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The study evaluates the resistance and susceptibility of adult female Anopheles gambiae s. l., Aedes aegypti and Culex quinquefasciatus mosquitoes sourced within Osogbo metropolis, Osun State, Nigeria to four groups of insecticides [Permethrin, Deltamethrin, Pirimiphos-methyl and DDT (Dichlorodiphenyltrichloroethane)] and the distribution of their larval habitat within the metropolis. Mosquito larvae of the three genera were collected during the wet season and reared to adult stage in the laboratory. Emerged adult female mosquitoes were exposed to insecticide impregnated papers of the four insecticide groups for 60mins using WHO kits to determine the knock down rate (kdr). Thereafter, they were transferred into holding tubes and left for 24hrs to assess their resistance and susceptibility according to the WHO protocol. Four types of larval habitats were identified (tires, ground pools, gutters and plastic containers). Anopheles gambiae s. l. showed the highest resistance to Permethrin (49%) (p = 0.04, p<0.05) while the highest susceptibility was recorded with Pirimiphos-methyl (69%) with the lowest against Permethrin (16%) (P = 0.002; p<0.05). The highest resistance of A. aegypti was against OC-Control (45%) (p = 0.031; p<0.05). Permethrin had the highest susceptibility (60%) against A. aegypti while OC-control had the lowest (11%) (p = 0.005; p< 0.05). Culex quinquefasciatus had a lower resistance to OC-control (38%) as compared with Aedes aegypti (45%). However, it was least susceptible to Pirimiphos-methyl (52%) and DDT (17%) respectively (p = 0.013; p<0.05). The susceptibility of A. gambiae s. l. and C. quinquefasciatus to Pirimiphos-methyl and A. aegypti to Permethrin is an indication of the possibility of success if employed for vector control of A. gambiae s. l., C. quinquefasciatus and A. aegypti respectively. This could be through their inclusion as active ingredients in insecticide treated nets (ITNs) and indoor residual spray (IRS) with a view to abating malaria and other life-threatening mosquito-borne diseases constituting global public health scourge. [ABSTRACT FROM AUTHOR]

Harris County, TX, is the third most populous county in the USA and upon detection of arboviruses Harris County Public Health applies insecticides (e.g., pyrethroid-based Permanone 31–66) against adults of Culex quinquefasciatus to prevent disease transmission. Populations of Aedes aegypti, while not yet a target of public health control, are likely affected by pyrethroid exposure. As this species is a vector of emerging arboviruses, its resistance status to Permanone and the kdr mutations in the voltage-gated sodium channel (VGSC) associated with pyrethroid resistance were investigated. We examined females of known genotype at the V1016I and F1534C sites (N = 716) for their genotype at the 410 amino acid position in the VGSC, and for the influence of their kdr genotype on survival to Permanone at three different distances from the insecticide source in field tests. Most females (81.8%) had at least one resistant L allele at the 410 position, being the first report of the V410L mutation in Ae. aegypti for Texas. When only genotypes at the 410 position were analyzed, the LL genotype exhibited higher survivorship than VL or VV. Out of 27 possible tri-locus kdr genotypes only 23 were found. Analyses of the probability of survival of tri-locus genotypes and for the V410L genotype using a multivariate logistic regression model including area, distance, and genotype found significant interactions between distance and genotype. When only the most common tri-locus genotypes were analyzed (LL/II/CC, 48.2%; VL/II/CC, 19.1%; and VV/II/CC, 10.1%) genotype had no effect on survival, but significant interactions of distance and genotype were found. This indicated that the V410L kdr allele increased survival probability at certain distances. Genotypes did not differ in survivorship at 7.62-m, but LL/II/CC had higher survivorship than VL/II/CC at 15.24- and 22.86-m. The model also identified differences in survivorship among the operational areas investigated. Author summary: Preventing Aedes aegypti populations from spreading arboviruses in highly populated areas primarily relies upon chemical control with insecticides, such as pyrethroids, applied by public health agencies to target the female mosquito vector. However, the development of insecticide resistance in mosquito populations jeopardizes these vector control strategies. The impact of the different kdr mutations conferring resistance to pyrethroids on the survival of Ae. aegypti in the field is not fully understood. We previously found that two knockdown resistance (kdr) mutations in the voltage gated sodium channel (VGSC) did not increase survivorship in field cage tests despite their widespread presence and high frequency. In this paper, we report the first detection of the V410L kdr mutation in combination with the V1016I and F1534C genotypes. Most females were detected with kdr mutations at one, two or three of these sites in the VGSC. Genotyping females after insecticide application in field cage tests showed that the V410L mutations were associated with higher survivorship only at the 15.24- and 22.86-meter distances from the source of the spray application, as we observed that the LL/II/CC genotype had higher survivorship than the VL/II/CC genotype at these distances. [ABSTRACT FROM AUTHOR]

