Assessment of larval and pupal indices of dengue mosquito vectors in a North-Eastern state of Tripura, India.

BACKGROUND OBJECTIVES: Dengue is a major vector-borne disease having public health importance. It is caused by Dengue Virus (DENV) and is transmitted by mosquitoes of Aedes species. With the unavailability of a vaccine, vector control remains the only preventive measure for dengue. Studies have already been conducted to establish the presence of dengue vectors in the north-eastern states of India. However, limited studies have been conducted in Tripura state. In the present study we aimed to identify the preferred breeding habitats of dengue vectors in the state. METHODS: Clinical case data of dengue since the last five years was studied and the areas with the highest case numbers were identified. Entomological investigation was carried out in areas reporting the highest number of cases. Larvae were collected from the breeding habitats using standard protocol followed by morphological and molecular identification. Further, House index (HI), Container index (CI) and Pupal index (PI) were determined. The positive pools were then processed for incrimination for the presence of dengue virus. Calculation of entomological indices was done. RESULTS: Of the total 815 containers searched, 36.80% containers were positive for mosquito larvae. Among the immature mosquito collection, 836 adults emerged and were identified as Aedes albopictus using standard taxonomic keys followed by molecular methods. HI, CI and PI, varied from 15.38% to 100%, 21% to 31.04 %, and 2.93% to 110.53% respectively. However, none of the pools was positive for dengue virus. INTERPRETATION CONCLUSION: The present study identified Ae. albopictus as a potential vector of dengue in Tripura. The study gave important insights on the preferred larval habitats and provides information on the indication of displacement of Ae. albopictus from rural to urban and semi-urban areas. However, longitudinal studies for longer time frame are necessary for any conclusive remarks.

Evaluation of Insect Growth Regulators (IGRs) as biological pesticides for control of Aedes aegypti mosquitoes.

BACKGROUND OBJECTIVES: Insect growth regulators (IGRs) are biological hormone analogue or mimics used as pesticides to inhibit the growth of larva during their molting and skin shedding. This study aimed to test the effect of IGRs on the eggs hatching and post-hatching inhibition of Aedes mosquitoes and understanding its effect in the mosquito breeding habitats for reduction in adult emergence. METHODS: Experiments on the evaluation of three insect growth regulators (IGRs) for the control of different stages of Aedes aegypti was carried out during 2020-21. Each experiment consisted of four treatments viz., Pyriproxyfen, Novaluron, and Larvicol at 1.0 ppm and distilled water as a control. All experiments were carried out in completely randomized design (CRD) except eggs which were carried out in factorial design each with three replications. RESULTS: All tested IGRs performed better in affecting eggs, larval and pupal stages of Ae. aegypti. Highest eggs hatching inhibition (80%) of fresh eggs occurred in Pyriproxyfen followed by Novaluron (66%) and lowest in Larvicol (62%). Eggs hatch inhibition of embryonated eggs was lower than fresh eggs. Pyriproxyfen caused 69%, Novaluron 59% and Larvicol 39% eggs hatch inhibition of embryonated eggs. Both Pyriproxyfen and Novaluron performed better in causing 98-100% larval mortality followed by Larvicol (39%). Larval development to pupal stage was completely prevented by both Pyriproxyfen and Novaluron. Although Larvicol resulted in lowest eggs hatch and larval inhibition but prevented pupae to emerge as adults. Results further showed 70-89% mortality of 3rd instar larvae of Ae. aegypti when exposed to Pyriproxyfen and Novaluron solutions after 30 days storage at lab. temperature (27±2°C), RH 70±5. INTERPRETATION CONCLUSION: None of the IGRs was more effective at the pupal stage but showed carry-on activity of growth inhibition and mortality of the successive stages of development when used against eggs stages. Therefore, we recommend early application of IGRs at mosquito habitats during the beginning and onset of the season when very early stages of mosquitoes are available in the field.

Ecotoxicological strategies employing biochemical markers and organisms to monitor the efficacy of malathion photolysis treatment.

