Spread of Aedes albopictus and decline of Ae. aegypti (Diptera: Culicidae) in Florida

Aedes albopictus is present in the lowlands of southern Zambia

Identifying the current geographic range of disease vectors is a critical first step towards determining effective mechanisms for controlling and potentially eradicating them. This is particularly true given that historical vector ranges may expand due to changing climates and human activity. The Aedes subgenus Stegomyia contains over 100 species, and among them, Ae. aegypti and Ae. albopictus mosquitoes represent the largest concern for public health, spreading dengue, chikungunya, and zika viruses. While Ae. aegypti has been observed in the country of Zambia for decades, Ae. albopictus has not. In 2015 we sampled four urban and three rural areas in Zambia for Aedes species. Using DNA barcoding, we confirmed the presence of immature and adult Ae. albopictus at two sites: Siavonga and Livingstone. These genotypes seem most closely related to specimens previously collected in Mozambique based on mtDNA barcoding. We resampled Siavonga and Livingstone sites in 2019, again observing immature and adult Ae. albopictus at both sites. Relative Ae. albopictus frequencies were similar between sites, with the exception of immature life stages, which were higher in Siavonga than in Livingstone in 2019. While Ae. albopictus frequencies did not vary through time in Livingstone, both immature and adult frequencies increased through time in Siavonga. This report serves to document the presence of Ae. albopictus in Zambia, which will contribute to understanding the potential public health implications of this disease vector in southern Africa.

Neurobiology and Changing Ecosystems: Mechanisms Underlying Responses to Human-Generated Environmental Impacts

Human generated environmental change profoundly affects organisms that reside across diverse ecosystems. Although nervous systems evolved to flexibly sense, respond, and adapt to environmental change, it is unclear whether the rapid rate of environmental change outpaces the adaptive capacity of complex nervous systems. Here, we explore neural systems mediating responses to, or impacted by, changing environments, such as those induced by global heating, sensory pollution, and changing habitation zones. We focus on rising temperature and accelerated changes in environments that impact sensory experience as examples of perturbations that directly or indirectly impact neural function, respectively. We also explore a mechanism involved in cross-species interactions that arises from changing habitation zones. We demonstrate that anthropogenic influences on neurons, circuits, and behaviors are widespread across taxa and require further scientific investigation to understand principles underlying neural resilience to accelerating environmental change.SIGNIFICANCE STATEMENT Neural systems evolved over hundreds of millions of years to allow organisms to sense and respond to their environments - to be receptive and responsive, yet flexible. Recent rapid, human-generated environmental changes are testing the limits of the adaptive capacity of neural systems. This presents an opportunity and an urgency to understand how neurobiological processes, including molecular, cellular, and circuit-level mechanisms, are vulnerable or resilient to changing environmental conditions. We showcase examples that range from molecular to circuit to behavioral levels of analysis across several model species, framing a broad neuroscientific approach to explore topics of neural adaptation, plasticity, and resilience. We believe this emerging scientific area is of great societal and scientific importance and will provide a unique opportunity to reexamine our understanding of neural adaptation and the mechanisms underlying neural resilience.

Insecticide resistance: Status and potential mechanisms in Aedes aegypti

Aedes aegypti, an important vector in the transmission of human diseases, has developed resistance to two commonly used classes of insecticides, pyrethroids and organophosphates, in populations worldwide. This study examined sensitivity/resistance to chlorpyrifos, fenitrothion, malathion, deltamethrin, permethrin, and β-cyfluthrin, along with possible metabolic detoxification and target site insensitivity, in three Aedes aegypti mosquito strains. The resistant strain (PR) had developed high levels of resistance to all three pyrethroid insecticides compared to a susceptible population, with 6, 500-, 3200- and 17,000-fold resistance to permethrin, β-cyfluthrin, and deltamethrin, respectively. A newly emerged Ae. aegypti population collected from St. Augustine, Florida (AeStA) showed elevated levels of resistance to malathion (12-fold) and permethrin (25-fold). Synergists DEF (S,S,S,-tributyl phosphorotrithioate) and DEM (diethyl maleate) showed no or minor effects on insecticide resistance in both the AeStA and PRG20strains, but PBO (piperonyl butoxide) completely abolished resistance to both malathion and permethrin in AeStA and partially suppressed resistance in PR. The voltage-gated sodium channel sequences were examined to explore the mechanism that only partially inhibited the suppression of resistance to PBO in PR. Two mutations, V1016G/I and F1534C substitutions, both of which are associated with the development of pyrethroid resistance, were identified in the PRG20 strain but not in AeStA. These results suggest that while cytochrome P450 mediated detoxification may not be solely responsible, it is the major mechanism governing the development of resistance in AeStA. Both P450 mediated detoxification and target site insensitivity through the mutations in the voltage-gated sodium channel contribute to the high levels of resistance in the PRG20 strain.

Impact of larvae of the Asian tiger mosquito Aedes albopictus on larvae of the Culex pipiens complex from Germany in laboratory co-breeding studies

Since the first detection of the Asian tiger mosquito Aedes albopictus (Diptera: Culicidae) eggs in Germany in 2007, several populations of this species have established in Germany. Although colloquially Ae. albopictus is called an 'invasive species', it is not considered 'invasive' and therefore to be controlled according to the European Union (EU) Environmental and Nature Protection Act since evidence of displacement of native species is missing. To test the competitive potential of Ae. albopictus towards mosquito species native to Germany, laboratory experiments were conducted with larvae of this species and indigenous Cx. pipiens complex species/biotypes. First instar larvae of Ae. albopictus and of one of the native taxa were exposed to different temperatures and fed with different food sources. The ratio of individuals developing into adults as well as the time the larvae needed for development were taken as a measure of competitive outcome. In addition, the size of emerging adults was compared between control and experimental groups. Regarding developmental time, no significant differences were found between treatments and controls while significant differences were found regarding developmental rate and average wing size of individuals. Because no evidence of competitive repression of the native species was found, Ae. albopictus cannot be included in the EU list of invasive species.

Persistent variation in insecticide resistance intensity in container breeding Aedes (Diptera: Culicidae) co-collected in Houston, TX

As observed in many locations worldwide, resistance to pyrethroids is common in Aedes aegypti (L.) in the southern United States and northern Mexico. Strong resistance in Aedes albopictus (Skuse) is less common and is not as well characterized. These 2 species have been undergoing range expansion and are sympatric in many locations including Houston, Texas. They are often collected from the same locations and lay eggs in the same larval habitats. In this study, we colonized both Ae. aegypti and Ae. albopictus from 4 locations in Houston and characterized insecticide resistance using permethrin as a model pyrethroid. We found differences in resistance intensity between the species at all 4 sites. Within the Ae. aegypti, resistance ratios ranged from 3.5- to 30.0-fold when compared to the ORL1952 laboratory susceptible strain. Expression of several P450s was higher than in the ORL1952 strain, but the pattern was similar between the field strains of Ae. aegypti. Higher resistance ratios did correlate with increasing percentages of the dilocus knockdown resistance (kdr) genotype. In contrast, Ae. albopictus from the 4 locations all had very low resistance ratios (<4-fold) when compared to the same laboratory susceptible strain. Five years later, we performed additional collections and characterization from the most resistant location to assess the temporal persistence of this difference in resistance between the species. The same pattern of high resistance in Ae. aegypti and low resistance in sympatric Ae. albopictus remained 5 yr later and this may have implications for operational efficacy.

Urban Green Spaces and Vector-Borne Disease Risk in Africa: The Case of an Unclean Forested Park in Libreville (Gabon, Central Africa)

In Africa, vector-borne diseases are a major public health issue, especially in cities. Urban greening is increasingly considered to promote inhabitants' well-being. However, the impact of urban green spaces on vector risk remains poorly investigated, particularly urban forests in poor hygienic conditions. Therefore, using larval sampling and human landing catches, this study investigated the mosquito diversity and the vector risk in a forest patch and its inhabited surroundings in Libreville, Gabon, central Africa. Among the 104 water containers explored, 94 (90.4%) were artificial (gutters, used tires, plastic bottles) and 10 (9.6%) were natural (puddles, streams, tree holes). In total, 770 mosquitoes belonging to 14 species were collected from such water containers (73.1% outside the forested area). The mosquito community was dominated by Aedes albopictus (33.5%), Culex quinquefasciatus (30.4%), and Lutzia tigripes (16.5%). Although mosquito diversity was almost double outside compared to inside the forest (Shannon diversity index: 1.3 vs. 0.7, respectively), the species relative abundance (Morisita-Horn index = 0.7) was similar. Ae. albopictus (86.1%) was the most aggressive species, putting people at risk of Aedes-borne viruses. This study highlights the importance of waste pollution in urban forested ecosystems as a potential driver of mosquito-borne diseases.

