Ensemble evaluation of potential distribution of Procambarus clarkii using multiple species distribution models

Procambarus clarkii is a notorious invasive species that has led to ecological concerns owing to its high viability and rapid reproduction. South Korea, a country exposed to a high risk of introduction of invasive species due to active international trade, has suffered from recent massive invasions by invasive species, necessitating the evaluation of potential areas requiring intensive monitoring. In this study, we developed two different types of species distribution models, CLIMEX and random forest, for P. clarkii using occurrence records from the United States. The potential distribution in the United States was predicted along coastal lines and inland regions located below 40°N latitude The model was then applied to evaluate the potential distribution in South Korea, and an ensemble map was constructed to identify the most vulnerable domestic regions. According to both models, the domestic potential distribution was highest in most areas located at low altitudes. In the ensemble model, most of the low-altitude western regions, the eastern coast, and some southern inland regions were predicted to be suitable for the distribution of P. clarkii, and a similar distribution pattern was predicted when the model was projected into the future climate. Through this study, it is possible to secure basic data that can be used for the early monitoring of the introduction and subsequent distribution of P. clarkii.

Geographic expansion of the introduced Aedes albopictus and other native Aedes species in the Democratic Republic of the Congo

BACKGROUND

Aedes albopictus has been reported in several Central African countries, including the Democratic Republic of the Congo (DRC). The establishment of this mosquito species poses a serious threat as a vector of various infectious diseases. Although Ae. albopictus has been reported in the western region of the DRC, information about its distribution is still scarce in the country. The aim of this study was to investigate the current nationwide distribution of the invasive Ae. albopictus, as well as other native Aedes mosquitoes, in the DRC and to identify suitable areas for its future expansion.

METHODS

Two entomological surveys were conducted in 2017-2019 and 2022. Based on the occurrence sites of Ae. albopictus, important environmental variables were identified. Then, geographical areas suitable for Ae. albopictus establishment were determined using the maximum entropy model. The distribution and abundance of Ae. albopictus were also compared with those of the major native Aedes species.

RESULTS

Aedes albopictus was found in the western, northern, central, and eastern regions of the DRC, but it was not found in the southeastern region. The maximum entropy model predicted that most parts of the DRC are suitable for the establishment of this mosquito. The unsuitable areas encompassed the eastern highlands, known for their low temperatures, and the southeastern highlands, which experience both low temperatures and a long dry season. The native Aedes species found were Aedes aegypti, Aedes simpsoni, Aedes africanus, and Aedes vittatus. Aedes albopictus dominated in the western and northern regions, while Ae. aegypti was more prevalent in other regions.

CONCLUSIONS

Aedes albopictus has been well established in the western and northern regions of the DRC. This mosquito is expanding its distribution while replacing the native Aedes species. Most of the country is suitable for the establishment of this mosquito species, except the highlands of the eastern and the southeastern regions.

Climate and Wolbachia Impacts on Anoplolepis gracilipes (Hymenoptera: Formicidae)

The yellow crazy ant (Anoplolepis gracilipes (Smith, 1857)) is a prominent invasive species exhibiting variable population dynamics. Through collecting long-term climate data and validating field surveys with MaxEnt SDM projections, our results indicated that winter temperature and precipitation accumulation strongly influence the population dynamics. An aggression analysis showed that A. gracilipes nests with higher aggression levels (over 2.5 scores) experienced a higher mean maximum temperature (31.84 ± 0.43 °C) and lower prevalence of wAgra (84.8 ± 4.70%) in A. gracilipes from June to October. The nest manipulation and aggression experiments confirmed that temperature increases aggression (1.3 to 2.8 scores) among A. gracilipes workers due to the reduced prevalence of wAgra. To the best of our knowledge, this is the first case of a notable reduction in the prevalence of Wolbachia (100 to 66%) within a colony of A. gracilipes while maintaining stable nests for further experiments.

Trends in mosquito species distribution modeling: insights for vector surveillance and disease control

Species distribution modeling (SDM) has become an increasingly common approach to explore questions about ecology, geography, outbreak risk, and global change as they relate to infectious disease vectors. Here, we conducted a systematic review of the scientific literature, screening 563 abstracts and identifying 204 studies that used SDMs to produce distribution estimates for mosquito species. While the number of studies employing SDM methods has increased markedly over the past decade, the overwhelming majority used a single method (maximum entropy modeling; MaxEnt) and focused on human infectious disease vectors or their close relatives. The majority of regional models were developed for areas in Africa and Asia, while more localized modeling efforts were most common for North America and Europe. Findings from this study highlight gaps in taxonomic, geographic, and methodological foci of current SDM literature for mosquitoes that can guide future efforts to study the geography of mosquito-borne disease risk.