The objective of this study was to assess the photolysis-mediated degradation of malathion in standard and commercial formulations, and to determine the toxicity of these degraded formulations. Degradation tests were carried out with 500 µg L-1 of malathion and repeated three times. The initial and residual toxicity was assessed by using Lactuca sativa seeds for phytotoxicity, Stegomyia aegypti larvae for acute toxicity, and Stegomyia aegypti mosquitoes (cultivated from the larval stage until emergence as mosquitoes) to evaluate the biochemical markers of sublethal concentrations. For the standard formulations the photolytic process efficiently reduced the initial concentration of malathion to levels below the regulatory limits however, the formation of byproducts was revealed by chromatography, which allowed for a more complete proposal of photolytic-mediated malathion degradation route. The degraded formulations inhibited the growth of L. sativa seeds, while only the untreated formulations showed larvicidal activity and mortality. Both formulations slightly inhibited acetylcholinesterase activity in S. aegypti mosquitoes, while the standard formulation decreased and the commercial formulation increased glutathione S-transferase activity. However, there were no significant differences for superoxide dismutase, esterase-α, esterase-ß and lipid peroxidation. These findings indicate that in the absence of the target compound, the presence of byproducts can alter the enzymatic activity. In general, photolysis effectively degrade malathion lower than the legislation values; however, longer treatment times must be evaluated for the commercial formulation.

Transmission dynamics of a reaction-advection-diffusion dengue fever model with seasonal developmental durations and intrinsic incubation periods.

In this paper, we propose a reaction-advection-diffusion dengue fever model with seasonal developmental durations and intrinsic incubation periods. Firstly, we establish the well-posedness of the model. Secondly, we define the basic reproduction number ℜ 0 for this model and show that ℜ 0 is a threshold parameter: if ℜ 0 < 1 , then the disease-free periodic solution is globally attractive; if ℜ 0 > 1 , the system is uniformly persistent. Thirdly, we study the global attractivity of the positive steady state when the spatial environment is homogeneous and the advection of mosquitoes is ignored. As an example, we use the model to investigate the dengue fever transmission case in Guangdong Province, China, and explore the impact of model parameters on ℜ 0 . Our findings indicate that ignoring seasonality may underestimate ℜ 0 . Additionally, the spatial heterogeneity of transmission may increase the risk of disease transmission, while the increase of seasonal developmental durations, intrinsic incubation periods and advection rates can all reduce the risk of disease transmission.

Projection of dengue fever transmissibility under climate change in South and Southeast Asian countries.

Vector-borne infectious disease such as dengue fever (DF) has spread rapidly due to more suitable living environments. Considering the limited studies investigating the disease spread under climate change in South and Southeast Asia, this study aimed to project the DF transmission potential in 30 locations across four South and Southeast Asian countries. In this study, weekly DF incidence data, daily mean temperature, and rainfall data in 30 locations in Singapore, Sri Lanka, Malaysia, and Thailand from 2012 to 2020 were collected. The effects of temperature and rainfall on the time-varying reproduction number (Rt) of DF transmission were examined using generalized additive models. Projections of location-specific Rt from 2030s to 2090s were determined using projected temperature and rainfall under three Shared Socioeconomic Pathways (SSP126, SSP245, and SSP585), and the peak DF transmissibility and epidemic duration in the future were estimated. According to the results, the projected changes in the peak Rt and epidemic duration varied across locations, and the most significant change was observed under middle-to-high greenhouse gas emission scenarios. Under SSP585, the country-specific peak Rt was projected to decrease from 1.63 (95% confidence interval: 1.39-1.91), 2.60 (1.89-3.57), and 1.41 (1.22-1.64) in 2030s to 1.22 (0.98-1.51), 2.09 (1.26-3.47), and 1.37 (0.83-2.27) in 2090s in Singapore, Thailand, and Malaysia, respectively. Yet, the peak Rt in Sri Lanka changed slightly from 2030s to 2090s under SSP585. The epidemic duration in Singapore and Malaysia was projected to decline under SSP585. In conclusion, the change of peak DF transmission potential and disease outbreak duration would vary across locations, particularly under middle-to-high greenhouse gas emission scenarios. Interventions should be considered to slow down global warming as well as the potential increase in DF transmissibility in some locations of South and Southeast Asia.