Aedes albopictus (Skuse) dispersion in Havana City, Cuba, 1995-2018

Various arboviruses are transmitted to humans by mosquitoes, particularly Aedes aegypti and Aedes albopictus, two invasive and frequently sympatric species. The objective of this study was to evaluate the dispersion and the behavior of Ae. albopictus in relation to houses and its association with other mosquitoes in the province of Havana, Cuba. All water-containing deposits in the houses or vacant lots in urban and peri‑urban municipalities of the province of Havana were sampled during the two study periods: 1995-1999 and 2010-2018. The following patterns in the presence of Ae. albopictus in the study area were observed: a persistent absence of Ae. albopictus in one of the municipalities; a rapid dispersion in the second period, staring from the absence of vector in the first period, in tow other municipalities; and a sustained decrease in the dispersion of Ae.albopictus in two other municipalities. The peripheral municipalities noted the highest presence of Ae. albopictus, but few associations with other mosquitoes. However, overall, we found an increase in this association when comparing the period 2010-2018 with the first period. Ae. albopictus was present in 8% (2016) to 21.5% (2013) inside the houses with an average of 15%, which evidences an initial domiciliation of the species. The results obtained in this work show an initiation of domiciliation of Ae. albopictus in the urban area of the province of Havana. This is important to alert the National Control Program to strengthen the entomological monitoring of Ae. albopictus, and not only Ae. aegypti. The follow-up of this domiciliation is important to guide control efforts, knowing its role as a vector of different arboviruses.

Invasion Pattern of Aedes aegypti in the Native Range of Ae. albopictus in Vietnam Revealed by Biogeographic and Population Genetic Analysis

Since its introduction to Asia, Aedes aegypti has coexisted with the native species Ae. albopictus and has been reported to transmit several infectious diseases. However, the development of efficient disease prevention and vector control is hindered by the relatively poor understanding of the biogeography and the genetic diversity of Ae. aegypti in the region. This study aimed to determine the invasion patterns of Ae. aegypti by evaluating the distribution and abundance of Ae. aegypti and Ae. albopictus in different climatic regions (northern temperate and southern tropical regions) and habitats (domestic, peri-domestic, and natural). We further analyzed the genetic diversity and phylogenetic relationships of Ae. aegypti populations in Vietnam using mitochondrial COI gene sequences. Both Aedes species were observed at most of the study sites, but only Ae. albopictus thrived in northern mountainous areas. In sympatric ranges, the individual abundance of the species was influenced by regional climate and habitats. The tropical climate and availability of domestic containers facilitated the dominance of Ae. aegypti, whereas temperate climates and natural breeding sites facilitated that of Ae. albopictus. In addition, many genetic polymorphisms were detected in the Ae. aegypti populations, which formed two distinct genetic groups; however, this genetic diversity is unlikely to be relevant to the invasive success of Ae. aegypti. These findings provide insights into the mechanisms and patterns of Ae. Aegypti invasion, which depend on the climate and reproductive strategies in the native range of Ae. albopictus in Asia.

Mosquito Surveillance and Insecticide Resistance Monitoring Conducted by the Florida Keys Mosquito Control District, Monroe County, Florida, USA

Mosquito control programs in the State of Florida are charged with protecting human and animal health, fostering economic development of the State, permitting enjoyment of the natural attractions in Florida, and improving the quality of life of citizens. Mosquito control programs must accomplish these tasks in such a manner as will protect the environment and terrestrial, marine, and freshwater ecosystems. The Florida Keys Mosquito Control District provides a science-based Integrated Pest Management mosquito control program to the residents of the Florida Keys, Monroe County, Florida. Operational decisions are based on surveillance of adult and immature mosquitoes. Mosquito populations are monitored by means of carbon dioxide-baited light traps BG Sentinel traps, truck traps, gravid traps, oviposition traps, and human landing rate counts. Larvae and pupae are monitored by inspections of natural and human-made immature habitats. Due to past and current reliance on chemical pesticides for control of mosquitoes, the District maintains a pesticide resistance detection program consisting of CDC bottle bioassays and larval bioassays, challenging local mosquito species with currently used adulticides and larvicides.

Larval Competition Between Aedes albopictus and Aedes aegypti (Diptera: Culicidae) in Argentina: Coexistence and Implications in the Distribution of the Asian Tiger Mosquito

Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) are worldwide vectors of dengue and yellow fever viruses. These species coexist in many countries and the biotic interactions between them can influence their abundances and distributions. In Argentina, Ae. aegypti is widely distributed in the north and center regions of the country, with temperate and subtropical climate, while both are sympatric only in the northeastern area of the subtropical region. Interspecific and intraspecific larval competition for food was evaluated to assess if their interaction influences on patterns of abundance and distribution. Finite rates of increase and survivorship for each species were estimated and the effects of mosquito density ratio and detritus availability were determined. The Lambda (λ´) index of population performance of both showed there is no competitive exclusion pattern. However, survival of Ae. albopictus was negatively affected by the presence of Ae. aegypti. These results suggest one possible explanation for the codominance pattern of both species display in rural regions of the southernmost distribution of Ae. albopictus in South America. They also show Ae. aegypti as a potential biotic barrier for the expansion of Ae. albopictus as was reported in regions of the United States.

First Detection of the Invasive Mosquito Vector Aedes albopictus (Diptera: Culicidae) in Benin, West Africa, 2021

Aedes albopictus (Skuse) is native to Southeast Asia and has colonized tropical and temperate regions worldwide in the last three to four decades. In Africa, data on its distribution is incomplete. Most studies having focused on the abundance, competition to other species, and phylogenetics of this vector are from the central African region. Here, we report the first detection of Ae. albopictus in Benin, West Africa. A total of 13 specimens were collected during the study period in 2021. The phylogenetic analysis of a cytochrome oxidase c subunit I gene fragment revealed a close relationship to populations from tropical India. Because of its close geographical proximity to areas where it has been found, it is assumed that the species was introduced several years before and is currently widely distributed in Benin. Additional studies are needed to explore its distribution, expansion range, and competitive effects on native species.

Interspecific mating bias may drive Aedes albopictus displacement of Aedes aegypti during its range expansion

Aedes albopictus is the most invasive mosquito in the world and often displaces Ae. aegypti in regions where their populations overlap. Interspecific mating has been proposed as a possible cause for this displacement, but whether this applies across the range of their sympatry remains unclear. Aedes albopictus and Ae. aegypti collected from allopatric and sympatric areas in China were allowed to interact in cage experiments with different crosses and sex-choices. The results confirm that asymmetric interspecific mating occurs in these populations with matings between allopatric Ae. albopictus males and Ae. aegypti females being significantly higher (55.2%) than those between Ae. aegypti males and Ae. albopictus females (27.0%), and sympatric mosquitoes showed a similar but lower frequency bias, 25.7% versus 6.2%, respectively. The cross-mated females can mate second time (remate) with the respective conspecific males and the 66.7% remating success of female Ae. albopictus was significantly higher than the 9.3% of Ae. aegypti females. Furthermore, 17.8% of the matings of Ae. albopictus males exposed to mixed pools of Ae. albopictus and Ae. aegypti females and 9.3% of the matings of Ae. aegypti males with mixed Ae. aegypti and Ae. albopictus females were interspecific. The difference in the length of clasper between male Ae. albopictus (0.524 mm) and Ae. aegypti (0.409 mm) may be correlated with corresponding mates. We conclude that stronger Ae. albopictus male interspecific mating and more avid female intraspecific remating result in a satyr effect and contribute to competitive displacement of Ae. aegypti as allopatric Ae. albopictus invade during range expansion.

