Aegypti Eggs Research Articles

Dengue Knowledge and Preventive Practices in Iquitos, Peru.

As part of a cluster-randomized trial to evaluate insecticide-treated curtains for dengue prevention in Iquitos, Peru, we surveyed 1,333 study participants to examine knowledge and reported practices associated with dengue and its prevention. Entomological data from 1,133 of these households were linked to the survey. Most participants knew that dengue was transmitted by mosquito bite (85.6%), but only few (18.6%) knew that dengue vectors bite during daytime. Most commonly recognized dengue symptoms were fever (86.6%), headache (76.4%), and muscle/joint pain (67.9%). Most commonly reported correct practices for mosquito control were cleaning homes (61.6%), using insecticide sprays (23%), and avoiding having standing water at home (12.3%). Higher education was associated with higher knowledge about dengue, including transmission and vector control. Higher socioeconomic status was associated with increased reported use of preventive practices requiring money expenditure. We were less likely to find Aedes aegypti eggs, larvae, or pupae in households that had < 5-year-old children at home. Although dengue has been transmitted in Iquitos since the 1990s and the Regional Health Authority routinely fumigates households, treats domestic water containers with larvicide, and issues health education messages through mass media, knowledge of dengue transmission and household practices for prevention could be improved.

Physical features and chitin content of eggs from the mosquito vectors Aedes aegypti, Anopheles aquasalis and Culex quinquefasciatus: Connection with distinct levels of resistance to desiccation

Mosquito eggs are laid in water but freshly laid eggs are susceptible to dehydration, if their surroundings dry out at the first hours of development. During embryogenesis of different mosquito vectors the serosal cuticle, an extracellular matrix, is produced; it wraps the whole embryo and becomes part of the eggshell. This cuticle is an essential component of the egg resistance to desiccation (ERD). However, ERD is variable among species, sustaining egg viability for different periods of time. While Aedes aegypti eggs can survive for months in a dry environment (high ERD), those of Anopheles aquasalis and Culex quinquefasciatus in the same condition last, respectively, for one day (medium ERD) or a few hours (low ERD). Resistance to desiccation is determined by the rate of water loss, dehydration tolerance and total amount of water of a given organism. The ERD variability observed among mosquitoes probably derives from diverse traits. We quantified several attributes of whole eggs, potentially correlated with the rate of water loss: length, width, area, volume, area/volume ratio and weight. In addition, some eggshell aspects were also evaluated, such as absolute and relative weight, weight/area relationship (herein called surface density) and chitin content. Presence of chitin specifically in the serosal cuticle as well as aspects of endochorion external surface were also investigated. Three features could be related to differences on ERD levels: chitin content, directly related to ERD, the increase in the egg volume during embryogenesis and the eggshell surface density, which were both inversely related to ERD. Although data suggest that the amount of chitin in the eggshell is relevant for egg impermeability, the participation of other yet unidentified eggshell attributes must be considered in order to account for the differences in the ERD levels observed among Ae. aegypti, An. aquasalis and Cx. quinquefasciatus.

Susceptibility profile of Aedes aegypti from Santiago Island, Cabo Verde, to insecticides

In 2009, Cabo Verde diagnosed the first dengue cases, with 21,137 cases reported and Aedes aegypti was identified as the vector. Since the outbreak, chemical insecticides and source reduction were used to control the mosquito population. This study aimed to assess the susceptibility of A. aegypti populations from Santiago, Cabo Verde to insecticides and identify the mechanisms of resistance. Samples of A. aegypti eggs were obtained at two different time periods (2012 and 2014), using ovitraps in different locations in Santiago Island to establish the parental population. F1 larvae were exposed to different concentrations of insecticides (Bacillus thuringiensis var israelensis (Bti), diflubenzuron and temephos) to estimate the lethal concentrations (LC90) and calculate the respective rate of resistance (RR90). Semi-field tests using temephos-ABATE® were performed to evaluate the persistence of the product. Bottle tests using female mosquitoes were carried out to determine the susceptibility to the adulticides malathion, cypermethrin and deltamethrin. Biochemical and molecular tests were performed to investigate the presence of metabolic resistance mechanisms, associated with the enzymes glutathione S-transferases (GSTs), esterases and mixed-function oxidases (MFO) and to detect mutations or alterations in the sodium channel and acetylcholinesterase genes. A. aegypti mosquitoes from Santiago exhibited resistance to deltamethrin, cypermethrin (mortality<80%) and temephos (RR90=4.4) but susceptibility to malathion (mortality≥98%), Bti and diflubenzuron. The low level of resistance to temephos did not affect the effectiveness of Abate®. The enzymatic analysis conducted in 2012 revealed slight changes in the activities of GST (25%), MFO (18%), α-esterase (19%) and β-esterase (17%), but no significant changes in 2014. Target site resistance mutations were not detected. Our results suggest that the A. aegypti population from Santiago is resistant to two major insecticides used for vector control, deltamethrin and temephos. To our knowledge, this is the first report of temephos resistance in an African A. aegypti population. The low level of temephos resistance was maintained from 2012–2014, which suggested the imposition of selective pressure, although it was not possible to identify the resistance mechanisms involved. These data show that the potential failures in the local mosquito control program are not associated with insecticide resistance.

