Control Of Aedes Aegypti Research Articles

Alterações morfo-histológicas em larvas de Aedes aegypti (linnaeus, 1762) (Diptera, Culicidae) causadas pelo tanino catéquico isolado da planta do cerrado Magonia pubescens (Sapindaceae)

The control of Aedes aegypti is nowadays one of the major public health problemsin Brazil, being the main vector of dengue and urban yellow fever. Of Africanorigin, this mosquito is well adapted to Brazilian climatic conditions and is nowdistributed in all states. The usual methods to combat and control the mosquito havebeen highly questioned. The chemical insecticides currently used have led to theemergence of resistant populations of mosquitoes and the consequent increase ofits density, causing significant epidemics of dengue. Insecticides of botanical originhave shown to be alternative candidates to their control. This work presents forthe first time, morphohistologic changes caused by the larvicidal activity of tannincatechin extracted from Magonia pubescens on larvae of A. aegypti, showing thepotential of this natural larvicidal compound. Larvae of the 3rd stage were submittedto a water solution of tannin catechins, at 37ppm, where they remained for up to 24h. Larvae that reached lethargic state were collected and fixed in paraformaldehydeat 4%, in sodium cacodylate buffer at 0.1 M and pH 7.2, included in resin, mountedon slides, stained with hematoxylin-eosin and analyzed by light microscope. Themain cell toxic effects of tannin catechin on larvae of A. aegypti were the highvacuolation and absence of cytoplasmic limits, vesicular apical formation withrelease of cytoplasmic content, increase in intercellular spaces and detachment ofcells from the basal membrane.

Insecticide resistance in Aedes aegypti populations from Ceará, Brazil

BackgroundOrganophosphates and pyrethroids are used widely in Brazil to control Aedes aegypti, the main vector of dengue viruses, under the auspices of the National Programme for Dengue Control. Resistance to these insecticides is widespread throughout Brazil. In Ceará the vector is present in 98% of districts and resistance to temephos has been reported previously. Here we measure resistance to temephos and the pyrethroid cypermethrin in three populations from Ceará and use biochemical and molecular assays to characterise resistance mechanisms.ResultsResistance to temephos varied widely across the three studied populations, with resistance ratios (RR95) of 7.2, 30 and 192.7 in Juazeiro do Norte, Barbalha and Crato respectively. The high levels of resistance detected in Barbalha and Crato (RR95 ≥ 30) imply a reduction of temephos efficacy, and indeed in simulated field tests reduced effectiveness was observed for the Barbalha population. Two populations (Crato and Barbalha) were also resistant to cypermethrin, whilst Juazeiro do Norte showed only an altered susceptibility. The Ile1011Met kdr mutation was detected in all three populations and Val1016Ile in Crato and Juazeiro do Norte. 1011Met was significantly associated with resistance to cypermethrin in the Crato population. Biochemical tests showed that only the activity of esterases and GSTs, among the tested detoxification enzymes, was altered in these populations when compared with the Rockefeller strain.ConclusionsOur results demonstrate that two A. aegypti populations from Ceará are under strong selection pressure by temephos, compromising the field effectiveness of this organophosphate. Our results also provide evidence that the process of reducing resistance to this larvicide in the field is difficult and slow and may require more than seven years for reversal. In addition, we show resistance to cypermethrin in two of the three populations studied, and for the first time the presence of the allele 1016Ile in mosquito populations from northeastern Brazil. A significant association between 1011Met and resistance was observed in one of the populations. Target-site mechanisms seem not to be implicated in temephos resistance, reinforcing the idea that for the studied populations, detoxification enzymes most likely play a major role in the resistance to this insecticide.

