Wing morphometric variability in Aedes aegypti (Diptera: Culicidae) from different urban built environments

BACKGROUND

Aedes aegypti is the main vector of the dengue, Zika and several other arboviruses. It is highly adapted to urbanized environments and can be found worldwide. Mosquito population control is considered the best strategy for fighting mosquito-borne diseases, making an understanding of their population dynamics vital for the development of more effective vector control programs. This study therefore sought to investigate how different levels of urbanization affect Aedes aegypti populations and modulate population structure in this species with the aid of wing geometric morphometrics.

METHODS

Specimens were collected from eleven locations in three areas with distinct levels of urbanization in the city of São Paulo, Brazil: conserved, intermediate and urbanized. The right wings of female mosquitoes collected were removed, and photographed and digitized. Canonical variate analysis and Mahalanobis distance were used to investigate the degree of wing-shape dissimilarity among populations. Thin-plate splines were calculated by regression analysis of Canonical Variation Analysis scores against wing-shape variation, and a cross-validated reclassification was performed for each individual; a neighbor-joining tree was then constructed.

RESULTS

Metapopulation and individual population analysis showed a clear segregation pattern in the Canonical Variation Analysis. Pairwise cross-validated reclassification yielded relatively high scores considering the microgeographical scale of the study and the fact that the study populations belong to the same species. The neighbor-joining tree showed that mosquitoes in the intermediate urban area segregated in the metapopulation and individual population analyses. Our findings show significant population structuring in Aedes aegypti mosquitoes in the areas studied. This is related to the different degrees of urbanization in the areas where the specimens were collected along with their geographical location.

CONCLUSIONS

Urbanization processes in the study areas appear to play an important role in microevolutionary processes triggered by man-made modifications in the environment, resulting in a previously unknown population structuring pattern of major epidemiological importance.

Generation of axenic Aedes aegypti demonstrate live bacteria are not required for mosquito development

The mosquito gut microbiome plays an important role in mosquito development and fitness, providing a promising avenue for novel mosquito control strategies. Here we present a method for rearing axenic (bacteria free) Aedes aegypti mosquitoes, consisting of feeding sterilized larvae on agar plugs containing a high concentration of liver and yeast extract. This approach allows for the complete development to adulthood while maintaining sterility; however, axenic mosquito's exhibit delayed development time and stunted growth in comparison to their bacterially colonized cohorts. These data challenge the notion that live microorganisms are required for mosquito development, and suggest that the microbiota's main role is nutritional. Furthermore, we colonize axenic mosquitoes with simplified microbial communities ranging from a single bacterial species to a three-member community, demonstrating the ability to control the composition of the microbiota. This axenic system will allow the systematic manipulation of the mosquito microbiome for a deeper understanding of microbiota-host interactions.

Ultrastructural Analysis of Chikungunya Virus Dissemination from the Midgut of the Yellow Fever Mosquito, Aedes aegypti

The transmission cycle of chikungunya virus (CHIKV) requires that mosquito vectors get persistently infected with the virus, following its oral acqsuisition from a vertebrate host. The mosquito midgut is the initial organ that gets infected with orally acquired CHIKV. Following its replication in the midgut epithelium, the virus exits the midgut and infects secondary tissues including the salivary glands before being transmitted to another host. Here, we investigate the pattern of CHIKV dissemination from the midgut of Aedes aegypti at the ultrastructural level. Bloodmeal ingestion caused overstretching of the midgut basal lamina (BL), which was disrupted in areas adjacent to muscles surrounding the midgut as shown by scanning electron microscopy (SEM). Using both transmission electron microscopy (TEM) and focused ion beam scanning electron microscopy (FIB-SEM) to analyze midgut preparations, mature chikungunya (CHIK) virions were found accumulating at the BL and within strands of the BL at 24⁻32 h post-infectious bloodmeal (pibm). From 48 h pibm onwards, virions no longer congregated at the BL and became dispersed throughout the basal labyrinth of the epithelial cells. Ingestion of a subsequent, non-infectious bloodmeal caused mature virions to congregate again at the midgut BL. Our study suggests that CHIKV needs a single replication cycle in the midgut epithelium before mature virions directly traverse the midgut BL during a relatively narrow time window, within 48 h pibm.

Glyphosate impairs learning in Aedes aegypti mosquito larvae at field-realistic doses

Glyphosate is the most widely used herbicide in the world. Over the past few years, the number of studies revealing deleterious effects of glyphosate on non-target species has been increasing. Here, we studied the impact of glyphosate at field-realistic doses on learning in mosquito larvae (Aedes aegypti). Larvae of A. aegypti live in small bodies of water and perform a stereotyped escape response when a moving object projects its shadow on the water surface. Repeated presentations of an innocuous visual stimulus induce a decrease in response due to habituation, a non-associative form of learning. In this study, different groups of larvae were reared in water containing different concentrations of glyphosate that are commonly found in the field (50 µg l-1, 100 µg l-1, 210 µg l-1 and 2 mg l-1). Larvae reared in a glyphosate solution of 2 mg l-1 (application dose) could complete their development. However, glyphosate at a concentration of 100 µg l-1 impaired habituation. A dose-dependent deleterious effect on learning ability was observed. This protocol opens new avenues to further studies aimed at understanding how glyphosate affects non-target organisms, such as insects. Habituation in mosquito larvae could serve as a parameter for testing the impact of pollutants in the water.

Location, seasonal, and functional characteristics of water holding containers with juvenile and pupal Aedes aegypti in Southern Taiwan: A cross-sectional study using hurdle model analyses

Background

Aedes aegypti carries several viruses of public health importance, including the dengue virus. Dengue is the most rapidly spreading mosquito-borne viral disease in the world. Prevention and control of dengue mainly rely on mosquito control as there is no antiviral treatment or a WHO-approved vaccine. To reduce the Ae. aegypti population, studying the characteristics of their habitats is necessary. Aedes aegypti prefer breeding in artificial water holding containers in peridomestic or domestic settings. Their juveniles (1^st - 4^th instar larvae and pupae) have a tendency to cluster in certain types of containers. To inform control strategies, it is important to assess whether the pupae subgroup has a distinct distribution by container type as compared to the overall group of juveniles. The objective of this study was to assess for distinct predictors (location, season, and function) of Ae. aegypti juveniles and pupae numbers in water holding containers by applying hurdle model analyses.

Methodology

The field component of this study was carried out from November 2013 to July 2015 in Southern Taiwan where annual autochthonous dengue has been reported for decades. Water holding containers with stagnant water were identified in a predefined urban area in Kaohsiung City (KH) and a rural area in Pingtung County. Given that mosquito survey data often include many containers with zero Ae. aegypti, a negative binomial hurdle model was applied to model the association between location, seasonal and functional characteristics of the water holding containers and the number of Ae. aegypti in each container.

Results

The results showed that Ae. aegypti were almost exclusively present in the urban area. In this area, the negative binomial hurdle model predicted significantly more juveniles as well as pupae Ae. aegypti in water holding containers during the wet season when compared to the dry season. Notably, the model predicted more juveniles in containers located on private property compared to those on government property, irrespective of season. As for pupae, the model predicted higher amounts in indoor containers used for water storage compared to outdoor water storage containers, irrespective of season. However, for the specific category ‘other water receptacle’, higher amounts of pupae were predicted in outdoor compared to indoor in water receptacles, such as flower pot saucers and water catchment buckets.

Conclusions

The difference in predictors for juveniles and the pupae subgroup was identified and it may be of importance to the control strategies of the authorities in KH. At present the authorities focus control activities on all water holding containers found on government property. To improve the ongoing control efforts in KH, the focus of control activities maintained by the KH authorities should be expanded to indoor water storage containers and outdoor water receptacles on both private and government properties to adequately address habitats harboring greater numbers of pupae. In addition, it is proposed to increase community engagement in managing water in all types of water holding containers located on privately owned properties (indoor and outdoor), especially during wet season.

Dengue is considered the most significant mosquito-borne disease, globally. It is transmitted by the mosquito Aedes aegypti throughout most affected countries. In order to prevent dengue, most control efforts focus on removing Ae. aegypti from the environment, as currently there are no anti-viral treatment or WHO approved vaccine. Removing or destroying the breeding sites of Ae. aegypti is generally recommended. However, this may be difficult as the mosquito breeds in a wide variety of water holding containers readily available in the human environment. The urban areas of Southern Taiwan have experienced annual dengue epidemics for decades in spite of substantial efforts to control Ae. aegypti. In this study we investigated whether containers harboring the highest number of Ae. aegypti differ between all active aquatic stages (larvae and pupae) and the final aquatic stage (pupae only). In Kaohsiung City in Southern Taiwan, we found that more Ae. aegypti were predicted to be in containers on private property, compared with government property, when assessing all aquatic stages. However, for pupae only, more were found in indoor containers used for water storage when compared with outdoor water storage containers. For the specific category ‘other water receptacle’ such as flower pot saucers and water catchment buckets, the model predicted more pupae in outdoor containers compared with indoor containers. We recommend that future control efforts target these types of containers to reduce the risk of dengue transmission in Southern Taiwan.