Cold Season Mortality Under Natural Conditions and Subsequent Hatching Response of Aedes (Stegomyia) aegypti (Diptera: Culicidae) Eggs in a Subtropical City of Argentina.

In temperate and subtropical regions, populations of Aedes (Stegomyia) aegypti (L.) survive unfavorable winter conditions in the egg stage. Knowing their survival rates can be of great interest for the health authorities in charge of control activities. In this study, we analyzed the mortality of Ae. aegypti eggs exposed to the cold season as well as their hatching patterns under laboratory conditions in the city of Resistencia, Chaco, Argentina. The mortality rate was 48.6%. No statistically significant differences were observed in the mortality of eggs exposed at different sites. Hatching response differed significantly among the successive postexposure immersions, with the highest proportion of hatched eggs during the first immersion. These results show that the mortality rate of Ae. aegypti eggs exposed to the cold season in a subtropical city of Argentina was higher than those from temperate climate region. The additional mortality of eggs in our study might be related to fungal development (an unexpected event), which was not observed in research in temperate climate. The hatching pattern observed in this study ensures a rapid increase of the population at the beginning of the favorable breeding season, but it also maintains a batch with delayed hatching eggs, posing a risk for the community.

Evidence forAedes aegypti(Diptera: Culicidae) Oviposition on Boats in the Peruvian Amazon

Dengue vector Aedes aegypti L. is invading peri-urban and rural areas throughout Latin America. Our previous research in the Peruvian Amazon has shown that river boats are heavily infested with immature and adult Ae. aegypti mosquitoes, likely playing a major role in their long-distance dispersal and successful invasion. However, the presence of immature mosquitoes provides no information about the timing of oviposition, and whether it took place in the boats. Here, we used baited ovitraps deployed on river boats to test the hypothesis that Ae. aegypti oviposition occurs during boat travel. We deployed 360 ovitraps on 60 different barges during August and October of 2013, and February 2014 (with 20 barges sampled during each month). We found that Ae. aegypti mosquitoes in 22 individual ovitraps from 15 of the 60 barges (premise index 25%) across all sampling dates. Further, the distribution of Ae. aegypti egg abundance was highly aggregated: 2.6% of traps (N=7) were responsible for 71.8% of eggs found, and 1.5% of traps (N=4) were responsible for all (100%) of the larvae found. Similarly, 5% of boats were responsible for the 71.47% of eggs. Our results provide strong evidence that Ae. aegypti oviposition commonly occurs during boat travel. Baited ovitraps could represent a cost-effective means of monitoring and controlling mosquito populations on boats.

Evaluation of Household Bleach as an Ovicide for the Control of Aedes aegypti.