Review of the ecology and behaviour of Aedes aegypti and Aedes albopictus in Western Africa and implications for vector control

Western Africa is vulnerable to arboviral disease transmission, having recently experienced major outbreaks of chikungunya, dengue, yellow fever and Zika. However, there have been relatively few studies on the natural history of the two major human arbovirus vectors in this region, Aedes aegypti and Ae. albopictus, potentially limiting the implementation of effective vector control. We systematically searched for and reviewed relevant studies on the behaviour and ecology of Ae. aegypti and Ae. albopictus in Western Africa, published over the last 40 years. We identified 73 relevant studies, over half of which were conducted in Nigeria, Senegal, or Côte d'Ivoire. Most studies investigated the ecology of Ae. aegypti and Ae. albopictus, exploring the impact of seasonality and land cover on mosquito populations and identifying aquatic habitats. This review highlights the adaptation of Ae. albopictus to urban environments and its invasive potential, and the year-round maintenance of Ae. aegypti populations in water storage containers. However, important gaps were identified in the literature on the behaviour of both species, particularly Ae. albopictus. In Western Africa, Ae. aegypti and Ae. albopictus appear to be mainly anthropophilic and to bite predominantly during the day, but further research is needed to confirm this to inform planning of effective vector control strategies. We discuss the public health implications of these findings and comment on the suitability of existing and novel options for control in Western Africa.

Aedes Mosquito Distribution along a Transect from Rural to Urban Settings in Yaoundé, Cameroon

INTRODUCTION

The surveillance of mosquito vectors is important for the control of arboviruses diseases worldwide. Detailed information on the bionomics and distribution of their main vectors, Aedes aegypti and Aedes albopictus, is essential for assessing disease transmission risk and for better planning of control interventions.

METHODS

Entomological surveys were carried out from November 2019 to November 2020 in six localities of Yaoundé city following a transect from urban to rural settings: two urban (Obili, Mvan), two peri-urban (Simbock, Ahala) and two rural areas (Lendom, Elig-essomballa)-during rainy and dry seasons. All water containers were inspected. Aedes mosquito abundance, species distribution and seasonal distribution patterns were compared using generalized linear models. Stegomyia indexes were estimated to determine the risk of arbovirus transmission.

RESULTS

A total of 6332 mosquitoes larvae were collected (2342 in urban areas, 1694 in peri-urban areas and 2296 in rural sites). Aedes species recorded included Ae. albopictus, Ae. aegytpi, Ae. simpsoni and Aedes spp. High mosquito abundance was registered in the rainy season (4706) compared to the dry season (1626) (p < 0.0001). Ae. albopictus was the most abundant Aedes species in urban (96.89%) and peri-urban (95.09%) sites whereas Ae. aegypti was more prevalent in rural sites (68.56%) (p < 0.0001). Both species were found together in 71 larval habitats. Ae. albopictus was mostly found in discarded tires (42.51%), whereas Ae. aegypti was more prevalent in plastic containers used for storing water (65.87%). The majority of Aedes mosquitoes' breeding places were situated close to human dwellings (0-10 m).

CONCLUSION

Uncontrolled urbanization seems to greatly favour the presence of Aedes mosquito species around human dwellings in Yaoundé. Controlling Aedes mosquito distribution is becoming urgent to reduce the risk of arbovirus outbreaks in the city of Yaoundé.

Spatial and temporal population dynamics of male and female Aedes albopictus at a local scale in Medellín, Colombia

BACKGROUND

Diseases transmitted by invasive Aedes aegypti and Aedes albopictus mosquitoes are public health issues in the tropics and subtropics. Understanding the ecology of mosquito vectors is essential for the development of effective disease mitigation programs and will allow for accurate predictions of vector occurrence and abundance. Studies that examine mosquito population dynamics are typically focused on female presence or total adult captures without discriminating the temporal and spatial distribution of both sexes.

METHODS

We collected immature and adult mosquitoes bimonthly for 2 years (2018-2019) in the Medellín Botanical Garden. Collection sites differed in proximity to buildings and nearby vegetation, and were classified by their overhead vegetation cover. We used linear mixed models (LMMs) and Spatial Analysis by Distance Indices (SADIE) to assess the spatial distribution of Ae. aegypti and Ae. albopictus. Using our Ae. albopictus captures exclusively, we assessed (1) the spatial and temporal distribution of males and females using SADIE and a generalized linear mixed model (GLMM), (2) the relationship between climatic variables/vegetation coverage and adult captures using GLMMs and LMMs, and (3) the correlation of male and female size in relation to climatic variables and vegetation coverage using LMMs.

RESULTS

Spatial analysis showed that Ae. aegypti and Ae. albopictus were distributed at different locations within the surveilled area. However, Ae. albopictus was the predominant species in the park during the study period. Adult Ae. albopictus captures were positively correlated with precipitation and relative humidity, and inversely correlated with temperature and wind speed. Moreover, we observed a spatial misalignment of Ae. albopictus males and females-the majority of males were located in the high vegetation coverage sites, while females were more evenly distributed. We observed significant associations of the size of our adult Ae. albopictus captures with precipitation, temperature, and wind speed for both sexes and found that overhead vegetation cover influenced male size, but observed no effect on female size.

CONCLUSIONS

Our work elucidates the differential dynamics of Ae. albopictus males and females, which is pivotal to develop accurate surveillance and the successful establishment of vector control programs based on the disruption of insect reproduction.

Hatching pattern and coexistence of Aedes aegypti and Aedes albopictus (Culicidae) in a subtropical city, Argentina, after three decades of coexistence

Aedes aegypti and Aedes albopictus are mosquito vectors of numerous arboviruses of sanitary importance. Presently in Argentina, neither Ae. aegypti nor Ae. albopictus, have displaced the other species in the places where they coexist, since the introduction of the latter in 1998. In this study, we evaluated whether these species coexist at different scales (ovitrap, microhabitat and habitat) in the city of Eldorado, Misiones province, northeast Argentina. We also analyzed the seasonal variation and climate variables related to the delay in egg hatching of both species. Mosquitoes were collected weekly, from June 2017 to May 2018, using ovitraps placed in urban areas. We conclude that Ae. aegypti and Ae. albopictus coexist in the study area, at the ovitrap, microhabitat and habitat scales. Furthermore, no pronounced pattern of delayed hatching has been observed for either species; however, eggs of Ae. albopictus laid during colder weeks and less rainfall needed a greater number of immersions to hatch, while for Ae. aegypti those laid during weeks with low rainfall and high temperatures showed the longest delay in hatching response.

Displacement of Aedes albopictus by Aedes aegypti in Gainesville, Florida

Aedes aegypti and Ae. albopictus are invasive mosquitoes, capable of vectoring arboviruses such as dengue, chikungunya, yellow fever, and Zika. Recent shifts in spatial distribution indicate there is a resurgence of Ae. aegypti in certain regions of Florida. After a 26-year absence, Ae. aegypti larvae were collected in a downtown neighborhood in Gainesville, Florida, in November 2019. Subsequent surveys confirmed that Ae. albopictus was completely displaced by Ae. aegypti in this neighborhood, whereas Ae. albopictus and Ae. aegypti coexisted around this community focus, and Ae. albopictus alone has been found elsewhere in the city and county since the 1990s. Field surveys revealed that Ae. aegypti is resurging in the downtown area of Gainesville and is actively dispersing to adjacent neighborhoods. Thus, Ae. aegypti could potentially replace Ae. albopictus across more of urban Gainesville in north-central Florida, as reported recently in coastal cities of northeastern Florida.