Global Distribution of Aedes aegypti and Aedes albopictus in a Climate Change Scenario of Regional Rivalry

Arboviral mosquito vectors are key targets for the surveillance and control of vector-borne diseases worldwide. In recent years, changes to the global distributions of these species have been a major research focus, aimed at predicting outbreaks of arboviral diseases. In this study, we analyzed a global scenario of climate change under regional rivalry to predict changes to these species' distributions over the next century. Using occurrence data from VectorMap and environmental variables (temperature and precipitation) from WorldClim v. 2.1, we first built fundamental niche models for both species with the boosted regression tree modelling approach. A scenario of climate change on their fundamental niche was then analyzed. The shared socioeconomic pathway scenario 3 (regional rivalry) and the global climate model Geophysical Fluid Dynamics Laboratory Earth System Model v. 4.1 (GFDL-ESM4.1; gfdl.noaa.gov) were utilized for all analyses, in the following time periods: 2021-2040, 2041-2060, 2061-2080, and 2081-2100. Outcomes from these analyses showed that future climate change will affect Ae. aegypti and Ae. albopictus distributions in different ways across the globe. The Northern Hemisphere will have extended Ae. aegypti and Ae. albopictus distributions in future climate change scenarios, whereas the Southern Hemisphere will have the opposite outcomes. Europe will become more suitable for both species and their related vector-borne diseases. Loss of suitability in the Brazilian Amazon region further indicated that this tropical rainforest biome will have lower levels of precipitation to support these species in the future. Our models provide possible future scenarios to help identify locations for resource allocation and surveillance efforts before a significant threat to human health emerges.

Releasing incompatible males drives strong suppression across populations of wild and Wolbachia-carrying Aedes aegypti in Australia

With over 40% of humans at risk from mosquito-borne diseases such as dengue, yellow fever, chikungunya, and Zika, the development of environmentally friendly mosquito-control tools is critical. The release of reproductively incompatible male mosquitoes carrying a Wolbachia bacterium can drive mating events that kill the eggs. Through replicated treatment and control experiments in northern Australia, regular releases of Aedes aegypti males infected with a Wolbachia from Aedes albopictus was shown to drive strong population suppression in mosaic populations of wild-type (no Wolbachia) and wMel-Wolbachia–carrying Ae. aegypti. In a demonstration of bidirectional incompatibility between different Wolbachia strains in the field, we also demonstrate that one season’s suppression experiment can also show an ongoing effect into the following season.

Releasing sterile or incompatible male insects is a proven method of population management in agricultural systems with the potential to revolutionize mosquito control. Through a collaborative venture with the “Debug” Verily Life Sciences team, we assessed the incompatible insect technique (IIT) with the mosquito vector Aedes aegypti in northern Australia in a replicated treatment control field trial. Backcrossing a US strain of Ae. aegypti carrying Wolbachia wAlbB from Aedes albopictus with a local strain, we generated a wAlbB2-F4 strain incompatible with both the wild-type (no Wolbachia) and wMel-Wolbachia Ae. aegypti now extant in North Queensland. The wAlbB2-F4 strain was manually mass reared with males separated from females using Verily sex-sorting technologies to obtain no detectable female contamination in the field. With community consent, we delivered a total of three million IIT males into three isolated landscapes of over 200 houses each, releasing ∼50 males per house three times a week over 20 wk. Detecting initial overflooding ratios of between 5:1 and 10:1, strong population declines well beyond 80% were detected across all treatment landscapes when compared to controls. Monitoring through the following season to observe the ongoing effect saw one treatment landscape devoid of adult Ae. aegypti early in the season. A second landscape showed reduced adults, and the third recovered fully. These encouraging results in suppressing both wild-type and wMel-Ae. aegypti confirms the utility of bidirectional incompatibility in the field setting, show the IIT to be robust, and indicate that the removal of this arbovirus vector from human-occupied landscapes may be achievable.

Ensemble evaluation of the potential risk areas of yellow-legged hornet distribution

Invasion of alien species facilitated by climate change and human assistant is one of global threats that cause irreversible damages on the local flora and fauna. One of these issued species, Vespa velutina nigrithorax du Buysson, 1905 (Hymenoptera:Vespidae), is a significant threat to entomofauna, including honeybees, in the introduced regions. This wasp is still expanding its habitats, prioritizing the development of a reliable species distribution model based on recently updated occurrence data. Therefore, the aim of this study was to evaluate the potential areas that are climatically exposed to V. v. nigrithorax invasion globally and in South Korea, where the wasp has caused severe damage to local ecosystems and apiculture after its recent introduction. We developed a new global scale ensemble model based on CLIMEX and Maxent models and applied it to South Korea using field survey data. As a result, risky areas were predicted to be temperate and subtropical climate regions, including the eastern USA, western Europe, Far East Asia, and small areas in South America and Australia. In particular, South Korea has a high potential risk throughout the country. We expect that this study would provide fundamental data for monitoring the environmental risks caused by V. v. nigrithorax using advanced species distribution modeling.