Accumulations of dormant eggs in container habitats allow Aedes aegypti populations to survive harsh environmental conditions and may frustrate control interventions directed at larval and adult life stages. While sodium hypochlorite solutions (NaOCl) have long been recognized as ovicides for use against dengue vectors, the susceptibility of eggs to spray applications has not been robustly evaluated on substrate materials representative of the most frequently utilized artificial container habitats. Experiments were performed under controlled and natural conditions by applying dilutions of household bleach (52.5ppt NaOCl) as a spray to eggs on plastic, rubber, and concrete surfaces, with and without a smectite clay thickener. Laboratory assays identified the minimum NaOCl concentrations required to eliminate eggs on plastic (10ppt), rubber (20ppt) and concrete (20ppt) surfaces. Addition of smectite clay reduced the minimum effective concentration to 10ppt NaOCl for all 3 substrates. A minimum exposure period of 24h was required to completely eliminate egg viability on concrete surfaces, even at the highest NaOCl concentration (52.5ppt). Field experiments verified that spray application of a 1∶3 dilution of household bleach mixed with smectite clay can reduce egg hatching by ≥ 99% in shaded and sun-exposed plastic containers. Similarly, 4∶1 dilution of household bleach (with or without smectite clay) eliminated ≥ 98% of eggs from concrete surfaces in outdoor, water-filled drums. In this study, we propose a practical, effective and safe strategy for using household bleach to eliminate Ae. aegypti eggs in a range of artificial container habitats.

Ecology of Aedes aegypti and Aedes albopictus in the Americas and disease transmission

The recent range expansion of the mosquito Aedes albopictus has been associated in some areas by declines in abundance or local elimination of Aedes aegypti, but the two species still coexist in large regions of the Americas. We offer a summary of the possible mechanisms responsible for the abundance and displacement pattern observed and of their significance in terms of disease transmission. Among these mechanisms we may mention the competition for limiting resources, the differences in the ability to withstand starvation, the apparent competition through differential effects of the parasite Ascogregarina taiwanensis, and the inhibition of Ae. aegypti egg development by Ae. albopictus larvae. Habitat segregation has been proposed as a mechanism promoting the coexistence of the two species through avoidance of direct competition. Aedes aegypti predominates in urban areas, Ae. albopictus in rural ones, and both species coexist in the suburbs. There is also evidence that in certain areas, habitat segregation in terms of distance from the coast can influence the distribution of both species. Another possible cause of the rapid disappearance of Ae. aegypti is reproductive interference between the species. According to this hypothesis, asymmetric effects of interspecific mating favor Ae. albopictus. This type of reproductive interference can result in the elimination of sympatric populations of the affected species and can be one of the major causes for the swiftness with which Ae. aegypti disappeared from some places in the Americas following invasions by Ae. albopictus.

Ecología de Aedes aegypti y Aedes albopictus en América y la transmisión de enfermedades

The recent range expansion of the mosquito Aedes albopictus has been associated in some areas by declines in abundance or local elimination of Aedes aegypti, but the two species still coexist in large regions of the Americas. We offer a summary of the possible mechanisms responsible for the abundance and displacement pattern observed and of their significance in terms of disease transmission.Among these mechanisms we may mention the competition for limiting resources, the differences in the ability to withstand starvation, the apparent competition through differential effects of the parasite Ascogregarina taiwanensis, and the inhibition of Ae. aegypti egg development by Ae. albopictus larvae.Habitat segregation has been proposed as a mechanism promoting the coexistence of the two species through avoidance of direct competition. Aedes aegypti predominates in urban areas, Ae. albopictus in rural ones, and both species coexist in the suburbs. There is also evidence that in certain areas, habitat segregation in terms of distance from the coast can influence the distribution of both species.Another possible cause of the rapid disappearance of Ae. aegypti is reproductive interference between the species. According to this hypothesis, asymmetric effects of interspecific mating favor Ae. albopictus. This type of reproductive interference can result in the elimination of sympatric populations of the affected species and can be one of the major causes for the swiftness with which Ae. aegypti disappeared from some places in the Americas following invasions by Ae. albopictus.

Standard operating procedures for standardized mass rearing of the dengue and chikungunya vectors Aedes aegypti and Aedes albopictus (Diptera: Culicidae) - I - egg quantification.