Life-history traits of Aedes aegypti (Linnaeus) distributed across a latitudinal range of 23 °N-6 °S.

The growth and associated traits of Aedes aegypti (L.) mosquitoes may adapt and evolve in response to the costs associated with body size in relation to latitudinal variation. We analyzed the life-history traits and energy reserves of field-collected mosquitoes from Taiwan, Thailand, and Indonesia along a latitudinal range spanning from 23°N to 6°S. A U-shaped relationship between body size and latitude was observed. Our study demonstrated the role of latitudinal temperature variations in determining the body size patterns of Ae. aegypti. Notably, the body size of the northern populations (from Taiwan) was significantly larger than those of the tropical populations from Thailand and Indonesia. Models have demonstrated that regional precipitation levels may contribute to body trait variations in certain high-latitude populations in Thailand. However, Indonesian populations have high development rates and large body sizes, indicating the involvement of other physiological traits in determining mosquito body size. The reproductive output of the adult females in this study was positively correlated with body size, but our measure of longevity did not covary significantly with the body size. By contrast, the reproductive output of mosquito-tested populations was in inverse proportion to longevity. Additionally, the mean teneral glycogen levels in the Indonesian and Thai populations were 2.5 times higher than those in the Taiwanese populations. The Indonesian and Thai populations had low mean generation and doubling times, resulting in a high intrinsic rate of increase compared with that of the Taiwanese populations, despite the Taiwanese populations having the highest net reproduction rate.

Pseudomonas protegens Affects Mosquito Survival and Development.

This study investigated the pathogenic potential of Pseudomonas protegens on mosquito larvae of the two species Culex pipiens and Aedes albopictus, representing major threats for disease transmission in the Mediterranean area and worldwide. The bacterium achieved to kill over 90% of the mosquito larvae within 72 h after exposition to a bacterial concentration of 100 million CFU/ml. These lethal effects were concentration dependent and a significantly higher susceptibility was associated with younger larvae of both mosquito species. Significant slowdown of immature (larval and pupal) development and decrease in adult emergence rate after treatment with sub-lethal doses of the bacterium were also detected. This study reports for the first time the insecticidal activity of a root-associated biocontrol bacterium against aquatic mosquito larvae.

Experiências em divulgação científica e sensibilização da população: importância do controle mecânico do vetor Aedes aegypti / Experiences in scientific outreach and public awareness: the importance of mechanical control of the Aedes aegypti vector / Experiencias en divulgación científica y sensibilización de la población: importancia del control mecánico del vector Aedes aegypti

Aedes aegypti é o principal vetor dos agentes etiológicos de dengue, zika e chikungunya, doenças para as quais não existem vacinas totalmente eficazes. Alternativas de controle visando mitigar essas arboviroses são primordiais. Entre essas, o controle mecânico aborda práticas de eliminação e/ou limpeza de criadouros do vetor. Neste relato, apresentamos e avaliamos criticamente ações realizadas pelo grupo, ocorridas entre 2016 e 2019, nas quais divulgamos informação científica clara através do diálogo com a população. Os métodos utilizados foram: 1) palestras em escolas (público infantojuvenil) utilizando slides, fotos e vídeos; 2) oficinas (público misto), estande com material in vivo do ciclo de vida do Aedes, jogos e desenhos. Analisamos dez palestras em escolas do ensino fundamental e médio e vinte oficinas realizadas em diferentes regiões do Brasil. Concluímos que tais ações e suas análises críticas devem ser realizadas continuamente para que sejam bem-sucedidas

Aedes aegypti is the main vector of dengue, zika, and chikungunya etiological agents, diseases for which no effective vaccines are available. Control alternatives aimed at mitigating these arboviruses are essential. Among such, mechanical control addresses practices of elimination and/or cleaning of vector breeding sites. Here, we presented and critically evaluated actions carried out by ourselves. These actions took place between 2016 and 2019, where we disseminated clear scientific information through dialogue with the population. The following methods were employed: 1) lectures in schools (children and youth audiences) using slides, photos, and videos; 2) workshops (mixed audience), stand with in vivo material from the Aedeslife cycle, games, and drawings. Ten lectures in elementary and high schools and twenty workshops held in different regions of Brazil were analyzed. It was concluded that such actions and their critical analyzes must be carried out continuously to be successful