Aedes albopictus (Diptera: Culicidae) Has Not Become the Dominant Species in Artificial Container Habitats in a Temperate Forest More Than a Decade After Establishment

Aedes albopictus (Skuse) (Diptera: Culicidae) is one of the most invasive species globally, and has led to rapid declines and local extirpations of resident mosquitoes where it becomes established. A potential mechanism behind these displacements is the superior competitive ability of Ae. albopictus in larval habitats. Research on the context-dependent nature of competitive displacement predicts that Ae. albopictus will not replace native Aedes triseriatus (Say) (Diptera: Culicidae) in treeholes but could do so in artificial container habitats. Aedes albopictus remains rare in temperate treeholes but less is known about how Ae. albopictus fares in artificial containers in forests. Tyson Research Center (TRC) is a field station composed of mostly oak-hickory forest located outside Saint Louis, MO. The container community has been studied regularly at TRC since 2007 with permanently established artificial containers on the property since 2013. Aedes albopictus was detected each year when these communities were sampled; however, its abundance remains low and it fails to numerically dominate other species in these communities. We present data that show Ae. albopictus numbers have not increased in the last decade. We compare egg counts from 2007 to 2016 and combine larval sample data from 2012 to 2017.We present average larval densities and prevalence of Ae. albopictus and two competitors, Ae. triseriatus and Aedes japonicus (Theobald) (Diptera: Culicidae), as well as monthly averages by year. These data highlight a circumstance in which Ae. albopictus fails to dominate the Aedes community despite it doing so in more human-impacted habitats. We present hypotheses for these patterns based upon abiotic and biotic environmental conditions.

Estimations of Fine-Scale Species Distributions of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Eastern Florida

Many species distribution maps indicate the ranges of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) overlap in Florida despite the well-documented range reduction of Ae. aegypti. Within the last 30 yr, competitive displacement of Ae. aegypti by Ae. albopictus has resulted in partial spatial segregation of the two species, with Ae. aegypti persisting primarily in urban refugia. We modeled fine-scale distributions of both species, with the goal of capturing the outcome of interspecific competition across space by building habitat suitability maps. We empirically parameterized models by sampling 59 sites in south and central Florida over time and incorporated climatic, landscape, and human population data to identify predictors of habitat suitability for both species. Our results show human density, precipitation, and urban land cover drive Ae. aegypti habitat suitability, compared with exclusively climatic variables driving Ae. albopictus habitat suitability. Remotely sensed variables (macrohabitat) were more predictive than locally collected metrics (microhabitat), although recorded minimum daily temperature showed significant, inverse relationships with both species. We detected minor Aedes habitat segregation; some periurban areas that were highly suitable for Ae. albopictus were unsuitable for Ae. aegypti. Fine-scale empirical models like those presented here have the potential for precise risk assessment and the improvement of operational applications to control container-breeding Aedes mosquitoes.

Reproductive interference between Aedes albopictus and Aedes flavopictus at a place of their origin

Aedes (Stegomyia) albopictus and Aedes (Stegomyia) flavopictus are related species that have overlapping distributions from southern to central Japan. To understand how they interact, we studied reproductive interference between them, particularly focusing on the body size difference between the mating pair. Here, we examined the effects of conspecific, heterospecific and double mating (i.e. heterospecific mating followed by conspecific mating) on copulation duration, egg production and hatchability of eggs using mosquitoes that varied in body size. Females mated only with heterospecific males produced few viable eggs, indicating that post-mating isolation is almost complete. When mated with heterospecific males before conspecific mating, the production of viable eggs was lower than when mated only with conspecific males, revealing the occurrence of reproductive interference. The degree of reproductive interference was larger in Ae. flavopictus than in Ae. albopictus when the female size was small but did not differ between them when the female size was large. Aedes albopictus females appear to be able to distinguish Ae. flavopictus males from conspecific males and larger females are more successful in the rejection of heterospecific males. On the other hand, Ae. flavopictus were not able to discriminate between conspecific and heterospecific males.

The role of heterogenous environmental conditions in shaping the spatiotemporal distribution of competing Aedes mosquitoes in Panama: implications for the landscape of arboviral disease transmission

Monitoring the invasion process of the Asian tiger mosquito Aedes albopictus and its interaction with the contender Aedes aegypti, is critical to prevent and control the arthropod-borne viruses (i.e., Arboviruses) they transmit to humans. Generally, the superior ecological competitor Ae. albopictus displaces Ae. aegypti from most geographic areas, with the combining factors of biology and environment influencing the competitive outcome. Nonetheless, detailed studies asserting displacement come largely from sub-tropical areas, with relatively less effort being made in tropical environments, including no comprehensive research about Aedes biological interactions in Mesoamerica. Here, we examine contemporary and historical mosquito surveillance data to assess the role of shifting abiotic conditions in shaping the spatiotemporal distribution of competing Aedes species in the Republic of Panama. In accordance with prior studies, we show that Ae. albopictus has displaced Ae. aegypti under suboptimal wet tropical climate conditions and more vegetated environments within the southwestern Azuero Peninsula. Conversely, in the eastern Azuero Peninsula, Ae. aegypti persists with Ae. albopictus under optimal niche conditions in a dry and more seasonal tropical climate. While species displacement was stable over the course of two years, the presence of both species generally appears to fluctuate in tandem in areas of coexistence. Aedes albopictus was always more frequently found and abundant regardless of location and climatic season. The heterogenous environmental conditions of Panama shape the competitive outcome and micro-geographic distribution of Aedes mosquitoes, with potential consequences for the transmission dynamics of urban and sylvatic zoonotic diseases.

SUPPLEMENTARY INFORMATION

The online version of this article (10.1007/s10530-021-02482-y).

Modelling distributions of Aedes aegypti and Aedes albopictus using climate, host density and interspecies competition

Florida faces the challenge of repeated introduction and autochthonous transmission of arboviruses transmitted by Aedes aegypti and Aedes albopictus. Empirically-based predictive models of the spatial distribution of these species would aid surveillance and vector control efforts. To predict the occurrence and abundance of these species, we fit a mixed-effects zero-inflated negative binomial regression to a mosquito surveillance dataset with records from more than 200,000 trap days, representative of 53% of the land area and ranging from 2004 to 2018 in Florida. We found an asymmetrical competitive interaction between adult populations of Aedes aegypti and Aedes albopictus for the sampled sites. Wind speed was negatively associated with the occurrence and abundance of both vectors. Our model predictions show high accuracy (72.9% to 94.5%) in validation tests leaving out a random 10% subset of sites and data since 2017, suggesting a potential for predicting the distribution of the two Aedes vectors.

Assessing the Potential Distributions of the Invasive Mosquito Vector Aedes albopictus and Its Natural Wolbachia Infections in México

The Asian tiger mosquito Aedes albopictus is currently the most invasive vector species, with a widespread global distribution. Aedes albopictus is the potential vector of diverse arboviruses, including Zika and dengue. This study updated the ecological niche model of Ae. albopictus and inferred the potential distribution of natural Wolbachia infections in Ae. albopictus in México. The ecological niche models were constructed based on diverse model settings to better estimate the potential distributions and uncertainty indices of both Ae. albopictus and its natural Wolbachia infections in México. The distribution of Ae. albopictus covered the states across Northern México, the Gulf of México, the Pacific Coast of México, Central México, and the southeast of México. The ecological niche model of the natural Wolbachia infections in Ae. albopictus populations anticipated the occurrence of natural Wolbachia infections in the southeast of México, the Chiapas border with Guatemala, and Veracruz. These results can be used to prioritize vector surveillance and control programs in México for strategic and future decision-making; however, it is still necessary to establish active surveillance programs to assess model predictions based on the independent sampling of Ae. albopictus from different invasion zones in México. Finally, vector surveillance should also screen the natural Wolbachia infections in Ae. albopictus to validate Wolbachia predictions across México, particularly in the southeast of México.