BackgroundQuantification of eggs prior to rearing the immature stages of mosquitoes is an essential step in establishing a standardized mass rearing system. To develop a simple and accurate method of egg quantification for Aedes aegypti and Aedes albopictus, the relationship between egg number and weight, as well as egg number and volume, were studied.MethodsKnown quantities of eggs (1,000, 3,000, 6,000, 12,000, 15,000, 18,000, 21,000 and 27,000) were counted and subsequently their weight and volume were measured. Best-fit curves and regression equations were used to describe relationships between Aedes egg number and both weight and volume.ResultsEighteen thousand Ae. aegypti eggs weighed 159.8 mg and had a volume of 277.4 μl, compared to measurements of 131.5 mg and 230.3 μl for Ae. albopictus. The eggs of Ae. aegypti were thus larger and heavier than those of Ae. albopictus. The use of weight and volume to quantify egg number was validated by counting volumes and weights of eggs expected to correspond to 3,000 and 18,000 eggs of each species; significant correlations were found in all cases except in the case of 3,000 Ae. albopictus eggs measured by volume.ConclusionMethods for egg quantification were validated and shown to be a consistent and practical means to achieve uniform distribution of Aedes larvae between rearing trays, important for optimal mass rearing of the immature stages of Aedes mosquitoes.

A photocatalytic process for the eradication of dengue through ˙OH generation in the presence of sunlight and iron oxide

Iron oxide was dispersed in a floating matrix based on autoclaved porous brick. Under an incidence of solar radiation ˙OH radicals are generated by the photocatalytic process, completely oxidizing the organic matter. This procedure makes the proliferation of dengue larva unfeasible. Additionally, ˙OH radicals have a remarkable deleterious effect on hatching of A aegypti eggs. The predominant iron phase was hematite (α-Fe2O3), as indicated by the Mossbauer spectroscopy. The formation of ˙OH species was demonstrated by typical m/z values obtained via ESI-MS.

Distinct variation in vector competence among nine field populations of Aedes aegypti from a Brazilian dengue-endemic risk city.

BackgroundIn Brazil, dengue epidemics erupt sporadically throughout the country and it is unclear if outbreaks may initiate a sustainable transmission cycle. There are few studies evaluating the ability of Brazilian Aedes aegypti populations to transmit dengue virus (DENV). The aim of this study was to compare DENV susceptibility of field-captured Ae. aegypti populations from nine distinct geographic areas of the city of Belo Horizonte in 2009 and 2011. Infection Rate (IR), Vector Competence (VC) and Disseminated Infection Rate (DIR) were determined.MethodsAedes aegypti eggs from each region were collected and reared separately in an insectary. Adult females were experimentally infected with DENV-2 and the virus was detected by qPCR in body and head samples. Data were analyzed with the Statistical Package for the Social Sciences version 17.ResultsIR varied from 40.0% to 82.5% in 2009 and 60.0% to 100.0% in 2011. VC ranged from 25.0% to 77.5% in 2009 and 25.0% to 80.0% in 2011. DIR oscillated from 68.7% to 100.0% in 2009 and 38.4% to 86.8 in 2011. When the results were evaluated by a logistic model using IR as covariate, North, Barreiro, South-Central and Venda Nova showed the strongest association in 2009. In 2011, a similar association was observed for South-Central, Venda Nova, West and Northeast regions. Using VC as covariate, South-Central and Venda Nova showed the most relevant association in 2009. In 2011, South-Central, Venda Nova and Barreiro presented the greatest revelation associations. When DIR data were analyzed by logistic regression models, Pampulha, South-Central, Venda Nova, West, Northeast and East (2009) as well as South-Central, Venda Nova and West (2011) were the districts showing the strongest associations.ConclusionsWe conclude that Ae. aegypti populations from Belo Horizonte exhibit wide variation in vector competence to transmit dengue. Therefore, vector control strategies should be adapted to the available data for each region. Further analysis should be conducted to better understand the reasons for this large variability in vector competence and how these parameters correlate with epidemiological findings in subsequent years.

Burchellin: study of bioactivity against Aedes aegypti

BackgroundThe dengue mosquito Aedes aegypti Linnaeus, 1762 is a widespread insect pest of serious medical importance. Since no effective vaccine is available for treating dengue, the eradication or control of the main mosquito vector is regarded as essential. Since conventional insecticides have limited success, plants may be an alternative source of larvicidal agents, since they contain a rich source of bioactive chemicals. The aim of this study was to evaluate the larvicidal activity of the neolignan burchellin isolated from Ocotea cymbarum (Lauraceae), a plant from the Amazon region, against third instar larvae of A. aegypti.MethodsBurchellin obtained from O. cymbarum was analyzed. The inhibitory activity against A. aegypti eggs and larvae and histological changes in the digestive system of treated L3 larvae were evaluated. In addition, nitric oxide synthase activity and nitric oxide levels were determined, and cytotoxicity bioassays performed.ResultsThe data showed that burchellin interfered with the development cycle of the mosquito, where its strongest toxic effect was 100% mortality in larvae (L3) at concentrations ≥ 30 ppm. This compound did not show target cell toxicity in peritoneal macrophages from BALB/c mice, and proved to have molecular stability when dissolved in water. The L3 and L4 larvae treated with the compound showed cellular destruction and disorganization, cell spacing, and vacuolization of epithelial cells in small regions of the midgut.ConclusionThe neolignan burchellin proved to be a strong candidate for a natural, safe and stable phytolarvicidal to be used in population control of A. aegypti.