Aedes aegypti es el principal vector de los agentes etiológicos del dengue, zika y chikungunya, enfermedades para las que no existen vacunas totalmente eficaces. Las alternativas de control para mitigar estas arbovirosis son fundamentales. El control mecánico, representa una de estas alternativas, aborda prácticas de eliminación y/o limpieza de criaderos del vector. En este informe presentamos y evaluamos de manera crítica las acciones realizadas por el grupo entre los años 2016 y 2019. Presentamos información científica clara a través del diálogo con la población mediante los siguientes métodos: 1) conferencias en escuelas (público infantil) utilizando diapositivas, fotos y videos; 2) Talleres (público mixto), stand con material in vivo del ciclo de vida del Aedes, juegos y dibujos. Analizamos diez conferencias en escuelas (primarias y secundarias) y veinte talleres realizados en diferentes regiones de Brasil. Concluimos que tales acciones y el análisis crítico de las mismas deben llevarse a cabo de manera continua para que resulten exitosas.

Occurrence of the Sylvatic Yellow Fever Vector Mosquito Haemagogus leucocelaenus (Diptera: Culicidae) in an Atlantic Forest Fragment of the Touristic State of Rio de Janeiro, Brazil.

The yellow fever virus is estimated to cause 30,000 deaths each year worldwide, with the majority of cases and deaths occurring in Africa. The virus is also endemic to Central and South America, including northern and western Brazil. The sylvatic cycle of the virus is related to wild and rural areas, with nonhuman primates as the primary host and wild mosquitoes, specifically from the genera Haemagogus, as vectors. The diversity of the mosquito community plays a significant role in the increase of pathogen transmission to humans. In the present study, we detected fluctuation in populations of vector mosquitoes using ovitraps for Culicidae egg collection. The study area is a forest fragment of the Atlantic Forest, one of the most threatened biomes in Brazil. This biome has been suffering significant deforestation due to anthropic activity. Worryingly, the proximity of human populations to forest environments increases the risk of spreading disease from forest fragments to urban areas. Our findings showed that the highest egg abundance occurred in December 2019, with a significant difference (p = 0.005) between rainy and dry seasons. Most eggs were collected during the rainy period. Subsequent quantification of specimens from epidemiologically relevant species hatched from field-collected eggs resulted in 1,131 (86%) Haemagogus leucocelaenus (Dyar & Shannon, 1924), 111 (8%) Aedes terrens (Walker, 1856), 47 (4%) Aedes albopictus (Skuse, 1894), and 21 (2%) Haemagogus janthinomys (Dyar, 1921). Finally, we assessed the behavior of different vector species performing oviposition on the same breeding site. The highest correlation coefficient was observed between Ae. albopictus and Ae. terrens (rho = 0.52) concerning other Culicidae species. Therefore, we believe that Culicidae population surveillance is crucial for disease monitoring since the increase in specimens of a number of vector species influences the emergence of yellow fever cases in nonhuman primates and human populations.

Incidência de casos confirmados de dengue no Estado do Paraná Brasil nos anos de 2016 a 2021 / Incidence of confirmed dengue cases in the State of Paraná Brazil in the years of 2016 to 2021 / Incidencia de casos confirmados de dengue en el Estado de Paraná Brasil en los años 2016 a 2021

A dengue é uma doença dolorosa e debilitante transmitida por insetos da espécie Aedes aegypti. Ela é definida como uma doença viral que, nos últimos anos, se espalhou vertiginosamente por todas as regiões tropicais e subtropicais do planeta. Este estudo teve como objetivo identificar e discutir o número e a taxa de incidência de casos de dengue no estado do Paraná utilizando-se dos boletins emitidos por semana epidemiológica nos anos de 2016 a 2021, considerando a sazonalidade da doença. Também se objetivou debater a incidência por macrorregional, as possíveis causas de períodos epidêmicos e ações de combate vetorial para redução dos casos da patologia. Foram utilizados como fonte de informações o banco de dados da Dengue/SVS/SESA, por meio de informes técnicos, disponibilizados pelo portal online de Boletins da Dengue Paraná da Secretaria de Estado de Saúde do Paraná. Conclui-se que o ano epidemiológico de 2019/2020 foi o de maior incidência e os anos epidemiológicos 2016/2017 e 2017/2018 apresentaram os menores casos durante todo período analisado. Dessa forma, a vigilância epidemiológica é muito importante para avaliação espacial da distribuição de casos para execução de ações estratégicas para redução da infestação do vetor. As políticas públicas e a disponibilização de inseticidas para aplicação também são essenciais para o combate da Dengue.