Potential geographic distribution of the tiger mosquito Aedes albopictus (Skuse, 1894) (Diptera: Culicidae) in current and future conditions for Colombia

In Colombia, little is known on the distribution of the Asian mosquito Aedes albopictus, main vector of dengue, chikungunya, and Zika in Asia and Oceania. Therefore, this work sought to estimate its current and future potential geographic distribution under the Representative Concentration Paths (RCP) 2.6 and 8.5 emission scenarios by 2050 and 2070, using ecological niche models. For this, predictions were made in MaxEnt, employing occurrences of A. albopictus from their native area and South America and bioclimatic variables of these places. We found that, from their invasion of Colombia to the most recent years, A. albopictus is present in 47% of the country, in peri-urban (20%), rural (23%), and urban (57%) areas between 0 and 1800 m, with Antioquia and Valle del Cauca being the departments with most of the records. Our ecological niche modelling for the currently suggests that A. albopictus is distributed in 96% of the Colombian continental surface up to 3000 m (p < 0.001) putting at risk at least 48 million of people that could be infected by the arboviruses that this species transmits. Additionally, by 2050 and 2070, under RCP 2.6 scenario, its distribution could cover to nearly 90% of continental extension up to 3100 m (≈55 million of people at risk), while under RCP 8.5 scenario, it could decrease below 60% of continental extension, but expand upward to 3200 m (< 38 million of people at risk). These results suggest that, currently in Colombia, A. albopictus is found throughout the country and climate change could diminish eventually its area of distribution, but increase its altitudinal range. In Colombia, surveillance and vector control programs must focus their attention on this vector to avoid complications in the national public health setting.

The Effect of Sound Lure Frequency and Habitat Type on Male Aedes albopictus (Diptera: Culicidae) Capture Rates With the Male Aedes Sound Trap

The global distribution of Aedes albopictus (Skuse) is rapidly expanding which has contributed to the emergence and re-emergence of dengue and chikungunya outbreaks. Improvements in vector surveillance are necessary to facilitate optimized, evidence-based vector control operations. Current trapping technology used to target Ae. albopictus and other Aedes species for vector surveillance are limited in both scale and scope, thus novel tools are required. Here, we evaluated the Male Aedes Sound Trap (MAST) for its capacity to sample male Ae. albopictus. Aims of this study were twofold: 1) to determine the most effective frequency for capturing male Ae. albopictus and 2) to investigate fine-scale variations in male Ae. albopictus abundance. MASTs which produced sound lure frequencies between 500 and 650 Hz captured significantly more male Ae. albopictus than those with sound lure frequencies set to 450 Hz. Further, the higher sound lure frequency of 700 Hz significantly reduced catches relative to 650 Hz. MASTs placed in woodland habitats captured significantly more male Ae. albopictus than MASTs placed near houses. These results provide baseline information for optimizing sound lure frequencies and placement of the MAST to sample male Ae. albopictus in remote areas.

Assessing the Risk of Exotic Mosquito Incursion through an International Seaport, Newcastle, NSW, Australia

Exotic mosquitoes, especially container-inhabiting species such as Aedes aegypti and Aedes albopictus, pose a risk to Australia as they bring with them potentially significant pest and public health concerns. Notwithstanding the threat to public health and wellbeing, significant economic costs associated with the burden of mosquito control would fall to local authorities. Detection of these mosquitoes at airports and seaports has highlighted pathways of introduction but surveillance programs outside these first ports of entry are not routinely conducted in the majority of Australian cities. To assist local authorities to better prepare response plans for exotic mosquito incursions, an investigation was undertaken to determine the extent of habitats suitable for container-inhabiting mosquitoes in over 300 residential properties adjacent to the Port of Newcastle, Newcastle, NSW. More than 1500 water-holding containers were recorded, most commonly pot plant saucers, roof gutters, and water-holding plants (e.g., bromeliads). There were significantly more containers identified for properties classified as untidy but there was no evidence visible that property characteristics could be used to prioritise property surveys in a strategic eradication response. The results demonstrate that there is potential for local establishment of exotic mosquitoes and that considerable effort would be required to adequately survey these environments for the purpose of surveillance and eradication programs.

Modeling the Distribution of the Invasive Alien Cycad Aulacaspis Scale in Africa Under Current and Future Climate Scenarios

The cycad aulacaspis scale, Aulacaspis yasumatsui Takagi (Hemiptera: Coccoidea: Diaspididae), is native to Southeast Asia but an invasive pest of the gymnosperm order Cycadales in many parts of the world. Aulacaspis yasumatsui was recently reported on the cycad genus Encephalartos in South Africa and is currently categorized as a 'prohibited terrestrial invertebrate' in the invasive species legislation, National Environmental Management: Biodiversity Act, 2004 (NEM:BA). Encephalartos is endemic to Africa, and 11 species are listed as critically endangered and four species as endangered. Seeing the limited distribution of A. yasumatsui in South Africa and only one unconfirmed record from the Ivory Coast, understanding the potential distribution range is essential for control and management. Here we model the potential distribution of A. yasumatsui under current and future climate scenarios in Africa, with a focus on South Africa. Future climatic scenarios were simulated using a bio-climatic software, CLIMEX. The model indicates that, under the current climatic scenario, all 17 African countries possessing Encephalartos are susceptible to A. yasumatsui establishment. However, under climatic change, the suitability decreases for large parts of Africa. In South Africa, 93% of the winter rainfall areas, and 90% of the temperate, summer rainfall areas are suitable for A. yasumatsui establishment. In this study, we highlight the urgent need for regulation, management, and research on A. yasumatsui in African countries with native cycads.

