Shallow Whole-Genome Sequencing of Aedes japonicus and Aedes koreicus from Italy and an Updated Picture of Their Evolution Based on Mitogenomics and Barcoding

Aedes japonicus and Aedes koreicus are two invasive mosquitoes native to East Asia that are quickly establishing in temperate regions of Europe. Both species are vectors of arboviruses, but we currently lack a clear understanding of their evolution. Here, we present new short-read, shallow genome sequencing of A. japonicus and A. koreicus individuals from northern Italy, which we used for downstream phylogenetic and barcode analyses. We explored associated microbial DNA and found high occurrences of Delftia bacteria in both samples, but neither Asaia nor Wolbachia. We then assembled complete mitogenomes and used these data to infer divergence times estimating the split of A. japonicus from A. koreicus in the Oligocene, which was more recent than that previously reported using mitochondrial markers. We recover a younger age for most other nodes within Aedini and other Culicidae. COI barcoding and phylogenetic analyses indicate that A. japonicus yaeyamensis, A. japonicus amamiensis, and the two A. koreicus sampled from Europe should be considered as separate species within a monophyletic species complex. Our studies further clarify the evolution of A. japonicus and A. koreicus, and indicate the need to obtain whole-genome data from putative species in order to disentangle their complex patterns of evolution.

Invasive Aedes mosquitoes in an urban-peri-urban gradient in northern Spain: evidence of the wide distribution of Aedes japonicus

BACKGROUND

The expansion of invasive mosquitoes throughout Europe has increased in recent decades. In northern Spain, Aedes albopictus was detected for the first time in 2014, and Aedes japonicus was detected in the three Basque provinces in 2020. This study aimed to evaluate the distribution of these mosquito species and their association with factors related to urbanization.

METHODS

In 2021, a total of 568 ovitraps were deployed in 113 sampling sites from 45 municipalities with > 10,000 inhabitants. Oviposition substrate sticks were replaced each fortnight and examined for Aedes eggs from June to November. Aedes eggs were counted, and the eggs from a selection of positive oviposition sticks, encompassing at least one stick from each positive ovitrap, were hatched following their life cycle until the adult stage. When egg hatching was not successful, PCR targeting the COI gene and sequencing of amplicons were carried out.

RESULTS

Eggs were detected in 66.4% of the sampling sites and in 32.4% of the ovitraps distributed in the three provinces of the Basque Country. Aedes albopictus and Ae. japonicus were widespread in the studied area, confirming their presence in 23 and 26 municipalities, respectively. Co-occurrence of both species was observed in 11 municipalities. The analysis of the presence of Aedes invasive mosquitoes and the degree of urbanization (urban, suburban, peri-urban) revealed that Ae. albopictus showed a 4.39 times higher probability of being found in suburban areas than in peri-urban areas, whereas Ae. japonicus had a higher probability of being found in peri-urban areas. Moreover, the presence of Ae. albopictus was significantly associated with municipalities with a higher population density (mean = 2983 inh/km²), whereas Ae. japonicus was associated with lower population density (mean = 1590 inh/km²).

CONCLUSIONS

The wide distribution of Ae. albopictus and Ae. japonicus observed confirmed the spread and establishment of these species in northern Spain. A new colonization area of Ae. japonicus in Europe was confirmed. Due to the potential impact of Aedes invasive mosquitoes on public health and according to our results, surveillance programs and control plans should be designed considering different urbanization gradients, types of environments, and population density.

The virome of the invasive Asian bush mosquito Aedes japonicus in Europe

The Asian bush mosquito Aedes japonicus is rapidly invading North America and Europe. Due to its potential to transmit multiple pathogenic arthropod-borne (arbo)viruses including Zika virus, West Nile virus, and chikungunya virus, it is important to understand the biology of this vector mosquito in more detail. In addition to arboviruses, mosquitoes can also carry insect-specific viruses that are receiving increasing attention due to their potential effects on host physiology and arbovirus transmission. In this study, we characterized the collection of viruses, referred to as the virome, circulating in Ae. japonicus populations in the Netherlands and France. Applying a small RNA-based metagenomic approach to Ae. japonicus, we uncovered a distinct group of viruses present in samples from both the Netherlands and France. These included one known virus, Ae. japonicus narnavirus 1 (AejapNV1), and three new virus species that we named Ae. japonicus totivirus 1 (AejapTV1), Ae. japonicus anphevirus 1 (AejapAV1) and Ae. japonicus bunyavirus 1 (AejapBV1). We also discovered sequences that were presumably derived from two additional novel viruses: Ae. japonicus bunyavirus 2 (AejapBV2) and Ae. japonicus rhabdovirus 1 (AejapRV1). All six viruses induced strong RNA interference responses, including the production of twenty-one nucleotide-sized small interfering RNAs, a signature of active replication in the host. Notably, AejapBV1 and AejapBV2 belong to different viral families; however, no RNA-dependent RNA polymerase sequence has been found for AejapBV2. Intriguingly, our small RNA-based approach identified an ∼1-kb long ambigrammatic RNA that is associated with AejapNV1 as a secondary segment but showed no similarity to any sequence in public databases. We confirmed the presence of AejapNV1 primary and secondary segments, AejapTV1, AejapAV1, and AejapBV1 by reverse transcriptase polymerase chain reaction (PCR) in wild-caught Ae. japonicus mosquitoes. AejapNV1 and AejapTV1 were found at high prevalence (87-100 per cent) in adult females, adult males, and larvae. Using a small RNA-based, sequence-independent metagenomic strategy, we uncovered a conserved and prevalent virome among Ae. japonicus mosquito populations. The high prevalence of AejapNV1 and AejapTV1 across all tested mosquito life stages suggests that these viruses are intimately associated with Ae. japonicus.

Temperature preference of sugar- or blood-fed Aedes japonicus mosquitoes under semi-natural conditions

Mosquito-borne diseases pose a major burden on humans and animals. Temperature strongly influences the physiology and life cycle of mosquitoes and also the pathogens they transmit. Thermoregulatory behaviour of mosquitoes has been addressed in a few laboratory studies. Here, we expand such studies by investigating the thermal preference when resting of Aedes japonicus, an invasive and putative vector species of many pathogens, in a semi-field setup during summers in a temperate climate. Blood-fed or sugar-fed Ae. japonicus females were released in the late afternoon in a large outdoor cage containing three resting boxes. The next morning, temperature treatments were applied to the boxes, creating a "cool" (over all experiments around 18 °C), and a "warm" (around 35 °C) microhabitat in addition to an untreated "ambient" (around 26 °C) one. The mosquitoes resting within the three boxes were counted five times, every 2 h between 9h and 17h. The highest proportions of mosquitoes (e.g. up to 21% of blood-fed ones) were found in the cool box while both blood-fed and sugar-fed mosquitoes avoided the warm box. The mean resting temperatures of Ae. japonicus were below the ambient temperatures measured by a nearby meteorological station, and this was more pronounced at higher outdoor temperatures and in blood-fed as compared to sugar-fed mosquitoes. Thus, over all experiments with blood-fed mosquitoes, the calculated average resting temperature was 4 °C below the outdoor temperature. As mosquitoes prefer cooler resting places than temperatures measured by weather stations in summer, models to predict mosquito-borne disease outbreaks need to account for the thermoregulatory behaviour of mosquitoes, especially in the wake of climate change.