Modeling intra-mosquito dynamics of Zika virus and its dose-dependence confirms the low epidemic potential of Aedes albopictus

Originating from African forests, Zika virus (ZIKV) has now emerged worldwide in urbanized areas, mainly transmitted by Aedes aegypti mosquitoes. Although Aedes albopictus can transmit ZIKV experimentally and was suspected to be a ZIKV vector in Central Africa, the potential of this species to sustain virus transmission was yet to be uncovered until the end of 2019, when several autochthonous transmissions of the virus vectored by Ae. albopictus occurred in France. Aside from these few locally acquired ZIKV infections, most territories colonized by Ae. albopictus have been spared so far. The risk level of ZIKV emergence in these areas remains however an open question. To assess Ae. albopictus' vector potential for ZIKV and identify key virus outbreak predictors, we built a complete framework using the complementary combination of (i) dose-dependent experimental Ae. albopictus exposure to ZIKV followed by time-dependent assessment of infection and systemic infection rates, (ii) modeling of intra-human ZIKV viremia dynamics, and (iii) in silico epidemiological simulations using an Agent-Based Model. The highest risk of transmission occurred during the pre-symptomatic stage of the disease, at the peak of viremia. At this dose, mosquito infection probability was estimated to be 20%, and 21 days were required to reach the median systemic infection rates. Mosquito population origin, either temperate or tropical, had no impact on infection rates or intra-host virus dynamic. Despite these unfavorable characteristics for transmission, Ae. albopictus was still able to trigger and yield large outbreaks in a simulated environment in the presence of sufficiently high mosquito biting rates. Our results reveal a low but existing epidemic potential of Ae. albopictus for ZIKV, that might explain the absence of large scale ZIKV epidemics so far in territories occupied only by Ae. albopictus. They nevertheless support active surveillance and eradication programs in these territories to maintain the risk of emergence to a low level.

Phenology of Rock Pool Mosquitoes in the Southern Appalachian Mountains: Surveys Reveal Apparent Winter Hatching of Aedes japonicus and the Potential For Asymmetrical Stage-Specific Interactions

The North American rock pool mosquito, Aedes atropalpus, has reportedly decreased in abundance following the introduction of Ae. japonicus japonicus to the USA, but the specific mechanisms responsible for the reduction remain unclear. Thus, there is a need for field studies to improve our knowledge of natural rock pool systems where both species co-occur. We sampled rock pool invertebrates over a 12-month period along the Chattooga River at a high-elevation site (728 m) near Cashiers, NC, and at a lower-elevation site (361 m) near Clayton, GA. We identified 12 orders of macroinvertebrates representing at least 19 families and 5 mosquito species. Aedes j. japonicus was present year-round at both sites. We observed overwintering Ae. j. japonicus larvae in pools with water temperatures as cold as 3°C and detected apparent winter egg hatching in water below 10°C. Aedes atropalpus was rarely encountered at the high-elevation site but was highly abundant in the summer months at the low-elevation site. Late-stage Ae. j. japonicus larvae inhabited pools in March 2019 when Ae. atropalpus first appeared in the same pools, creating the potential for asymmetrical stage-specific interactions. Our observations provide evidence of overwintering and early hatching of Ae. j. japonicus in the southeastern climate. Further study of the importance of stage-dependent competition and winter egg hatching of diapausing Ae. j. japonicus eggs is warranted.

Quantifying species traits related to oviposition behavior and offspring survival in two important disease vectors

Animals with complex life cycles have traits related to oviposition and juvenile survival that can respond to environmental factors in similar or dissimilar ways. We examined the preference-performance hypothesis (PPH), which states that females lacking parental care select juvenile habitats that maximize fitness, for two ubiquitous mosquito species, Aedes albopictus and Culex quinquefasciatus. Specifically, we examined if environmental factors known to affect larval abundance patterns in the field played a role in the PPH for these species. We first identified important environmental factors from a field survey that predicted larvae across different spatial scales. We then performed two experiments, the first testing the independent responses of oviposition and larval survival to these environmental factors, followed by a combined experiment where initial oviposition decisions were allowed to affect larval life history measures. We used path analysis for this last experiment to determine important links among factors in explaining egg numbers, larval mass, development time, and survival. For separate trials, Aedes albopictus displayed congruence between oviposition and larval survival, however C. quinquefasciatus did not. For the combined experiment path analysis suggested neither species completely fit predictions of the PPH, with density dependent effects of initial egg number on juvenile performance in A. albopictus. For these species the consequences of female oviposition choices on larval performance do not appear to fit expectations of the PPH.

Effects of Mosquito Biology on Modeled Chikungunya Virus Invasion Potential in Florida

Arboviruses transmitted by Aedes aegypti and Aedes albopictus have been introduced to Florida on many occasions. Infrequently, these introductions lead to sporadic local transmission and, more rarely, sustained local transmission. Both mosquito species are present in Florida, with spatio-temporal variation in population composition. We developed a two-vector compartmental, deterministic model to investigate factors influencing Chikungunya virus (CHIKV) establishment. The model includes a nonlinear, temperature-dependent mosquito mortality function based on minimum mortality in a central temperature region. Latin Hypercube sampling was used to generate parameter sets used to simulate transmission dynamics, following the introduction of one infected human. The analysis was repeated for three values of the mortality function central temperature. Mean annual temperature was consistently important in the likelihood of epidemics, and epidemics increased as the central temperature increased. Ae. albopictus recruitment was influential at the lowest central temperature while Ae. aegypti recruitment was influential at higher central temperatures. Our results indicate that the likelihood of CHIKV establishment may vary, but overall Florida is permissive for introductions. Model outcomes were sensitive to the specifics of mosquito mortality. Mosquito biology parameters are variable, and improved understanding of this variation will improve our ability to predict the outcome of introductions.

Vector competence of Aedes albopictus populations for chikungunya virus is shaped by their demographic history

The mosquito Aedes albopictus is one of the most dangerous invasive species. Its worldwide spread has created health concerns as it is a major vector of arboviruses of public health significance such as chikungunya (CHIKV). Dynamics of different genetic backgrounds and admixture events may have impacted competence for CHIKV in adventive populations. Using microsatellites, we infer the genetic structure of populations across the expansion areas that we then associate with their competence for different CHIKV genotypes. Here we show that the demographic history of Ae. albopictus populations is a consequence of rapid complex patterns of historical lineage diversification and divergence that influenced their competence for CHIKV. The history of adventive populations is associated with CHIKV genotypes in a genotype-by-genotype interaction that impacts their vector competence. Thus, knowledge of the demographic history and vector competence of invasive mosquitoes is pivotal for assessing the risk of arbovirus outbreaks in newly colonized areas.

Patterns of Ecological Adaptation of Aedes aegypti and Aedes albopictus and Stegomyia Indices Highlight the Potential Risk of Arbovirus Transmission in Yaoundé, the Capital City of Cameroon

The dynamic of arbovirus vectors such as Aedes aegypti and Ae. albopictus remains poorly understood in large cities in central Africa. Here, we compared the larval ecology, geographical distribution and degree of infestation of Ae. aegypti and Ae. albopictus in Yaoundé, the capital city of Cameroon, and estimated their Stegomyia indices revealing a significant potential risk of arbovirus transmission. An entomological survey was conducted in April-May 2018 in a cluster of houses randomly selected. Each selected house was inspected, the number of inhabitants was recorded, and potential and positive containers for Aedes were characterized. Stegomyia and pupae-based indices were estimated. Overall, 447 houses and 954 containers were inspected comprising 10,801 immature stages of Aedes with 84.95% of Ae. albopictus and 15.05% of Ae. aegypti. Both species bred mainly in discarded tanks and used tyres, associated with turbid water and the presence of plant debris inside containers. Aedes albopictus was the most prevalent species in almost all neighbourhoods. The house index, Breteau index, and container index were higher for Ae. albopictus (38.26%, 71.81%, and 29.61%) compared to those of Ae. aegypti (25.73%, 40.93%, and 16.88%). These indices are high compared to the thresholds established by Pan American Health Organization and World Health Organization, which suggests a high potential risk of arbovirus transmission.