Dengue is a painful and debilitating disease transmitted by insects of the Aedes aegypti species. It is defined as a viral disease that, in recent years, has spread vertiginously throughout the tropical and subtropical regions of the planet. This study aimed to identify and discuss the number and incidence rate of dengue cases in the state of Paraná using the bulletins issued by epidemiological week in the years 2016 to 2021, considering the seasonality of the disease. The aim was also to discuss the incidence per macro-region, the possible causes of epidemic periods, and vectorial combat actions to reduce the cases of the pathology. The Dengue/SVS/SESA database was used as a source of information, through technical reports, made available by the online portal of Dengue Paraná Bulletins of the Paraná State Health Department. It is concluded that the epidemiological year 2019/2020 was the one with the highest incidence and the epidemiological years 2016/2017 and 2017/2018 had the lowest cases during the entire period analyzed. Thus, epidemiological surveillance is very important for the spatial assessment of the distribution of cases to carry out strategic actions to reduce vector infestation. Public policies and the availability of insecticides for application are also essential to combat Dengue.

El dengue es una enfermedad dolorosa y debilitante transmitida por insectos de la especie Aedes aegypti. Se define como una enfermedad viral que, en los últimos años, se ha extendido vertiginosamente por las regiones tropicales y subtropicales del planeta. Este estudio tuvo como objetivo identificar y discutir el número y la tasa de incidencia de los casos de dengue en el estado de Paraná utilizando los boletines emitidos por la semana epidemiológica en los años 2016 a 2021, considerando la estacionalidad de la enfermedad. También se pretendía discutir la incidencia por macrorregiones, las posibles causas de los periodos epidémicos y las acciones de control de vectores para la reducción de los casos de la enfermedad. Se utilizó como fuente de información la base de datos de Dengue/SVS/SESA, por medio de informes técnicos, puestos a disposición por el portal online de Boletines de Dengue Paraná de la Secretaría de Salud del Estado de Paraná. Se concluye que el año epidemiológico 2019/2020 fue el de mayor incidencia y los años epidemiológicos 2016/2017 y 2017/2018 presentaron los menores casos durante todo el periodo analizado. Por lo tanto, la vigilancia epidemiológica es muy importante para la evaluación espacial de la distribución de los casos para la implementación de acciones estratégicas para reducir la infestación del vector. Las políticas públicas y la disponibilidad de insecticidas para su aplicación también son esenciales para combatir el dengue.

Essential functions of mosquito ecdysone importers in development and reproduction.

The primary insect steroid hormone ecdysone requires a membrane transporter to enter its target cells. Although an organic anion-transporting polypeptide (OATP) named Ecdysone Importer (EcI) serves this role in the fruit fly Drosophila melanogaster and most likely in other arthropod species, this highly conserved transporter is apparently missing in mosquitoes. Here we report three additional OATPs that facilitate cellular incorporation of ecdysone in Drosophila and the yellow fever mosquito Aedes aegypti. These additional ecdysone importers (EcI-2, -3, and -4) are dispensable for development and reproduction in Drosophila, consistent with the predominant role of EcI. In contrast, in Aedes, EcI-2 is indispensable for ecdysone-mediated development, whereas EcI-4 is critical for vitellogenesis induced by ecdysone in adult females. Altogether, our results indicate unique and essential functions of these additional ecdysone importers in mosquito development and reproduction, making them attractive molecular targets for species- and stage-specific control of ecdysone signaling in mosquitoes.

Competition and resource depletion shape the thermal response of population fitness in Aedes aegypti.