Invasive Aedes japonicus Mosquitoes Dominate the Aedes Fauna Collected with Gravid Traps in Wooster, Northeastern Ohio, USA

Aedes japonicus (Diptera: Culicidae), or the Asian rock pool mosquito, is an invasive mosquito in Europe and America. It was first detected outside of Asia in 1990 in Oceania. It has since expanded to North America and Europe in 1998 and 2000, respectively. Even though it is classified as a secondary vector of pathogens, it is competent to several arboviruses and filarial worms, and it is contributing to the transmission of La Crosse virus (LACV) and West Nile virus (WNV). In this study, CDC light, BG-sentinel, and gravid traps were used to collect mosquitoes between June and October 2021, in Wooster, Northeastern Ohio, USA. Morphological identification or/and Sanger sequencing were performed to identify the collected mosquitoes. Our results revealed that (adult) Ae. japonicus mosquitoes were the most abundant mosquito species collected with gravid traps in Wooster in 2021, confirming its establishment in Ohio. Molecular analyses of Ae. japonicus showed 100% nucleotide similarity with Ae. japonicus collected in Iowa (USA) and Canada, suggesting multiple introductions. Its presence may increase the risk of future arbovirus outbreaks in Wooster, Ohio. This study stresses the importance of actively monitoring the density and distribution of all members of the Ae. japonicus complex.

Putative roles of mosquitoes (Culicidae) and biting midges (Culicoides spp.) as mechanical or biological vectors of lumpy skin disease virus

The stable fly Stomoxys calcitrans (Diptera: Muscidae) is considered as the main mechanical vector of the lumpy skin disease virus (LSDV). In addition, the mosquito species Aedes aegypti (Diptera: Culicidae) was shown to transmit the virus from donor to receptor animals. Retention of the virus for several days was shown for two additional tropical mosquito species and the biting midge Culicoides nubeculosus (Diptera: Ceratopogonidae). In the present study, viral retention for 10- or 7-days post feeding on virus-spiked blood through a membrane was shown for field-collected Aedes japonicus and laboratory-reared Culex pipiens, two widely distributed mosquito species in temperate regions. Viral DNA could be detected from honey-coated Flinders Technology Associates (FTA) cards and shedded faeces for 1 or 4 days after an infectious blood meal was given to Ae. aegypti. Virus increase over time and virus dissemination was observed in laboratory-reared C. nubeculosus, but the virus could be isolated from field-collected biting midges only from the day of exposure to the blood meal. Thus, mosquitoes might serve as mechanical vectors of LSDV in case of interrupted feeding. A putative biological virus transmission by Culicoides biting midges, as suspected from field observations, deserves further investigations.

Emergence of the invasive Asian bush mosquito Aedes (Hulecoeteomyia) japonicus (Theobald, 1901) in the Czech Republic

BACKGROUND

Aedes japonicus is a mosquito species native to North-East Asia that was first found established outside its original geographic distribution range in 1998 and has since spread massively through North America and Europe. In the Czech Republic, the species was not reported before 2021.

METHODS

Aedes invasive mosquitoes (AIM) are routinely surveyed in the Czech Republic by ovitrapping at potential entry ports. This surveillance is supported by appeals to the population to report uncommon mosquitoes. The submission of an Ae. japonicus specimen by a citizen in 2021 was followed by local search for aquatic mosquito stages in the submitter's garden and short-term adult monitoring with encephalitis virus surveillance (EVS) traps in its surroundings. Collected Ae. japonicus specimens were subjected to nad4 haplotype and microsatellite analyses.

RESULTS

Aedes japonicus was detected for the first time in the Czech Republic in 2021. Aquatic stages and adults were collected in Prachatice, close to the Czech-German border, and eggs in Mikulov, on the Czech-Austrian border. Morphological identification was confirmed by molecular taxonomy. Genetic analysis of specimens and comparison of genetic data with those of other European populations, particularly from Germany, showed the Prachatice specimens to be most closely related to a German population. The Mikulov specimens were more distantly related to those, with no close relatives identifiable.

CONCLUSIONS

Aedes japonicus is already widely distributed in Germany and Austria, two countries neighbouring the Czech Republic, and continues to spread rapidly in Central Europe. It must therefore be assumed that the species is already present at more than the two described localities in the Czech Republic and will further spread in this country. These findings highlight the need for more comprehensive AIM surveillance in the Czech Republic.

A Survey on Native and Invasive Mosquitoes and Other Biting Dipterans in Northern Spain

PURPOSE

Haematophagous Diptera, such as mosquitoes (Culicidae), biting midges (Ceratopogonidae), and black flies (Simuliidae), are important insects for public and animal health due to their capacity to bite and transmit pathogens. Outdoor recreation areas are usually affected by biting species and provide suitable habitats to both adult and immature stages. This study aimed to determine the species diversity and larval sites of these Diptera groups in two golf courses.

METHODS

A multi-method collection approach using ultraviolet-CDC traps, human landing catches, collection in breeding sites, and ovitraps was implemented during summer 2020 in northern Spain. Insects were determined by morphological features accompanied by DNA barcoding.

RESULTS

A total of ten native mosquito species were recorded either as adults or as larval stages. The invasive species Aedes japonicus was collected only at egg or pupa stage in ovitraps. Culex pipiens s.l. and Culex torrentium were both common mosquito species accounting for 47.9% of the total larval site collections and their larvae might be found in a wide range of natural and artificial sites. Culiseta longiareolata specimens were also prominent (30.1% of the total) and occurred exclusively in man-made water-filled containers. A total of 13 Culicoides species were identified, 10 of which were captured by ultraviolet-CDC traps, particularly members of the Obsoletus complex (Culicoides obsoletus/Culicoides scoticus, 74.9%) and seven species by emergence traps, being the two most abundant C. kibunensis (44.8%) and C. festivipennis (34.9%). Simulium cryophilum was also collected hovering around the operator under field sampling.

CONCLUSION

A comprehensive representation of the blood-sucking Diptera fauna and their larval sites was obtained by the multi-method approach in two Spanish golf courses.

Xenosurveillance proof-of-principle: Detection of Toxoplasma gondii and SARS-CoV-2 antibodies in mosquito blood meals by (pan)-specific ELISAs

Blood-fed insects can be used to analyse the host blood for circulating vertebrate pathogens or antibodies directed against them. We tested whether naturally acquired antibodies in different host species can be detected by host-specific and pan-specific ELISAs in mosquito blood meals. Cat- and alpaca-specific ELISAs could detect antibodies against Toxoplasma gondii or SARS-CoV-2 in blood meals of Aedes japonicus for 48 and at least 24 h, respectively. In the pan-specific ELISA, a conjugated protein A/G and anti-IgY were used to detect antibodies of mammalian and bird hosts. Thus, Toxoplasma antibodies could be detected in mosquitoes fed on blood from humans, chicken, pig, and sheep up to 72 h after the blood meal. The results, however, demonstrated differences in sensitivities between different host species, and the assay requires further evaluation. Xenosurveillance with antibody detection in mosquito blood meals can be an additional surveillance tool that would especially be helpful when it is difficult to sample the potential animal reservoirs.

