector control in the future. The interactions between bacteria and mosquito make mosquito microbiota really promising from a disease control perspective. Here, the impact of Chromobacterium violaceum infections, isolated from both larvae and adult of wild-caught Anopheles gambiae sensu lato mosquitoes in Burkina Faso, was evaluated on mosquito survival, blood feeding and fecundity.MethodsTo assess entomopathogenic effects of C. violaceum infection on mosquitoes, three different types of bioassays were performed in laboratory. These bioassays aimed to evaluate the impact of C. violaceum infection on mosquito survival, blood feeding and fecundity, respectively. During bioassays mosquitoes were infected through the well-established system of cotton ball soaked with 6% glucose containing C. violaceum.ResultsChromobacterium violaceum kills pyrethroid resistant Anopheles coluzzii (LT80 of 8.78 days ± 0.18 at 108 bacteria cell/ml of sugar meal). Interestingly, this bacterium had other negative effects on mosquito lifespan by significantly reducing (~ 59%, P < 0.001) the mosquito feeding willingness from day 4-post infection (~ 81% would seek a host to blood feed) to 9- day post infection (22 ± 4.62% would seek a host to blood feed). Moreover, C. violaceum considerably jeopardized the egg laying (~ 16 eggs laid/mosquito with C. violaceum infected mosquitoes vs ~ 129 eggs laid/mosquito with control mosquitoes) and hatching of mosquitoes (a reduction of ~ 22% of hatching rate with C. violaceum infected mosquitoes). Compared to the bacterial uninfected mosquitoes, mosquitoes infected with C. violaceum showed significantly higher retention rates of immature eggs and follicles.ConclusionThese data showed important properties of Burkina Faso C. violaceum strains, which are highly virulent against insecticide-resistant An. coluzzii, and reduce both mosquito blood feeding and fecundity propensities. However, additional studies as the sequencing of C. violaceum genome and the potential toxins secreted will provide useful information render it a potential candidate for the biological control strategies of malaria and other disease vectors.

Dengue Vector Control: A Review for Wolbachia-Based Strategies

Mosquito-borne diseases continue to pose a major health problem globally and have had a significant impact on human life and economy. Consequently, many countries have implemented national vector control programs in an effort to suppress/eradicate mosquitos contributing to spread of diseases including Malaria, Dengue, Yellow fever, Rift valley fever, West Nile fever, Zika, Chikungunya etc. Of these endemic diseases, Dengue fever is an arbovirus and transmitted primarily by Aedes aegypti mosquito that has become a rapidly emerging infection, especially in the tropical countries. Insecticides spraying remains the main method to control the transmition of dengue virus. However, the overuse and misuse of insecticides can result in negative consequences such as the development of insecticides resistance. This, in part, has led to the development of a more eco-friendly measures to suppress mosquitoes e.g. gene-drive based controls and Wolbachia-based approaches. The latter approach has the ability to block the dengue virus transmission by inhibiting virus intracellular replication in mosquito. In addition, Wolbachia decreases adult mosquito lifespan and can be naturally passed from one generation to the next. In recent years, Aedes aegypti mosquitos infected with Wolbachia released and tested in the field in several countries and have achieved very promising results. In this review, we focus and discuss the emerging Wolbachia-based biocontrol approaches that are already being deployed, evaluated and tested in the field.

Laboratory testing of low concentration (

IntroductionLarvicide application in ovitrap is one of the currently available methods used in mosquito eradication campaign. We previously reported that copper in liquid form is a promising candidate due to its potent larvicide properties in a laboratory setting and in the field. In the field study, several larvae survived in outdoor ovitrap due to the dilution of copper concentration by rainwater. The surviving larvae were smaller and less motile. This led our interest to study the effect of a sub-lethal dose of copper in ovitrap on mosquito larval development, pupation time and lifespan in the adult stage.MethodsFirst instar larvae of Aedes albopictus, Anopheles stephensi, and Culex pipiens were put in water containing 0.15 ppm, 0.30 ppm, and 0.60 ppm of copper. The surviving larvae, the emerging pupae, and adult mosquitoes were observed and counted every 24-hour and statistically analyzed by t-test or Mann-Whitney U test. Inter-species difference in response to different concentration of copper were also analyzed.ResultsCopper showed a potent larvicide effect at 0.60 ppm concentration. Prolonged pupation time and a lower number of adult mosquitoes were observed at 0.15 ppm concentration. Copper exposure did not affect adult mosquitoes’ lifespan. Culex pipiens was the most susceptible species to copper exposure.ConclusionThis study demonstrates the efficacy of copper at <1 ppm to kill mosquito larvae and to prolong pupation and adult emergence time. Utilization of copper at a low concentration is cost-efficient in the public health setting and remains an open option as an environmentally safe vector control strategy.