Aedes albopictus oviposits with other Aedes species in artificial oviposition cups: a case study in Knox County, Tennessee, U.S.A

Interspecific associations between two mosquito species can lead to effects such as competition, species displacement, and species stability. To better understand Aedes albopictus (Skuse) and other Aedes species, we monitored eggs in artificial oviposition cups (ovitraps) within Knox County, TN, U.S.A., during the 2016 and 2017 mosquito seasons. In 2016, one black and one white ovitrap were placed at 18 sites for 21 weeks, while in 2017 black and white ovitraps baited with grass-infused or deionized water were placed at 11 sites for nine weeks. Eggs were identified to species and resulting counts were used to determine the degree of interspecific association using Cole's coefficients (C₇ ) and the degree of heterogeneity across space and time using generalized linear mixed models (GLMM). Here, Aedes mosquitoes are generally ovipositing in black cups with grass-infused water, and Ae. albopictus eggs co-occurred with other Aedes species more often than would be expected. Finding a positive significant interspecific association between Ae. albopictus and other Aedes eggs suggests that methods used to control Ae. albopictus may also control other Aedes mosquitoes. Finding that Ae. albopictus co-occurs with other Aedes mosquitoes warrants additional research to evaluate outcomes associated with co-occurrence within the study area.

An investigation of Dirofilaria immitis infection and its effects on mosquito wingbeat frequencies

Each mosquito species has a different wingbeat frequency by which they attract mates. With just a brief recording (<1/10th of a second) these acoustic signatures can be analyzed to quickly determine if mosquitoes belong to a species that is known to transmit different pathogens. A recent study has shown that mobile phones are capable of capturing acoustic data from mosquito wingbeats. We examined wingbeat signatures and flight duration patterns of D. immitis infected and non-infected Aedes aegypti to determine if mobile phone recordings of wingbeat frequencies can be used to distinguish infected mosquitoes from non-infected ones. Female mosquitoes were recorded prior to and at various time points after feeding on infected or non-infected dog blood by placing individual mosquitoes into a collection vial and recording for 60 s using the Voice Memo app for iPhone 7 plus and 8. To uniformly analyze audio data, recordings were processed using a previously described automated algorithm in Python 3.0 to determine wingbeat frequency. A total of 1669 recordings were gathered, and mosquitoes were dissected to confirm the presence and number of D. immitis larvae. Our findings indicate that there was a significant effect on wingbeat frequency with an increasing number of L3 larvae. Specifically, as the number of L3, infective stage larvae increases, a decrease in wingbeat frequency is seen. However, there was no significant effect of increasing number of L1 or L2 larvae causing increasing wingbeat frequencies. The detection of a significant difference in wingbeat frequencies between mosquitoes harboring infective stage D. immitis larvae is unique and suggests the possibility of using wingbeat recordings as a tool for vector species and pathogen surveillance and monitoring.

Potential mosquito (Diptera: Culicidae) vectors of Dirofilaria immitis from residential entryways in Northeast Arkansas

The nematode Dirofilaria immitis causes serious disease of canines in the United States. Transmitted by a variety of mosquito species, several studies have examined the prevalence of D. immitis in mosquitoes. However, no prevalence studies have focused on diurnal mosquitoes that could potentially enter homes. Mosquitoes were collected under doorway awnings at four residences to identify the diurnal blood-feeding mosquito species and prevalence of potential vectors harboring D. immitis in Jonesboro, Arkansas. Mosquitoes were collected from May to December 2016 using pheromone traps and aerial nets. Each mosquito was individually dissected and observed for larvae in the head, thorax, and abdomen to identify infective and non-infective larvae. Ten mosquito species from five genera were identified. Larvae, presumed to be D. immitis, were observed in five mosquito species, including Aedes albopictus, Anopheles quadrimaculatus, Culex pipiens quinquefasciatus, Culiseta inornata, and Psorophora columbiae and four genera, including Anopheles spp., Culex spp., Culiseta spp., and Psorophora spp. The diurnal mosquito, Ae. albopictus composed 3.4% of the total mosquitoes collected. An. quadrimaculatus and Anopheles spp. were the most abundant mosquitoes, composing 59.7 and 19.6% of the total mosquitoes collected, respectively. Of the 536 mosquitoes dissected, 60 (11.2%) were observed with D. immitis, and 33 (55.0%) of the heartworm-positive mosquitoes harbored infective (L₃) larvae in the head or proboscis upon dissection. The high proportion of infective D. immitis larvae found in the mosquitoes aggregating under doorway awnings may increase the exposure of indoor dogs and cats to heartworm disease in northeast Arkansas.

The Developmental Transcriptome of Aedes albopictus, a Major Worldwide Human Disease Vector

Aedes albopictus mosquitoes are important vectors for a number of human pathogens including the Zika, dengue, and chikungunya viruses. Capable of displacing Aedes aegypti populations, this mosquito adapts to cooler environments which increases its geographical range and transmission potential. There are limited control strategies for Aedes albopictus mosquitoes which is likely attributed to the lack of comprehensive biological studies on this emerging vector. To fill this void, here using RNAseq we characterized Aedes albopictus mRNA expression profiles at 34 distinct time points throughout development providing the first high-resolution comprehensive view of the developmental transcriptome of this worldwide human disease vector. This enabled us to identify several patterns of shared gene expression among tissues as well as sex-specific expression patterns. To illuminate the similarities and differences with Aedes aegypti, a related human disease vector, we also performed a comparative analysis between the two developmental transcriptomes, identifying life stages where the two species exhibit similar and distinct gene expression patterns. These findings provide insights into the similarities and differences between Aedes albopictus and Aedes aegypti mosquito biology. In summary, the results generated from this study should form the basis for future investigations on the biology of Aedes albopictus and provide a gold mine resource for the development of transgene-based vector control strategies.

Oviposition Responses and Potential Larval Control Methods of Aedes albopictus (Diptera: Culicidae) in Downspout Extensions

Aedes albopictus (Skuse) is an important invasive species and vector of several important arboviruses across the globe. This species uses small water-holding cryptic containers as egg laying sites, which pose serious challenges to effective control of adult mosquito populations. Herein, we examined the response of gravid female Ae. albopictus to various features of common downspout extension tubes associated with human dwellings and the effectiveness of control efforts to eliminate larvae. Controlled field trials quantified oviposition in 1) extensions versus rubber bowls meant to mimic other container types, 2) among different shapes and materials of extensions, and 3) among different colors of extensions. We also investigated how flushing and use of Bti larvicides could control larvae. Females were more likely to lay eggs in flat plastic or metal extensions compared to rubber bowls. Eggs were also more plentiful in flat plastic extensions versus either corrugated or metal, and dark brown corrugated extensions had more eggs compared to tan or white. Flushing reduced nearly all larvae when the extensions were properly angled, and applications of Bti pellets or dunks were effective at killing most larvae. We show that dark extensions were preferred over other colors, and that larvae can be effectively removed with minimal effort. However, effective control will likely only come from better education of the public about proper installation of extensions.

State-wide survey of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Florida

Aedes aegypti and Aedes albopictus are invasive mosquito species with geographic ranges that have oscillated within Florida since their presence was first documented. Local transmission of dengue, chikungunya, and Zika viruses serves as evidence of the public health importance of these two species. It is important to have detailed knowledge of their distribution to aid in mosquito control efforts and understand the risk of arbovirus transmission to humans. Through a partnership involving the University of Florida Institute of Food and Agricultural Sciences Cooperative Extension Service and the Florida Medical Entomology Laboratory; the Florida Department of Health; and mosquito control agencies throughout Florida, a container mosquito surveillance program involving all life stages was launched in the summer of 2016 to detect the presence of Ae. aegypti and Ae. albopictus. Results from this survey were mapped to provide a picture of the current known distribution of Ae. aegypti and Ae. albopictus in Florida. Aedes aegypti and/or Ae. albopictus were detected in the 56 counties that were part of the survey. Only Aedes albopictus was detected in 26 counties, primarily in the panhandle region of Florida. The results of this work underscore the importance of maintaining container mosquito surveillance in a state where chikungunya, dengue, and Zika viruses are present and where there is continued risk for exotic arbovirus introductions.

Tiger in the sun: A report of Aedes albopictus in Jamaica

This report describes the presence of Aedes albopictus (Skuse) in Jamaica. The adults were found while conducting an ongoing survey of mosquitoes on the island. Specimens were collected using a combination of modified Center for Disease Control (CDC) miniature light traps and BG sentinel traps. A total of six adult female Ae. albopictus mosquitoes were collected at two different locations in October of 2018. This finding increases the number of Aedes mosquito species on the island bringing with it public health implications.