Isolation and Characterization of Mosquito-Associated Spiroplasma cantharicola from Aedes japonicus Collected in Hokkaido, Japan

Species of the genus Spiroplasma are common within arthropods and plants worldwide. Mosquito-associated Spiroplasma spp. have been reported to show pathogenicity toward mosquitoes, which serve as vectors of several infectious diseases that have detrimental effects on public health. Although Spiroplasma spp. are expected to have potential use as biological vector-control tools, characteristics such as their distribution, host species, and cytopathogenic effects (CPEs) are not well understood. In this study, we isolated a Spiroplasma sp. from a female Aedes japonicus collected in Hokkaido, northern Japan. Phylogenetic analysis based on the 16S rRNA gene sequence indicated our isolate was closely related to S. cantharicola. We screened 103 mosquito pools consisting of 3 genera and 9 species, but only detected S. cantharicola in the first isolation. In an in vitro assay, our isolate grew well at 28 °C, but no propagation was observed at 37 °C. Furthermore, the isolate showed strong CPE on a mosquito-derived cultured cell line (C6/36), and its propagation slightly increased when co-cultured with C6/36 cells. To our knowledge, this is the third report of the isolation of S. cantharicola from mosquitoes and the first case in Asia. Our findings provide epidemiological data on S. cantharicola distribution in the region.

Global potential distribution of three underappreciated arboviruses vectors (Aedes japonicus, Aedes vexans and Aedes vittatus) under current and future climate conditions

Arboviruses (arthropod-borne viruses) are expanding their geographic range, posing significant health threats to millions of people worldwide. This expansion is associated with efficient and suitable vector availability. Apart from the well-known Aedes aegypti and Ae. albopictus, other Aedes species may potentially promote the geographic spread of arboviruses because these viruses have similar vector requirements. Aedes japonicus, Ae. vexans and Ae. vittatus are a growing concern, given their potential and known vector competence for several arboviruses including dengue, chikungunya, and Zika viruses. In the present study, we developed detailed maps of their global potential distributions under both current and future (2050) climate conditions, using an ecological niche modeling approach (Maxent). Under present-day conditions, Ae. japonicus and Ae. vexans have suitable areas in the northeastern United States, across Europe and in southeastern China, whereas the tropical regions of South America, Africa and Asia are more suitable for Ae. vittatus. Future scenarios anticipated range changes for the three species, with each expected to expand into new areas that are currently not suitable. By 2050, Ae. japonicus will have a broader potential distribution across much of Europe, the United States, western Russia and central Asia. Aedes vexans may be able to expand its range, especially in Libya, Egypt and southern Australia. For Ae. vittatus, future projections indicated areas at risk in sub-Saharan Africa and the Middle East. As such, these species deserve as much attention as Ae. aegypti and Ae. albopictus when processing arboviruses risk assessments and our findings may help to better understand the potential distribution of each species.

The invasive Korean bush mosquito Aedes koreicus (Diptera: Culicidae) in Germany as of 2020

Background

The Korean bush mosquito Aedes koreicus was recently reported to have established a population in western Germany (Wiesbaden) in 2016. The species is difficult to distinguish morphologically from its close relative, the invasive Japanese bush mosquito Ae. japonicus, which is already widely distributed in many parts of Germany, including the area colonised by Ae. koreicus. Genetic confirmation of morphologically identified “Ae. japonicus” collection material, however, had only been done exceptionally before the German Ae. koreicus population became known.

Methods

Dried archived “Ae. japonicus” specimens both from the municipality of Wiesbaden and from deliberately and randomly selected distribution sites all over Germany were re-examined morphologically and genetically for admixture by Ae. koreicus. Moreover, cemeteries in the greater Wiesbaden area were sampled in 2019 and 2020 to check for Ae. koreicus spread. Korean and Japanese bush mosquitoes submitted to the German citizen science mosquito monitoring scheme “Mueckenatlas” in 2019 and 2020 were also subjected to particularly thorough species identification. The ND4 DNA sequences generated in this study in the context of species identification were phylogenetically compared to respective GenBank entries of Ae. koreicus. As a by-product, several genetic markers were evaluated for their suitability to identify Ae. koreicus.

Results

Aedes koreicus specimens could be identified in mosquito collection material and submissions from Wiesbaden from 2015 onwards, suggesting establishment to have happened in the same year as Ae. japonicus establishment. Detections of Ae. koreicus from 2019 and 2020 in Wiesbaden indicate a negligible enlargement of the populated area as described for 2018. Two Ae. koreicus specimens were also submitted from the city of Munich, southern Germany, in 2019 but further specimens could not be identified during immediate local inspections. Comparison of ND4 sequences generated in this and other studies demonstrate a high degree of homology, suggesting that this DNA region is not informative enough for clarification of origins and relationships of Ae. koreicus populations. For genetic identification of Ae. koreicus, PCR primers used for classical CO1 barcoding were found to lead to mismatches and produce no or incorrect amplicons. Alternative CO1 primers or a validated ND4 marker should be used instead.

Conclusions

Aedes koreicus is probably introduced into Germany every now and then but rarely succeeds in becoming established. As with most European populations, the German population is characterised by a limited expansion tendency. Since Ae. koreicus is a potential vector, however, Asian bush mosquitoes found at new places should be examined quite carefully and known distribution areas of Ae. japonicus regularly checked for the presence of Ae. koreicus.

Graphical Abstract

Zika Virus Potential Vectors among Aedes Mosquitoes from Hokkaido, Northern Japan: Implications for Potential Emergence of Zika Disease

The Zika virus (ZIKV) is a rapidly expanding mosquito-borne virus that causes febrile illness in humans. Aedes aegypti and Ae. albopictus are the primary ZIKV vectors; however, the potential vector competence of other Aedes mosquitoes distributed in northern Japan (Palearctic ecozone) are not yet known. In this study, the susceptibility to Zika virus infection of three Aedes mosquitoes distributed in the main city of the northern Japan and their capacities as vectors for ZIKV were evaluated. Field-collected mosquitoes were fed ad libitum an infectious blood meal containing the ZIKV PRVABC59. The Zika virus was detected in the abdomen of Ae. galloisi and Ae. japonicus at 2–10 days post infection (PI), and from the thorax and head of Ae. galloisi at 10 days PI, resulting in 17.6% and 5.9% infection rates, respectively. The Zika virus was not detected from Ae. punctor at any time. Some northern Japanese Aedes could be suspected as vectors of ZIKV but the risk may be low when compared with major ZIKV vectors.

