Chemical Ecology and Management of Dengue Vectors.

Dengue, caused by the dengue virus, is the most widespread arboviral infectious disease of public health significance globally. This review explores the communicative function of olfactory cues that mediate host-seeking, egg-laying, plant-feeding, and mating behaviors in Aedes aegypti and Aedes albopictus, two mosquito vectors that drive dengue virus transmission. Aedes aegypti has adapted to live in close association with humans, preferentially feeding on them and laying eggs in human-fabricated water containers and natural habitats. In contrast, Ae. albopictus is considered opportunistic in its feeding habits and tends to inhabit more vegetative areas. Additionally, the ability of both mosquito species to locate suitable host plants for sugars and find mates for reproduction contributes to their survival. Advances in chemical ecology, functional genomics, and behavioral analyses have improved our understanding of the underlying neural mechanisms and reveal novel and specific olfactory semiochemicals that these species use to locate and discriminate among resources in their environment. Physiological status; learning; and host- and habitat-associated factors, including microbial infection and abundance, shape olfactory responses of these vectors. Some of these semiochemicals can be integrated into the toolbox for dengue surveillance and control.

A high heterozygosity genome assembly of Aedes albopictus enables the discovery of the association of PGANT3 with blood-feeding behavior.

The Asian tiger mosquito, Aedes albopictus, is a global invasive species, notorious for its role in transmitting dangerous human arboviruses such as dengue and Chikungunya. Although hematophagous behavior is repulsive, it is an effective strategy for mosquitoes like Aedes albopictus to transmit viruses, posing a significant risk to human health. However, the fragmented nature of the Ae. albopictus genome assembly has been a significant challenge, hindering in-depth biological and genetic studies of this mosquito. In this research, we have harnessed a variety of technologies and implemented a novel strategy to create a significantly improved genome assembly for Ae. albopictus, designated as AealbF3. This assembly boasts a completeness rate of up to 98.1%, and the duplication rate has been minimized to 1.2%. Furthermore, the fragmented contigs or scaffolds of AealbF3 have been organized into three distinct chromosomes, an arrangement corroborated through syntenic plot analysis, which compared the genetic structure of Ae. albopictus with that of Ae. aegypti. Additionally, the study has revealed a phylogenetic relationship suggesting that the PGANT3 gene is implicated in the hematophagous behavior of Ae. albopictus. This involvement was preliminarily substantiated through RNA interference (RNAi) techniques and behavioral experiment. In summary, the AealbF3 genome assembly will facilitate new biological insights and intervention strategies for combating this formidable vector of disease. The innovative assembly process employed in this study could also serve as a valuable template for the assembly of genomes in other insects characterized by high levels of heterozygosity.

Combining transinfected Wolbachia and a genetic sexing strain to control Aedes albopictus in laboratory-controlled conditions.

The global expansion of Aedes albopictus has stimulated the development of environmentally friendly methods aiming to control disease transmission through the suppression of natural vector populations. Sterile male release programmes are currently being deployed worldwide, and are challenged by the availability of an efficient sex separation which can be achieved mechanically at the pupal stage and/or by artificial intelligence at the adult stage, or through genetic sexing, which allows separating males and females at an early development stage. In this study, we combined the genetic sexing strain previously established based on the linkage of dieldrin resistance to the male locus with a Wolbachia transinfected line. For this, we introduced either the wPip-I or the wPip-IV strain from Culex pipiens in an asymbiotic Wolbachia-free Ae. albopictus line. We then measured the penetrance of cytoplasmic incompatibility and life-history traits of both transinfected lines, selected the wPip-IV line and combined it with the genetic sexing strain. Population suppression experiments demonstrated a 90% reduction in population size and a 50% decrease in hatching rate. Presented results showed that such a combination has a high potential in terms of vector control but also highlighted associated fitness costs, which should be reduced before large-scale field assay.