Process-oriented fidelity research assists in evaluation, adjustment and scaling-up of community-based interventions

Fidelity research can help to answer essential questions about the diffusion process of innovative health interventions and provide insights for further scaling-up and institutionalization. This study assessed fidelity and reinvention in the implementation of a community-based control strategy for Aedes aegypti control. The intervention was implemented in 16 study areas in La Lisa, a municipality of Havana, Cuba. Its major components were: organization & management, capacity-building, community work and surveillance. A participatory assessment of process data was performed to determine whether the components and subcomponents were implemented, not-implemented or modified. Frequencies were tabulated over all circumscriptions (lowest level of local government) and the average was calculated for the four components. Spearman Rank correlation coefficients were calculated to explore the relationships between components. In addition, semi-structured interviews were conducted with co-ordinators of the strategy at different levels to identify difficulties encountered in the strategy's implementation. Surveillance was the most implemented component (72.9%) followed by capacity-building (54.7%). Community work and organization & management were less implemented or modified (50% and 45%, respectively). Apart from surveillance and capacity-building, all components are significantly and strongly correlated (Spearman Rank correlation coefficient > 0.70, P < 0.01). If one component is implemented in a circumscription, the other components are also likely to be implemented. It is noticeable that areas which did not undergo organizational changes commonly did not implement community work activities. Within the whole strategy, few activities were added. Scarcely implemented subcomponents were the most innovative. The difficulties encountered during implementation were related to appropriate training and skills, available time, lack of support and commitment to the strategy, lack of motivation of local leadership, and integration of actors and resources. The study showed a wide variability of fidelity in the implementation of the intervention and highlighted challenges for scaling-up and institutionalization of the community-based intervention.

Evaluación de un método de barrido rápido sobre la superficie para estimar el número total de estados larvarios tardíos de Aedes aegypti (Diptera: Culicidae) en depósitos de agua de grandes capacidades: comparación con estimativos de pupas

Since the methodologies used to calculate Stegomyia indices have been shown to be inadequate for assessing the risk of dengue virus transmission and targeting Aedes aegypti control strategies, new surveillance methods are needed. To evaluate the water-surface sweeping method in combination with calibration factors to estimate the total number of Ae. aegypti late larval stages (L3/L4) in large water-storage containers at different temperatures at which transmission of dengue virus occurs. Calibration factors were derived based on the proportion of L3/L4 recovered from a predetermined number of larvae using a net of specific dimensions and water-storage containers of different capacities and water levels in semi-field conditions and at four different altitudes (14, 358, 998 and 1,630 meters above sea level). The calibration factors obtained at 14 masl were then fully validated in a field study site at this altitude. Four calibration factors were derived at 14 masl (28-30°C) that were used to estimate the total L3/L4 numbers in large water storage containers greater than 20 L (n=478) at 1/3, 2/3 and full water-levels. This methodology was accurate and robust within and between the 10 pairs of field workers who applied it. Different calibration factors were, however, derived to accurately estimate the total L3/L4 numbers at each of the study sites located at 358, 998 and 1,630 masl, where average temperatures were 19°C, 24°C, and 26°C respectively. The accurate estimates of L3/L4 numbers calculated using the water surface sweeping method can be useful for evaluating intervention strategies directed against the larval stages.

Sampling Biases of the BG-Sentinel Trap With Respect to Physiology, Age, and Body Size of Adult Aedes aegypti (Diptera: Culicidae)

AbstractCurrently, Aedes aegypti (L.) control strategies are being developed that involve manipulation of the vector at the adult stage (e.g., the use of the bacterial endosymbiont Wolbachia to shorten the life span of the vector population). These novel strategies demand adult sampling methods to measure changes in population size, structure (age, sex ratio), and, ultimately, the success of the program. Each sampling method presents certain biases. Once these biases are defined, methods used to estimate population size and structure can be calibrated accordingly, resulting in more accurate and complex estimates of the vector population. A series of mark-release-recapture experiments with adult Ae. aegypti were conducted in a large outdoor flight cage and an indoor setting in far north Queensland, Australia. The biases of the BG-Sentinel trap (BGS) were investigated across several categories, as follows: 1) mosquito age; 2) sex; 3) physiological status; and 4) body size. Biases were not detected across age groups or body sizes. A significant bias was detected across physiological groups: nulliparous females were recaptured at a significantly lower rate than all other groups except blood-fed parous females, which were also recaptured at a low rate by the BGS. Males were recaptured at a higher rate than all groups, but only a significant difference in recapture rates was observed between males and nulliparous females. Previous studies show that the BGS is a highly effective tool for Ae. aegypti surveillance. The BGS proves to be a reliable tool in Ae. aegypti surveillance with consistent sampling outcomes. The sampling bias of the BGS is measurable and can be used to generate more accurate estimates of the adult population and its attributes.