Peridomestic conditions affect La Crosse virus entomological risk by modifying the habitat use patterns of its mosquito vectors

Anthropogenic land-use change may affect the transmission risk for endemic vector-borne diseases such as La Crosse encephalitis. In this study, we applied a comparative ecological approach to evaluate differences in vector species abundance, gonotrophic status, and environmental variables among six residential habitats (historical case houses) and six paired adjacent forest patches in a La Crosse virus endemic area of North Carolina. A total of 93,158 container Aedes spp. eggs were obtained by ovistrips and 1,040 resting mosquito adults were collected by large-bore aspiration from 10 June through 8 October, 2010. At sites characterized by high densities of artificial containers, the totals of eggs and adult mosquitoes were higher in the peridomestic plots. At sites characterized by lower densities of artificial containers, the totals of eggs and adult mosquitoes were higher in the forested plots. Although Aedes triseriatus, the primary La Crosse virus vector, was more commonly found in forested habitat overall, in sites characterized by high density of artificial containers, it was found in higher abundance in the peridomestic habitat. Similarly, the proportion of gonotrophically active (parous and gravid) mosquitoes was higher in the peridomestic habitat for sites with highartificial container density. Our study suggests that La Crosse virus transmission risk may be higher at peridomestic habitats with higher densities of artificial containers and thus reinforces the importance of public health measures to improve source reduction efforts.

Emergence of the invasive Asian bush mosquito, Aedes (Finlaya) japonicus japonicus, in an urban area, Romania

Background

A study conducted at the International Airport of Cluj-Napoca, Romania, with the aim of investigating the presence/absence of invasive Aedes mosquito species resulted in finding Aedes japonicus japonicus (Theobald 1901) eggs in one of the ovitraps placed on site.

Methods

The study was carried out between 30 June and 29 September 2020. On 24 August, 26 eggs were collected and later hatched at the University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca’s insectary. On 15 October another adult female Ae. japonicus was caught entering a building in the center of the city, about 7 km from the first sampling spot.

Results

The mosquitoes were identified morphologically and confirmed by molecular analysis, based on the genetic analysis of the mitochondrial gene cytochrome c oxidase subunit 1 (COI).

Conclusion

This is the first report of the species in Romania, highlighting the need for surveillance and implemented control methods. However, in Romania to our knowledge only Aedes albopictus has been established; further studies are required to learn about this new invasive species' status in Romania.

Molecular relationships of introduced Aedes japonicus (Diptera: Culicidae) populations in British Columbia, Canada using mitochondrial DNA

Aedes japonicus japonicus (Theobald) is a relatively recent immigrant to the Pacific Northwest, having been collected in Washington State in 2001 and in British Columbia (BC) since 2014. We applied a molecular barcoding approach to determine the phylogenetic relationship of Ae. j. japonicus populations in BC with those from around the world. We sequenced a 617 base-pair segment of the cytochrome c oxidase 1 gene and a 330 base-pair region of the NADH dehydrogenase 4 gene to find genetic variation and characterize phylogenetic and haplotypic relationships based on nucleotide divergences. Our results revealed low genetic diversity in the BC samples, suggesting that these populations arose from the same introduction event. However, our approach lacked the granularity to identify the exact country of origin of the Ae. j. japonicus collected in BC. Future efforts should focus on detecting and preventing new Ae. j. japonicus introductions, recognizing that current molecular techniques are unable to pin-point the precise source of an introduction.

Assessing the role of two populations of Aedes japonicus japonicus for Zika virus transmission under a constant and a fluctuating temperature regime

BACKGROUND

Since the huge epidemic of Zika virus (ZIKV) in Brazil in 2015, questions were raised to understand which mosquito species could transmit the virus. Aedes aegypti has been described as the main vector. However, other Aedes species (e.g. Ae. albopictus and Ae. japonicus) proven to be competent for other flaviviruses (e.g. West Nile, dengue and yellow fever), have been described as potential vectors for ZIKV under laboratory conditions. One of these, the Asian bush mosquito, Ae. japonicus, is widely distributed with high abundances in central-western Europe. In the present study, infection, dissemination and transmission rates of ZIKV (Dak84 strain) in two populations of Ae. japonicus from Switzerland (Zürich) and France (Steinbach, Haut-Rhin) were investigated under constant (27 °C) and fluctuating (14-27 °C, mean 23 °C) temperature regimes.

RESULTS

The two populations were each able to transmit ZIKV under both temperature regimes. Infectious virus particles were detected in the saliva of females from both populations, regardless of the incubation temperature regime, from 7 days post-exposure to infectious rabbit blood. The highest amount of plaque forming units (PFU) (400/ml) were recorded 14 days post-oral infection in the Swiss population incubated at a constant temperature. No difference in terms of infection, dissemination and transmission rate were found between mosquito populations. Temperature had no effect on infection rate but the fluctuating temperature regime resulted in higher dissemination rates compared to constant temperature, regardless of the population. Finally, transmission efficiency ranged between 7-23% and 7-10% for the constant temperature and 0-10% and 3-27% under fluctuating temperatures for the Swiss and the French populations, respectively.

CONCLUSIONS

To the best of our knowledge, this is the first study confirming vector competence for ZIKV of Ae. japonicus originating from Switzerland and France at realistic summer temperatures under laboratory conditions. Considering the continuous spread of this species in the northern part of Europe and its adaptation at cooler temperatures, preventative control measures should be adopted to prevent possible ZIKV epidemics.

Classification of Mosquitoes with Infrared Spectroscopy and Partial Least Squares-Discriminant Analysis

Mosquito-borne diseases are responsible for considerable morbidity and mortality globally. Given the absence of effective vaccines for most arthropod-borne viruses, mosquito control efforts remain the dominant method of disease prevention. Ideal control efforts begin with entomologic surveillance in order to determine the abundance, identity, and infection status of pathogen-vectoring mosquito populations. Traditionally, much of the surveillance work involves morphological species identification by trained entomologists. Limited operational funding and lack of specialized training is a known barrier to surveillance and effective control efforts for many operational mosquito control personnel. Therefore, there is a need for surveillance workflow improvements and rapid mosquito identification methods. Herein, is presented a proof of concept study in which infrared spectroscopy coupled with partial least squares-discriminant analysis was explored as a means of automatically classifying mosquitoes at the species level. The developed method resulted in greater than 94% accuracy for four mosquitoes of public health relevance: Aedes aegypti, Aedes albopictus, Aedes japonicus, and Aedes triseriatus.

Vector competence of Virginia mosquitoes for Zika and Cache Valley viruses

Background

Vector-borne diseases are a major public health concern and cause significant morbidity and mortality. Zika virus (ZIKV) is the etiologic agent of a massive outbreak in the Americas that originated in Brazil in 2015 and shows a strong association with congenital ZIKV syndrome in newborns. Cache Valley virus (CVV) is a bunyavirus that causes mild to severe illness in humans and ruminants. In this study, we investigated the vector competence of Virginia mosquitoes for ZIKV and CVV to explore their abilities to contribute to potential outbreaks.