Patterns of genetic divergence among populations of Aedes aegypti L. (Diptera: Culicidae) in the southeastern USA

Background

The yellow fever mosquito, Aedes aegypti is a public health concern in the USA, especially in the wake of emergent diseases such as Zika and chikungunya. Aedes aegypti populations dwindled after the invasion of Aedes albopictus in the 1980s and many populations were extirpated. However, in some areas Ae. aegypti persisted in small populations and there are reports of recent resurgences of Ae. aegypti in Florida, Louisiana, Nevada and California. We assessed the population genetic structure of Ae. aegypti in Florida and Georgia, which has concomitant consequences related to mosquito dispersal, pesticide resistance and vectorial capacity.

Methods

We collected Ae. aegypti across Florida and in Georgia using ovitraps. We hatched the eggs and reared them to adults, and after sacrifice we extracted their DNA. We then probed each individual for variation in 6 microsatellite markers, which we used to address population genetic characteristics.

Results

We collected Ae. aegypti and genotyped seven Florida populations and one Georgia population using microsatellite markers. We found evidence of isolation by distance model of gene flow supported by driving distance among cities within Florida and two theoretic genetic clusters.

Conclusions

Significant genetic structure between some populations with substantial gene flow between geographically distant cities suggests regional genetic structuring of Ae. aegypti in Florida. This study provides information on the genetic exchange between populations of Ae. aegypti in the southeastern USA and suggests potential routes of spread of this species.

Consensus and uncertainty in the geographic range of Aedes aegypti and Aedes albopictus in the contiguous United States: Multi-model assessment and synthesis

Aedes (Stegomyia) aegypti (L.) and Ae. (Stegomyia) albopictus (Skuse) mosquitoes can transmit dengue, chikungunya, yellow fever, and Zika viruses. Limited surveillance has led to uncertainty regarding the geographic ranges of these vectors globally, and particularly in regions at the present-day margins of habitat suitability such as the contiguous United States. Empirical habitat suitability models based on environmental conditions can augment surveillance gaps to describe the estimated potential species ranges, but model accuracy is unclear. We identified previously published regional and global habitat suitability models for Ae. aegypti (n = 6) and Ae. albopictus (n = 8) for which adequate information was available to reproduce the models for the contiguous U.S. Using a training subset of recently updated county-level surveillance records of Ae. aegypti and Ae. albopictus and records of counties conducting surveillance, we constructed accuracy-weighted, probabilistic ensemble models from these base models. To assess accuracy and uncertainty we compared individual and ensemble model predictions of species presence or absence to both training and testing data. The ensemble models were among the most accurate and also provided calibrated probabilities of presence for each species. The quantitative probabilistic framework enabled identification of areas with high uncertainty and model bias across the U.S. where improved models or additional data could be most beneficial. The results may be of immediate utility for counties considering surveillance and control programs for Ae. aegypti and Ae. albopictus. Moreover, the assessment framework can drive future efforts to provide validated quantitative estimates to support these programs at local, national, and international scales.

Aedes aegypti and Ae. albopictus mosquitoes can transmit dengue, chikungunya, yellow fever, and Zika viruses, yet because of limited data the edges of the geographic range of these important species remain uncertain. We assessed numerous previously published model-based estimates of the range of these mosquitoes in the United States and combined those models to produce calibrated estimates of the probability of finding each mosquito in each county. Comparing these estimates to county-level data, we found that there are areas of substantial uncertainty and specific areas where model-based predictions do not align well with available data. The results provide specific information that can help guide national- or state-level efforts to monitor and control Ae. aegypti and Ae. albopictus. Beyond the specific findings, this approach to leveraging limited data and multiple quantitative models can be employed in other settings to better characterize the distribution of these species and other medically important vectors globally.

Globe-Trotting Aedes aegypti and Aedes albopictus: Risk Factors for Arbovirus Pandemics

Introduction: Two species of Aedes (Ae.) mosquitoes (Ae. aegypti and Ae. albopictus) are primary vectors for emerging arboviruses that are a significant threat to public health and economic burden worldwide. Distribution of these vectors and the associated arboviruses, such as dengue virus, chikungunya virus, yellow fever virus, and Zika virus, was for a long time restricted by geographical, ecological, and biological factors. Presently, arbovirus emergence and dispersion are more rapid and geographically widespread, largely due to expansion of the range for these two mosquitoes that have exploited the global transportation network, land perturbation, and failure to contain the mosquito population coupled with enhanced vector competence. Ae. aegypti and Ae. albopictus may also sustain transmission between humans without having to depend on their natural reservoir forest cycles due to arthropod adaptation to urbanization. Currently, there is no single strategy that is adequate to control these vectors, especially when managing arbovirus outbreaks.

Objective: This review aimed at presenting the characteristics and abilities of Ae. aegypti and Ae. albopictus, which can drive a global public health risk, and suggests strategies for prevention and control.

Methods: This review presents the geographic range, reproduction and ecology, vector competence, genetic evolution, and biological and chemical control of these two mosquito species and how they have changed and developed over time combined with factors that may drive pandemics and mitigation measures.

Conclusion: We suggest that more efforts should be geared toward the development of a concerted multidisciplinary approach.

Detecting space-time clusters of dengue fever in Panama after adjusting for vector surveillance data

Long term surveillance of vectors and arboviruses is an integral aspect of disease prevention and control systems in countries affected by increasing risk. Yet, little effort has been made to adjust space-time risk estimation by integrating disease case counts with vector surveillance data, which may result in inaccurate risk projection when several vector species are present, and when little is known about their likely role in local transmission. Here, we integrate 13 years of dengue case surveillance and associated Aedes occurrence data across 462 localities in 63 districts to estimate the risk of infection in the Republic of Panama. Our exploratory space-time modelling approach detected the presence of five clusters, which varied by duration, relative risk, and spatial extent after incorporating vector species as covariates. The Ae. aegypti model contained the highest number of districts with more dengue cases than would be expected given baseline population levels, followed by the model accounting for both Ae. aegypti and Ae. albopictus. This implies that arbovirus case surveillance coupled with entomological surveillance can affect cluster detection and risk estimation, potentially improving efforts to understand outbreak dynamics at national scales.

Dengue cases have increased in tropical regions worldwide owing to urbanization, globalization, and climate change facilitating the spread of Aedes mosquito vectors. National surveillance programs monitor trends in dengue fever and inform the public about epidemiological scenarios where outbreak preventive actions are most needed. Yet, most estimations of dengue risk so far derive only from disease case data, ignoring Aedes occurrence as a key aspect of dengue transmission dynamic. Here we illustrate how incorporating vector presence and absence as a model covariate can considerably alter the characteristics of space-time cluster estimations of dengue cases.

The ecological and epidemiological consequences of reproductive interference between the vectors Aedes aegypti and Aedes albopictus

Vector ecology is integral to understanding the transmission of vector-borne diseases, with processes such as reproduction and competition pivotal in determining vector presence and abundance. The arbovirus vectors Aedes aegypti and Aedes albopictus compete as larvae, but this mechanism is insufficient to explain patterns of coexistence and exclusion. Inviable interspecies matings-known as reproductive interference-is another candidate mechanism. Here, we analyse mathematical models of mosquito population dynamics and epidemiology which include two Aedes-specific features of reproductive interference. First, as these mosquitoes use hosts to find mates, reproductive interference will only occur if the same host is visited. Host choice will, in turn, be determined by behavioural responses to host availability. Second, females can become sterilized after mis-mating with heterospecifics. We find that a species with an affinity for a shared host will suffer more from reproductive interference than a less selective competitor. Costs from reproductive interference can be 'traded-off' against costs from larval competition, leading to competitive outcomes that are difficult to predict from empirical evidence. Sterilizations of a self-limiting species can counterintuitively lead to higher densities than a competitor suffering less sterilization. We identify that behavioural responses and reproductive interference mediate a concomitant relationship between vector ecological dynamics and epidemiology. Competitors with opposite behavioural responses can maintain disease where human hosts are rare, due to vector coexistence facilitated by a reduced cost from reproductive interference. Our work elucidates the relative roles of the competitive mechanisms governing Aedes populations and the associated epidemiological consequences.