Integrating statistical and mechanistic approaches with biotic and environmental variables improves model predictions of the impact of climate and land-use changes on future mosquito-vector abundance, diversity and distributions in Australia

Changes to Australia's climate and land-use patterns could result in expanded spatial and temporal distributions of endemic mosquito vectors including Aedes and Culex species that transmit medically important arboviruses. Climate and land-use changes greatly influence the suitability of habitats for mosquitoes and their behaviors such as mating, feeding and oviposition. Changes in these behaviors in turn determine future species-specific mosquito diversity, distribution and abundance. In this review, we discuss climate and land-use change factors that influence shifts in mosquito distribution ranges. We also discuss the predictive and epidemiological merits of incorporating these factors into a novel integrated statistical (SSDM) and mechanistic species distribution modelling (MSDM) framework. One potentially significant merit of integrated modelling is an improvement in the future surveillance and control of medically relevant endemic mosquito vectors such as Aedes vigilax and Culex annulirostris, implicated in the transmission of many arboviruses such as Ross River virus and Barmah Forest virus, and exotic mosquito vectors such as Aedes aegypti and Aedes albopictus. We conducted a focused literature search to explore the merits of integrating SSDMs and MSDMs with biotic and environmental variables to better predict the future range of endemic mosquito vectors. We show that an integrated framework utilising both SSDMs and MSDMs can improve future mosquito-vector species distribution projections in Australia. We recommend consideration of climate and environmental change projections in the process of developing land-use plans as this directly impacts mosquito-vector distribution and larvae abundance. We also urge laboratory, field-based researchers and modellers to combine these modelling approaches. Having many different variations of integrated (SDM) modelling frameworks could help to enhance the management of endemic mosquitoes in Australia. Enhanced mosquito management measures could in turn lead to lower arbovirus spread and disease notification rates.

Phenotypic Plasticity for Desiccation Resistance, Climate Change, and Future Species Distributions: Will Plasticity Have Much Impact?

AbstractWhile species distribution models (SDMs) are widely used to predict the vulnerability of species to climate change, they do not explicitly indicate the extent to which plastic responses ameliorate climate change impacts. Here we use data on plastic responses of 32 species of Drosophila to desiccation stress to suggest that basal resistance, rather than adult hardening, is relatively more important in determining species differences in desiccation resistance and sensitivity to climate change. We go on to show, using the semimechanistic SDM CLIMEX, that the inclusion of plasticity has some impact on current species distributions and future vulnerability for widespread species but has little impact on the distribution of arguably more vulnerable tropically restricted species.

Chikungunya Virus Transmission at Low Temperature by Aedes albopictus Mosquitoes

Aedes albopictus is an important vector of chikungunya virus (CHIKV). In Australia, Ae. albopictus is currently only known to be present on the islands of the Torres Strait but, should it invade the mainland, it is projected to spread to temperate regions. The ability of Australian Ae. albopictus to transmit CHIKV at the lower temperatures typical of temperate areas has not been assessed. Ae. albopictus mosquitoes were orally challenged with a CHIKV strain from either Asian or East/Central/South African (ECSA) genotypes (10⁷ pfu/mL), and maintained at a constant temperature of either 18 °C or 28 °C. At 3- and 7-days post-infection (dpi), CHIKV RNA copies were quantified in mosquito bodies, and wings and legs using real time polymerase chain reaction (qRT-PCR), while the detection of virus in saliva (a proxy for transmission) was performed by amplification in cell culture followed by observation of cytopathic effect in Vero cells. Of the ≥95% of Ae. albopictus that survived to 7 dpi, all mosquitoes became infected and showed body dissemination of CHIKV at both temperatures and time points. Both the Asian and ECSA CHIKV genotypes were potentially transmissible by Australian Ae. albopictus at 28 °C within 3 days of oral challenge. In contrast, at 18 °C none of the mosquitoes showed evidence of ability to transmit either genotype of CHIKV at 3 dpi. Further, at 18 °C only Ae. albopictus infected with the ECSA genotype showed evidence of virus in saliva at 7 dpi. Overall, infection with the ECSA CHIKV genotype produced higher virus loads in mosquitoes compared to infection with the Asian CHIKV genotype. Our results suggest that lower ambient temperatures may impede transmission of some CHIKV strains by Ae. albopictus at early time points post infection.

Population structuring of the invasive mosquito Aedes albopictus (Diptera: Culicidae) on a microgeographic scale

Aedes albopictus is an invasive mosquito species that has spread globally and can transmit several arboviruses, including dengue, chikungunya and yellow fever. The species was first reported in Brazil in 1986 and since then has been found in 24 of the 27 Brazilian states, often in peri-urban environments close to highly urbanized areas. To date, population genetics of this important mosquito in areas in the city of São Paulo has not been investigated. In this study, we used 12 microsatellite loci to investigate the microgeographic population genetics of Ae. albopictus, which is present throughout the city of São Paulo. All the analyses revealed structuring of the populations studied, divided into two groups with restricted gene flow between them and without evidence of isolation by distance. We propose two hypotheses to explain the results: (i) low dispersal capability—limited gene flow between populations is due to the low dispersal capability inherent to Ae. albopictus; and (ii) multiple introductions—the structure identified here results from multiple introductions, which led to different dispersal patterns within the city and more genetic heterogeneity. The ability of Ae. albopictus to invade new areas and expand may explain why these mosquito populations appear to be well established and thriving in the city of São Paulo.