Methods

To determine vector competence, mosquitoes were fed a blood meal comprised of defibrinated sheep blood and virus. The presence of midgut or salivary gland barriers to ZIKV infection were determined by intrathoracic inoculation vs oral infection. After 14-days post-exposure, individual mosquitoes were separated into bodies, legs and wings, and saliva expectorant. Virus presence was detected by plaque assay to determine midgut infection, dissemination, and transmission rates.

Results

Transmission rates for Ae. albopictus orally infected (24%) and intrathoracically inoculated (63%) with ZIKV was similar to Ae. aegypti (48% and 71%, respectively). Transmission rates of ZIKV in Ae. japonicus were low, and showed evidence of a midgut infection barrier demonstrated by low midgut infection and dissemination rates from oral infection (3%), but increased transmission rates after intrathoracic inoculation (19%). Aedes triseriatus was unable to transmit ZIKV following oral infection or intrathoracic inoculation. CVV transmission was dose-dependent where mosquitoes fed high titer (ht) virus blood meals developed higher rates of midgut infection, dissemination, and transmission compared to low titer (lt) virus blood meals. CVV was detected in the saliva of Ae. albopictus (ht: 68%, lt: 24%), Ae. triseriatus (ht: 52%, lt: 7%), Ae. japonicus (ht: 22%, lt: 0%) and Ae. aegypti (ht: 10%; lt: 7%). Culex pipiens and Cx. restuans were not competent for ZIKV or CVV.

Conclusions

This laboratory transmission study provided further understanding of potential ZIKV and CVV transmission cycles with Aedes mosquitoes from Virginia. The ability for these mosquitoes to transmit ZIKV and CVV make them a public health concern and suggest targeted control programs by mosquito and vector abatement districts.

Predation on the invasive mosquito Aedes japonicus (Diptera: Culicidae) by native copepod species in Germany

Some limnic copepod species are predators of mosquito larvae. Seven species belonging to the order Cyclopoida, family Cyclopidae, were collected in the field in Germany and tested for the first time in laboratory bioassays for their potential to serve as biological control agents of the invasive Asian bush mosquito Aedes japonicus (Theobald), a vector of various pathogens causing disease. Females of Diacyclops bicuspidatus (Claus) did not attack 1^st instar larvae of Ae. japonicus, but Macrocyclops distinctus (Richard), Cyclops divergens Lindberg, and C. heberti Einsle predated a mean of 14, 18, or 19 1^st instar larvae, respectively. Acanthocyclops einslei Mirabdullayev and Defaye killed 30 larvae, and high predation rates with a mean of 39 or 46 larvae, respectively, were obtained by Megacyclops viridis (Jurine) and M. gigas (Claus). In regression analyses, predation rates by M. viridis correlated with body size, with specimens of 1.8 mm length being more effective than smaller or bigger ones. Based on the presented data, the two Megacyclops species seem to be promising candidates for use in field studies on the biological control of Ae. japonicus.

Loop-mediated isothermal amplification (LAMP) for the identification of invasive Aedes mosquito species

Invasive Aedes mosquito species (Diptera: Culicidae) are of public health concern in Europe because they are either recognized or potential vectors of pathogens. Loop-mediated isothermal amplification (LAMP) is a rapid and simple method for amplifying DNA with high specificity and efficiency, with the technique having potential for application in the field, including in high-throughput format. Specific LAMP assays based on rDNA internal transcribed spacers 1 or 2 sequences, considering intraspecies variability at these loci, were developed for Aedes aegypti, Aedes albopictus, Aedes japonicus, Aedes koreicus and the indigenous Aedes geniculatus. No such assays could be developed for Aedes atropalpus and Aedes triseriatus because both loci were too short to serve as target. The assays rely on the clearly visible colour change from violet to sky blue after successful amplification. Sensitivity of egg detection was confirmed with ratios of up to one mosquito egg in 99 other eggs. Simple sample preparation of adults or eggs by mechanical homogenization in water required an additional heat treatment or centrifugation step to avoid non-specific colour changes. Thus, further technical improvements are needed to render these assays truly field-applicable, which would greatly facilitate surveillance of these invasive mosquito species and allow for prompt implementation of control measures.

Population genetics of the invasive Asian bush mosquito Aedes japonicus (Diptera, Culicidae) in Germany-a re-evaluation in a time period of separate populations merging

The Asian bush mosquito Aedes japonicus, endemic to East Asia, is one of the most expansive mosquito species in the world and has as yet established in 15 countries of Europe. Within Germany, the species has been spreading tremendously during the last years, and its four once geographically isolated populations were on the verge of merging in 2017. To reveal relationships and carry-over ways between the various populations, and thus, migration and displacement routes, the genetic make-up of Ae. japonicus from ten different locations throughout its German distribution area was investigated. For this purpose, a part of the mitochondrial DNA (nad4 gene) of collected specimens was sequenced and seven loci of short tandem repeats (microsatellites) were genotyped. When related to similar genetic studies carried out between 2012 and 2015, the results suggest that admixtures had since occurred, but no complete genetic mixture of populations had taken place. At the time of sampling for the present study, the western collection sites were still uniform in their genetic make-up; however, a carry-over of individuals from the southeastern to the northern and southwestern German populations was determined. Further introductions from abroad are possible. In summary, the genetic diversity of Ae. japonicus in Germany had grown considerably, thus increasing ecological variability and adaptability of the species. At this point (10 years after the first detection), it is not possible anymore to draw conclusions on the origins of the populations.

Modeled distributions of Aedes japonicus japonicus and Aedes togoi (Diptera: Culicidae) in the United States, Canada, and northern Latin America

The Asian bush mosquito, Aedes japonicus japonicus, and the coastal rock pool mosquito, Aedes togoi, are potential disease vectors present in both East Asia and North America. While their ranges are fairly well-documented in Asia, this is not the case for North America. We used maximum entropy modeling to estimate the potential distributions of Ae. togoi and Ae. j. japonicus in the United States, Canada, and northern Latin America under contemporary and future climatic conditions. Our results suggest suitable habitat that is not known to be occupied for Ae. j. japonicus in Atlantic and western Canada, Alaska, the western, midwestern, southern, and northeastern United States, and Latin America, and for Ae. togoi along the Pacific coast of North America and the Hawaiian Islands. Such areas are at risk of future invasion or may already contain undetected populations of these species. Our findings further predict that the limits of suitable habitat for each species will expand northward under future climatic conditions.