Mathematical models that incorporate the temperature dependence of lab-measured life history traits are increasingly being used to predict how climatic warming will affect ectotherms, including disease vectors and other arthropods. These temperature-trait relationships are typically measured under laboratory conditions that ignore how conspecific competition in depleting resource environments-a commonly occurring scenario in nature-regulates natural populations. Here, we used laboratory experiments on the mosquito Aedes aegypti, combined with a stage-structured population model, to investigate this issue. We find that intensified larval competition in ecologically-realistic depleting resource environments can significantly diminish the vector's maximal population-level fitness across the entire temperature range, cause a ~6 °C decrease in the optimal temperature for fitness, and contract its thermal niche width by ~10 °C. Our results provide evidence for the importance of considering intra-specific competition under depleting resources when predicting how arthropod populations will respond to climatic warming.

A comparative study of dengue virus vectors in major parks and adjacent residential areas in Ho Chi Minh City, Vietnam.

The primary dengue virus vectors, Aedes aegypti and Aedes albopictus, are primarily daytime biting mosquitoes. The risk of infection is suspected to be considerable in urban parks due to visitor traffic. Despite the importance of vector control for reducing dengue transmission, little information is available on vector populations in urban parks. The present study characterized mosquito habitats and estimated vector densities in the major urban parks in Ho Chi Minh City, Vietnam and compared them with those in adjacent residential areas. The prevalences of habitats where Aedes larvae were found were 43% and 9% for the parks and residential areas, respectively. The difference was statistically significant (prevalence ratio [PR]: 5.00, 95% CI: 3.85-6.49). The prevalences of positive larval habitats were significantly greater in the parks for both species than the residential areas (PR: 1.52, 95% CI: 1.04-2.22 for A. aegypti, PR: 10.10, 95% CI: 7.23-14.12 for A. albopictus). Larvae of both species were positively associated with discarded containers and planters. Aedes albopictus larvae were negatively associated with indoor habitats, but positively associated with vegetation shade. The adult density of A. aegypti was significantly less in the parks compared with the residential areas (rate ratio [RR]; 0.09, 95% CI: 0.05-0.16), while the density of A. albopictus was significantly higher in the parks (RR: 9.99, 95% CI: 6.85-14.59). When the species were combined, the density was significantly higher in the parks (RR: 2.50, 95% CI: 1.92-3.25). The urban parks provide suitable environment for Aedes mosquitoes, and A. albopictus in particular. Virus vectors are abundant in the urban parks, and the current vector control programs need to have greater consideration of urban parks.

Ecological and environmental factors affecting transmission of sylvatic yellow fever in the 2017-2019 outbreak in the Atlantic Forest, Brazil.

BACKGROUND: Yellow fever virus (YFV) is an arbovirus that, despite the existence of a safe and effective vaccine, continues to cause outbreaks of varying dimensions in the Americas and Africa. Between 2017 and 2019, Brazil registered un unprecedented sylvatic YFV outbreak whose severity was the result of its spread into zones of the Atlantic Forest with no signals of viral circulation for nearly 80 years. METHODS: To investigate the influence of climatic, environmental, and ecological factors governing the dispersion and force of infection of YFV in a naïve area such as the landscape mosaic of Rio de Janeiro (RJ), we combined the analyses of a large set of data including entomological sampling performed before and during the 2017-2019 outbreak, with the geolocation of human and nonhuman primates (NHP) and mosquito infections. RESULTS: A greater abundance of Haemagogus mosquitoes combined with lower richness and diversity of mosquito fauna increased the probability of finding a YFV-infected mosquito. Furthermore, the analysis of functional traits showed that certain functional groups, composed mainly of Aedini mosquitoes which includes Aedes and Haemagogus mosquitoes, are also more representative in areas where infected mosquitoes were found. Human and NHP infections were more common in two types of landscapes: large and continuous forest, capable of harboring many YFV hosts, and patches of small forest fragments, where environmental imbalance can lead to a greater density of the primary vectors and high human exposure. In both, we show that most human infections (~ 62%) occurred within an 11-km radius of the finding of an infected NHP, which is in line with the flight range of the primary vectors. CONCLUSIONS: Together, our data suggest that entomological data and landscape composition analyses may help to predict areas permissive to yellow fever outbreaks, allowing protective measures to be taken to avoid human cases.