Effects of deltamethrin exposure on the cytochrome P450 monooxygenases of Aedes albopictus (Skuse) larvae from a dengue-endemic region of northern part of West Bengal, India.

Aedes albopictus is highly prevalent in the northern part of West Bengal and is considered to be responsible for the recent dengue outbreaks in this region. Control of this vector is largely relied on the use of synthetic pyrethroids, which can lead to the development of resistance. In the present study, larvae of three wild Ae. albopictus populations from the dengue-endemic regions were screened for deltamethrin resistance, and the role of cytochrome P450 monooxygenases (CYPs) was investigated in deltamethrin exposed and unexposed larvae. Two populations were incipient resistant, and one population was completely resistant against deltamethrin. Monooxygenase titration assay revealed the involvement of CYPs in deltamethrin resistance along with an induction effect of deltamethrin exposure. Gene expression studies revealed differential expression of five CYP6 family genes, CYP6A8, CYP6P12, CYP6A14, CYP6N3 and CYP6N6, with high constitutive expression of CYP6A8 and CYP6P12 in all the populations before and after deltamethrin exposure. From these findings, it was evident that CYPs play an important role in the development of deltamethrin resistance in the Ae. albopictus populations in this region.

Influence of insular conditions on wing phenotypic variation in two dominant mosquito vectors, Aedes albopictus and Armigeres subalbatus (Diptera: Culicidae), in the border archipelagos of Thailand.

Insects geographically separated into island and mainland populations often exhibit phenotypic variations, a phenomenon known as insular conditions. These conditions can lead to rapid evolutionary changes that affect the morphological characteristics of mosquito vectors. Nevertheless, studies that specifically examine phenotype differences between island and mainland mosquito populations have been limited. In this study, wing variation in size and shape was investigated using the geometric morphometric (GM) technique in two dominant mosquito vectors, Aedes albopictus and Armigeres subalbatus, in the Ranong and Trat archipelagos of Thailand. Significant differences in average wing centroid size (CS) were found in 6 out of 15 population pairs for Ae. albopictus (p < 0.05) and in 5 population pairs for Ar. subalbatus (p < 0.05). After removing the allometric effect, canonical variate analyses (CVA) based on wing shape analysis revealed overlap across all populations for both Ae. albopictus and Ar. subalbatus. However, the statistical analysis indicated that Ar. subalbatus exhibited wing shape differences across all populations (p < 0.05), and most Ae. albopictus populations also displayed distinct wing shapes (p < 0.05), except for the populations from Chang Island and the mainland of Ranong, which showed no significant differences (p > 0.05). These findings enhance our understanding of mosquito adaptability in island regions and provide valuable data for the surveillance and monitoring of vector evolution.

Aedes albopictus colonies from different geographic origins differ in their sleep and activity levels but not in the time of peak activity.

Mosquitoes occupy a wide range of habitats where they experience various environmental conditions. The ability of some species, such as the tiger mosquito, Aedes albopictus, to adapt to local conditions certainly contributes to their invasive success. Among traits that remain to be examined, mosquitoes' ability to time their activity with that of the local host population has been suggested to be of significant epidemiological importance. However, whether different populations display heritable differences in their chronotype has not been examined. Here, we compared laboratory strains originating from eight populations from three continents, monitored their spontaneous locomotor activity patterns and analysed their sleep-like states. Overall, all strains showed conserved diurnal activity concentrated in the hours preceding the crepuscule. Similarly, they all showed increased sleep levels during the morning and night hours. However, we observed strain-specific differences in the activity levels at each phase of the day. We also observed differences in the fraction of time that each strain spends in a sleep-like state, explained by variations in the sleep architecture across strains. Human population density and the latitude of the site of the geographic origin of the tested strain showed significant effects on sleep and activity patterns. Altogether, these results suggest that Ae. albopictus mosquitoes adapt to local environmental conditions via heritable adaptations of their chronotype.