Sampling Biases of the BG-Sentinel Trap With Respect to Physiology, Age, and Body Size of Adult &lt;I&gt;Aedes aegypti&lt;/I&gt; (Diptera: Culicidae)

Currently, Aedes aegypti (L.) control strategies are being developed that involve manipulation of the vector at the adult stage (e.g., the use of the bacterial endosymbiont Wolbachia to shorten the life span of the vector population). These novel strategies demand adult sampling methods to measure changes in population size, structure (age, sex ratio), and, ultimately, the success of the program. Each sampling method presents certain biases. Once these biases are defined, methods used to estimate population size and structure can be calibrated accordingly, resulting in more accurate and complex estimates of the vector population. A series of mark-release-recapture experiments with adult Ae. aegypti were conducted in a large outdoor flight cage and an indoor setting in far north Queensland, Australia. The biases of the BG-Sentinel trap (BGS) were investigated across several categories, as follows: 1) mosquito age; 2) sex; 3) physiological status; and 4) body size. Biases were not detected across age groups or body sizes. A significant bias was detected across physiological groups: nulliparous females were recaptured at a significantly lower rate than all other groups except blood-fed parous females, which were also recaptured at a low rate by the BGS. Males were recaptured at a higher rate than all groups, but only a significant difference in recapture rates was observed between males and nulliparous females. Previous studies show that the BGS is a highly effective tool for Ae. aegypti surveillance. The BGS proves to be a reliable tool in Ae. aegypti surveillance with consistent sampling outcomes. The sampling bias of the BGS is measurable and can be used to generate more accurate estimates of the adult population and its attributes.

Diptera, Ceratopogonidae, Dasyhelea necrophila Spinelli and Rodriguez, 1999: detection of eggs in ovitraps, in Uruguay

Ovitraps with eggs of Dasyhelea necrophila were detected at five localities in Uruguay during surveillance and control of Aedes aegypti. Relevant dates of oviposition in wild of this Ceratopogonidae species are included in addition to previous laboratory work on the species. Eggs of D. necrophila were deposited together with eggs of Culicidae and Psychodidae. These are the first records of the species from Uruguay.

Custos diretos do programa de prevenção e controle da dengue no Município de São Paulo em 2005

To estimate the direct costs associated with the control of Aedes aegypti and prevention of dengue fever in the City of São Paulo Dengue Control Program, Brazil, in 2005. The following items were considered: human resources, uniforms, field materials, individual protection equipment, spraying equipment, strategic supplies (insecticides and larvicides), and vehicles. The costs associated with laboratory tests for entomological surveillance and dengue fever diagnosis were also calculated, as well as costs relating to information and printed materials for educational campaigns. The total direct costs of the City of São Paulo Dengue Fever Program in 2005 were R$ 21,774,282.82 (US$ 12,486,941.34 considering the dollar/real exchange rate in December 2009). Of this amount, 59.4% were directed to human resources, 38.3% to epidemic control measures, and 2.2% to capital expenditure. The cost per capita was R$ 1.99 in 2005. The control of dengue fever is essential given the growth of epidemics. Knowledge about the costs of strategies and priority items employed in dengue fever control and prevention programs can guide decision-making regarding the application of budget resources in both the City of São Paulo and Brazil as a whole.