Exposure to copper sulfate impairs survival, post-embryonic midgut development and reproduction in Aedes aegypti.

Aedes aegypti is a vector of several global human viruses responsible for high human morbidity and mortality. The method to prevent the transmission of vector-borne viruses is mainly based on the control of the insect vector using insecticides. Among these chemicals, copper sulfate is a compound widely used in agriculture with the potential to be used as an alternative to control these insects. This study evaluated the effects of the exposure of A. aegypti larvae to copper sulfate on survival, midgut morphology, blood-feeding and fecundity. The exposure to CuSO4 decreased the survival of A. aegypti during the immature phase. Adults obtained from exposed larvae had their lifespan decreased at all tested concentrations. The exposure to CuSO4 impaired the development in the transition from larvae to pupae and from pupae to adult. The number of eggs laid by females developed from larvae treated with CuSO4 was significantly lower than in control. In addition, the egg hatching rates were also negatively affected. The midguts of treated larvae and pupae showed epithelial disorganization. The number of cleaved caspase-3 cells increased in the midgut of exposed pupae compared to control. Moreover, there was a reduction in proliferating cells in treated larvae and pupae compared to the control. In conclusion, the results reveal that CuSO4 exposure has insecticidal activity against A. aegypti, which may be related to the impairment of the midgut metamorphosis and reduced proliferation of stem cells, with the consequent impairment of female mosquito fertility and fecundity.

Statewide Efficacy Assessment of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: An Alternative Control Strategy?

The efficacy of three groups of insect growth regulators, namely juvenile hormone mimics (methoprene and pyriproxyfen), chitin synthesis inhibitors (diflubenzuron and novaluron), and molting disruptor (cyromazine) was evaluated for the first time, against Aedes albopictus Skuse (Diptera: Culicidae) larvae from 14 districts in Sabah, Malaysia. The results showed that all field populations of Ae. albopictus were susceptible towards methoprene, pyriproxyfen, diflubenzuron, novaluron, and cyromazine, with resistance ratio values ranging from 0.50-0.90, 0.60-1.00, 0.67-1.17, 0.71-1.29, and 0.74-1.07, respectively. Overall, the efficacy assessment of insect growth regulators in this study showed promising outcomes and they could be further explored as an alternative to conventional insecticides.

Impact of Cymbopogon flexuosus (Poaceae) essential oil and primary components on the eclosion and larval development of Aedes aegypti.

The current study describes the effects of sub-lethal concentrations and constituent compounds (citral and geranyl acetate) of Cymbopogon flexuosus essential oil (EO) on the development of Aedes aegypti. We treated eggs with 6, 18, or 30 mg L-1 and larvae with 3 or 6 mg L-1 of EO and its major compounds (citral and geranyl acetate). Citral and geranyl acetate were evaluated at 18, 30, and 42 mg L-1 and compared with commercial growth inhibitors (diflubenzuron and methoprene). We measured larval head diameter, siphon length, and larval length. Finally, we examined concentrations of molt hormone (MH) and juvenile hormone III (JH III) using high-performance liquid chromatography coupled to mass spectrometry. All geranyl acetate concentrations decreased egg hatching, while EO altered molting among larval instars and between larvae and pupae, with an increase in the larval length (3 mg L-1: 6 ± 0.0 mm; 6 mg L-1: 6 ± 0.7 mm) and head width (3 mg L-1: 0.8 ± 0 mm; 6 mg L-1: 0.8 ± 0.0 mm) compared with the control group. We did not detect chromatographic signals of MH and JH III in larvae treated with C. flexuosus EO or their major compounds. The sub-lethal concentrations C. flexuosus EO caused a similar effect to diflubenzuron, namely decreased hormone concentrations, an extended larval period, and death.

Urbanization favors the proliferation of Aedes aegypti and Culex quinquefasciatus in urban areas of Miami-Dade County, Florida.