Insecticide resistance status of Aedes aegypti and Aedes albopictus mosquitoes in Papua New Guinea

BACKGROUND

Aedes aegypti and Ae. albopictus are important vectors of infectious diseases, especially those caused by arboviruses such as dengue, chikungunya and Zika. Aedes aegypti is very well adapted to urban environments, whereas Ae. albopictus inhabits more rural settings. Pyrethroid resistance is widespread in these vectors, but limited data exist from the Southwest Pacific Region, especially from Melanesia. While Aedes vector ecology is well documented in Australia, where incursion of Ae. albopictus and pyrethroid resistance have so far been prevented, almost nothing is known about Aedes populations in neighbouring Papua New Guinea (PNG). With pyrethroid resistance documented in parts of Indonesia but not in Australia, it is important to determine the distribution of susceptible and resistant Aedes populations in this region.

METHODS

The present study was aimed at assessing Aedes populations for insecticide resistance in Madang and Port Moresby, located on the north and south coasts of PNG, respectively. Mosquitoes were collected using ovitraps and reared in an insectary. Standard WHO bioassays using insecticide-treated filter papers were conducted on a total of 253 Ae. aegypti and 768 Ae. albopictus adult mosquitoes. Subsets of samples from both species (55 Ae. aegypti and 48 Ae. albopictus) were screened for knockdown resistance mutations in the voltage-sensitive sodium channel (Vssc) gene, the target site of pyrethroid insecticides.

RESULTS

High levels of resistance against pyrethroids were identified in Ae. aegypti from Madang and Port Moresby. Aedes albopictus exhibited susceptibility to pyrethroids, but moderate levels of resistance to DDT. Mutations associated with pyrethroid resistance were detected in all Ae. aegypti samples screened. Some genotypes found in the present study had been observed previously in Indonesia. No Vssc mutations associated with pyrethroid resistance were found in the Ae. albopictus samples.

CONCLUSIONS

To our knowledge, this is the first report of pyrethroid resistance in Ae. aegypti mosquitoes in PNG. Interestingly, usage of insecticides in PNG is low, apart from long-lasting insecticidal nets distributed for malaria control. Further investigations on how these resistant Ae. aegypti mosquito populations arose in PNG and how they are being sustained are warranted.

Impact of recent and future climate change on vector-borne diseases

Climate change is one of the greatest threats to human health in the 21st century. Climate directly impacts health through climatic extremes, air quality, sea-level rise, and multifaceted influences on food production systems and water resources. Climate also affects infectious diseases, which have played a significant role in human history, impacting the rise and fall of civilizations and facilitating the conquest of new territories. Our review highlights significant regional changes in vector and pathogen distribution reported in temperate, peri-Arctic, Arctic, and tropical highland regions during recent decades, changes that have been anticipated by scientists worldwide. Further future changes are likely if we fail to mitigate and adapt to climate change. Many key factors affect the spread and severity of human diseases, including mobility of people, animals, and goods; control measures in place; availability of effective drugs; quality of public health services; human behavior; and political stability and conflicts. With drug and insecticide resistance on the rise, significant funding and research efforts must to be maintained to continue the battle against existing and emerging diseases, particularly those that are vector borne.

Assessing the current and future biological control potential of Trichogramma ostriniae on its hosts Ostrinia furnacalis and Ostrinia nubilalis

BACKGROUND

Understanding interactions between biocontrol agents and their pest hosts under climate change should assist implementation of biocontrol strategies, by identifying appropriate biocontrol agents for release or determining the optimal timing of releases. Species distribution models (SDMs) were applied to evaluate the distributions of Trichogramma ostriniae and its native host, Ostrinia furnacalis, in southeastern Asia, and a non-native host, Ostrinia nubilalis, in a novel range, North America, using MAXENT and CLIMEX modelling approaches.

RESULTS

The models led to similar predictions about the expected distribution of the two species in Asia, and emphasized likely mismatches between host and natural enemy. Trichogramma ostriniae was predicted to occur in the summer corn region of China, with distribution limits linked to its sensitivity to cold, seasonality of radiation and precipitation. The modelled Ostrinia nubilalis distribution overlapped with the main corn production areas of the northeastern USA and Canada; temporary/seasonal suitable habitat was also predicted across the southeastern USA. Climate change scenarios are predicted to favour T. ostriniae over its hosts in northeastern China and North America.

CONCLUSION

The modelling approaches used here proved useful for assessing environmental factors linked to an egg parasitoid and its lepidopteran hosts and identifying areas potentially suitable for inundative releases. © 2017 Society of Chemical Industry.

Evaluation of the impacts of climate change on disease vectors through ecological niche modelling

Vector-borne diseases are exceptionally sensitive to climate change. Predicting vector occurrence in specific regions is a challenge that disease control programs must meet in order to plan and execute control interventions and climate change adaptation measures. Recently, an increasing number of scientific articles have applied ecological niche modelling (ENM) to study medically important insects and ticks. With a myriad of available methods, it is challenging to interpret their results. Here we review the future projections of disease vectors produced by ENM, and assess their trends and limitations. Tropical regions are currently occupied by many vector species; but future projections indicate poleward expansions of suitable climates for their occurrence and, therefore, entomological surveillance must be continuously done in areas projected to become suitable. The most commonly applied methods were the maximum entropy algorithm, generalized linear models, the genetic algorithm for rule set prediction, and discriminant analysis. Lack of consideration of the full-known current distribution of the target species on models with future projections has led to questionable predictions. We conclude that there is no ideal 'gold standard' method to model vector distributions; researchers are encouraged to test different methods for the same data. Such practice is becoming common in the field of ENM, but still lags behind in studies of disease vectors.