Neochloris aquatica induces larval mortality, molting defects, and unstable flightless adults in the Asian tiger mosquito.

The Asian tiger mosquito, Aedes albopictus, is a highly invasive and aggressive species capable of transmitting a large number of etiological agents of medical and veterinary importance, posing a high risk for the transmission of emerging viruses between animals and humans. In this work, we evaluated the mosquitocidal activity of Neochloris aquatica against A. albopictus throughout its development and analyzed whether this effect was potentiated when the microalga was cultivated under stress conditions due to nutrient deprivation. Our results suggest that N. aquatica produces metabolites that have negative effects on these insects, including larval mortality, interruption of pupal development, and incomplete emergence of adults when fed on microalgae in the larval stages. When microalgae were cultured under stress conditions, an increase in molting defects was recorded, and the number of healthy adults emerged drastically decreased. Histological studies revealed severe signs of total disintegration of different tissues and organs in the thorax and abdomen regions. The muscles and fat bodies in the midgut and foregut were severely distorted. In particular, larval intestinal tissue damage included vacuolization of the cytoplasm, destruction of brush border microvilli, and dilation of the intercellular space, which are distinctive morphological characteristics of apoptotic cells. Evidence suggests that N. aquatica produces metabolites with mosquitocidal effects that affect development and, therefore, the ability to vector etiological agents of medical and veterinary importance.

Cross-infectivity of Vorticella sp. across genera of mosquitoes for development of biological mosquito control strategies.

Protists in general comprise about one-third of the parasitic species infecting arthropod vectors, the role of free-living and epibiotic ciliates on mosquitoes have been insufficiently studied either due to their low pathogenicity or facultative parasites. Studies have shown that exposure of Paramecium ciliate protists, like Vorticella species, to first instar Culex nigripalpus Theobald, larvae delayed larval development and reduced biomass of emerged adults due to competition for food sources like bacteria and other microbes essential to mosquito growth and survival. Thus, we report on the capacity of a Vorticella sp. protist's ability to cross-infect host species and parasitize multiple mosquito larvae. The unique adapted behavior with the ability to remain on the exuviae in tree hole habitats provide a novel delivery system to develop products for target species-specific mosquitocides, larvicides, or viricides to be applied and sustained in aquatic systems.

History of research on Aedes albopictus (Diptera: Culicidae) in Europe: approaching the world's most invasive mosquito species from a bibliometric perspective.

The Asian tiger mosquito, Aedes albopictus (Skuse), is an invasive species native to Southeast Asia. This insect, which is an important vector of arbovirus such as dengue, Zika, and chikungunya, has spread rapidly to several parts of the world over the last few decades. This study employed a bibliometric approach to explore, for the first time, Ae. albopictus research activity and output in Europe. We used the Web of Science Core Collection data source to characterize the current scientific research. A total of 903 publications from 1973 to 2022 were retrieved. We also provided a comprehensive analysis by year of publication; distribution by most productive European countries, institutions, and authors; collaboration networks; research topics; most productive journals; and most cited publications. Results showed a notable increase in the number of studies after the chikungunya virus outbreak in Northeast Italy in 2007. More than 60% of these publications across the entire European continent originated from France and Italy. Research output related to 'population and community ecology' topics was significantly high. The most common type of collaboration was national, which occurred between institutions in the same European country. By providing an overview of Ae. albopictus research in Europe, this work contributes to upcoming debates, decision-making, planning on research and development, and public health strategies on the continent and worldwide.

Resistance of Aedes albopictus (Diptera: Culicidae) larvae and adults to insecticides based on bioassays and knockdown resistance (kdr) mutations in Zhejiang Province, China.