Monitoring of alien mosquitoes of the genus Aedes (Diptera: Culicidae) in Austria

Systematic, continuous mosquito surveillance is considered the most reliable tool to predict the spread and establishment of alien mosquito species such as the Asian tiger mosquito (Aedes albopictus), Japanese bush mosquito (Aedes japonicus), and the transmission risk of mosquito-borne arboviruses to humans. Only single individuals of Ae. albopictus have been found in Austria so far. However, it is likely that the species will be able to establish populations in the future due to global trade and traffic as well as increasing temperatures in the course of global climate change. In summer 2017, a project surveilling the oviposition of newly introduced Aedes mosquitoes, using ovitraps, was set up by means of citizen scientists and researchers and was performed in six federal provinces of Austria-Tyrol, Carinthia, Vienna, Lower Austria, Styria, and Burgenland. Eggs of Ae. albopictus were identified in Tyrol during the months August and September, while Ae. japonicus was found in Lower Austria, Styria, and Burgenland. In Vienna and Carinthia, all ovitraps were negative for Aedes eggs; however, Ae. japonicus was found for the first time in Vienna in July 2017 during routine sampling of adult mosquitoes. With this project, we demonstrated the benefits of citizen scientists for ovitrap-based mosquito surveillance. The finding of Ae. albopictus eggs in Northern Tyrol is not yet a proof of the establishment of a self-sustaining population, although it indicates the ongoing introduction of this species along main traffic routes from Italy, where this mosquito is well established. The risk of establishment of the tiger mosquito in the Lower Inn Valley is therefore a given and informing the public about preventive measures to hinder and delay this development is highly recommended.

First record and morphological characterization of an established population of Aedes (Hulecoeteomyia) koreicus (Diptera: Culicidae) in Germany

BACKGROUND

The East Asian mosquito species Aedes koreicus was recorded out of its native range for the first time in Belgium in 2008. Since then, several other European populations or single individuals have been observed throughout Europe with reports from Italy, Switzerland, European Russia, Slovenia, Germany and Hungary. The Italian population seems to be the only one that is expanding rapidly, so the Swiss population very likely derives from it.

RESULTS

In a surveillance program for invasive mosquito species, a single larva of Ae. koreicus was found in a cemetery vase in 2016 in the city of Wiesbaden, Germany. In the following year the finding was confirmed and an established population could be proven over an area of about 50 km2. The morphological identification of the first larva was confirmed by sequencing of a region within the nad4 sequence. A study of adult females showed that the morphological characteristics of this population are not identical to the populations from Belgium and Italy. The eggs and larvae were found together with Aedes j. japonicus in the same breeding sites and ovitraps, as well as with other indigenous mosquito species such as Culex pipiens/Culex torrentium, Aedes geniculatus and Anopheles plumbeus.

CONCLUSIONS

Since the newly discovered population in Germany shows different morphological characteristics to the populations in Belgium and Italy, it seems to originate from an independent introduction. It remains unknown how the introduction took place. A further spread similar to the one in northern Italy can be assumed for the future due to similar climatic conditions.

Experimental evaluation of infection, dissemination, and transmission rates for two West Nile virus strains in European Aedes japonicus under a fluctuating temperature regime

West Nile virus (WNV) is continuously spreading in Eastern and Southern Europe. However, the extent of vector competence of Aedes japonicus (Theobald, 1901) is controversial. In this work, we elucidated the dynamics of virus growth in this invasive mosquito species. Females of Ae. japonicus were reared from eggs collected in the field in Switzerland and fed on bovine blood spiked with two WNV lineage 1 strains (FIN, Italy; NY99, USA). Fully engorged females were incubated for 14 days under a fluctuating temperature regime of 24 ± 7 °C (average 24 °C), 45–90% relative humidity, which is realistic for a Central European mid-summer day. Infection, dissemination, and transmission rates were assessed from individual mosquitoes by analyzing the abdomen, legs and wings, and saliva for the presence of viral RNA. Saliva was also investigated for the presence of infectious virus particles. Overall, 302 females were exposed to WNV strain FIN and 293 to strain NY99. A higher infection rate was observed for NY99 (57.4%) compared to FIN (30.4%) (p = 0.003). There was no statistical evidence that the dissemination rate (viral RNA in legs and wings) was different between females infected with FIN (57.1%) compared to NY99 (35.5%) (p = 0.16). Viral RNA load of FIN compared to NY99 was significantly higher in the hemocoel (p = 0.031) of exposed females but not at other sites (legs and wings, saliva). This is the first study describing the vector competence parameters for two WNV strains in a European population of Ae. japonicus. The high dissemination and transmission rates for WNV under a realistic temperature regime in Ae. japonicus together with recent findings on its opportunistic feeding behavior (mammals and birds) indicate its potential role in WNV transmission in Central Europe where it is highly abundant.

First Record of Aedes japonicus In Florida

The presence of Aedes j. japonicus in Florida is reported for the first time. Four adult females were collected by a Mosquito Magnet® X trap baited with pressurized CO₂ in Okaloosa County, FL, in August 2012 and later identified as Ae. japonicus in 2014. Additional adult and larval specimens were collected during 2014-17 from Bay, Leon, Okaloosa, Santa Rosa, or Walton counties, Florida. Notes are provided on the location, general habitats, and mosquito associates that may be found with Ae. japonicus in northwestern Florida. The role of Ae. japonicus in arbovirus transmission within Florida is currently unknown and should be further explored.

The roles of history: age and prior exploitation in aquatic container habitats have immediate and carry-over effects on mosquito life history

Per-capita resource availability in aquatic habitats is influenced directly by consumer density via resource competition and indirectly via delayed resource competition when temporally non-overlapping cohorts of larvae exploit the same resources. In detritus-based systems, resources are likely to be influenced by the age of the aquatic habitat, as detritus changes in quality over time and may be replenished by new inputs.For aquatic insects that exploit detritus-based habitats, feeding conditions experienced during immature stages can influence fitness directly via effects on development and survivorship, but also indirectly by influencing adult traits such as fecundity and longevity.Larval habitat age and prior resource exploitation were manipulated in a field experiment using the container mosquito Aedes triseriatus.It was found that A. triseriatus from older habitats had greater larval survival, faster development and greater adult longevity. Exploitation of larval habitats by a prior cohort of larvae had a significant negative effect on subsequent cohorts of larvae by delaying development.It is suggested that extended conditioning of detritus probably resulted in conversion of recalcitrant resources to more available forms which improved the quality of the habitat.In a parallel study, evidence was found of carry-over effects of habitat age and prior exploitation on adult longevity for A. triseriatus and Aedes japonicus collected from unmanipulated aquatic habitats.These results indicate the importance of detritus dynamics and the discontinuous nature of resource competition in these mosquito-dominated aquatic systems.

Update on the Distribution of Aedes japonicus in Maine, 2001-15

The first confirmed collection of Aedes japonicus in Maine was in Cumberland County in 2001. Since that initial collection, it has been found in 7 of Maine's 16 counties between 2001 and 2015. These collections include the northernmost collection of Ae. japonicus in the eastern USA, from Madawaska in Aroostook County. Though mosquito surveillance is limited in the state, it is evident that Ae. japonicus is more widely distributed in Maine than previously believed although its role in arboviral transmission in the region is unknown.