Evaluation of Moringa oleifera seed lectin in traps for the capture of Aedes aegypti eggs and adults under semi-field conditions

The water-soluble lectin isolated from Moringa oleifera seeds (WSMoL) is a larvicidal, ovicidal, and oviposition-stimulating agent against Aedes aegypti under laboratory conditions. This study investigated the effect of WSMoL in traps for the capture of A. aegypti eggs and adult females under semi-field conditions and determined whether gravid females could detect WSMoL by an olfactory response. WSMoL was isolated according to a previously described procedure using chitin chromatography. The bioassays were performed in large cages (12.5 m(3)). Two traps for collection of eggs (ovitrap) or adult mosquitoes (MosquiTRAP(TM)) were placed in a cage. One was filled with WSMoL (0.1 mg/mL) and the other with tap water (negative control). An infusion of Panicum maximum leaves was used as a positive control. Forty gravid females were then released in each cage. After 2 (for oviposition) or 3 h (for female capture), the traps were removed, and the number of eggs or females was counted. An olfactometry assay was performed to investigate whether the effect of WSMoL on gravid females was linked to an olfactory response. WSMoL showed an oviposition-stimulating effect (65 ± 14%) that was similar (p < 0.05) to that promoted by the P. maximum infusion (67 ± 11%). The efficiency of MosquiTRAP(TM) in capturing gravid females was not increased by WSMoL. The olfactometry assay indicated that the response of females to WSMoL did not involve the stimulation of olfactory sensilla. WSMoL effectively captured eggs when used in ovitraps under semi-field conditions; this property, together with the ovicidal and larvicidal activities of this lectin, makes it an interesting candidate for A. aegypti control.

Serosal cuticle formation and distinct degrees of desiccation resistance in embryos of the mosquito vectors Aedes aegypti, Anopheles aquasalis and Culex quinquefasciatus

Given their medical importance, mosquitoes have been studied as vectors of parasites since the late 1800’s. However, there are still many gaps concerning some aspects of their biology, such as embryogenesis. The embryonic desiccation resistance (EDR), already described in Aedes and Anopheles gambiae mosquitoes, is a peculiar trait. Freshly laid eggs are susceptible to water loss, a condition that can impair their viability. EDR is acquired during embryogenesis through the formation of the serosal cuticle (SC), protecting eggs from desiccation. Nevertheless, conservation of both traits (SC presence and EDR acquisition) throughout mosquito evolution is unknown. Comparative physiological studies with mosquito embryos from different genera, exhibiting distinct evolutionary histories and habits is a feasible approach. In this sense, the process of EDR acquisition of Aedes aegypti, Anopheles aquasalis and Culex quinquefasciatus at 25°C was evaluated. Completion of embryogenesis occurs in Ae. aegypti, An. aquasalis and Cx. quinquefasciatus at, respectively 77.4, 51.3 and 34.3hours after egg laying, Cx. quinquefasciatus embryonic development taking less than half the time of Ae. aegypti. In all cases, EDR is acquired in correlation with SC formation. For both Ae. aegypti and An. aquasalis, EDR and SC appear at 21% of total embryonic development, corresponding to the morphological stage of complete germ band elongation/beginning of germ band retraction. Although phylogenetically closer to Ae. aegypti than to An. aquasalis, Cx. quinquefasciatus acquires both EDR and serosal cuticle later, with 35% of total development, when the embryo already progresses to the middle of germ band retraction. EDR confers distinct egg viability in these species. While Ae. aegypti eggs demonstrated high viability when left up to 72hours in a dry environment, those of An. aquasalis and Cx. quinquefasciatus supported these conditions for only 24 and 5hours, respectively. Our data suggest that serosa development is at least partially uncoupled from embryo development and that, depending upon the mosquito species, EDR bestows distinct levels of egg viability.

