Local environmental factors drive distributions of ecologically-contrasting mosquito species (Diptera: Culicidae).

Mosquitoes are important vectors of disease pathogens and multiple species are undergoing geographical shifts due to global changes. As such, there is a growing need for accurate distribution predictions. Ecological niche modelling (ENM) is an effective tool to assess mosquito distribution patterns and link these to underlying environmental preferences. Typically, macroclimatic variables are used as primary predictors of mosquito distributions. However, they likely undervalue local conditions and intraspecific variation in environmental preferences. This is problematic, as mosquito control takes place at the local scale. Utilising high-resolution (10 × 10 m) Maxent ENMs on the island of Bonaire as model system, we explore the influence of local environmental variables on mosquito distributions. Our results show a distinct set of environmental variables shape distribution patterns across ecologically-distinct species, with urban variables strongly associated with introduced species like Aedes aegypti and Culex quinquefasciatus, while native species show habitat preferences for either mangroves, forests, or ephemeral water habitats. These findings underscore the importance of distinct local environmental factors in shaping distributions of different mosquitoes, even on a small island. As such, these findings warrant further studies aimed at predicting high-resolution mosquito distributions, opening avenues for preventative management of vector-borne disease risks amidst ongoing global change and ecosystem degradation.

[West Nile virus unexpectedly in the Netherlands]. / Het westnijlvirus in 2020 toch in Nederland.

West Nile virus (WNV) was first detected in birds, mosquitoes and subsequently in humans in the Netherlands in 2020. In 2016 , we had discussed the factors that influence the introduction, establishment and dissemination of WNV in the Netherlands and considered the probability that each of these three phases could occur in the Netherlands, and cause West Nile fever in humans, still relatively small. In the current article we evaluate on the basis of our reasoning at the time, whether we have missed important factors and/or whether new factors have appeared on the horizon. We then explain what the findings/ this progressive insight of 2020 mean for the near future.

[Birds, mosquitoes and West Nile virus: little risk of West Nile fever in the Netherlands]. / Van vogels, muggen en West-Nijl-virus: weinig kans op West-Nijl-koorts in Nederland.

Due to increased incidence of West Nile fever (WNF) in Europe and the rapid spread of West Nile virus (WNV) in the US, it is commonly thought that it will only be a matter of time before WNV reaches the Netherlands. However, assessing whether WNV is really a threat to the Dutch population is challenging, due to the numerous factors affecting transmission of the virus. Some of these factors are known to limit the risk of WNF in the Netherlands. This risk is determined by the interaction between the pathogen (WNV), the vectors (Culex mosquitoes), the reservoirs (birds) and the exposure of humans to infected mosquitoes. In this paper, we discuss the factors influencing introduction, establishment and spread of WNV in the Netherlands. The probability that each of these three phases will occur in the Netherlands is currently relatively small, as is the risk of WNF infection in humans in the Netherlands.

Copulation Activity, Sperm Production and Conidia Transfer in Aedes aegypti Males Contaminated by Metarhizium anisopliae: A Biological Control Prospect.

BACKGROUND: Dengue is the most prevalent arboviral disease transmitted by Aedes aegypti worldwide, whose chemical control is difficult, expensive, and of inconsistent efficacy. Releases of Metarhizium anisopliae--exposed Ae. aegypti males to disseminate conidia among female mosquitoes by mating represents a promising biological control approach against this important vector. A better understanding of fungus virulence and impact on reproductive parameters of Ae. aegypti, is need before testing auto-dissemination strategies. METHODOLOGY/PRINCIPAL FINDINGS: Mortality, mating competitiveness, sperm production, and the capacity to auto-disseminate the fungus to females up to the 5 th copulation, were compared between Aedes aegypti males exposed to 5.96 x 10(7) conidia per cm2 of M. anisopliae and uninfected males. Half (50%) of fungus-exposed males (FEMs) died within the first 4 days post-exposure (PE). FEMs required 34% more time to successively copulate with 5 females (165 ± 3 minutes) than uninfected males (109 ± 3 minutes). Additionally, fungus infection reduced the sperm production by 87% at 5 days PE. Some beneficial impacts were observed, FEMs were able to successfully compete with uninfected males in cages, inseminating an equivalent number of females (about 25%). Under semi-field conditions, the ability of FEMs to search for and inseminate females was also equivalent to uninfected males (both inseminating about 40% females); but for the remaining females that were not inseminated, evidence of tarsal contact (transfer of fluorescent dust) was significantly greater in FEMs compared to controls. The estimated conidia load of a female exposed on the 5th copulation was 5,200 mL(-1) which was sufficient to cause mortality. CONCLUSION/SIGNIFICANCE: Our study is the first to demonstrate auto-dissemination of M. anisopliae through transfer of fungus from males to female Ae. aegypti during mating under semi-field conditions. Our results suggest that auto-dissemination studies using releases of FEMs inside households could successfully infect wild Ae. aegypti females, providing another viable biological control tool for this important the dengue vector.