Bacterial diversity of cosmopolitan Culex pipiens and invasive Aedes japonicus from Germany

Symbiotic bacteria have gained significant attention in recent years. For example, microbiota of some mosquito species seems to influence the development and transmission of pathogens. Furthermore, several attempts using bacteria as a paratransgenetic tool have been made in order to assist the control of mosquito-borne diseases. In this study, we examined the bacterial diversity of wild-caught adult Culex (Cx.) pipiens and laboratory-reared adult Aedes japonicus (Ae. japonicus) in Germany using a culture-independent method. Genomic DNA was extracted from each specimen and submitted to PCR amplification of eubacterial 16S rDNA. After the cloning reaction, 28 bacterial transformants per sample containing the 16S rDNA inserts were selected per each sample for sequencing. The analysed specimens of Cx. pipiens as well as of Ae. japonicus showed a diverse bacterial community including some common bacterial genera. Blast analysis allowed to identify 21 bacterial genera belonging to 2 phyla among the 23 specimens of Cx. pipiens. The 14 analysed Ae. japonicus revealed 11 bacterial genera belonging to 3 phyla. In both mosquito species, identified isolates were mainly Proteobacteria. Only 4 of the bacterial genera were found in both mosquito species, with the most prevalent genera Sphingomonas and Rahnella in Cx. pipiens and in Ae. japonicus respectively. Most of the bacterial genera found in our study have been identified in other mosquito species before. Due to the currently scarce data situation, ongoing examinations on the very abundant bacterial genera or species are strongly required to determine their relevance for the biology and adaptiveness of mosquitoes including pathogen-host relationship.

Development of Dirofilaria immitis and Dirofilaria repens in Aedes japonicus and Aedes geniculatus

Background

The mosquito-borne filarial nematodes Dirofilaria immitis and Dirofilaria repens primarily affect dogs but also cats, causing heartworm disease or subcutaneous dirofilariosis, respectively, and both may also cause zoonotic diseases in humans. Several mosquito species have been reported as competent vectors for these nematodes, but no data are available for the invasive mosquito species Aedes japonicus (Theobald, 1901). The objective of this study was to describe the development of both D. immitis and D. repens under standardised experimental laboratory conditions in mosquitoes.

Methods

For this purpose, both a laboratory strain and field-collected individuals of the invasive mosquito species Ae. japonicus and, for comparative purposes, a laboratory strain of Aedes geniculatus, a rare indigenous species sharing habitats with Ae. japonicus, and of the tropical species Aedes aegypti were used. Anticoagulated microfilariaemic blood was fed at a density of 3000 mf/ml to mosquitoes with a hemotek system. Blood-fed mosquitoes were incubated at 27 °C and 85% relative humidity, and specimens were dissected under the microscope at pre-set time points to observe developmental stages of both Dirofilaria species. Additionally, real-time PCRs were carried out in some microscopically negative samples to determine the infection rates.

Results

In field-collected Ae. japonicus infectious L3 larvae of both D. immitis and D. repens developed, rendering this mosquito species an efficient vector for both filarial species. Additionally, Ae. geniculatus was shown to be an equally efficient vector for both filarial species. Aedes japonicus mosquitoes from a laboratory colony were refractory to D. immitis but susceptible to D. repens, whereas Ae. aegypti was refractory to both filarial species.

Conclusions

To our knowledge, Aedes japonicus was for the first time shown to be an efficient vector for both D. immitis and D. repens, indicating that this invasive and locally highly abundant species may contribute to a transmission of filarial worms. The data emphasize the necessity to perform vector competence studies with local mosquito populations as basis for risk assessments. We further demonstrated that detection of filarial DNA in a mosquito species alone does not allow to draw reliable conclusions with regard to its vector competence.

Spread of Aedes japonicus japonicus (Theobald, 1901) in Austria, 2011-2015, and first records of the subspecies for Hungary, 2012, and the principality of Liechtenstein, 2015

Background

The Asian bush mosquito, Aedes (Hulecoeteomyia) japonicus japonicus (Theobald, 1901) (Diptera: Culicidae), was first identified in Austria in August 2011 in the federal state of Styria at the border to Slovenia.

Methods

Between 2011 and 2015 the spread of Ae. j. japonicus was monitored in southern, eastern and western Austrian provinces as well as in neighbouring countries by checking natural and man-made container habitats for the aquatic stages. The search concentrated around the most recent occurrence of Ae. j. japonicus and extended up to several kilometres until the subspecies could not be found anymore.

Results

Between May and July 2012 the distribution area of Ae. j. japonicus was found to be extended westwards into Carinthia, and eastwards towards the federal state of Burgenland. In August 2012, the subspecies was found in Hungary, representing the first record of an invasive mosquito species in this country. In 2013 its expansion was confirmed at several sites in Austria. Additionally, between April and July 2015, the subspecies was detected in all districts of the westernmost Austrian state Vorarlberg reaching the alpine Montafon valley at the end of October 2015, at all three examined sites in southern Bavaria bordering Vorarlberg, and in the adjacent Principality of Liechtenstein, for which it also represents the first record of an invasive mosquito species. One remarkable finding of the subspecies was located close to the city of Kufstein in the lower Inn valley of the Tyrol in September 2015, which is an isolated occurrence without spatial connection to any known established population.

Conclusions

Our findings demonstrate the ongoing spread of Ae. j. japonicus towards all directions within Austria and beyond. Together with the absence of supposed natural barriers, e.g. high mountain chains, at the borders of the current subspecies’ distribution area in south-eastern Austria, these findings suggest a further spread to the Austrian capital Vienna and the Hungarian tourist region of Lake Balaton within the upcoming few years. The observed intrusions in western Austria represent most probably extensions of the population established and spreading in eastern Switzerland and southern Germany. The putative role of the subspecies in pathogen transmission together with its rapid spread observed argues for the implementation of comprehensive nation-wide surveillance and response preparedness.

First record of the Asian bush mosquito, Aedes japonicus japonicus, in Italy: invasion from an established Austrian population

Background

In 2011 we identified the Asian bush mosquito, Aedes japonicus japonicus (Theobald, 1901) (Diptera: Culicidae) for the first time in northern Slovenia and in the bordering Austrian federal state of Styria. Between May and July 2012 the distribution area of Ae. j. japonicus was already found to be extended westwards into Carinthia and eastwards towards Burgenland and bordering Hungary. In August 2012 the species was first detected in a western province of Hungary. In subsequent years, follow-up field studies demonstrated an active spread westwards throughout Carinthia, reaching the border to northern Italy.

Findings

In July 2015 several aquatic-stage specimens of the species were discovered at three different sites in the Friuli Venezia Giulia region, north-eastern Italy. In September 2015, co-occurrence of Ae. j. japonicus and Aedes albopictus (Skuse, 1895) was observed in the same sample in that region.

Conclusions

Ae. j. japonicus actively extended its geographic range from an established population in Carinthia (Austria) southwards to northern Italy by crossing Alpine ranges. Since Ae. albopictus and Aedes koreicus (Edwards, 1917) are already well established in northern Italy, it will be pivotal to monitor the consequences of a third invasive mosquito species trying to populate the same geographic region.