The effect of parasite infection on the recombination rate of the mosquito Aedes aegypti

Sexual reproduction and meiotic recombination generate new genetic combinations and may thereby help an individual infected by a parasite to protect its offspring from being infected. While this idea is often used to understand the evolutionary forces underlying the maintenance of sex and recombination, it also suggests that infected individuals should increase plastically their rate of recombination. We tested the latter idea with the mosquito Aedes aegypti and asked whether females infected by the microsporidian Vavraia culicis were more likely to have recombinant offspring than uninfected females. To measure the rate of recombination over a chromosome we analysed combinations of microsatellites on chromosome 3 in infected and uninfected females, in the (uninfected) males they copulated with and in their offspring. As predicted, the infected females were more likely to have recombinant offspring than the uninfected ones. These results show the ability of a female to diversify her offspring in response to parasitic infection by plastically increasing her recombination rate.

Target and non-target toxicity of fern extracts against mosquito vectors and beneficial aquatic organisms

Dengue and malaria are significant mosquito-borne diseases that are rapidly spread worldwide, mainly in temperate countries. Pteridophytes were identified to be a significant source of novel mosquitocidal agents. The present research was to explore the eco-friendly larvicides from methanol extracts of ferns, viz., Actiniopteris radiata, Adiantum caudatum, Cheilanthes swartzii, Hemionitis arifolia and Lycopodium clavatum. The larvicidal potential of the extracts screened using larvae of dengue vector Aedes aegypti (III and IV instar) and malarial vector Anopheles stephensi (III and IV instar), showed 10-100% mortality rates. Biosafety assessment was made on embryos of Danio rerio and Artemia nauplii. The phyto-constituents of the methanol extract of A. radiata leaves were identified through gas chromatography-mass spectrometry (GC-MS). Methanolic leaf extracts of A. radiata, A. caudatum and C. swartzii exhibited larvicidal activity against III and IV instar larvae of Ae. aegypti (LC₅₀: 37.47, 74.51 and 152.38 and 67.58, 95.89 and 271.46 ppm) and An. stephensi (LC₅₀: 70.35, 112.12 and 301.05 and 113.83, 175.30 and 315.19 ppm), respectively. The GC-MS of the methanol extract of A. radiata leaves revealed the presence of 7 phyto-components among which, Carbamic acid, phenyl-, (2-Nitrophenyl) methyl ester (1), Benzoic acid, 3- methylbenzoate (2) and 4-(benzylimino)- 1,4-dihydro-1-(p-toluoylmethyl) pyridine (3) were dominant. Biosafety assessment of methanol extract of A. radiata leaves on embryos of Danio rerio (Zebra fish) and Artemia nauplii (micro crustacean) revealed that there were no destructive or teratogenic effects. To conclude, the larvicidal activity and insignificant toxicity to non-target aquatic organisms of A. radiata leaves makes it a potential and environment safe biocontrol agent against dengue and malarial vectors.

Changes in Larval Mosquito Microbiota Reveal Non-target Effects of Insecticide Treatments in Hurricane-Created Habitats

Ephemeral aquatic habitats and their associated microbial communities (microbiomes) play important roles in the growth and development of numerous aquatic insects, including mosquitoes (Diptera). Biological control agents, such as Bacillus thuringiensis israelensis (Bti) or insect growth regulators (e.g., methoprene), are commonly used to control mosquitoes in these habitats. However, it is unknown how commonly used control compounds affect the mosquito internal microbiome and potentially alter their life history traits. The objectives of this study were threefold: characterize the internal microbiota of Aedes larvae (Culicidae) in ephemeral forested mosquito habitat using high-throughput amplicon based sequencing, assess how mosquito control treatments affect the internal microbial communities of larval mosquitoes, and determine if changes to the microbiome resulted from direct or indirect treatment effects. The larval microbiome varied in community composition and diversity with development stage and treatment, suggesting potential effects of control compounds on insect microbial ecology. While microbial community differences due to Bti treatment were a result of indirect effects on larval development, methoprene had significant impacts on bacterial and algal taxa that could not be explained by indirect treatment effects. These results provide new information on the interactions between pesticide treatments and insect microbial communities.

Determination of the efficiency of diets for larval development in mass rearing Aedes aegypti (Diptera: Culicidae)

Larval diet quality and rearing conditions have a direct and irreversible effect on adult traits. Therefore, the current study was carried out to optimize the larval diet for mass rearing of Aedes aegypti, for Sterile Insect Technique (SIT)-based applications in Sri Lanka. Five batches of 750 first instar larvae (L1) of Ae. aegypti were exposed to five different concentrations (2-10%) of International Atomic Energy Agency (IAEA) recommended the larval diet. Morphological development parameters of larva, pupa, and adult were detected at 24 h intervals along with selected growth parameters. Each experiment was replicated five times. General Linear Modeling along with Pearson's correlation analysis were used for statistical treatments. Significant differences (P < 0.05) among the larvae treated with different concentrations were found using General Linear Modeling in all the stages namely: total body length and the thoracic length of larvae; cephalothoracic length and width of pupae; thoracic length, thoracic width, abdominal length and the wing length of adults; along with pupation rate and success, sex ratio, adult success, fecundity and hatching rate of Ae. aegypti. The best quality adults can be produced at larval diet concentration of 10%. However, the 8% larval diet concentration was most suitable for adult male survival.

Distribution and breeding sites of Aedes aegypti and Aedes albopictus in 32 urban/peri-urban districts of Mozambique: implication for assessing the risk of arbovirus outbreaks

Background

Aedes-borne arboviruses have emerged as an important public health problem worldwide and, in Mozambique, the number of cases and its geographical spread have been growing. However, information on the occurrence, distribution and ecology of Aedes aegypti and Ae. albopictus mosquitoes remain poorly known in the country.

Methods

Between March and April 2016, a cross-sectional study was conducted in 32 districts in Mozambique to determine the distribution and breeding sites of Ae. aegypti and Ae. albopictus. Larvae and pupae were collected from a total of 2,807 water-holding containers using pipette, dipper, funnel and sweeping procedures, depending on the container type and location. Both outdoor and indoor water-holding containers were inspected. The immature forms were reared to adults and the identifications of the mosquito species was carried out with a stereomicroscope using a taxonomic key.

Results

Aedes aegypti was found in every district sampled, while Ae. albopictus was only found in Moatize district, situated in Tete Province in the central part of the country. Six hundred and twenty-eight of 2,807 (22.4%) containers were positive for Ae. aegypti but only one (0.03%) was positive for Ae. albopictus. The Container Index (CI) of Aedes was highest in densely populated suburban areas of the central region (260/604; 43.0%), followed by suburban areas in northern areas (228/617; 36.9%) whilst the lowest proportion was found in urbanized southern areas (140/1586; 8.8%). The highest CI of Aedes was found in used tires (448/1268; 35.3%), cement tanks (20/62; 32.3%) and drums (21/95; 22.1%).

Conclusion

Data from our study showed that Ae. aegypti is present nation-wide, since it occurred in every sampled district, whilst Ae. albopictus had a limited distribution. Therefore, the risk of transmission of dengue and chikungunya is likely to have been underestimated in Mozambique. This study highlights the need for the establishment of a national entomological surveillance program for Aedes spp. in Mozambique in order to gain a better understanding about vector bionomics and to support the development of informed effective vector control strategies.

Dengue, chikungunya and Zika are a group of rapidly spreading mosquito-borne diseases worldwide. These arboviral diseases have received increasing attention in Mozambique as a consequence of recent dengue outbreaks, which occurred in the northern region. There has also been an increase in the number of cases of chikungunya reported in the country. Additionally, earlier evidence obtained from neutralizing antibodies against Zika revealed an overall prevalence of 4% in 249 individuals (142 adults and 107 children) sampled from 22 localities across Mozambique in the 1950’s. These arboviruses are primarily transmitted by the bites of infected Aedes (Stegomyia) females, especially Ae. aegypti and Ae. albopictus. However, data on the distribution and the bio-ecology of both Aedes species are scarce. This lack of information is a major barrier for the implementation of public health interventions to prevent Aedes-borne arbovirus infections. In this study, we investigated the distribution and abundance of Ae. aegypti and Ae. albopictus in 32 districts of Mozambique. We found Ae. aegypti in every district sampled, although with heterogeneous abundance, while Ae. albopictus had limited occurrence. Aedes aegypti breeding sites varied among districts. The predominant containers were used tires, cement tank and drums, all present at high densities in central and northern Mozambique. This is the first study that investigates the distribution of breeding sites and abundance of Aedes spp. in a large number of districts in Mozambique and provides relevant baseline data for the establishment of a vector surveillance and control interventions for arboviruses in the country.