[Fighting mosquitoes in the Netherlands: risks and control of exotic mosquitoes]. / Muggenbestrijding in Nederland: risico's en bestrijding van exotische muggen.

Mosquitoes play a significant role globally in the transmission of so-called vector-borne diseases. In the Netherlands, native mosquitoes are capable of transmitting infectious disease. This has not resulted in outbreaks of disease over the last 50 years. The establishment of exotic mosquito species could pose risks to public health, especially in the case of the Asian tiger mosquito (Aedes albopictus). Several organisations are working together to prevent the establishment of exotic mosquitoes in the Netherlands. A plan for controlling native mosquito species is also currently being developed.

[Dengue and chikungunya acquired during travel in the tropics]. / Dengue en chikungunya bij reizen naar de tropen.

The global incidence of dengue and chikungunya has greatly increased over recent decades, partly due to the increase of geographic distribution of both vectors. These infections are endemic to the tropics and subtropics, however autochthonous transmission and outbreaks have been described in non-endemic areas. Currently, there is a large chikungunya outbreak in the western hemisphere which started in the Caribbean. Chikungunya had not previously been endemic to this region. Both arboviral infections are important causes of fever in Dutch travellers returning from tropical destinations. The clinical presentations of dengue and chikungunya overlap; both are characterised by high fever and arthralgia. Bleeding and plasma leakage are potentially life-threatening complications of dengue, while persistent arthralgia typifies chikungunya. The prevention of mosquito bites, by using protective clothing and insect repellents, is the only way to prevent infection. No vaccine is yet available.

Prioritizing emerging zoonoses in the Netherlands.

BACKGROUND: To support the development of early warning and surveillance systems of emerging zoonoses, we present a general method to prioritize pathogens using a quantitative, stochastic multi-criteria model, parameterized for the Netherlands. METHODOLOGY/PRINCIPAL FINDINGS: A risk score was based on seven criteria, reflecting assessments of the epidemiology and impact of these pathogens on society. Criteria were weighed, based on the preferences of a panel of judges with a background in infectious disease control. CONCLUSIONS/SIGNIFICANCE: Pathogens with the highest risk for the Netherlands included pathogens in the livestock reservoir with a high actual human disease burden (e.g. Campylobacter spp., Toxoplasma gondii, Coxiella burnetii) or a low current but higher historic burden (e.g. Mycobacterium bovis), rare zoonotic pathogens in domestic animals with severe disease manifestations in humans (e.g. BSE prion, Capnocytophaga canimorsus) as well as arthropod-borne and wildlife associated pathogens which may pose a severe risk in future (e.g. Japanese encephalitis virus and West-Nile virus). These agents are key targets for development of early warning and surveillance.

Improving efficacy of Box gravid traps for collecting Culex quinquefasciatus.

In outdoor screen cages, one and two-choice assays were conducted with gravid Cx. quinquefasciatus to assess and improve the efficacy of the Box gravid trap. Subsequently, in a field trial, a modified Box gravid trap was compared with three other gravid traps: the CDC gravid trap, the CFG gravid trap, and a novel design of a sticky gravid trap. A major disadvantage of the Box gravid trap, a relatively low trapping efficacy, was overcome with a simple modification to the trap configuration. By replacing the solid lid of the collecting tray with mosquito netting, the air velocity through the trap inlet was doubled and the quality of the resting sites for caught females was improved. As a result, the modified Box gravid trap caught and retained twice as many Cx. quinquefasciatus as its predecessor in two-choice bioassays in the screened cages and proved as effective as the commercially available CDC gravid trap in the field, but without damaging the collected specimens. Captures with the Box and CDC gravid traps were significantly greater than those of either the Counter Flow Geometry gravid trap or a sticky gravid trap.