Effects of Pyriproxifen on Aedes japonicus Development and Its Auto-Dissemination by Gravid Females in Laboratory Trials

In a series of laboratory experiments, we investigated the effects of the juvenile-hormone analog pyriproxyfen on the inhibition of Aedes japonicus adult emergence after exposure of late-stage (3rd/4th) larvae (either field-collected or lab-reared from field-collected eggs) to pyriproxyfen. Emergence inhibition was 74%, 83%, 86%, and 92% at 0.01, 0.5, 2.5, and 5 μg/liter, respectively. Additionally, following a 1-day exposure of larvae to pyriproxyfen-containing water (5 μg/liter), and for a separate cohort exposed to that same water 10 days later, significantly more pupae died resulting in fewer adults emerged in the treatment versus control group. In 4 tent trials, gravid adult females were able to auto-disseminate a 5% pyriproxyfen powder to larval development habitats at high enough concentrations to cause a significant increase in inhibition of adult emergence. Therefore, we conclude that pyriproxyfen has a great potential for use in controlling this invasive cryptic breeder.

Comparison of Mosquito Magnet and Biogents Sentinel Traps for Operational Surveillance of Container-Inhabiting Aedes (Diptera: Culicidae) Species

Container-inhabiting Aedes are among the most medically important mosquito vectors of diseases. They also impact health and quality of life by their persistent and severe biting. Monitoring of container-inhabiting Aedes species is challenging due to the need for specialized traps and lures. Biogents Sentinel (BGS) trap has become a standard for Aedes albopictus (Skuse) surveillance; however, it has substantial problems with durability, quality of construction, and sample exposure to the elements. The goal of this study was to develop a methodology for collecting medically important container-inhabiting Aedes species in numbers sufficient for population trend analysis, control efficacy studies, and pathogen testing. Mosquito Magnets (MM) baited with BG lure and R-octenol were selected as the most practical alternative to BGS, collecting significantly more Ae. albopictus (32.1 ± 0.7 vs. 5.6 ± 0.1), Aedes japonicus (Theobald) (10.1 ± 0.4 vs. 1.2 ± 0.02), and Aedes triseriatus (Say) (0.9 ± 0.04 vs. 0.04 ± 0.004) females on average per trapping under a variety of weather conditions. MM can be particularly useful for long-term surveillance or when large numbers of specimens are required for pathogen isolation, such as at the sites with suspected dengue or chikungunya transmission.

La Crosse Virus in Aedes japonicus japonicus mosquitoes in the Appalachian Region, United States

La Crosse virus (LACV), a leading cause of arboviral encephalitis in children in the United States, is emerging in Appalachia. For local arboviral surveillance, mosquitoes were tested. LACV RNA was detected and isolated from Aedes japonicus mosquitoes. These invasive mosquitoes may significantly affect LACV range expansion and dynamics.

La Crosse Encephalitis Virus Infection in Field-Collected Aedes albopictus, Aedes japonicus, and Aedes triseriatus in Tennessee

La Crosse virus (LACV) is a mosquito-borne virus and a major cause of pediatric encephalitis in the USA. La Crosse virus emerged in Tennessee and other states in the Appalachian region in 1997. We investigated LACV infection rates and seasonal abundances of the native mosquito vector, Aedes triseriatus, and 2 recently introduced mosquito species, Ae. albopictus and Ae. japonicus, in an emerging disease focus in Tennessee. Mosquitoes were collected using multiple trapping methods specific for Aedes mosquitoes at recent human case sites. Mosquito pools were tested via reverse transcriptase-polymerase chain reaction (RT-PCR) of the S segment to detect multiple Bunyamwera and California serogroup viruses, including LACV, as well as real-time RT-PCR of the M segment. A total of 54 mosquito pools were positive, including wild-caught adult females and laboratory-reared adults, demonstrating transovarial transmission in all 3 species. Maximum likelihood estimates (per 1,000 mosquitoes) were 2.72 for Ae. triseriatus, 3.01 for Ae. albopictus, and 0.63 for Ae. japonicus. We conclude that Ae. triseriatus and Ae. albopictus are important LACV vectors and that Ae. japonicus also may be involved in virus maintenance and transmission.

Bacterial Communities and Midgut Microbiota Associated with Mosquito Populations from Waste Tires in East-Central Illinois

Mosquito-microbe interactions tend to influence larval nutrition, immunity, and development, as well as fitness and vectorial capacity of adults. Understanding the role of different bacterial species not only improves our knowledge of the physiological and ecological consequences of these interactions, but also provides the basis for developing novel strategies for controlling mosquito-borne diseases. We used culture-dependent and culture-independent techniques to characterize the bacterial composition and abundance in water and midgut samples of larval and adult females of Aedes japonicus (Theobald), Aedes triseriatus (Say), and Culex restuans (Theobald) collected from waste tires at two wooded study sites in Urbana, IL. The phylum-specific real-time quantitative polymerase chain reaction assay revealed a higher proportion of Actinobacteria and a lower proportion of gamma-Proteobacteria and Bacteroidetes in water samples and larval midguts compared to adult female midguts. Only 15 of the 57 bacterial species isolated in this study occurred in both study sites. The number of bacterial species was highest in water samples (28 species from Trelease Woods; 25 species from South Farms), intermediate in larval midguts (13 species from Ae. japonicus; 12 species from Ae. triseriatus; 8 species from Cx. restuans), and lowest in adult female midguts (2 species from Ae. japonicus; 3 species from Ae. triseriatus). These findings suggest that the composition and richness of bacterial communities varies both between habitats and among mosquito species and that the reduction in bacteria diversity during metamorphosis is more evident among bacteria detected using the culture-dependent method.

Effects of Competition and Predation by Native Mosquitoes on the North American Invasion of Aedes japonicus japonicus (Diptera: Culicidae)

The success and effects of a biological invasion can be dependent on species interactions with resident competitors and predators. Indirect interactions between competition and predation, such as keystone predation, can influence both invasion success and the impact of an invasive species on resident competitors. The invasive mosquito Aedes japonicus japonicus (Theobald) has been established within the North American range of the indigenous competitor Aedes triseriatus (Say) and indigenous mosquito predator Toxorhynchites rutilus (Coquillett). The effects of Tx. rutilus predation on competition between Ae. j. japonicus and Ae. triseriatus were tested in laboratory microcosms. Consistent with a prior study, there was minimal evidence of competitive asymmetry between Ae. j. japonicus and Ae. triseriatus, with similar effects of intraspecific versus interspecific interactions on both species. Tx. rutilus predation caused high mortality of both Ae. j. japonicus and Ae. triseriatus, and minimized the effects of density-dependent competition. Ae. japonicus females that survived predation had larger adult body sizes than those in treatments without predators. Ae. triseriatus females that survived Tx. rutilus predation were larger and developed quicker than individuals in treatments without predators. Intraspecific competition and predation negatively affected the finite rate of population increase for Ae. j. japonicus, but only affected individual fitness correlates for Ae. triseriatus, indicating that the overall population performance of the invader is more sensitive to these interactions than the native species. Based on these results, we predict that predation is likely to be an important barrier to the establishment and spread of Ae. j. japonicus in tree holes in North America.