Impact of water renewal on the residual effect of larvicides in the control of Aedes aegypti

This study was carried out to evaluate the residual effect of three larvicides under laboratory conditions for 100 days in Aedes aegypti. The larval mortality rate was measured without water renewal or with daily water renewal (80%). With temephos, there was 100% mortality in both groups until the 70th day. In the Bacillus thuringiensis israelensis (Bti)-WDG test, there was no difference during the first 20 days. With Bti-G, without water renewal, mortality was sustained above 90% for up to 35 days. The second experiment (with water renewal) reduced the mortality to below 90% after the first 20 days. When renewed water was provided, the residual effect was significantly lower for all larvicides.

An entomological surveillance system based on open spatial information for participative dengue control

Aedes aegypti is a very efficient disseminator of human pathogens. This condition is the result of evolutionary adaptations to frequent haematophagy, as well as to the colonization of countless types of habitats associated with environmental and cultural factors that favor the proliferation of this mosquito in urban ecosystems. Studies using sensitive methods of monitoring demonstrate that the methods of surveillance used in the Brazilian program do not show the high degrees of the infestation of cities by this vector. To increase the capacity of the health sector, new tools are needed to the practice of surveillance, which incorporate aspects of the vector, place and human population. We describe here the SMCP-Aedes - Monitoring System and Population Control of Aedes aegypti, aiming to provide an entomological surveillance framework as a basis for epidemiological surveillance of dengue. The SMCP-Aedes is uphold in the space technology information, supported by the intensive use of the web and free software to collect, store, analyze and disseminate information on the spatial-temporal distribution of the estimated density for the population of Aedes, based on data systematically collected with the use of ovitraps. Planned control interventions, intensified where and when indicated by the entomological surveillance, are agreed with the communities, relying on the permanent social mobilization.

Characterizing the Aedes aegypti Population in a Vietnamese Village in Preparation for a Wolbachia-Based Mosquito Control Strategy to Eliminate Dengue

BackgroundA life-shortening strain of the obligate intracellular bacteria Wolbachia, called wMelPop, is seen as a promising new tool for the control of Aedes aegypti. However, developing a vector control strategy based on the release of mosquitoes transinfected with wMelPop requires detailed knowledge of the demographics of the target population.Methodology/Principal FindingsIn Tri Nguyen village (611 households) on Hon Mieu Island in central Vietnam, we conducted nine quantitative entomologic surveys over 14 months to determine if Ae. aegypti populations were spatially and temporally homogenous, and to estimate population size. There was no obvious relationship between mosquito (larval, pupal or adult) abundance and temperature and rainfall, and no area of the village supported consistently high numbers of mosquitoes. In almost all surveys, key premises produced high numbers of Ae. aegypti. However, these premises were not consistent between surveys. For an intervention based on a single release of wMelPop-infected Ae. aegypti, release ratios of infected to uninfected adult mosquitoes of all age classes are estimated to be 1.8–6.7∶1 for gravid females (and similarly aged males) or teneral adults, respectively. We calculated that adult female mosquito abundance in Tri Nguyen village could range from 1.1 to 43.3 individuals of all age classes per house. Thus, an intervention could require the release of 2–78 wMelPop-infected gravid females and similarly aged males per house, or 7–290 infected teneral female and male mosquitoes per house.Conclusions/SignificanceGiven the variability we encountered, this study highlights the importance of multiple entomologic surveys when evaluating the spatial structure of a vector population or estimating population size. If a single release of wMelPop-infected Ae. aegypti were to occur when wild Ae. aegypti abundance was at its maximum, a preintervention control program would be necessary to ensure that there was no net increase in mosquito numbers. However, because of the short-term temporal heterogeneity, the inconsistent spatial structure and the impact of transient key premises that we observed, the feasibility of multiple releases of smaller numbers of mosquitoes also needs to be considered. In either case, fewer wMelPop-infected mosquitoes would then need to be released, which will likely be more acceptable to householders.