Habitat segregation of mosquito arbovirus vectors in south Florida.

Oviposition traps set in rural to urban environments in three south Florida counties were colonized predominantly by Culex quinquefasciatus Say (35.1%), Aedes albopictus (Skuse) (34.5%), Aedes aegypti (L.) (23.8%), and Culex nigripalpus Theobald (6.6%) during 1 yr of monthly sampling. Significant differences were detected among counties for abundances of Cx. quinquefasciatus and for percentage composition of that species and Ae. albopictus. Aerial images of habitats around each collection site were digitized, and coverages by each of 16 habitat variables were recorded. Abundances ofAe. aegypti were positively related to habitat variables associated with urbanization and negatively correlated to those reflecting rural characteristics. Multiple regression models of habitat selection explained similar proportions of variances in abundance of Ae. aegypti and Ae. albopictus, but signs of significant variables were opposite for these two species. No consistent trends of habitat associations were observed among counties for the two Culex spp. Co-occurrences of the four species in individual traps depended on container type (tub versus cup), and, for Aedes spp. with Culex spp., county. The results underscore the importance of scale in evaluating habitat selection and the utility of quantifiable habitat characteristics of intermediate scale to identify site characteristics favored by the arboviral vectors Ae. aegypti and Ae. albopictus.

The invasion of urban forest by dengue vectors in Rio de Janeiro.

The invasion of a secondary forest within the city of Rio de Janeiro by Aedes aegypti and Ae. albopictus was evaluated from July 1997 to June 1998 through collections of immature stages in ovitraps set at 1 m, 10 m, 100 m, 500 m, and 1,000 m into the forest from houses on the periphery. Both mosquito species were much more abundant close to houses (1-10 m). Aedes aegypti was not collected beyond 100 m, while Ae. albopictus was the most abundant species overall and in ovitraps at all distances from houses. Abundances of Ae. albopictus were significantly correlated with time-lagged rainfall and with abundances of Ae. aegypti. Co-occurrences of Ae. albopictus in traps with Ae. aegypti and Limatus durhami, but not with Culex dolosus, were more likely close to houses. The results suggest that the urban forest is a refuge for both Aedes species, but especially for Ae. albopictus, whose abundance both near houses and in the forest raises concern that this invader may transmit arboviruses to humans that are presently restricted to the sylvan environment.

Convergent habitat segregation of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in southeastern Brazil and Florida.

During the rainy season of 2001, the incidence of the dengue vectors Aedes aegypti and Ae. albopictus was examined in different habitats of two cities (Rio de Janeiro and Nova Iguaçu) in Rio de Janeiro State, Brazil, and in two cities (Palm Beach and Boca Raton) in Florida. Oviposition trap collections were performed in urban, suburban, and rural habitats in both areas. Our hypothesis that the abundances and frequencies of occurrence of Ae. aegypti and Ae albopictus are affected in opposite ways by increasing urbanization was only partially supported. City, habitat, and their interaction significantly affected the abundance of both species. Cities with high abundance of Ae. aegypti also had a high abundance of Ae. albopictus. The two species were most abundant in the cities of Rio de Janeiro state and the lowest in Boca Raton. Habitat had a significant but opposite effect on the abundances of Ae. aegypti and Ae. albopictus. In general, Ae. aegypti was most prevalent in highly urbanized areas and Ae. albopictus in rural, suburban, and vegetated urban areas in Rio de Janeiro state and Florida. However, abundances of the two species were similar in most suburban areas. Analyses of frequencies of occurrence showed an unexpected high level of co-occurrence of both species in the same oviposition trap. Despite the different geographical origins of Ae. albopictus in Brazil and the United States, the habitats used by this recent invader are remarkably similar in the two countries.