Plant-derived compounds regulate formation of the insect juvenile hormone receptor complex

Insect growth regulators (IGRs) are attractive pest control agents due to their high target specificity and relative safety to the environment. Recently, plants have been shown to synthesize IGRs that affect the insect juvenile hormone (JH) as a part of their defense mechanisms. Using a yeast two-hybrid system transformed with the Aedes aegypti JH receptor as a reporter system, we identified several JH agonists (JHAs) and antagonists (JHANs) causing retardation in the ovarian development of female Asian tiger mosquito, Aedes albopictus, from plant essential oil compounds. While the JHAs increased the expression of a JH-induced gene, the JHANs caused a reduction in the expression of the same gene. The compounds identified in this study could provide insights into plant-insect interactions and may be useful for the development of novel IGR insecticides.

Entomological Investigation of Aedes aegypti In Neighborhoods With Confirmed Human Arbovirus Infection In Puerto Rico

The exotic arboviruses chikungunya (CHIKV) and Zika (ZIKV) recently caused large outbreaks and continue to circulate in Puerto Rico, prompting entomological investigations at 9 locations with confirmed CHIKV- or ZIKV-infected human cases. Adult mosquitoes were collected using the Centers for Disease Control and Prevention autocidal gravid ovitraps over a 14-day period at each site. Mean female Aedes aegypti captured per trap-week ranged from 13.47 per trap-week to 1.27 per trap-week. Arbovirus-positive pools were detected at 7 of the 9 sampling sites. We investigated vertical transmission by collecting Ae. aegypti eggs in a single location where ZIKV was found in adult mosquitoes. We discuss the relationship between vector density and infection rates and its implications for determining mosquito density thresholds of novel invasive arboviruses such as CHIKV and ZIKV.

Habitat Characteristics For Immature Stages of Aedes aegypti In Zanzibar City, Tanzania

Aedesaegypti is the main vector for dengue, chikungunya, yellow fever, Zika, and other arboviruses of public health importance. The presence of Ae. aegypti has never been systematically assessed in Zanzibar, including its preferred larval habitats. In 2016 we conducted a cross-sectional entomological survey to describe the preferred larval habitats of Ae. aegypti in Zanzibar City, the main urban area of the Zanzibar archipelago. The surveys for container habitats were conducted for a 17-wk period beginning in January 2016. Immature stages (larvae and pupae) were collected, reared to adulthood, and identified to species. The positive and potential habitats were categorized on the basis of physical, biological, and chemical parameters. A total of 200 samples were collected, of which 124 (62.0%) were positive for immature stages of mosquitoes and 114 (92%) for Ae. aegypti larvae and pupae. Presence of vegetation (odds ratio [OR] = 2.11, 95% confidence interval [CI] = 1.19-3.74), organic matter (OR = 2.37, 95% CI = 1.21-4.60), inorganic matter (OR = 1.78, 95% CI = 1.01-3.13), and sun exposure (OR = 2.34, 95% CI = 1.24-4.36) were all significantly associated with the presence of immature stages of Ae. aegypti, suggesting that these conditions promote colonization of containers. Plastic containers supported 64% of the immature stages and produced approximately 50% of the pupae. Although immature counts were the highest in discarded artifacts, higher pupal counts were found in domestic water storage containers. Our observations suggest that effective control of Ae. aegypti in Zanzibar City must include improved solid waste management (collection and proper disposal of potential container habitats) and reliable supply of domestic water to minimize water-storing practices that provide larval habitats for Ae. aegypti.

Tracking Aedes aegypti (Diptera: Culicidae) Larval Behavior Across Development: Effects of Temperature and Nutrients on Individuals' Foraging Behavior

Immature mosquitoes alter their foraging behavior in response to variation in nutrients, predators, and temperature, with consequences on the adult stage where pathogens are transmitted. These patterns of behavior have not been described with respect to both developmental stage and environmental variation, nor has behavior been examined within an individual across instars. We hypothesized that individual larvae have distinct behavioral syndromes, and predict that the rank of foraging activity in the third instar will be correlated with foraging activity in the fourth instar for an individual across all conditions. We also hypothesized that individuals that fail to achieve adulthood forage more intensely than those that will emerge due to the need for greater resources. To examine these hypotheses, we conducted an experiment in which we exposed 96 individual Aedes aegypti L. (Diptera: Culicidae) larvae to four combinations of temperature and nutrients. We recorded larvae in the third and fourth instar, and generated time budgets of active and passive foraging behaviors. We found correlations between individual behavior in the third and fourth instar when conditions were the most stressful (cool temperatures and low nutrients). Controlling for this intra-individual behavior, there was variation between instar behaviors, but this was dependent on both temperature and nutrients. We also found that larvae that failed to pupate within 28 d before emergence foraged more intensely than those that emerged. While we found no evidence that mosquitoes have distinct behavioral syndromes in Ae. aegypti, we did find support that nutrients and temperature affect behavior differently at different instars.

Estimating air temperature using MODIS surface temperature images for assessing Aedes aegypti thermal niche in Bangkok, Thailand

Dengue, the most widespread urban vector-borne disease, is transmitted to human by the mosquito Aedes aegypti. Its distribution in urban areas is heterogeneous over time and space. In time, it is linked to seasonal variations such as warm and cold seasons, as well as rainy and dry seasons. In space, it is linked to social and environmental conditions, which alternate between rich and deprived neighborhoods, vegetated and densely built areas. These variations in terms of land cover can affect surface and air temperature. As a result of its influence on the mosquito's life cycle, temperature plays a crucial part in dengue epidemics potential. Thus, deciphering the thermal variations effects within cities could lead to the identification of precise thermal comfort zones, favorable to the survival of mosquito populations during inter-epidemic periods. The maps that could be produced as a result would enable health authorities to target specific areas. Most cities are equipped with meteorological stations. However, the network is generally not dense enough to precisely identify thermal comfort zones. Remote sensing can be used as a tool to solve this issue. The methodological objective of this paper is to assess the potential of the TVX (Temperature-Vegetation indeX) approach applied to MODIS thermal images for the purpose of estimating daily minimum and maximum air temperatures in the city of Bangkok, Thailand. The TVX approach has been seldom used over urban areas due to the heterogeneous nature of cities in terms of land cover. However, our study shows that in vegetated cities such as Bangkok, the TVX method provides valuable results which can be used to assess thermal niche of A. aegypti.

Zika might not be acting alone: Using an ecological study approach to investigate potential co-acting risk factors for an unusual pattern of microcephaly in Brazil

Zika virus infections can cause a range of neurologic disorders including congenital microcephaly. However, while Zika infections have been notified across all regions in Brazil, there has been an unusual number of congenital microcephaly case notifications concentrated in the Northeast of the country. To address this observation, we investigated epidemiological data (2014–2016) on arbovirus co-distribution, environmental and socio-economic factors for each region in Brazil. Data on arbovirus reported cases and microcephaly were collected from several Brazilian Ministry of Health databases for each Federal unit. These were complemented by environmental management, social economic and Aedes aegypti infestation index data, extracted from multiple databases. Spatial time “ecological” analysis on the number of arboviruses transmitted by Aedes mosquitoes in Brazil show that the distribution of dengue and Zika was widespread in the whole country, with higher incidence in the West-Central region. However, reported chikungunya cases were higher in the Northeast, the region also with the highest number of microcephaly cases registered. Social economic factors (human development index and poverty index) and environmental management (water supply/storage and solid waste management) pointed the Northeast as the less wealthy region. The Northeast is also the region with the highest risk of Aedes aegypti house infestation due to the man-made larval habitats. In summary, the results of our ecological analysis support the hypothesis that the unusual distribution of microcephaly might not be due to Zika infection alone and could be accentuated by poverty and previous or co-infection with other pathogens. Our study reinforces the link between poverty and the risk of disease and the need to understand the effect on pathogenesis of sequential exposure to arboviruses and co-viral infections. Comprehensive large-scale cohort studies are required to corroborate our findings. We recommend that the list of infectious diseases screened, particularly during pregnancy, be regularly updated to include and effectively differentiate all viruses from ongoing outbreaks.

Prediction of dengue outbreaks in Mexico based on entomological, meteorological and demographic data

Dengue virus has shown a complex pattern of transmission across Latin America over the last two decades. In an attempt to explain the permanence of the disease in regions subjected to drought seasons lasting over six months, various hypotheses have been proposed. These include transovarial transmission, forest reservoirs and asymptomatic human virus carriers. Dengue virus is endemic in Mexico, a country in which half of the population is seropositive. Seropositivity is a risk factor for Dengue Hemorrhagic Fever upon a second encounter with the dengue virus. Since Dengue Hemorrhagic Fever can cause death, it is important to develop epidemiological mathematical tools that enable policy makers to predict regions potentially at risk for a dengue epidemic. We formulated a mathematical model of dengue transmission, considering both human behavior and environmental conditions pertinent to the transmission of the disease. When data on past human population density, temperature and rainfall were entered into this model, it provided an accurate picture of the actual spread of dengue over recent years in four states (representing two climactic conditions) in Mexico.