Development of a Low Cost Bioprocess for Endotoxin Production by Bacillus thuringiensis var israelensis Intended for Biological Control of Aedes aegypti

Aedes aegypti is the vector of Dengue disease, responsible for 20,000 deaths/year worldwide. Bacillus thuringiensis var israelensis - Bti releases selective and effective toxins (crystal proteins) against A. aegypti larvae. We present a low cost bioprocess for toxin production, accomplished by a selected Brazilian strain Bti (BR-LPB01) and employment of low cost substrates. Soybean meal and sugarcane molasses lead to high toxic effectiveness after 2L bioreactor fermentation (LD50=26ng/mL), near to the reference strain IPS82 (LD50=17.3 ng/mL). The pH ranged between 5.8 and 7.0 during the exponential growth period and between 7.0 and 8.4 during the stationary phase, with low activity. Thus, control of foam and pH 7.0 were started and proved to be crucial for high activity. It was verified that the fermentation could be discontinued after 20 hours, when the highest activity was present.

Intersectoral coordination, community empowerment and dengue prevention: six years of controlled interventions in Playa Municipality, Havana, Cuba

To document the process, outcome and effectiveness of a community-based intervention for dengue control. The primary intervention, focused on strengthening intersectoral coordination, was initiated by researchers in January 2000 in a pilot area in Playa municipality, Havana. In August 2002 health authorities extended the intervention to neighbouring areas, one of which was selected for evaluation. In August 2003 a complementary strategy, focused on community empowerment, was initiated in half of the pilot area. In our control area, routine dengue activities continued throughout the study period. Longitudinal process assessment was carried out using document analysis, interviews and group discussions. Random population surveys in 1999, 2002 and 2005 assessed levels of participation and behavioural changes. Entomological surveillance data from 1999 to 2005 were used to determine effectiveness. Mean scores for participation in the pilot area were 1.6, 3.4 and 4.4 at baseline, and 2 years after initiating intersectoral coordination and intersectoral coordination plus community empowerment interventions, respectively. While in the control area little behavioural change was observed over time, changes were considerable in the pilot and extension areas, with 80% of households involved in the community empowerment intervention showed adequate behavioural patterns. The pilot and extension areas attained comparable entomological effectiveness with significantly lower Breteau indices (BIs) than the control area. The pilot (sub-) area with the community empowerment intervention reached BIs below 0.1 that continued to be significantly lower than the one in the control area until the end of the study. The study showed a trend in the levels and quality of participation, behavioural change and effectiveness of Aedes control from the routine activities only over an intervention with intersectoral coordination to one that combined intersectoral coordination and community empowerment approach.

Use of Mapping and Spatial and Space-Time Modeling Approaches in Operational Control of Aedes aegypti and Dengue

The aims of this review paper are to 1) provide an overview of how mapping and spatial and space-time modeling approaches have been used to date to visualize and analyze mosquito vector and epidemiologic data for dengue; and 2) discuss the potential for these approaches to be included as routine activities in operational vector and dengue control programs. Geographical information system (GIS) software are becoming more user-friendly and now are complemented by free mapping software that provide access to satellite imagery and basic feature-making tools and have the capacity to generate static maps as well as dynamic time-series maps. Our challenge is now to move beyond the research arena by transferring mapping and GIS technologies and spatial statistical analysis techniques in user-friendly packages to operational vector and dengue control programs. This will enable control programs to, for example, generate risk maps for exposure to dengue virus, develop Priority Area Classifications for vector control, and explore socioeconomic associations with dengue risk.

Community beliefs and practices about dengue in Puerto Rico

In spite of long-term endemicity and repeated government and private efforts, effective, sustained community participation for dengue prevention remains a challenge in Puerto Rico. This study explored differences found in interviews conducted in 2001 in attitudes toward dengue and its prevention by respondents' gender and whether they had a prior dengue infection. Findings may be used to develop messages to promote Aedes aegypti control practices. From September to October 2003, 11 focus groups were conducted in San Juan, Puerto Rico. Fifty-nine persons (35 women, 24 men), >or= 18 years of age, who had been identified through the Puerto Rico dengue surveillance system participated in the focus groups. Analysis was based on grounded theory. Women considered dengue important because of its economic, emotional, and health impact, and they were concerned more often than men about insufficient garbage removal and water disposal. Participants with a previous dengue diagnosis were more concerned about risk of the disease, were more knowledgeable about dengue and its prevention, and recommended use of repellents more often than their counterparts without a previous dengue diagnosis. Barriers to sustained dengue prevention included misconceptions from outdated educational materials, "invisibility" of dengue compared with chronic diseases, and lack of acceptance of responsibility for dengue prevention. Suggested strategies to motivate residents' actions included working with government agencies to address structural problems that increase mosquito populations, improving access to information on garbage collection and water disposal through telephone hotlines, increasing publicity and information about dengue by mass media campaigns, and educating health professionals.