Aedes albopictus, a common mosquito in Zhejiang Province, is a carrier of more than twenty arboviruses. There are dozens or even hundreds of imported cases of dengue fever every year in Zhejiang Province, and there have also been many local outbreaks caused by imported cases of dengue fever. The objectives were to assess the resistance of larvae and adults of several Ae. albopictus strains in Zhejiang Province to commonly used pyrethroid insecticides (beta-cypermethrin, deltamethrin and permethrin), and detect mutations in the sodium channel gene, to further analyse the relationship between phenotypic resistance and the frequency of mutations. The resistance of eight field strains of Ae. albopictus larvae to beta-cypermethrin, deltamethrin and permethrin ranged from 8.17 to 36.06, 12.12-107.3 and 1.55-81.9, respectively, and there was a significant positive correlation of interaction resistance among the three insecticides. The mutation frequencies of I1532T and F1534S in the larvae of Ae. albopictus were 0-6.25 % and 42.19-100.00 %. Moreover, the diagnostic doses of the three pyrethroids for adult Ae. albopictus mosquitoes were 0.2510 g/L, 0.1562 g/L, and 0.9072 g/L. Except for the Zhoushan strain, which was suspected to be resistant to beta-cypermethrin, the other field strains were resistant to the three pyrethroids, and there was a significant positive correlation of cross-resistance among the three insecticides. The mutation frequencies of I1532T and F1534S of adult Ae. albopictus were 0-1.56 % and 62.50-100.00 %. In addition, the LC50 of the larvae and the mortality rate of adult Ae. albopictus after treatment with the three pyrethroids were significantly and positively correlated with the frequency of the F1534S mutation. F1534S mutation occurred earlier than I1532T mutation in both larvae and adult Ae. albopictus. F1534S mutation in the sodium channel gene may be a particular biomolecular detection marker for resistance to pyrethroid insecticides in Ae. albopictus in Zhejiang Province.

Detection of dengue in German tourists returning from Ibiza, Spain, related to an autochthonous outbreak, August to October 2022.

In February 2023, German public health authorities reported two dengue cases (one confirmed, one probable) and four possible cases who travelled to Ibiza, Spain, in late summer/autumn 2022; the infection was probably acquired through mosquito bites. Case 1 visited Ibiza over 1 week in late August with two familial companions; all three developed symptoms the day after returning home. Only Case 1 was tested; dengue virus (DENV) infection was confirmed by presence of NS1 antigen and IgM antibodies. Case 2 travelled to Ibiza with two familial companions for 1 week in early October, and stayed in the same town as Case 1. Case 2 showed symptoms on the day of return, and the familial companions 1 day before and 3 days after return; Case 2 tested positive for DENV IgM. The most probable source case had symptom onset in mid-August, and travelled to a dengue-endemic country prior to a stay in the same municipality of Ibiza for 20 days, until the end of August. Dengue diagnosis was probable based on positive DENV IgM. Aedes albopictus, a competent vector for dengue, has been present in Ibiza since 2014. This is the first report of a local dengue transmission event on Ibiza.

Aedes albopictus is a competent vector of five arboviruses affecting human health, greater Paris, France, 2023.

Aedes albopictus collected in 2023 in the greater Paris area (Île-de-France) were experimentally able to transmit five arboviruses: West Nile virus from 3 days post-infection (dpi), chikungunya virus and Usutu virus from 7 dpi, dengue virus and Zika virus from 21 dpi. Given the growing number of imported dengue cases reported in early 2024 in France, surveillance of Ae. albopictus should be reinforced during the Paris Olympic Games in July, when many international visitors including from endemic countries are expected.

Assessment of sublethal effects of permethrin on adult life characteristics and resistance dynamics in Aedes albopictus (Diptera: Culicidae).