Genetic and environmental influences on the size-fecundity relationship in Aedes albopictus (Diptera: Culicidae): Impacts on population growth estimates?

Population growth models are integral to ecological studies by providing estimates of population performance across space and time. Several models have been developed that estimate population growth through correlates of demographic traits, as measuring each parameter of the model can be prohibitive in experimental studies. Since differences in female size can accurately reflect changes in fecundity for many taxa, Livdahl and Sugihara developed a population growth index that incorporates size-fecundity relationships as a proxy for fecundity. To investigate the extent to which this model is robust to variation of this proxy, we tested if genetic (source population), temperature and resource treatments affect the size-fecundity relationship in Aedes albopictus (Skuse), the Asian tiger mosquito. We then determined if variation in the size-fecundity relationship alters the population growth estimates, lambda (λ'), when applied to Livdahl and Sugihara's model. We performed 2 laboratory experiments in which we reared cohorts of four different geographic populations of A. albopictus across 5 temperature treatments (18, 21, 25, 18, 31°C) and three resource treatments (low, medium, high larval resources). We determined if the slope of the size-fecundity relationship varied by source population, temperature, or resource; and if variation in this relationship affects lambda (λ') estimates in a competition study between A. albopictus and Culex pipiens (Linnaeus), the northern house mosquito. Temperature treatments significantly affected the size-fecundity relationship, resource level marginally affected the relationship, while source population had no effect. We found positive relationships between size and fecundity when mosquito larvae were reared at high temperatures and low resource levels but the relationship disappeared when mosquitoes were reared at a low temperature or with high levels of resources. The variation in the size-fecundity relationship produced from different temperatures resulted in statistically different lambda (λ') estimates. However, these changes in lambda (λ') did not alter the trends in the population performance across treatments or conclusions of the competition study. This study provides evidence that the population growth model is sensitive to variation in size-fecundity relationships and we recommend biologists apply the most compatible size-fecundity relationship to the models to obtain the most accurate estimates of population performance.

Biology of two larval morphological phenotypes of Aedes aegypti in Abidjan, Côte d'Ivoire

Since 2008, several outbreaks of yellow fever and dengue occurred in Abidjan, the economic capital of Côte d'Ivoire. A better knowledge of the biology of Aedes aegypti populations, the main vector of yellow fever and dengue viruses, is necessary to tailor vector control strategies implemented in the city. This study was designed to determine some biological parameters, occurring during the life cycle of two morphological phenotypes of Ae. aegypti larvae. Mosquitoes were sampled in a suburb of Abidjan (Treichville) using the WHO layer-traps technique. Biological parameters were studied in laboratory under standard conditions of temperature (27°C ± 2°C) and relative humidity (80% ± 10%). Our results indicated that the mean eggs laid by females from 'brown larvae' (BL) (85.95, 95% confidence interval (CI 95%) 78.87-93.02) was higher than those from 'white larvae' (WL) (64.40%, CI 95% 55.27-73.54). The gonotrophic cycle was 3 and 4 days in females from BL and WL, respectively. The overall yield of breeding mosquitoes from BL (63.88%, CI 95% 62.61-65.14) was higher compared with those of mosquitoes from WL (59.73%, CI 95% 58.35-61.12). The sex ratio (male/female) was 0.95 and 1.68 in Ae. aegypti populations from BL and WL, respectively. Females from BL lived slightly longer than those from WL (t = -2.332; P = 0.021). This study shows that Ae. Aegypti populations from BL and WL present different biological parameters during their life cycle. This could have an implication on their ability to transmit human disease viruses such as dengue and yellow fever. Further molecular studies are needed to determine genetic divergence between these Ae. aegypti populations.

Classification of containers with Aedes aegypti pupae using a Neural Networks model

Introduction

This paper discusses the presence of Aedes aegypti pupae in different types of containers considering: volume, pH of the container, among other variables.

Methods

A nonlinear method for selection was applied, based on Mutual Information, by placing in order of importance the most appropriate variables for identifying containers with and without Aedes aegypti pupae. Such variables were used for input into a Neural Network in layers for classification.

Results

Among the experiments carried out, the best result obtained used the first eight variables selected by order of importance. The percentage of hits for containers which had no Aedes aegypti pupae was 73.3%, and 80.9% for those which did have Aedes aegypti pupae in the containers. This Neural Network method, a model with the capacity to emulate non-linear data, got better results in comparison with the discriminant power of the Logistic Regression model. Thus, the outcomes of using the Neural Networks method achieved better separability in classifying the containers with pupae and those with no pupae.

Conclusion

This type of analysis will aid in the efforts to design an efficient program to control Aedes aegypti that can concentrate principally on containers which present the greatest productivity.

The authors discuss a nonlinear method, based on Mutual Information, for selection of the presence of Aedes aegypti pupae in different breeding sites. The authors compare this method with the logistic regression model. In this study, using the Neural Network model, the variables that better discriminate the containers with Aedes aegypti pupae from the containers without pupae were size—the larger the container volume the greater the proportion of containers positive for pupae–, the presence of another type of pupa other than Aedes aegypti and the location of the container outside the home. The Neural Network method, a model with the capacity to emulate non-linear data, got better results in comparison with the discriminant power of the Logistic Regression model. Thus, the outcomes of the Neural Networks method achieved better separability in classifying the containers with pupae and those with no pupae. This type of analysis will aid in the efforts to design an efficient program to control Aedes aegypti that can concentrate principally on containers which present the greatest productivity.

Hydrophobic Nanoprecipitates of β-Cyclodextrin/Avermectins Inclusion Compounds Reveal Insecticide Activity against Aedes aegypti Larvae and Low Toxicity against Fibroblasts

In the present work, hydrophobic nanoprecipitates (HNPs) of inclusion complexes formed between β-cyclodextrin (βCD) and the avermectins (AVMs) named eprinomectin (EPRI) and ivermectin (IVER) were synthesized and characterized, and their larvicidal activity against Aedes aegypti and human safety against fibroblasts were evaluated. Initially, thermogravimetric analysis/differential thermal analysis data revealed that inclusion increased the thermal stability of AVMs in the presence of βCD. Nuclear magnetic resonance experiments and density functional theory calculations pointed out the inclusion of the benzofuran ring of the two AVMs in the βCD cavity. Isothermal titration calorimetry experiments allowed identification of different binding constants for EPRI/βCD ( K_b = 1060) and βCD/IVER ( K_b = 1700) systems, despite the structural similarity. Dynamic light scattering titrations of AVMs' dimethyl sulfoxide solution in βCD aqueous solution demonstrated that the formed HNPs have lower sizes in the presence of βCD. Finally, the inclusion of EPRI in βCD increased its larval toxicity and reduced its human cytotoxicity, while for IVER/βCD no beneficial effect was observed upon inclusion. These results were rationalized in terms of structural differences between the two molecules. Finally, the EPRI/βCD complex has great potential as an insecticide against A. aegypti larvae with high human safety.

Quantitative structure-activity relationship (QSAR) analysis of plant-derived compounds with larvicidal activity against Zika Aedes aegypti (Diptera: Culicidae) vector using freely available descriptors

BACKGROUND

We have developed a quantitative structure-activity relationship (QSAR) model for predicting the larvicidal activity of 60 plant-derived molecules against Aedes aegypti L. (Diptera: Culicidae), a vector of several diseases such as dengue, yellow fever, chikungunya and Zika. The balanced subsets method (BSM) based on k-means cluster analysis (k-MCA) was employed to split the data set. The replacement method (RM) variable subset selection technique coupled with multivariable linear regression (MLR) proved to be successful for exploring 18 326 molecular descriptors and fingerprints calculated with PaDEL, Mold² and EPI Suite open-source softwares.

RESULTS

A robust QSAR model (Rtrain2=0.84, S_train  = 0.20 and Rtest2=0.92, S_test  = 0.23) involving five non-conformational descriptors was established. The model was validated and tested through the use of an external test set of compounds, the leave-one-out (LOO) and leave-more-out (LMO) cross-validation methods, Y-randomization and applicability domain (AD) analysis.

CONCLUSION

The QSAR model surpasses previously published models based on geometrical descriptors, thereby representing a suitable tool for predicting larvicidal activity against the vector A. aegypti using a conformation-independent approach. © 2018 Society of Chemical Industry.

Both living bacteria and eukaryotes in the mosquito gut promote growth of larvae

We recently reported that larval stage Aedes aegypti and several other species of mosquitoes grow when living bacteria are present in the gut but do not grow when living bacteria are absent. We further reported that living bacteria induce a hypoxia signal in the gut, which activates hypoxia-induced transcription factors and other processes larvae require for growth. In this study we assessed whether other types of organisms induce mosquito larvae to grow and asked if the density of non-living microbes or diet larvae are fed obviate the requirement for living organisms prior results indicated are required for growth. Using culture conditions identical to our own prior studies, we determined that inoculation density of living Escherichia coli positively affected growth rates of Ae. aegypti larvae, whereas non-living E. coli had no effect on growth across the same range of inoculation densities. A living yeast, alga, and insect cell line induced axenic Ae. aegypti first instars to grow, and stimulated similar levels of midgut hypoxia, HIF-α stabilization, and neutral lipid accumulation in the fat body as E. coli. However, the same organisms had no effect on larval growth if heat-killed. In addition, no axenic larvae molted when fed two other diets, when fed diets supplemented with heat-killed microbes or lysed and heat-killed microbes. Experiments conducted with An. gambiae yielded similar findings. Taken together, our results indicate that organisms from different prokaryotic and eukaryotic groups induce mosquito larvae to grow, whereas no conditions were identified that stimulated larvae to grow in the absence of living organisms.