Larval species diversity, seasonal occurrence and larval habitat preference of mosquitoes transmitting Rift Valley fever and malaria in Baringo County, Kenya

Background

Baseline information that is essential for determining the areas to target with larval control includes estimates of vector diversity and larval habitat preferences. Due to a lack of such information in Baringo County, Kenya, this study assessed species diversity and larval habitat preference of potential mosquito vectors of Rift Valley fever (RVF) and malaria.

Methods

Mosquito larvae were sampled from nine types of larval habitats and were identified morphologically. Species diversity was estimated by the Shannon’s diversity index while larval habitat preference by RVF and malaria vectors was determined by ANOVA.

Results

A total of 7724 immature mosquitoes comprising 17 species belonging to four genera, namely Anopheles, Culex, Aedes and Mansonia, were identified. Among the 17 species, three Anopheles species are responsible for malaria transmission: An. gambiae (s.l.), An. funestus (s.l.) and An. pharoensis. Rift Valley fever vectors included Mansonia spp. and Culex spp. The highest Shannon's diversity index was observed during the cold dry season (H = 2.487) and in the highland zone (H = 2.539) while the lowest diversity was recorded during the long rain season (H = 2.354) and in the riverine zone (H = 2.085). Ditches had the highest mean number of Anopheles larvae (16.6 larvae per sample) followed by swamp (12.4) and seasonal riverbed (10.7). Water pit and water pan had low mean numbers of Anopheles larvae (1.4 and 1.8, respectively) but relatively high mean numbers of culicines (16.9 and 13.7, respectively). Concrete tank was the least sampled type of habitat but had highest mean number of culicine larvae (333.7 l) followed distantly by water spring (38.9) and swamp (23.5). Overall, larval habitats were significantly different in terms of larval density (F_(8,334) = 2.090, P = 0.036).

Conclusions

To our knowledge, the present study reports culicine larval species diversity in Baringo for the first time and the most preferred habitats were concrete tanks, water springs and swamps. Habitats preferred by Anopheles were mainly riverbed pools, ditches and swamps. Environmental management targeting the habitats most preferred by potential vectors can be part of integrated vector control in Baringo, especially during dry seasons.

Aquatic thermal conditions predict the presence of native and invasive rock pool Aedes (Diptera: Culicidae) in the southern Appalachians, U.S.A

The native rock pool mosquito, Aedes atropalpus (Coquillett), and the invasive Aedes japonicus (Theobald) have been found in many types of artificial and natural containers throughout North America. Little is known about the ecology of these two species in habitats where they co-occur, although multiple investigators have reported the decline of the native species concurrent with the introduction and spread of the invasive species. Here we report the results of riverine rock pool collections (n=503) in the southern Appalachian Mountains between 2009-2015. Surface water temperatures strongly predicted the presence of each species across a broad range of observed temperatures (11-39.8° C). For every unit of increase in temperature (°C) the odds of collecting Ae. atropalpus larvae increased by 0.34 while the odds of collecting Ae. japonicus larvae decreased by 0.28. No Ae. japonicus larvae or pupae were collected at temperatures greater than 36° C; however, immature Ae. atropalpus were found in rock pools with temperatures up to 39.8° C. In contrast, Ae. japonicus were highly abundant in cooler rock pools (<17° C) where Ae. atropalpus were infrequent or absent. Our findings suggest that in spite of the successful invasion by Ae. japonicus, Ae. atropalpus remains well established in the southern Appalachian Mountains. Given the strong correlation of temperature with the presence of the two species and the contrasting absence of each species at observed temperature extremes, the role of thermal conditions should be carefully explored in the context of other ecological factors likely influencing the range and abundance of these mosquitoes.

High infestation of invasive Aedes mosquitoes in used tires along the local transport network of Panama

BACKGROUND

The long-distance dispersal of the invasive disease vectors Aedes aegypti and Aedes albopictus has introduced arthropod-borne viruses into new geographical regions, causing a significant medical and economic burden. The used-tire industry is an effective means of Aedes dispersal, yet studies to determine Aedes occurrence and the factors influencing their distribution along local transport networks are lacking. To assess infestation along the primary transport network of Panama we documented all existing garages that trade used tires on the highway and surveyed a subset for Ae. aegypti and Ae. albopictus. We also assess the ability of a mass spectrometry approach to classify mosquito eggs by comparing our findings to those based on traditional larval surveillance.

RESULTS

Both Aedes species had a high infestation rate in garages trading used tires along the highways, providing a conduit for rapid dispersal across Panama. However, generalized linear models revealed that the presence of Ae. aegypti is associated with an increase in road density by a log-odds of 0.44 (0.73 ± 0.16; P = 0.002), while the presence of Ae. albopictus is associated with a decrease in road density by a log-odds of 0.36 (0.09 ± 0.63; P = 0.008). Identification of mosquito eggs by mass spectrometry depicted similar occurrence patterns for both Aedes species as that obtained with traditional rearing methods.

CONCLUSIONS

Garages trading used tires along highways should be targeted for the surveillance and control of Aedes-mosquitoes and the diseases they transmit. The identification of mosquito eggs using mass spectrometry allows for the rapid evaluation of Aedes presence, affording time and cost advantages over traditional vector surveillance; this is of importance for disease risk assessment.

Predicting aquatic development and mortality rates of Aedes aegypti

Mosquito-borne pathogens continue to be a significant burden within human populations, with Aedes aegypti continuing to spread dengue, chikungunya, and Zika virus throughout the world. Using data from a previously conducted study, a linear regression model was constructed to predict the aquatic development rates based on the average temperature, temperature fluctuation range, and larval density. Additional experiments were conducted with different parameters of average temperature and larval density to validate the model. Using a paired t-test, the model predictions were compared to experimental data and showed that the prediction models were not significantly different for average pupation rate, adult emergence rate, and juvenile mortality rate. The models developed will be useful for modeling and estimating the upper limit of the number of Aedes aegypti in the environment under different temperature, diurnal temperature variations, and larval densities.

Dominance of the tiger: The displacement of Aedes aegypti by Aedes albopictus in parts of the Torres Strait, Australia

Most of the inhabited islands in the Torres Strait region of Australia have experienced dengue outbreaks transmitted by Aedes aegypti at various times since at least the 1890s. However, another potential dengue vector, Aedes albopictus, the Asian tiger mosquito, was detected for the first time in 2005 and it expanded across most of the Torres Strait within a few years. In 2016, a survey of container-inhabiting mosquitoes was conducted in all island communities and Ae. aegypti was undetectable on most of the islands which the species had previously occupied, and had been replaced by Ae. albopictus. It is suspected that competitive displacement was responsible for the changes in species distribution. Aedes aegypti was only detected on Boigu Island and Thursday Island. Recent dengue outbreaks in the Torres Strait have apparently been driven by both Ae. albopictus and Ae. aegypti. The findings have major implications on management of dengue outbreaks in the region.

Container Size Alters the Outcome of Interspecific Competition Between Aedes aegypti (Diptera: Culicidae) and Aedes albopictus

Aedes aegypti L. and Aedes albopictus Skuse co-occur in a variety of water-filled containers where they compete for resources. Larvae of Ae. albopictus Skuse often outcompete those of Ae. aegypti L., but variation in biotic and abiotic parameters can modify the outcome of this interspecific competition. We tested whether container size can alter the magnitude and direction of intra- and interspecific competition by rearing three Ae. aegypti and Ae. albopictus larval combinations (100:0, 50:50 and 0:100) in three container sizes (small, medium, and large). For both mosquito species, individuals raised in small- and medium-sized containers had shorter development time to adulthood, higher survival to adulthood, and larger adult body size compared to individuals from large containers. For Ae. aegypti but not Ae. albopictus, survival to adulthood was significantly influenced by a two-way interaction between container size and larval competition. The negative effect of interspecific competition was stronger in the small and medium containers and the negative effect of intraspecific competition was stronger in large containers. Our results show that container size can affect the outcome of intra- and interspecific competition between Ae. aegypti and Ae. albopictus and may help account for the observed patterns of both competitive exclusion and coexistence documented in the field for these two medically important mosquito species.