Zika (ZIKV) and chikungunya (CHIKV) are arboviruses that cause infections in humans and can cause clinical complications, representing a worldwide public health problem. Aedes aegypti is the primary vector of these pathogens and Culex quinquefasciatus may be a potential ZIKV vector. This study aimed to evaluate fecundity, fertility, survival, longevity, and blood feeding activity in Ae. aegypti after exposure to ZIKV and CHIKV and, in Cx. quinquefasciatus exposed to ZIKV. Three colonies were evaluated: AeCamp (Ae. aegypti—field), RecL (Ae. aegypti—laboratory) and CqSLab (Cx. quinquefasciatus—laboratory). Seven to 10 days-old females from these colonies were exposed to artificial blood feeding with CHIKV or ZIKV. CHIKV caused reduction in fecundity and fertility in AeCamp and reduction in survival and fertility in RecL. ZIKV impacted survival in RecL, fertility in AeCamp and, fecundity and fertility in CqSLab. Both viruses had no effect on blood feeding activity. These results show that CHIKV produces a higher biological cost in Ae. aegypti, compared to ZIKV, and ZIKV differently alters the biological performance in colonies of Ae. aegypti and Cx. quinquefasciatus. These results provide a better understanding over the processes of virus-vector interaction and can shed light on the complexity of arbovirus transmission. [ABSTRACT FROM AUTHOR]

Mosquitoes of the genera Aedes, Anopheles and Culex vector a wide range of pathogens seriously affecting humans and livestock on a global scale. Over-reliance on insecticides and repellents has driven research into alternative, naturally-derived compounds to fulfil the same objectives. Steam distilled extracts of four plants with strong, yet attractive, volatile profiles were initially assessed for repellency in a dual-port olfactometer using Aedes aegypti as the model species. Picea sitchensis was found to be the most repellent, proving comparable to leading products when applied at 100% (p = 1.000). Key components of conifer-derived volatile profiles were then screened via electroantennography before those components eliciting an electrophysiological response were assayed individually in the olfactometer; according to WHO protocol. The most promising 5 were selected for reductive analyses to produce an optimised semiochemical blend. This combination, and a further two variations of the blend, were then progressed to a multi-species analysis using the BG-test whereby bite-attempt frequency on hands was assessed under different repellent treatments; assays were compared between Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus. Efficacy was found against all three species, although it was found that Ae. aegypti was the most susceptible to the repellent, with An. gambiae being the least. Here, a novel, naturally-derived blend is presented with weak spatial repellency, as confirmed in laboratory assays. Further work will be required to assess the full extent of the potential of the products, both in terms of field application and species screening; however, the success of the products developed demonstrate that plant metabolites have great capacity for use in the repellent sector; both to improve upon known compounds and to reduce the usage of toxic products currently on the market. [ABSTRACT FROM AUTHOR]

Background: After the unprecedented Zika virus (ZIKV) outbreak in the western hemisphere from 2015–2018, Aedes aegypti and Ae. albopictus are now well established primary and secondary ZIKV vectors, respectively. Consensus about identification and importance of other secondary ZIKV vectors remain. This systematic review aims to provide a list of vector species capable of transmitting ZIKV by reviewing evidence from laboratory vector competence (VC) studies and to identify key knowledge gaps and issues within the ZIKV VC literature. Methods: A search was performed until 15th March 2022 on the Cochrane Library, Lilacs, PubMed, Web of Science, WHOLIS and Google Scholar. The search strings included three general categories: [1] "ZIKA"; [2] "vector"; [3] "competence", "transmission", "isolation", or "feeding behavior" and their combinations. Inclusion and exclusion criteria has been predefined and quality of included articles was assessed by STROBE and STROME-ID criteria. Findings: From 8,986 articles retrieved, 2,349 non-duplicates were screened by title and abstracts,103 evaluated using the full text, and 45 included in this analysis. Main findings are 1) secondary vectors of interest include Ae. japonicus, Ae. detritus, and Ae. vexans