West Nile virus and other mosquito-borne viruses present in Eastern Europe

Eastern Europe (EE) has been severely affected by mosquito-borne viruses (moboviruses). In this review, we summarize the epidemiology of moboviruses, with particular attention to West Nile virus (WNV). The study of WNV human cases in EE between 2010 and 2016, revealed that the epidemiology of WNV in EE is complex with the combination of introduction of different WNV strains from lineages 1 and 2, and the establishment of endemic cycles. We found a positive correlation between the risk of WNV re-emergence in an area and the number of human cases reported in the previous year. We also report the main ecological and biological characteristics of the key mosquito species vectors of moboviruses. Recent expansion of invasive mosquito species in EE, mainly Aedes albopictus but also Aedes aegypti and Culex quinquefasciatus, may result in new scenarios with an increased risk of transmission of moboviruses. Main gaps of knowledge in relation to moboviruses and their vectors in EE are identified. Understanding the epidemiology of moboviruses in EE is essential for the improvement of their surveillance and the control of the diseases they cause.

Socioeconomic and Human Behavioral Factors Associated With Aedes aegypti (Diptera: Culicidae) Immature Habitat in Tucson, AZ

Aedes aegypti (L.; Diptera: Culicidae) has been established in the southwestern United States for several decades, but relationships between humans and mosquitoes in this arid region are not well-characterized. In August 2012, the outdoor premises of 355 houses within 20 neighborhoods in Tucson, Arizona were surveyed for containers that could provide larval habitat for Ae. aegypti mosquitoes. At the same time, a knowledge, attitudes and practices (KAP) questionnaire was administered to a resident of each house surveyed for immature mosquitoes. The KAP questionnaire assessed respondents' knowledge and concerns about vector-borne illnesses as well as practices they used to avoid mosquitoes. Of the houses surveyed, 91% had at least one container present, and 64% had at least one container with standing water. On average, each house had 2.2 containers with water at the time of the survey. The overall House Index (proportion of premises surveyed with at least one container with Ae. aegypti immatures present) was 13%. Based on questionnaire responses, there was a significant positive association between the number of residents in the home and the odds of finding Ae. aegypti positive containers on the premises, while household income showed a significant negative association. The reported frequency of checking for standing water was also significantly associated with the odds of finding immatures, although the nature of this association was ambiguous. Flower pots were the principal type of container with Ae. aegypti larvae. These findings show that larval habitat is widely available even in an arid environment and city with good housing and sanitation infrastructure.

Seasonal Distribution and Container Preference Ratio of the Dengue Fever Vector (Aedes aegypti, Diptera: Culicidae) in Rawalpindi, Pakistan

Aedes aegypti (L.) and Aedes albopictus (Skuse) are known vectors of dengue, chikungunya, and other pathogens; however, their ecology and role in virus transmission has not been well studied in Pakistan. Here, we report on an intensive survey of potential breeding sites of Ae. aegypti in Rawalpindi, Punjab Province, Pakistan. The study continued for 11 mo and was divided into three seasons: January to June (pre-monsoon), July to September (monsoon), and October-November (post-monsoon). Larval mosquitoes were collected from all wet containers present in and around the houses. Altogether 5,570,418, 2,930,508, and 1,507,111 water-filled containers were examined during each season, of which 2,703, 8,843, and 3,439 were found positive for Ae. aegypti larvae or pupae, yielding Breteau indices of 0.46, 2.92, and 1.99%, respectively. Among 14 container types examined, the breeding preference ratio during all seasons was highest for roof-top water tanks and room evaporative coolers, followed by discarded tires and urban trash. The study concluded that increased urbanization, insufficient water supply and inefficient removal of urban trash resulted in increased numbers of nonbiodegradable containers around human dwellings, thereby creating ideal breeding habitats for Ae. aegypti. Measures such as integrated vector management, minimization of the breeding potential of Ae. aegypti by water management, proper disposal of discarded tires and urban trash, and health education were recommended for control of Ae. aegypti.

Mosquitocidal Activity of a Naturally Occurring Isochroman and Synthetic Analogs from the Plant Pathogenic Fungus, Diaporthe eres Against Aedes aegypti (Diptera: Culicidae)

The culture filtrate of a plant pathogenic fungus that infects English ivy (Hedera helix L., Araliaceae) was investigated for mosquitocidal constituents by bioassay-guided isolation. The fungus responsible for pathogenic effects on the plant H. helix has been identified as Diaporthe eres Nitschke by molecular techniques. The mosquito adulticidal constituent in the culture filtrate was identified as 3,4-dihydro-8-hydroxy-3,5-dimethylisocoumarin (1) by spectroscopic techniques. Laboratory bioassays showed that (1) had larvicidal activity against permethrin-susceptible and -resistant Aedes aegypti strains. This compound was not active as an adulticide when tested by topical bioassay. Several analogs of (1) were synthesized and had better mosquitocidal activities than the naturally occurring (1) constituent.

First insights into insecticidal activity against Aedes aegypti and partial biochemical characterization of a novel low molecular mass chymotrypsin-trypsin inhibitor purified from Lonchocarpus sericeus seeds

BACKGROUND

Arboviroses such as dengue, Zika and chikungunya represent a serious public health issue as a consequence of the absence of approved vaccines or specific antiviral drugs against the arboviruses that cause them. One way to prevent these diseases is by combating the vector mosquito, Aedes aegypti (Diptera), which has serine proteases in the midgut. Protease inhibitors are molecules that can block enzyme activity, impairing digestion and nutrition, which can lead to death. Thus, we purified and characterized a novel chymotrypsin-trypsin inhibitor (LsCTI) from Lonchocarpus sericeus seeds and investigated its effect upon Ae. aegypti egg hatching, larval development and digestive proteases.

RESULTS

LsCTI showed a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the molecular mass determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was 8870.45 Da. Kinetics analyses revealed a noncompetitive type of inhibition and low inhibition constant (K_i ) for chymotrypsin (8.24 x 10^-8 m). The thermal resistance was remarkable, even at 100 °C for 180 min. The inhibitor concentration required for 50-percent enzyme inhibition (IC₅₀ ) of LsCTI was 4.7 x 10^-7 m for Ae. aegypti midgut larval enzymes. LsCTI did not affect egg hatchability at 0.3 mg mL^-1 , but caused a high larval mortality rate (77%) and delayed development (37%).

CONCLUSIONS

LsCTI is a novel protease inhibitor with remarkable biochemical characteristics and is a potential tool to control Ae. aegypti development. © 2017 Society of Chemical Industry.

A SURVEY OF THE MOSQUITOES OF KOSRAE STATE, FEDERATED STATES OF MICRONESIA, 2016

In response to an outbreak of Zika virus that started in February 2016 on Kosrae Island, Kosrae State, Federated States of Micronesia, we conducted entomological investigations, including a survey to characterize the mosquito fauna on Kosrae, from November 29 to December 8, 2016. Mosquitoes were collected using several surveillance methods in order to sample all stages of the mosquito life cycle. Eggs were collected using ovicups, larvae and pupae were sampled using standard dippers, and adults were collected using aspirators and Biogents-2 Sentinel traps. All species previously recorded from Kosrae State were found in the current survey, confirming their continued presence on the island. Aedes aegypti was detected on Lelu Island, representing a new municipal record. The collection of Ae. vexans nocturnus represents a new species record for Kosrae, increasing the number of known taxa on this island from 6 to 7. The report herein provides updated knowledge of the mosquitoes that occur on Kosrae State, Federated States of Micronesia.

Report of Chikungunya Virus in Wild Populations of Aedes aegypti in Guerrero State, Mexico

We detected vertical transmission of chikungunya virus (CHIKV) in wild populations of Aedes aegypti from San Marcos, Guerrero, Mexico, with real-time reverse transcriptase-polymerase chain reaction. A total of 20 pools (1-11 specimens/pool) of larvae, male, and female mosquitoes were tested. We report the detection of CHIKV in 2 of 11 larval pools, 4 of 5 male pools, and 1 of 4 female pools, from field-collected mosquitoes.