Urbanization processes are increasing globally. Anthropogenic alterations in the environment have profound effects on biodiversity. Decreased biodiversity due to biotic homogenization processes as a consequence of urbanization often result in increased levels of mosquito vector species and vector-borne pathogen transmission. Understanding how anthropogenic alterations in the environment will affect the abundance, richness, and composition of vector mosquito species is crucial for the implementation of effective and targeted mosquito control strategies. We hypothesized that anthropogenic alterations in the environment are responsible for increasing the abundance of mosquito species that are adapted to urban environments such as Aedes aegypti and Culex quinquefasciatus. Therefore, our objective was to survey mosquito relative abundance, richness, and community composition in Miami-Dade County, Florida, in areas with different levels of urbanization. We selected 24 areas, 16 remote areas comprised of natural and rural areas, and 8 urban areas comprised of residential and touristic areas in Miami-Dade County, Florida. Mosquitoes were collected weekly in each area for 24 h for 5 consecutive weeks from August to October 2020 using BG-Sentinel traps baited with dry ice. A total of 36,645 mosquitoes were collected, from which 34,048 were collected in the remote areas and 2,597 in the urban areas. Our results show a clear and well-defined pattern of abundance, richness, and community composition according to anthropogenic modifications in land use and land cover. The more urbanized a given area the fewer species were found and those were primary vectors of arboviruses, Ae. aegypti and Cx. quinquefasciatus.

Modeling the effects of Aedes aegypti's larval environment on adult body mass at emergence.

Mosquitoes vector harmful pathogens that infect millions of people every year, and developing approaches to effectively control mosquitoes is a topic of great interest. However, the success of many control measures is highly dependent upon ecological, physiological, and life history traits of mosquito species. The behavior of mosquitoes and their potential to vector pathogens can also be impacted by these traits. One trait of interest is mosquito body mass, which depends upon many factors associated with the environment in which juvenile mosquitoes develop. Our experiments examined the impact of larval density on the body mass of Aedes aegypti mosquitoes, which are important vectors of dengue, Zika, yellow fever, and other pathogens. To investigate the interactions between the larval environment and mosquito body mass, we built a discrete time mathematical model that incorporates body mass, larval density, and food availability and fit the model to our experimental data. We considered three categories of model complexity informed by data, and selected the best model within each category using Akaike's Information Criterion. We found that the larval environment is an important determinant of the body mass of mosquitoes upon emergence. Furthermore, we found that larval density has greater impact on body mass of adults at emergence than on development time, and that inclusion of density dependence in the survival of female aquatic stages in models is important. We discuss the implications of our results for the control of Aedes mosquitoes and on their potential to spread disease.

Starvation at the larval stage increases the vector competence of Aedes aegypti females for Zika virus.

Aedes aegypti is the primary vector of Zika virus (ZIKV), a flavivirus which typically presents itself as febrile-like symptoms in humans but can also cause neurological and pregnancy complications. The transmission cycle of mosquito-borne arboviruses such as ZIKV requires that various key tissues in the female mosquito get productively infected with the virus before the mosquito can transmit the virus to another vertebrate host. Following ingestion of a viremic blood-meal from a vertebrate, ZIKV initially infects the midgut epithelium before exiting the midgut after blood-meal digestion to disseminate to secondary tissues including the salivary glands. Here we investigated whether smaller Ae. aegypti females resulting from food deprivation as larvae exhibited an altered vector competence for blood-meal acquired ZIKV relative to larger mosquitoes. Midguts from small 'Starve' and large 'Control' Ae. aegypti were dissected to visualize by transmission electron microscopy (TEM) the midgut basal lamina (BL) as physical evidence for the midgut escape barrier showing Starve mosquitoes with a significantly thinner midgut BL than Control mosquitoes at two timepoints. ZIKV replication was inhibited in Starve mosquitoes following intrathoracic injection of virus, however, Starve mosquitoes exhibited a significantly higher midgut escape and population dissemination rate at 9 days post-infection (dpi) via blood-meal, with more virus present in saliva and head tissue than Control by 10 dpi and 14 dpi, respectively. These results indicate that Ae. aegypti developing under stressful conditions potentially exhibit higher midgut infection and dissemination rates for ZIKV as adults, Thus, variation in food intake as larvae is potentially a source for variable vector competence levels of the emerged adults for the virus.