at higher temperature 2) Culex quinquefasciatus was not found to be a competent vector of ZIKV, 3) considerable heterogeneity in VC, depending on the local mosquito strain and virus used in testing was observed. Critical issues or gaps identified included 1) inconsistent definitions of VC parameters across the literature; 2) equivalency of using different mosquito body parts to evaluate VC parameters for infection (mosquito bodies versus midguts), dissemination (heads, legs or wings versus salivary glands), and transmission (detection or virus amplification in saliva, FTA cards, transmission to neonatal mice); 3) articles that fail to use infectious virus assays to confirm the presence of live virus; 4) need for more studies using murine models with immunocompromised mice to infect mosquitoes. Conclusion: Recent, large collaborative multi-country projects to conduct large scale evaluations of specific mosquito species represent the most appropriate approach to establish VC of mosquito species. Author summary: The mosquitoes Aedes aegypti and Ae. albopictus are known to transmit Zika virus (ZIKV) but it is important to identify other potential secondary vectors. We conducted a systematic review of the literature to answer this question. We searched four databases (PubMed, Lilacs, Cochrane Library Web of Science), WHOLIS and Google Scholar using different combinations of Zika, Aedes, Culex, vector, or competence in the title/abstract, up to March 2022. Most of the studies reviewed were of high quality methodologically, but the methods were different making it hard to compare them. There is a need for standardization to better interpret these studies and make appropriate recommendations. Secondary vectors of ZIKV with evidence of low transmission rates comparable to primary vectors are Ae. japonicus, Ae. detritus and Ae. vexans at higher temperatures. Culex quinquefasciatus was not found to be a competent vector of ZIKV. Future research should focus on well-defined and established experimental approaches (midguts/bodies for infection, legs+wings/heads for dissemination and the use of murine models/other artificial feeding systems). Importantly, development large collaborative multi-country projects to conduct large scale evaluations of specific mosquito species with common protocols to appropriately address the inherent geographic variation in both mosquito and ZIKV strains are needed. [ABSTRACT FROM AUTHOR]

Background: Endogenous circadian rhythms result from genetically-encoded molecular clocks, whose components and downstream output factors cooperate to generate cyclic changes in activity. Mating is an important activity of mosquitoes, however, the key aspects of mating rhythm patterns and their regulatory mechanisms in two vector mosquito species, Aedes albopictus and Culex quinquefasciatus, remain unclear. Methodology/Principal findings: We determined and compared the diel mating activity rhythms of these two mosquito species and discovered that Ae. albopictus had mating peaks in the light/dark transition periods (ZT0-3 and ZT9-12), while Cx. quinquefasciatus only had a mating peak at ZT12-15. Knockouts of the clock (clk) orthologous genes (Aalclk and Cxqclk) resulted in phase delay or phase reversal of the mating peaks in Ae. albopictus and Cx. quinquefasciatus, respectively. In addition, the temporal expression pattern of the desaturase orthologous genes, desat1, in both mosquito species was also different in respective wild-type strains and showed phase changes similar to the mating rhythms in clk mutant strains. Inhibition of desat1 expression resulted in decreased mating activity in male mosquitoes of both species but not females. In addition, desat1 regulated cuticular hydrocarbons' synthesis in both species. Silencing desat1 in male Ae. albopictus resulted in decreases of nonadecane and tricosane, which promoted mating, with concomitant increases of heptacosane, which inhibited mating. Silencing desat1 in male Cx. quinquefasciatus also resulted in decreases of tricosane, which promoted mating. Conclusions/Significance: These results suggest that Aalclk and Cxqclk have significant roles in the mating activity rhythms in both Ae. albopictus and Cx. quinquefasciatus by regulating the temporal expression of the desat1 gene under LD cycles, which affects sex pheromone synthesis and mating. This work provides insights into the molecular regulatory mechanism of distinct mating rhythm of Ae. albopictus and Cx. quinquefasciatus and may provide a basis for the control of these two important vector mosquitoes. Author summary: Aedes albopictus and Culex quinquefasciatus are globally-distributed and important vector mosquito species that transmit a variety of pathogens. The two mosquito species have different circadian patterns, with Ae. albopictus being diurnal and Cx. quinquefasciatus being nocturnal. Mating is an important activity of mosquitoes, however, the mating rhythms and their regulatory mechanisms in Ae. albopictus