Sargassum wightii-synthesized ZnO nanoparticles - from antibacterial and insecticidal activity to immunostimulatory effects on the green tiger shrimp Penaeus semisulcatus

The green synthesis of metal nanoparticles using phytochemical from marine seaweeds is a fast-growing research field in nanotechnology. Here, the biosynthesis of zinc oxide nanoparticles was achieved using the hot water extract of Sargassum wightii. The hot water extract prepared from S. wightii (H Sw) and ZnO NPs were studied by UV-visible and FTIR spectroscopy, SEM and XRD. Then, both products were evaluated for antibiofilm activity towards aquatic pathogens. The nanoparticles' immunostimulating potential on green tiger prawns, Penaeus semisulcatus was studied through immersion and dietary administration. Shrimp immune parameters (i.e., total hemocytes count (THC), respiratory bursts (RBs), phenoloxidase (PO) and superoxide dismutase (SOD) activity) were significantly affected by exposure or ingestion of ZnO nanoparticles. In addition, the hot water extract and ZnO nanoparticles had high antibiofilm activity against Gram-positive (B. subtilis, S. aureus) and Gram-negative (S. sonnei, P. aeruginosa) microbial pathogens. It was accomplished that the ZnO nanoparticles can be used as the bacteriostatic and immunostimulant agents through immersion and dietary administration enhancing immunity of green tiger shrimp. Furthermore, the toxicity effects of ZnO nanoparticles were 100% at 24 h on Aedes aegypti 3 rd instar larvae at the concentration of 100 μg/mL and the greatest efficacy was accomplished by H Sw ZnO NPs against the Ae. aegypti after 24 h (LC50 49.22; LC90 86.96 mg/mL), if compared to the seaweed extract alone. Morphological and histological damages triggered by nanoexposure were investigated.

Lack of Resistance in Aedes vexans Field Populations After 36 Years of Bacillus thuringiensis subsp. Israelensis Applications in the Upper Rhine Valley, Germany

Bacillus thuringiensis subsp. israelensis (Bti) has been widely and solely used against floodwater mosquitoes, mostly Aedes vexans, for 36 years in the Upper Rhine Valley by the German Mosquito Control Association. During this period, almost 5,000 tons of Bti formulations were applied to an area of approximately 400,000 ha. To investigate a possible resistance development after such a long-term and widespread application of Bti, the susceptibility of Ae. vexans larvae to Bti in 3 untreated (Lake Constance) and 6 treated areas on both sides of the Rhine within the Upper Rhine Valley was assessed by bioassays following World Health Organization guidelines. Comparing log-probit analyses, it was shown that neither the median lethal concentration (LC₅₀ values) nor slopes of the probit lines of bioassays of the larvae deriving from treated and untreated areas showed significant differences. These results have been confirmed by resistance ratios, which varied from 0.80 to 1.12 in all tests. The results provided the evidence that no restistance in the target species Ae. vexans has developed in the areas of the Upper Rhine Valley, despite the large-scale use of Bti for 36 years.

Evaluation of the effects of the larvicides temephos on reproductive performance, embryofetal development and DNA integrity of Swiss mice

Temephos is considered the gold standard by the Ministry of Health for controlling the larvae of the mosquito Aedes aegypti. The present study evaluated the effects of Temephos larvicide on the reproductive performance, embryo-fetal development and DNA integrity of Swiss mice. This study used 30 pregnant female mice: 10 were controls treated with drinking water at a dosage of 0.1 mL/10 g (body weight - b.w., administered orally - a.o.), and 20 were treated with Temephos at doses of 0.0043 mg/kg and 0.043 mg/kg (b.w., a.o.) during the gestational period. Statistical analysis showed that Temephos did not alter the biometric or reproductive parameters. Comparing the weight of the fetus to the stage of pregnancy demonstrated that the 0.0043 mg/kg dosage increased the size of the fetuses. No external malformations were detected. However, the 0.043 mg/kg dosage induced changes in the sternum, with the main change being the center of the sternum, xiphoid processes and absence of the manubrium. The other skeletal and visceral alterations did not differ from the control group and are considered variants of normality. The analysis of head measurements showed an increase in the anterior/posterior measurements of the glabella, the external occipital protuberance and the biauricular plane. The circumference and area of the head did not present significant differences. The micronucleus test showed only a 0.043 mg/kg increase in 48 h. Thus, it is considered that Temephos has a low teratogenic and genotoxic risk.

Modeling the Heterogeneity of Dengue Transmission in a City

Dengue fever is one of the most important vector-borne diseases in the world, and modeling its transmission dynamics allows for determining the key influence factors and helps to perform interventions. The heterogeneity of mosquito bites of humans during the spread of dengue virus is an important factor that should be considered when modeling the dynamics. However, traditional models generally assumed homogeneous mixing between humans and vectors, which is inconsistent with reality. In this study, we proposed a compartmental model with negative binomial distribution transmission terms to model this heterogeneity at the population level. By including the aquatic stage of mosquitoes and incorporating the impacts of the environment and climate factors, an extended model was used to simulate the 2014 dengue outbreak in Guangzhou, China, and to simulate the spread of dengue in different scenarios. The results showed that a high level of heterogeneity can result in a small peak size in an outbreak. As the level of heterogeneity decreases, the transmission dynamics approximate the dynamics predicted by the corresponding homogeneous mixing model. The simulation results from different scenarios showed that performing interventions early and decreasing the carrying capacity for mosquitoes are necessary for preventing and controlling dengue epidemics. This study contributes to a better understanding of the impact of heterogeneity during the spread of dengue virus.

Bioefficacy of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidea) From Sarawak, Malaysia: A Statewide Survey

The susceptibility status of Aedes albopictus (Skuse; Diptera: Culicidea) larvae collected from 13 districts in Sarawak state, Malaysia was evaluated against five insect growth regulators (IGRs) namely, methoprene, pyriproxyfen, diflubenzuron, cyromazine, and novaluron. Field populations of Ae. albopictus were susceptible to methoprene, pyriproxyfen, cyromazine and novaluron with resistance ratios (RRs) ranging from 0.19-0.38, 0.05-0.14, 0.50-0.95, and 0.75-1.00, respectively. Nevertheless, tolerance towards diflubenzuron (0.33-1.33) was observed in this study. In general, these IGRs exhibited promising results and can be used as alternative control agents against field populations of Ae. albopictus in Sarawak, Malaysia.

The influence of urban heat islands and socioeconomic factors on the spatial distribution of Aedes aegypti larval habitats

We addressed the potential associations among the temporal and spatial distribution of larval habitats of Aedes (Stegomyia) aegypti, the presence of urban heat islands and socioeconomic factors. Data on larval habitats were collected in Santa Bárbara d'Oeste, São Paulo, Brazil, from 2004 to 2006, and spatial and temporal variations were analysed using a wavelet-based approach. We quantified urban heat islands by calculating surface temperatures using the results of wavelet analyses and grey level transformation from Thematic Mapper images (Landsat 5). Ae. aegypti larval habitats were geo-referenced corresponding to the wavelet analyses to test the potential association between geographical distribution of habitats and surface temperature. In an inhomogeneous spatial point process, we estimated the frequency of occurrence of larval habitats in relation to temperature. The São Paulo State Social Vulnerability Index in the municipality of Santa Barbára d'Oeste was used to test the potential association between presence of larval habitats and social vulnerability. We found abundant Ae. aegypti larval habitats in areas of higher surface temperature and social vulnerability and fewer larval habitats in areas with lower surface temperature and social vulnerability.

Urban environmental clustering to assess the spatial dynamics of Aedes aegypti breeding sites

The identification of Aedes aegypti breeding hotspots in urban areas is crucial for the rational design of control strategies against this disease vector. Remote sensing and geographic information systems offer valuable tools for mapping habitat suitability of a given area. However, predicting species occurrences by means of probability distribution maps based on transversal entomological surveys has limited utility for local authorities. The aim of the present study was to carefully examine the temporal evolution of the number of houses infested with immature stages of Ae. aegypti in each individual neighbourhood and to explore the value of producing environmental clusters generated with information provided by remotely sensed variables to explain the observed differential temporal behaviour. Entomological surveys were conducted between 2011 and 2013 throughout a small town in Argentina registering the number of houses with containers harbouring immature stages of Ae. aegypti. A SPOT 5 satellite image was used to obtain land cover variables, which were subsequently submitted to k-means partitioning for grouping neighbourhoods into four environmental clusters. Finally, a generalized linear model was fitted showing that the number of houses found to be positive for Ae. aegypti was jointly affected by the interaction between environmental clusters and the year of sampling. Moreover, the number of positive houses in one of the clusters was 9.5 times higher (P<0.005, SE=0.37) in 2013 than in 2012, but we did not observe any other statistically significant increases.