Mosquitoes are regularly exposed to adverse effects of insecticides employed in field during vector control campaigns. Its primary goal is to eliminate the vector population; nevertheless, this practise typically ignores the residual impacts and long-term repercussions on the remaining population. Here, the current study analysed how sublethal exposure of insecticides alter the life qualities, genotypic and biochemical characteristics of mosquitoes. The resistance ratio value in Laboratory Resistant (Lab-R) larvae increased 10 times (0.010 mg/l to 0.108 mg/l) compared to Laboratory Susceptible (LabS) larvae. It also revealed that the surviving mosquitoes had 50% reduction in hatchability but had longer larval and pupal periods (15 days and 2 days), respectively. The survival rates decrease in female by 2 days but increase in male by 7 days which is of concern and necessitates additional study. Moreover, major role of monooxygenase was confirmed behind resistance development which was further supported by piperonyl butoxide assay where reduction in Tolerance Ratio (TR50) by 12-fold occurred and gene expression profile also showed high expression level of CYP6P12 gene. In resistant strain, cuticular thickness increased by 1.23 times and alteration at codon 1532 (ATC to TTC) on VGSC gene leads to mutation I1532F. The data gleaned from our work highlights the threat of sublethal insecticides on vector control techniques and offers ample evidence that the larval selection alters adult life qualities, metabolic properties and transgenerational features which contributes to the damage caused by resistance.

Challenges of Robust RNAi-Mediated Gene Silencing in Aedes Mosquitoes.

In this study, we report the complexities and challenges associated with achieving robust RNA interference (RNAi)-mediated gene knockdown in the mosquitoes Aedes aegypti and Aedes albopictus, a pivotal approach for genetic analysis and vector control. Despite RNAi's potential for species-specific gene targeting, our independent efforts to establish oral delivery of RNAi for identifying genes critical for mosquito development and fitness encountered significant challenges, failing to reproduce previously reported potent RNAi effects. We independently evaluated a range of RNAi-inducing molecules (siRNAs, shRNAs, and dsRNAs) and administration methods (oral delivery, immersion, and microinjection) in three different laboratories. We also tested various mosquito strains and utilized microorganisms for RNA delivery. Our results reveal a pronounced inconsistency in RNAi efficacy, characterized by minimal effects on larval survival and gene expression levels in most instances despite strong published effects for the tested targets. One or multiple factors, including RNase activity in the gut, the cellular internalization and processing of RNA molecules, and the systemic dissemination of the RNAi signal, could be involved in this variability, all of which are barely understood in mosquitoes. The challenges identified in this study highlight the necessity for additional research into the underlying mechanisms of mosquito RNAi to develop more robust RNAi-based methodologies. Our findings emphasize the intricacies of RNAi application in mosquitoes, which present a substantial barrier to its utilization in genetic control strategies.

Assessment of barrier treatments impacting Aedes albopictus (diptera: culicidae) using lambda-cyhalothrin and pyriproxyfen in a suburban neighborhood in Eastern North Carolina, 2018.

Pyrethroids are commonly used in barrier treatments but less is known about how mosquitoes are affected by the simultaneous application of an insect growth regulator (i.e., pyriproxyfen) used in barrier treatments. This field study, conducted from May 14 - October 16, 2018, evaluated the effect of lambda-cyhalothrin (pyrethroid adulticide) and pyriproxyfen on the reproduction (measured by fecundity and adult emergence) and abundance of Aedes albopictus. Nine properties were treated with Demand®CS 0.06% + Archer® 0.010% (every 60 days) and three control properties received no treatment (N=12 total properties). No significant (P>0.05) differences were observed between abundance of Ae. albopictus in treatment compared to control groups. However, significant differences were observed in abundance of Ae. albopictus adults between weeks at both control (P = 0.003) and treatment (P < 0.0001) properties. Results from our research show that continued studies are needed to determine the efficacy of barrier treatments for this species. .

Autochthonous Dengue Outbreak, Paris Region, France, September-October 2023.

We describe clinical and laboratory findings of 3 autochthonous cases of dengue in the Paris Region, France, during September-October 2023. Increasing trends in cases, global warming, and growth of international travel mean that such infections likely will increase during warm seasons in France, requiring stronger arbovirus surveillance networks.