Impact of the Argemone mexicana Stem Extracts on the Reproductive Fitness and Behavior of Adult Dengue Vector, Aedes aegypti L. (Diptera: Culicidae).

Present investigations evaluated the impact of Argemone mexicana stem extracts on the reproductive fitness of dengue vector, Aedes aegypti, assessed in terms of oviposition deterrent and ovicidal potential. The oviposition deterrent studies of the extracts, prepared using petroleum ether, hexane, benzene, acetone, and ethanol as the solvents, revealed the maximum deterrence potency of the petroleum ether extracts with a significant 15.6% ED at 60 ppm rising by 83.8% at 1000 ppm to 99.4% effective deterrence (ED). Other stem extracts were found to be ineffective at 60 ppm, though resulted in 85.3–96.2% ED and diminished fecundity in A. aegypti at 1000 ppm. Further, A. mexicana stem extracts exhibited moderate ovicidal potential against A. aegypti eggs causing only 42.65–67.85% egg mortality at 1000 ppm, the lowest hatch of 32.15% caused by the benzene extract. Other stem extracts also failed to express effective ovicidal potency with the percent egg hatch ranging between 96.6 and 99.0 at 400 ppm, and 78.8 and 99.0 at 600 ppm. Our results suggest the significant but variable efficacy of A. mexicana stem extracts causing reproductive disadvantage in A. aegypti.

Hatching Response ofAedes aegypti(Diptera: Culicidae) Eggs at Low Temperatures: Effects of Hatching Media and Storage Conditions

In temperate regions, Aedes aegypti (L.) (Diptera: Culicidae) populations remain in the egg stage during the cold season. To ensure the start of a new breeding season, eggs should hatch at the beginning of a favorable period. The aim of the current study was to investigate the hatching response of two Ae. aegypti egg batches collected and stored for 3 mo under different conditions, to different low immersion temperatures. Two different hatching media (water and yeast solution) were used for the first batch and only one (water) for the second egg batch. Eggs were immersed for 8 d, during which the number of hatched eggs was recorded daily. The proportion of hatched eggs, delay of the hatching response, proportion of dead larvae, and proportion of remaining eggs within the first egg batch were compared between the two hatching media at each temperature. These parameters also were compared between the two batches immersed in water. Hatching rates were higher and faster in the yeast solution. The hatching response was lower at lower immersion temperatures and among eggs stored under field conditions at colder temperatures (second batch). Among the eggs stored in the laboratory (first batch), older eggs exhibited lower hatching response. The proportion of dead larvae was higher in the yeast solution and in the eggs stored in the laboratory. The conditions that triggered a lower hatching response led to higher proportions of remaining eggs, allowing the population to maintain an egg bank for future favorable opportunities.

Trypsin inhibitor from Moringa oleifera flowers interferes with survival and development of Aedes aegypti larvae and kills bacteria inhabitant of larvae midgut

Moringa oleifera flower extract, with trypsin inhibitor activity, is a larvicidal agent on Aedes aegypti. This work reports the isolation of trypsin inhibitor (M. oleifera flower trypsin inhibitor (MoFTI)) and its effect on A. aegypti egg hatching, viability of newly hatched larvae, survival of pupae, and growth of inhabitant bacteria from midgut of fourth-instar larvae (L4). MoFTI (K i, 2.4 μM), isolated by affinity chromatography on trypsin-agarose column, was an 18.2 kDa polypeptide on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Flower extract (at concentrations of 8.5-17.0 mg/mL) reduced egg hatchability while MoFTI (0.05-0.5 mg/mL) did not affect the hatching rate. Mortality of newly hatched larvae ranged from 3.5 to 19.1 % in the presence of the extract (4.0-17.0 mg/mL) and was also promoted by MoFTI (LC50, 0.3 mg/mL). After 72 h, larvae incubated with extract at 13.0 and 17.0 mg/mL were at stages L2 and L1, respectively, while in control they reached L3 instar. In the presence of MoFTI, at all concentrations tested, the larvae did not pass the first instar. Flower extract and MoFTI did not interfere on pupae survival. The extract and MoFTI inhibited the growth of L4 gut bacteria (minimum inhibitory concentrations of 3.47 and 0.031 mg/mL, respectively) but only the inhibitor showed bactericide effect (minimum bactericidal concentration of 1.0 mg/mL). The findings reported herein indicate that MoFTI constitutes a larvicidal principle from M. oleifera flowers against A. aegypti newly hatched larvae and is an antibacterial agent active against the microbiota from L4 gut.