The Effectiveness of Asian Bush Mosquito (Aedes japonicus japonicus) Control Actions in Colonised Peri-urban Areas in the Netherlands

The Asian bush mosquito (Aedes japonicus japonicus (Theobald)) is an invasive mosquito species in Europe. In 2012, it was for the first time detected in the Netherlands, in the municipality of Lelystad. After further research, thousands of specimens were found in the surrounding peri-urban areas of the city. A targeted mosquito control campaign began in 2015 with the objective of reducing populations in locations with the highest concentrations of Ae. japonicus breeding sites: allotment garden complexes. Mosquito control consisted of source reduction combined with application of the larvicide Vectomax in breeding sites. At eight complexes, mosquito control effectiveness has been systematically measured by sampling larvae from breeding sites. Six measurements were performed between 2015 and 2016. Results show that the effectiveness of mosquito control actions was similar in all treated allotment gardens and resulted in a significant reduction in Ae. japonicus larval abundance. Rain barrels at the allotments represent the most frequent breeding site in Lelystad, but every water filled artificial container is a potential breeding site for the species. Ae. japonicus was not found in the samples taken in other allotment gardens in the province of Flevoland; however, the collection methodology used proven to be effective in detecting this species when it has newly colonized surrounding areas. Targeted mosquito control actions at the breeding sites are crucial for successful reduction of populations of an invasive mosquito species, and systematic measurements of the effectiveness, is in this case, the base to understand the dynamics of Ae. japonicus populations after mosquito control.

Occurrence of sweet refuse at disposal sites: rainwater retention capacity and potential breeding opportunities for Aedes aegypti

Nectar is the staple diet of adult mosquitoes in the wild, but its availability is inconsistent and can be affected by rainfall. In urban centers, Aedes vectors commonly use man-made containers as their major habitat; however, they can colonize any items replenished by rainfall. Garbage output has increased significantly in recent years, at a time when collection frequency is reducing. Such garbage usually includes organic components, some of which are sweet and can be fed upon by other animals or become can containers for rainwater. Despite evidence that Aedes larvae can thrive in containers comprised of organic waste material, which can be produced by rodents gnawing on fruits or vegetables, and that adults can survive on sweet waste fluids, the capacity of organic waste materials to accumulate rainwater and act as egg deposition sites has not been examined. It is also unknown for how long sweet extracts can sustain the life of adult vectors. Here, we investigated the abundance of sweet leftovers at garbage sites and the rainwater retention capacity of some organic materials through a field survey and laboratory bioassays. We also examined whether sweet waste fluids impact egg hatching success and longevity of Aedes aegypti. The results of this study indicated that sweet products with leftovers are highly prevalent in garbage. When exposed to rain, food items (BAFrc, banana fruit resembling container; and BSPrc, boiled sweet potato resembling container) and the packaging of sweet foods (SMIc, sweetened condensed milk can) retained water. When provided an opportunity to oviposit in cups containing BAF extract (BAFex), BSP extract (BSPex), and SMI extract (SMIex), eggs were deposited in all media. Egg maturation in the BAFex environment resulted in similar larval eclosion success to that resulting from embryo development in a water milieu. Adults maintained on sweet waste extracts had long lifespans, although shorter than that of their sugar solution (SUS)-fed counterparts. Taken together, these results indicated that sweet waste materials are useful to dengue mosquitoes, acting both as oviposition sites and energy sources.

The new European invader Aedes (Finlaya) koreicus: a potential vector of chikungunya virus

Arthropod-borne disease outbreaks, facilitated by the introduction of exotic mosquitoes, pose a significant public health threat. Recent chikungunya virus (CHIKV) epidemics in Europe highlight the importance of understanding the vector potential of invading mosquitoes. In this paper we explore the potential of Aedes koreicus, a mosquito new to Europe, to transmit CHIKV. Mosquitoes were challenged with CHIKV and maintained at two temperatures: 23 °C and a fluctuating temperature. Total CHIKV infection rates at 3, 10 and 14 days post-feeding were low for both temperature treatments (13.8% at 23 °C; 6.2% at fluctuating T). A low percentage (6.1%, n = 65) of mosquitoes maintained at a constant 23 °C showed dissemination of the virus to the wings and legs. Infection of mosquito saliva, with live virus, occurred in 2 mosquitoes. No dissemination was noted under the fluctuating temperature regime. Based on these results we conclude that CHIKV transmission by this species is possible.

Seasonal field efficacy of pyriproxyfen autodissemination stations against container-inhabiting mosquito Aedes albopictus under different habitat conditions

BACKGROUND

Control of the container-inhabiting mosquito, Aedes albopictus, is difficult using conventional methods due to its selection of cryptic peri-domestic habitats. We evaluated whether autodissemination stations can deliver sufficient pyriproxyfen to sentinel containers to produce significant pupal mortality in different habitats such as competing oviposition sites, peri-domestic habitats, junkyards and tire piles. We also tested how far the pesticide could be transferred over a 200-m range.

RESULTS

Autodissemination stations performed effectively for 8-12 weeks under field conditions. Pupal mortality was reduced in sentinel cups with high-competing oviposition habitats (5 versus 20) in isolated plots; however, similar results were not seen in residential areas. Increasing the number of stations per plot (from 1 to 4) enhanced the efficacy. Peri-domestic habitat trials showed the highest pupal mortality (50.4%) and site contamination with pyriproxyfen (82.2%) among the trials. Autodissemination stations were able to contaminate habitats in a junkyard (50.0%) and tire piles (40.2%). Pyriproxyfen was detected in sentinel cups up to 200 m from stations. Detection of pyriproxyfen by residue analysis (0.005-0.741 µg L^-1 ) in field samples confirmed the transfer of the insect growth regulator.

CONCLUSION

Autodissemination stations have shown promising potential as a novel pest management tool against container mosquitoes in field trials in different habitats confronted by mosquito control personnel. © 2017 Society of Chemical Industry.

Larvicidal and residual activity of imidazolium salts against Aedes aegypti (Diptera: Culicidae)

BACKGROUND

Aedes aegypti is an important mosquito species that can transmit several arboviruses such as dengue fever, yellow fever, chikungunya and zika. Because these mosquitoes are becoming resistant to most chemical insecticides used around the world, studies with new larvicides should be prioritized. Based on the known biological profile of imidazolium salts (IS), the objective of this study was to evaluate the potential of six IS as larvicides against Ae. aegypti, as tested against Ae. aegypti larvae. Larval mortality was measured after 24 and 48 h, and residual larvicidal activity was also evaluated.

RESULTS

Promising results were obtained with aqueous solutions of two IS: 1-n-octadecyl-3-methylimidazolium chloride (C₁₈ MImCl) and 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆ MImMeS), showing up to 90% larval mortality after 48 h exposure. C₁₈ MImCl was more effective than C₁₆ mIMeS, causing mortality until day 15 after exposure. An application of C₁₈ MImCl left to dry under ambient conditions for at least 2 months and then dissolved in water showed a more pronounced residual effect (36 days with 95% mortality and 80% mortality up to 78 days).

CONCLUSION

This is the first study to show the potential of IS in the control of Ae. aegypti. Further studies are needed to understand the mode of action of these compounds in the biological development of this mosquito species. © 2017 Society of Chemical Industry.

Alternative control of Aedes aegypti resistant to pyrethroids: lethal and sublethal effects of monoterpene bioinsecticides

BACKGROUND

The mosquito Aedes aegypti is intensively controlled because it is a vector of viruses that cause numerous diseases, especially in tropical regions. As a consequence of the indiscriminate use of insecticides, populations from different regions have become resistant to pyrethroids. Here, we analyzed the lethal and sublethal effects of essential oil of Aristolochia trilobata and its major compounds on A. aegypti from susceptible and pyrethroid-resistant populations.

RESULTS

Our results showed that the toxicity of the different compounds and behavioral changes in response to them are dependent on the stage of the insect life cycle. The monoterpene ρ-cymene caused high mortality in both larvae and adult females of A. aegypti, including those from the pyrethroid-resistant population. The monoterpenes limonene and linalool caused a sublethal effect in the larvae, triggering changes in the swimming pattern.

CONCLUSION

This study highlights the potential of the essential oil of A. trilobata and its major compounds ρ-cymene and limonene for the control of A. aegypti and reveals the importance of analyzing sublethal effects on the population dynamics of the A. aegypti mosquito. © 2017 Society of Chemical Industry.

Development of an eco-friendly mosquitocidal agent from Alangium salvifolium against the dengue vector Aedes aegypti and its biosafety on the aquatic predator

Plant extracts with their enriched chemical constituents have established potential alternative mosquito control agents. In this research, we developed an eco-friendly mosquitocidal agent from Alangium salvifolium leaves against the dengue and Zika virus vector Aedes aegypti and we investigated its biosafety on the mosquito aquatic predator Toxorhynchites splendens. Results showed that the methanolic extract of A. salvifolium leaves was composed by eight main compounds, with major peak area for hexadecenoic acid (21.74%). LC₅₀ and LC₉₀ values calculated on Ae. aegypti fourth instar larvae were 104.80 and 269.15 ppm respectively. The methanolic extract tested at 100 ppm decreased the α-β carboxylesterase and SOD ratio significantly and upregulated the GST and CYP450 level. The A. salvifolium methanolic extract displayed significant repellent and adulticidal activity at 100 and 400 ppm respectively. The treatment with 100 ppm of the methanolic extract led to 210 min of protection from Ae. aegypti bites. Four hundred parts per million of the extract showed 98% adult mortality within 30 min from the treatment. Lastly, biosafety assays on the mosquito aquatic predator Tx. splendens showed that the toxicity of the A. salvifolium extract was significantly lower if compared to the cypermethrin-based treatments. The methanolic extract of A. salvifolium showed a maximum of 47.3% mortality rate at the concentration of 1000 ppm, while 0.7 ppm of cypermethrin achieved 91.3% mortality rate on Tx. splendens. Overall, our study enhances basic knowledge on how to improve natural larvicidal agents against dengue and Zika virus mosquito vector with harmless responses on non-target aquatic predators.