Genomic Shifts, Phenotypic Clines, and Fitness Costs Associated With Cold Tolerance in the Asian Tiger Mosquito.

Climatic variation is a key driver of genetic differentiation and phenotypic traits evolution, and local adaptation to temperature is expected in widespread species. We investigated phenotypic and genomic changes in the native range of the Asian tiger mosquito, Aedes albopictus. We first refine the phylogeographic structure based on genome-wide regions (1,901 double-digest restriction-site associated DNA single nucleotide polymophisms [ddRAD SNPs]) from 41 populations. We then explore the patterns of cold adaptation using phenotypic traits measured in common garden (wing size and cold tolerance) and genotype-temperature associations at targeted candidate regions (51,706 exon-capture SNPs) from nine populations. We confirm the existence of three evolutionary lineages including clades A (Malaysia, Thailand, Cambodia, and Laos), B (China and Okinawa), and C (South Korea and Japan). We identified temperature-associated differentiation in 15 out of 221 candidate regions but none in ddRAD regions, supporting the role of directional selection in detected genes. These include genes involved in lipid metabolism and a circadian clock gene. Most outlier SNPs are differently fixed between clades A and C, whereas clade B has an intermediate pattern. Females are larger at higher latitude yet produce no more eggs, which might favor the storage of energetic reserves in colder climate. Nondiapausing eggs from temperate populations survive better to cold exposure than those from tropical populations, suggesting they are protected from freezing damages but this cold tolerance has a fitness cost in terms of egg viability. Altogether, our results provide strong evidence for the thermal adaptation of A. albopictus across its wide temperature range.

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

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

Urban mosquito distributions are modulated by socioeconomic status and environmental traits in the USA.

The distribution of mosquitoes and associated vector diseases (e.g., West Nile, dengue, and Zika viruses) is likely to be a function of environmental conditions in the landscape. Urban environments are highly heterogeneous in the amount of vegetation, standing water, and concrete structures covering the land at a given time, each having the capacity to influence mosquito abundance and disease transmission. Previous research suggests that socioeconomic status is correlated with the ecology of the landscape, with lower-income neighborhoods generally having more concrete structures and standing water via residential abandonment, garbage dumps, and inadequate sewage. Whether these socioecological factors affect mosquito distributions across urban environments in the USA remains unclear. Here, we present a meta-analysis of 42 paired observations from 18 articles testing how socioeconomic status relates to the overall mosquito burden in urban landscapes in the USA. We also analyzed how socioecological covariates (e.g., abandoned buildings, vegetation, education, and garbage containers) varied across socioeconomic status in the same mosquito studies. The meta-analysis revealed that lower-income neighborhoods (regions with median household incomes

The global emergence of Chikungunya infection: An integrated view.

Chikungunya virus (CHIKV) is one of the emerging viruses around the globe. It belongs to the family Togaviridae and genus Alphavirus and is an arthropod borne virus that transmits by the bite of an infected mosquito, mainly through Aedes aegypti and Aedes albopcitus. It is a spherical, enveloped virus with positive single stranded RNA genome. It was first discovered during 1952-53 in Tanganyika, after which outbreaks were documented in many regions of the world. CHIKV has two transmission cycles; an enzootic sylvatic cycle and an urban cycle. CHIKV genome contains 11,900 nucleotides and two open reading frames and shows great sequence variability. Molecular mechanisms of virus host-cell interactions and the pathogenesis of disease are not fully understood. The disease involves three phases; acute, post-acute and chronic with symptoms including high-grade fever, arthralgia, macupapular rashes and headache. There is no licensed vaccine or specific treatment for CHIKV infection. This lack of specific interventions combined with difficulties in making a precise diagnosis together make the disease difficult to manage. In this review we aim to present the current knowledge of global epidemiology, transmission, structure, various aspects of diagnosis as well as highlight potential antiviral drugs and vaccines against CHIKV.