and Cx. quinquefasciatus have yet to be described. Here, we compared the diel mating activities of these two mosquito species and discovered that Ae. albopictus and Cx. quinquefasciatus have distinct mating rhythms, which can be entrained by daily LD cycles. CRISPR/Cas9 technologies were used to knock out the core clock gene clock (clk) in the two mosquito species and found that Aalclk and Cxqclk have significant roles in the mating activity rhythms in both Ae. albopictus and Cx. quinquefasciatus by regulating the temporal expression of the desaturase desat1 gene, which can affect sex pheromone synthesis and mating. These findings establish the basis for an in-depth understanding of the mating rhythms for mosquito vectors, which may provide insights in the development of novel and precise mosquito control. [ABSTRACT FROM AUTHOR]

Mosquitoes are important vectors that transmit pathogens to human and other vertebrates. Each mosquito species has specific ecological requirements and bionomic traits that impact human exposure to mosquito bites, and hence disease transmission and vector control. A study of human biting mosquitoes and their bionomic characteristics was conducted in West Sumba and Southwest Sumba Districts, Nusa Tenggara Timur Province, Indonesia from May 2015 to April 2018. Biweekly human landing catches (HLC) of night biting mosquitoes both indoors and outdoors caught a total of 73,507 mosquito specimens (59.7% non-Anopheles, 40.3% Anopheles). A minimum of 22 Culicinae species belonging to four genera (Aedes, Armigeres, Culex, Mansonia), and 13 Anophelinae species were identified. Culex quinquefasciatus was the dominant Culicinae species, Anopheles aconitus was the principal Anopheles species inland, while An. sundaicus was dominant closer to the coast. The overall human biting rate (HBR) was 10.548 bites per person per night (bpn) indoors and 10.551 bpn outdoors. Mosquitoes biting rates were slightly higher indoors for all genera with the exception of Anopheles, where biting rates were slightly higher outdoors. Diurnal and crepuscular Aedes and Armigeres demonstrated declining biting rates throughout the night while Culex and Anopheles biting rates peaked before midnight and then declined. Both anopheline and non-anopheline populations did not have a significant association with temperature (p = 0.3 and 0.88 respectively), or rainfall (p = 0.13 and 0.57 respectively). The point distribution of HBR and seasonal variables did not have a linear correlation. Data demonstrated similar mosquito–human interactions occurring outdoors and indoors and during early parts of the night implying both indoor and outdoor disease transmission potential in the area–pointing to the need for interventions in both spaces. Integrated vector analysis frameworks may enable better surveillance, monitoring and evaluation strategies for multiple diseases. Author summary: This study outlines the array of mosquitoes that bite humans at night on the island of Sumba, Indonesia, with data on behavioural traits that impact when and where disease transmission may occur. Biweekly human landing catches (HLCs) were performed in four selected houses in 12 clusters (villages) from sunset to sunrise over a three years period (May 2015 to April 2018). The collection and analysis of 73,507 mosquito specimens revealed the presence of various species of Anopheles, Aedes, Culex, Armigeres and Mansonia, that potentially transmit several diseases including malaria, filaria, dengue and other mosquito borne viral diseases. Even though these data represent only night-time collections, this represents a comprehensive geographic description and inventory of species, bionomics and temporal distribution of mosquitoes on the island of Sumba. Data demonstrate that the high diversity of species with associated diversity in behaviours results in mosquito-human contact occurring throughout the night and both indoors and outdoors–relevant to both disease transmission and intervention applicability. Vector specific behaviours are specifically relevant to intervention strategies for specific diseases. The use of molecular methods to determine and validate morphological identification of specimens resulted in the characterization of multiple novel sequences–indicating the presence of undescribed species, members of cryptic species complexes or species without molecular data. Species identification using molecular methods are essential towards determine vector species compositions–especially in areas where data is absent. Though the correlation between temperature, rainfall and HBR was not statistically significant, the presence of mosquito populations throughout the year allow for perennial transmission of mosquito-borne diseases. Overall, these findings represent baseline and novel data for Sumba and may be utilized to develop disease and vector-specific or integrated strategies that mitigate the transmission of mosquito borne diseases in Indonesia. [ABSTRACT FROM AUTHOR]