Developing Health-Related Indicators of Climate Change: Australian Stakeholder Perspectives

Climate-related health indicators are potentially useful for tracking and predicting the adverse public health effects of climate change, identifying vulnerable populations, and monitoring interventions. However, there is a need to understand stakeholders’ perspectives on the identification, development, and utility of such indicators. A qualitative approach was used, comprising semi-structured interviews with key informants and service providers from government and non-government stakeholder organizations in South Australia. Stakeholders saw a need for indicators that could enable the monitoring of health impacts and time trends, vulnerability to climate change, and those which could also be used as communication tools. Four key criteria for utility were identified, namely robust and credible indicators, specificity, data availability, and being able to be spatially represented. The variability of risk factors in different regions, lack of resources, and data and methodological issues were identified as the main barriers to indicator development. This study demonstrates a high level of stakeholder awareness of the health impacts of climate change, and the need for indicators that can inform policy makers regarding interventions.

Rapid Surveillance for Vector Presence (RSVP): Development of a novel system for detecting Aedes aegypti and Aedes albopictus

Background

The globally important Zika, dengue and chikungunya viruses are primarily transmitted by the invasive mosquitoes, Aedes aegypti and Aedes albopictus. In Australia, there is an increasing risk that these species may invade highly urbanized regions and trigger outbreaks. We describe the development of a Rapid Surveillance for Vector Presence (RSVP) system to expedite presence- absence surveys for both species.

Methodology/Principal findings

We developed a methodology that uses molecular assays to efficiently screen pooled ovitrap (egg trap) samples for traces of target species ribosomal RNA. Firstly, specific real-time reverse transcription-polymerase chain reaction (RT-PCR) assays were developed which detect a single Ae. aegypti or Ae. albopictus first instar larva in samples containing 4,999 and 999 non-target mosquitoes, respectively. ImageJ software was evaluated as an automated egg counting tool using ovitrap collections obtained from Brisbane, Australia. Qualitative assessment of ovistrips was required prior to automation because ImageJ did not differentiate between Aedes eggs and other objects or contaminants on 44.5% of ovistrips assessed, thus compromising the accuracy of egg counts. As a proof of concept, the RSVP was evaluated in Brisbane, Rockhampton and Goomeri, locations where Ae. aegypti is considered absent, present, and at the margin of its range, respectively. In Brisbane, Ae. aegypti was not detected in 25 pools formed from 477 ovitraps, comprising ≈ 54,300 eggs. In Rockhampton, Ae. aegypti was detected in 4/6 pools derived from 45 ovitraps, comprising ≈ 1,700 eggs. In Goomeri, Ae. aegypti was detected in 5/8 pools derived from 62 ovitraps, comprising ≈ 4,200 eggs.

Conclusions/Significance

RSVP can rapidly detect nucleic acids from low numbers of target species within large samples of endemic species aggregated from multiple ovitraps. This screening capability facilitates deployment of ovitrap configurations of varying spatial scales, from a single residential block to entire suburbs or towns. RSVP is a powerful tool for surveillance of invasive Aedes spp., validation of species eradication and quality assurance for vector control operations implemented during disease outbreaks.

Aedes (Stegomyia) vectors of dengue, Zika and chikungunya viruses utilize artificial and natural containers as larval habitats. Adults do not usually disperse far (< 500 m) from these larval habitats in urban and peri-urban environments. Highly heterogeneous distributions raise significant logistic challenges to conduct informative surveillance. Public health imperatives require contemporaneous vector mosquito presence-absence data for highly urbanized regions that are both vulnerable to invasions and have frequent exposure to viremic travellers. We developed a promising tool to expedite presence-absence surveillance of Aedes aegypti and Aedes albopictus by integrating molecular diagnostics with ovitraps and automated egg quantification software. The high sensitivity of the molecular assays enabled samples from multiple ovitraps to be pooled and processed for each diagnostic test. This innovation resolves the considerable logistic constraints inherent in traditional ovitrap surveillance programs. Proof of concept was evaluated in field trials in Queensland geographies where Ae. aegypti is considered either absent, present or at the margin of its range (Brisbane, Rockhampton and Goomeri, respectively). Aedes aegypti was detected in Goomeri and Rockhampton and not detected in Brisbane. Further investigation is required to address the inaccuracy of automated egg counting software whenever contaminants are present. RSVP can accommodate varied ovitrap designs and deployment configurations, improves efficiency in laboratory and labor costs for high volumes of samples, and enables a rapid turnaround of results. The RSVP system can innovate surveillance programs for early-warning of invasion, eradication, and quality assurance for vector control in disease response contexts.