INFESTAÇÃO DE Aedes aegypti (LINNAEUS, 1762) (DIPTERA: CULICIDAE) DETERMINADA POR ARMADILHAS DE OVIPOSIÇÃO (OVITRAMPAS) NO MUNICÍPIO DE COSTA RICA, ESTADO DE MATO GROSSO DO SUL

Objective: to determine characteristics of Aedes aegypti infestation in the city of Costa Rica, such as spatial distribution and its correlation with climatic factors, in order to use the data for vector control. Methodology: Fifty-one weekly samplings were carried out using ovitraps, distributed at 60 collecting points. Results: Index variance/mean showed an aggregate distribution for Ae. aegypti. Tests for fit to a negative binomial distribution showed that all samples from the population gave excellent correspondence with such a distribution, which was not the case for either positive binomial or Poisson distributions. Density of Ae. aegypti eggs increased according to the rate of rainfall. Conclusion: The rainfall was the abiotic factor that significantly influenced the level of vector infestation. The aggregate distribution observed for this species can be explained by environmental factors, such as the presence of materials disposed of in backyards and vacant lots, and by its genetic traits.

Tadpoles as dengue mosquito (Aedes aegypti) egg predators

Mosquito eggs survive drought conditions while harboring pathogens, perpetuating diseases through seasons. Biological control of mosquitoes using vertebrates mostly highlights the role of larvivorous fish. Here we show that tadpoles with different life-history characteristics predate on Aedes aegypti (vector mosquito of dengue virus) eggs. We did four experiments involving tadpoles of Polypedates cruciger to determine: (i) egg laying preference of female mosquitoes, in normal water, water in which tadpoles were previously present, and water in which tadpoles were present at the time of experiment; (ii) survivability of mosquito eggs in tanks in presence vs. absence of tadpoles; (iii) egg predation through direct observation (video-recording) and gut content analysis; (iv) if egg predation is prevalent among different species of tadpoles of four species of randomly selected genera, Bufo, Ramanella, Euphlyctis and Hoplobatrachus were subjected to experiment (iii) only. We show that mosquitoes have a preference to lay eggs in tadpole water and that tadpoles destroy such eggs laid. Direct observations substantiate that all tadpole species tested are mosquito egg predators. With about seven thousand frog species worldwide, living in a diversity of aquatic habitats where fish cannot reach, the role of tadpoles in biological control of mosquitoes can be significant than currently understood.

The pyrethroid resistance status and mechanisms in Aedes aegypti from the Guerrero state, Mexico

Dengue is one of the most important vector-borne diseases worldwide and is a public health problem in Mexico. Most programs in dengue endemic countries rely on insecticides for Aedes control. In Mexico, pyrethroid insecticides (mainly permethrin and deltamethrin) have been extensively used over a decade as adulticides and represented a strong selection for insecticide resistance for dengue vectors in several parts of the country. We studied the type, frequency and distribution of insecticide resistance mechanisms in Aedes aegypti from six municipalities in the state of Guerrero selected on the basis of historically intense chemical control and a high risk for dengue transmission. Ae. aegypti eggs were collected from October 2009 to January 2010 using ovitraps. F1 adults, emerged from these collections, were exposed to permethrin, deltamethrin and DDT in WHO diagnostic tests and showed high resistance levels to both pyrethroids and DDT. This was consistent with the presence of increased metabolic enzyme activities and target site insensitivity due to kdr mutations. Biochemical assays showed elevated esterase and glutathione S-transferase activities in the six municipalities. The V1016I kdr mutation on the IIS6 domain of the sodium channel gene was present in an overall frequency of 0.80. A second mutation, F1534C on the IIIS6 domain of the same gene was also detected, being the first report of this mutation in Guerrero. The multiple resistance mechanisms present in Ae. aegypti from Guerrero state represent a warning for the efficacy of the pyrethroid usage and consequently for the success of the dengue control program.