Cytochrome P450 metabolic resistance (CYP6P9a) to pyrethroids imposes a fitness cost in the major African malaria vector Anopheles funestus

Metabolic resistance threatens the sustainability of pyrethroid-based malaria control interventions. Elucidating the fitness cost and potential reversal of metabolic resistance is crucial to design suitable resistance management strategies. Here, we deciphered the fitness cost associated with the CYP6P9a (P450-mediated metabolic resistance) in the major African malaria vector Anopheles funestus. Reciprocal crosses were performed between a pyrethroid susceptible (FANG) and resistant (FUMOZ-R) laboratory strains and the hybrid strains showed intermediate resistance. Genotyping the CYP6P9a-R resistance allele in oviposited females revealed that CYP6P9a negatively impacts the fecundity as homozygote susceptible mosquitoes (CYP6P9a-SS) lay more eggs than heterozygote (OR = 2.04: P = 0.01) and homozygote resistant mosquitoes. CYP6P9a also imposes a significant fitness cost on the larval development as homozygote resistant larvae (CYP6P9a-RR) developed significantly slower than heterozygote and homozygote susceptible mosquitoes (χ2 = 11.2; P = 0.0008). This fitness cost was further supported by the late pupation of homozygote resistant than susceptible mosquitoes (OR = 2.50; P < 0.01). However, CYP6P9a does not impact the longevity as no difference was observed in the life span of mosquitoes with different genotypes (χ2 = 1.6; P = 0.9). In this hybrid strain, a significant decrease of the resistant CYP6P9a-RR genotype was observed after ten generations (χ2 = 6.6; P = 0.01) suggesting a reversal of P450-based resistance in the absence of selection. This study shows that the P450-mediated metabolic resistance imposes a high fitness cost in malaria vectors supporting that a resistance management strategy based on rotation could help mitigate the impact of such resistance.

Consequences of larval competition and exposure to permethrin for the development of the rodent malaria Plasmodium berghei in the mosquito Anopheles gambiae

BackgroundMosquitoes and other vectors are often exposed to sublethal doses of insecticides. Larvae can be exposed to the run-off of agricultural use, and adults can be irritated by insecticides used against them and move away before they have picked up a lethal dose. This sublethal exposure may affect the success of control of insect-borne diseases, for it may affect the competence of insects to transmit parasites, in particular if the insects are undernourished.MethodsWe assessed how exposure of larvae and adults to a sublethal dose of permethrin (a pyrethroid) and how larval competition for food affect several aspects of the vector competence of the mosquito Anopheles gambiae for the malaria parasite Plasmodium berghei. We infected mosquitoes with P. berghei and measured the longevity and the prevalence and intensity of infection to test for an effect of our treatments.ResultsOur general result was that the exposure to the insecticide helped mosquitoes deal with infection by malaria. Exposure of either larvae or adults decreased the likelihood that mosquitoes were infected by about 20%, but did not effect the parasite load. Exposure also increased the lifespan of infected mosquitoes, but only if they had been reared in competition. Larval competition had no effect on the prevalence of infection, but increased parasite load. These effects may be a consequence of the machinery governing oxidative stress, which underlies the responses of mosquitoes to insecticides, to food stress and to parasites.ConclusionsWe conclude that insecticide residues are likely to affect the ability of mosquitoes to carry and transmit pathogens such as malaria, irrespective of the stage at which they are exposed to the insecticide. Our results stress the need for further studies to consider sublethal doses in the context of vector ecology and vector-borne disease epidemiology.