Boswellia ovalifoliolata (Burseraceae) essential oil as an eco-friendly larvicide? Toxicity against six mosquito vectors of public health importance, non-target mosquito fishes, backswimmers, and water bugs

The use of synthetic pesticides to control vector populations is detrimental to human health and the environment and may lead to the development of resistant strains. Plants can be alternative sources of safer compounds effective on mosquito vectors. In this study, the mosquito larvicidal activity of Boswellia ovalifoliolata leaf essential oil (EO) was evaluated against Anopheles stephensi, Anopheles subpictus, Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Culex tritaeniorhynchus. GC-MS revealed that the B. ovalifoliolata EO contained at least 20 compounds. The main constituents were β-pinene, α-terpineol, and caryophyllene. In acute toxicity assays, the EO was toxic to larvae of An. stephensi, Ae. aegypti, Cx. quinquefasciatus, An. subpictus, Ae. albopictus, and Cx. tritaeniorhynchus with LC₅₀ values of 61.84, 66.24, 72.47, 82.26, 89.80, and 97.95 μg/ml, respectively. B. ovalifoliolata EO was scarcely toxic to mosquito fishes, backswimmers, and water bugs predating mosquito larvae with LC₅₀ from 4186 to 14,783 μg/ml. Overall, these results contribute to develop effective and affordable instruments to magnify the reliability of Culicidae control programs.

Establishment of a medium-scale mosquito facility: tests on mass production cages for Aedes albopictus (Diptera: Culicidae)

BACKGROUND

Mass egg production is an important component of Aedes albopictus mosquito control programs, such as the sterile insect technique and incompatible insect technique, which requires the releases of large number of sterile males. Developing standard operating procedures and optimized cages for adult maintenance of Ae. albopictus can improve the mass rearing efficiency.

METHODS

Three different sex ratios of females to males with a total number of 4,000 mosquitoes were tested by evaluating the insemination rate, egg production (total number of eggs per cage), female fecundity and egg hatch rate in small cage (30 × 30 × 30 cm). Blood meals with adenosine triphosphate (ATP, 0.05 g/ml), cage structures (Big cage A: 90 × 30 × 30 cm; Big cage B: 90 × 30 × 50 cm or 90 × 50 × 30 cm) and rearing densities (12,000, 16,000 and 20,000 mosquitoes, corresponding to 0.9 cm2/mosquito, 0.675 cm2/mosquito and 0.54 cm2/mosquito, respectively) were also tested and evaluated on the basis of egg production, female fecundity and egg hatch rate. An adult rearing unit holding 15 of Big cage A with optimal egg production was designed to produce 10 million eggs per rearing cycle in a 1.8 m2 space.

RESULTS

Female to male ratios at 3:1 in small cages resulted in higher egg production but did not affect insemination rate, female fecundity and egg hatch rate. A concentration of 0.05 g/ml of ATP added to blood meals improved the blood-feeding frequency and thus increased the overall egg production per cage. Cage structures affected the egg production per cage, but not egg hatch rate. A medium rearing density at 0.675 cm2/mosquito (16,000 mosquitoes) resulted in higher egg production compared to both low and high densities. An adult rearing unit for Ae. albopictus on the basis of Big cage A has been developed with the capacity of producing 10 million eggs within 15 days.

CONCLUSIONS

Our results have indicated that the adult rearing methods and adult maintenance unit are recommended for Ae. albopictus mass rearing in support of the establishment of a medium-sized mosquito factory.

Assessment of Aedes albopictus reference genes for quantitative PCR at different stages of development

Members of the Aedes genus of mosquitoes are widely recognized as vectors of viral diseases. Ae.albopictus is its most invasive species, and are known to carry viruses such as Dengue, Chikugunya and Zika. Its emerging importance puts Ae.albopictus on the forefront of genetic interaction and evolution studies. However, a panel of suitable reference genes specific for this insect is as of now undescribed. Nine reference genes, namely ACT, eEF1-γ, eIF2α, PP2A, RPL32, RPS17, PGK1, ILK and STK were evaluated. Expression patterns of the candidate reference genes were observed in a total of seventeen sample types, separated by stage of development and age. Gene stability was inferred from obtained quantification data through three widely cited evaluation algorithms i.e. BestKeeper, geNorm, and NormFinder. No single gene showed a satisfactory degree of stability throughout all developmental stages. Therefore, we propose combinations of PGK and ILK for early embryos; RPL32 and RPS17 for late embryos, all four larval instars, and pupae samples; eEF1-γ with STK for adult males; eEF1-γ with RPS17 for non-blood fed females; and eEF1-γ with eIF2α for both blood-fed females and cell culture. The results from this study should be able to provide a more informed selection of normalizing genes during qPCR in Ae.albopictus.

Impacts of diurnal temperature and larval density on aquatic development of Aedes aegypti

The increasing range of Aedes aegypti, vector for Zika, dengue, chikungunya, and other viruses, has brought attention to the need to understand the population and transmission dynamics of this mosquito. It is well understood that environmental factors and breeding site characteristics play a role in organismal development and the potential to transmit pathogens. In this study, we observe the impact of larval density in combination with diurnal temperature on the time to pupation, emergence, and mortality of Aedes aegypti. Experiments were conducted at two diurnal temperature ranges based on 10 years of historical temperatures of Houston, Texas (21–32°C and 26.5–37.5°C). Experiments at constant temperatures (26.5°C, 32°C) were also conducted for comparison. At each temperature setting, five larval densities were observed (0.2, 1, 2, 4, 5 larvae per mL of water). Data collected shows significant differences in time to first pupation, time of first emergence, maximum rate of pupation, time of maximum rate of pupation, maximum rate of emergence, time of maximum rate of emergence, final average proportion of adult emergence, and average proportion of larval mortality. Further, data indicates a significant interactive effect between temperature fluctuation and larval density on these measures. Thus, wild population estimates should account for temperature fluctuations, larval density, and their interaction in low-volume containers.

The non-canonical Notch signaling is essential for the control of fertility in Aedes aegypti

The Notch signaling pathway is a highly evolutionarily-conserved cell-cell signaling pathway that regulates many events during development. It plays a pivotal role in the regulation of fundamental cellular processes, such as cell proliferation, stem cell maintenance, and differentiation during embryonic and adult development. However, functions of Notch signaling in Aedes aegypti, the major mosquito vector for dengue, are largely unknown. In this study, we identified a unique feature of A. aegypti Notch (AaNotch) in the control of the sterile-like phenotype in female mosquitoes. Silencing AaNotch with a reverse genetic approach significantly reduced the fecundity and fertility of the mosquito. Silencing AaNotch also resulted in the prevention of micropyle formation, which led to impaired fertilization. In addition, JNK phosphorylation (a signaling molecule in the non-canonical Notch signaling pathway) was inhibited in the absence of AaNotch. Furthermore, treatment with a JNK inhibitor in the mosquito resulted in impaired fecundity and fertility. Taken together, our results demonstrate that non-canonical Notch signaling is essential for controlling fertility in the A. aegypti mosquito.

Effect of Travel Speed on Dispersion of Aqualuer 20-20 Sprayed by a Truck-Mounted Ultra-Low-Volume Sprayer Against Caged Aedes aegypti1

The effect of travel speed of a truck-mounted ultra-low-volume (ULV) sprayer on its application efficacy was studied at St. Johns County Fairground, Elkton, FL, during summer 2015. The efficacy was assessed by spray deposition, droplet size spectrum, and 24-h mortality of caged adult Aedes aegypti, using 2 rows of sampling locations, 15 m apart and spread up to 122 m from the spray. Each location had a bioassay cage and an impinger droplet sampler, 1 m apart from each other, at 1.5 m off the ground. Aqualuer^® 20-20 (20.6% permethrin AI and 20% piperonyl butoxide) was applied at the maximum label rate, travelling at 8, 16, and 32 km/h. Three replications were completed on 3 days at least a week apart, with 1 replication of each travel speed per day. On each application day the travel speeds were rotated. Overall, a travel speed of 32 km/h achieved the highest efficacy of Aqualuer^® 20-20, followed by 16 km/h, and then 8 km/h, in an open field. In general, droplet size, deposition, and mosquito mortality increased with increasing travel speed. The increased travel speed will also enhance the work rate of a sprayer and operator, thus reducing the cost of ULV applications.