Holding back the tiger: Successful control program protects Australia from Aedes albopictus expansion

Background

The Asian tiger mosquito, Aedes albopictus, is an important vector of dengue, chikungunya and Zika viruses and is a highly invasive and aggressive biter. Established populations of this species were first recognised in Australia in 2005 when they were discovered on islands in the Torres Strait, between mainland Australia and Papua New Guinea. A control program was implemented with the original goal of eliminating Ae. albopictus from the Torres Strait. We describe the evolution of management strategies that provide a template for Ae. albopictus control that can be adopted elsewhere.

Methodology / Principal findings

The control strategy implemented between 2005 and 2008 targeted larval habitats using source reduction, insect-growth regulator and pyrethroid insecticide to control larvae and adults in the containers. However, the infrequency of insecticide reapplication, the continual accumulation and replacement of containers, and imminent re-introduction of mosquitoes through people’s movement from elsewhere compromised the program. Consequently, in 2009 the objective of the program changed from elimination to quarantine, with the goal of preventing Ae albopictus from infesting Thursday and Horn islands, which are the transport hubs connecting the Torres Strait to mainland Australia. However, larval control strategies did not prevent the species establishing on these islands in 2010. Thereafter, an additional strategy adopted by the quarantine program in early 2011 was harborage spraying, whereby the vegetated, well shaded resting sites of adult Ae. albopictus were treated with a residual pyrethroid insecticide. Inclusion of this additional measure led to a 97% decline in Ae. albopictus numbers within two years. In addition, the frequency of container treatment was increased to five weeks between treatments, compared to an average of 8 weeks that occurred in the earlier iterations of the program. By 2015 and 2016, Ae. albopictus populations on the two islands were undetectable in 70–90% of surveys conducted. Importantly, a comprehensive surveillance network in selected strategic areas has not identified established populations of this species on the Australian mainland.

Conclusions / Significance

The program has successfully reduced Ae. albopictus populations on Thursday Island and Horn Island to levels where it is undetectable in up to 90% of surveys, and has largely removed the risk of mainland establishment via that route. The vector management strategies adopted in the later years of the program have been demonstrably successful and provide a practical management framework for dengue, chikungunya or Zika virus outbreaks vectored by Ae. albopictus. As of June 2016, Ae. albopictus had not established on the Australian mainland and this program has likely contributed significantly to this outcome.

Aedes albopictus is a disease vector and biting nuisance of major public health concern. Established populations of Ae. albopictus were first recognised in Australia in 2005 after they were discovered on islands in the Torres Strait. Consequently, a control program was established in the same year to eliminate Ae. albopictus populations in the Torres Strait in order to reduce the risk of disease, as well as to prevent the mosquito from spreading to the mainland of Australia. In 2009, the goal of the program changed from elimination to quarantine (cordon sanitaire) focusing mainly on the inner islands of Thursday Island and Horn Island, which are the major population, administrative and transport centres linking the Torres Strait region to the Australian mainland. The cordon sanitaire strategy involved an integrated approach composed of harborage spraying, source reduction, insecticide treatment of containers, lethal tire piles, mosquito population monitoring and public awareness campaigns. Strategic improvements in management techniques led to a 97% decline in Ae. albopictus numbers on the two islands between 2011 and 2012. By 2015, the program had successfully reduced Ae. albopictus populations on Thursday Island and Horn Island to levels where the species was frequently undetectable, and had largely removed the risk of mainland incursion via that route. In 2016 the improved management strategies were also adopted to successfully control a dengue outbreak in which Ae. albopictus was the implicated vector on two outer islands of the Torres Strait.

Ten years of the Tiger: Aedes albopictus presence in Australia since its discovery in the Torres Strait in 2005

The “Asian tiger mosquito”, Aedes albopictus, is highly invasive, an aggressive biter and a major arbovirus vector. It is not currently present on mainland Australia despite being intercepted on numerous occasions at international ports and infesting the Torres Strait of Australia since at least 2004. In the current paper, we describe the invasion and current status of Ae. albopictus in the Torres Strait, as well as research conducted to assess the threat of this species becoming established in arbovirus transmission cycles on the Australian mainland. Genetic analysis of the invading population demonstrated that the Indonesian region was the likely origin of the invasion and not Papua New Guinea (PNG) as initially suspected. There was also intermixing between Torres Strait, PNG and Indonesian populations, indicating that the species could be re-introduced into the Torres Strait compromising any successful eradication programme. Vector competence experiments with endemic and exotic viruses revealed that Ae. albopictus from the Torres Strait are efficient alphavirus vectors, but less efficient flavivirus vectors. Ae.albopictus obtains blood meals from a range of vertebrate hosts (including humans), indicating that it could play a role in both zoonotic and human-mosquito arbovirus transmission cycles in Australia. Predictive models coupled with climate tolerance experiments suggest that a Torres Strait strain of Ae. albopictus could colonise southern Australia by overwintering in the egg stage before proliferating in the warmer months. Cohabitation experiments demonstrated that the presence of Aedes notoscriptus larvae in containers would not prevent the establishment of Ae. albopictus. Evidence from these studies, coupled with global experience suggests that we need to be prepared for the imminent invasion of Australia by Ae. albopictus by thoroughly understanding its biology and being willing to embrace emerging control technologies.

The Usual Suspects: Comparison of the Relative Roles of Potential Urban Chikungunya Virus Vectors in Australia

The global re-emergence of chikungunya virus (CHIKV) over the last decade presents a serious public health risk to Australia. An increasing number of imported cases further underline the potential for local transmission to occur if local mosquitoes bite an infected traveller. Laboratory experiments have identified a number of competent Australian mosquito species, including the primary vectors of CHIKV abroad, Aedes aegypti and Aedes albopictus, and local endemic species Aedes vigilax and Aedes notoscriptus. The implication of these additional endemic species as potential vectors has generated much uncertainty amongst public health professionals regarding their actual role in CHIKV transmission in the field. Using data estimated from or documented in the literature, we parameterise a simple vectorial capacity model to evaluate the relative roles of Australian mosquito species in potential CHIKV transmission. The model takes into account a number of key biological and ecological variables which influence the role of a species in field transmission, including population density, human feeding rates, mosquito survival rates and vector competence. We confirm the relative importance of Ae. aegypti and Ae. albopictus in sustaining potential CHIKV transmission in Australia. Even at maximum estimated densities and human feeding rates, Ae. vigilax and Ae. notoscriptus are likely to play a relatively minor role in CHIKV transmission, when compared with either Ae. aegypti or Ae. albopictus. This relatively straightforward analysis has application for any region where mosquito species have been incriminated in vector competence experiments, but where their actual role in CHIKV transmission has not been established.

The Spread of Aedes albopictus in Metropolitan France: Contribution of Environmental Drivers and Human Activities and Predictions for a Near Future

Invasion of new territories by insect vector species that can transmit pathogens is one of the most important threats for human health. The spread of the mosquito Aedes albopictus in Europe is emblematic, because of its major role in the emergence and transmission of arboviruses such as dengue or chikungunya. Here, we modeled the spread of this mosquito species in France through a statistical framework taking advantage of a long-term surveillance dataset going back to the first observation of Ae. albopictus in the Metropolitan area. After validating the model, we show that human activities are especially important for mosquito dispersion while land use is a major factor for mosquito establishment. More importantly, we show that Ae. albopictus invasion is accelerating through time in this area, resulting in a geographic range extending further and further year after year. We also show that sporadic “jump” of Ae. albopictus in a new location far from the colonized area did not succeed in starting a new invasion front so far. Finally, we discuss on a potential adaptation to cooler climate and the risk of invasion into Northern latitudes.

Effects of Cohabitation on the Population Performance and Survivorship of the Invasive Mosquito Aedes albopictus and the Resident Mosquito Aedes notoscriptus (Diptera: Culicidae) in Australia

The presence of Aedes albopictus (Skuse) in the Torres Strait of northern Australia increases the potential for colonization and establishment on the mainland. However, there is a possibility that native species that occupy the same habitats may influence the population performance of Ae. albopictus, potentially affecting the establishment of this species in Australia. Cohabitation experiments were performed with the endemic Aedes notoscriptus (Skuse), which has been found occupying the same larval habitats as Ae. albopictus in the Torres Strait and is the most widespread container-inhabiting Aedes species in Australia. The influence of environmental factors and cohabitation between the two species was examined using different climates, food resource levels, food resource types, and species densities. Survivorship proportions and a population performance index (λ') were calculated and compared. The consequences of increased Ae. notoscriptus densities were reduced survivorship and λ' for Ae. albopictus. Despite this, the mean λ' of Ae. albopictus and Ae. notoscriptus was consistently ≥ 1.06, indicating both species could increase under all conditions, potentially due to increasing conspecific densities negatively affecting Ae. notoscriptus. The outcomes from this study suggest that the preexisting presence of Ae. notoscriptus may not prevent the establishment of Ae. albopictus in Australia.

Ability for Aedes albopictus (Diptera: Culicidae) to survive at the climatic limits of its potential range in eastern Australia

Aedes albopictus (Skuse) is one of the most invasive mosquito species in the world and has infested islands in the Torres Strait, off the northern coast of Australia since at least 2004. This has led to fears that it may establish on the Australian mainland, including highly populated cities in southern temperate regions. To supplement theoretical projections addressing the range expansion of Ae. albopictus into Australia, laboratory-based trials were conducted to assess the performance of a Torres Strait Ae. albopictus population under a range of Australian conditions. First-instar larvae were placed in individual microcosms and maintained on a natural food resource, under average climatic conditions representing different regions of Australia's east coast. Larvae could not survive winter conditions in southern Australia. As the population performance index was >1.0 for tropical winter and summer conditions, and temperate summer conditions, populations would likely increase during these times. To test whether Ae. albopictus could overwinter during adverse conditions as eggs, we exposed cohorts to four different temperature (7, 17, 27, and 33 degrees C) and relative humidity (35, 55, and 80%) combinations for up to 3 mo. High temperatures and low humidity were most detrimental to egg survival. However, those eggs maintained under cooler climates remained viable after 3 mo, including 17% of eggs kept at 7 degrees C. Overall, this study suggests that a Torres Strait Ae. albopictus strain could proliferate all year round under northern tropical conditions and could overwinter in the egg stage before proliferating in the summer in southern temperate regions.