Effect of the chitin synthesis inhibitor triflumuron on the development, viability and reproduction of Aedes aegypti

The control of Aedes aegypti is impaired due to the development of resistance to chemical insecticides. Insect Growth Regulators (IGR) exhibit distinct mechanisms of action and are considered potential vector control alternatives. Studies regarding the effects of sublethal IGR doses on the viability of resulting adults will contribute to eval-uating their impact in the field. We analyzed several aspects of Ae. aegypti adults surviving exposure to a partially lethal dose of triflumuron, a chitin synthesis inhibitor. A highly significant difference in the proportion of males and females was noted in the triflumuron-exposed group (65.0% males) compared to the controls (50.2% males). Triflumuron affected adult longevity, particularly for females; after 16 days, only 29.2% of males and 13.8% of females were alive, in contrast with 94% survival of the control mosquitoes. The locomotor activity was reduced and the blood-feeding ability of the treated females was also affected (90.4% and 48.4% of the control and triflumuron-exposed females, respectively, successfully ingested blood). Triflumuron-surviving females ingested roughly 30% less blood and laid 25% fewer eggs than the control females. The treated males and females exhibited a diminished ability to copulate, resulting in less viable eggs.

Community involvement in dengue vector control: cluster randomised trial

Objective To assess the effectiveness of an integrated community based environmental management strategy to control Aedes aegypti, the vector of dengue, compared with a routine strategy.Design Cluster randomised trial.Setting Guantanamo,...

Evaluation of Mosquito Densoviruses for Controlling Aedes aegypti (Diptera: Culicidae): Variation in Efficiency due to Virus Strain and Geographic Origin of Mosquitoes

Four mosquito densovirus strains were assayed for mortality and infectivity against Aedes aegypti larvae from different geographic regions. The viral titers were quantified by real-time PCR using TaqMan technology. Firstinstar larvae were exposed to the same titer of each densovirus strain for 48 hours. All strains of densoviruses exhibited larvicidal activity and caused more than 80% mortality and infectivity in the three mosquito strains. AalDNV-exposed larvae had the highest mortality rate. The mean time to death of AalDNV-exposed larvae was shorter than other DNVs-exposed larvae. We can conclude that different densovirus strains exhibit some variations in their pathogenicity to different populations of Ae. aegypti mosquitoes. A few mosquitoes from Chachoengsao and Bangkok exposed to AeDNV and AThDNV survived to the adult stage to lay eggs and showed 22% to 50% vertical transmission in the F1 generation. Phylogenetic analysis of four densovirus strains indicated that mosquito densoviruses are separated into two distinct clades.

Criterios del personal de apoyo en el trabajo contra el Aedes aegypti en Ciudad de La Habana. 2006

Introduction: In the fight against Aedes aegypti several sectors as well as the population throughout the country have participated in an intensive and organized way. Objectives: To identify criteria of the staff that has worked in support of this fight against the mosquito and to supplement the information collected from a research work aimed at characterizing the organizational system of surveillance and anti-vector control units in City of Havana province, taking as a basis a survey among operators, supervisors, heads of brigades and of areas. This study was conducted in the same health areas of the previous research work in 2006. Methods: A descriptive study was conducted on a non- probabilistic sample, following the authority criteria, in 13 health care areas from 12 municipalities in Havana City. The sample was finally composed of 175 persons: 104 who had been mobilized by the Communist Party of Cuba and 71 by the Cuban government on behalf of several economic sectors. Data gathering technique was the in-depth interview made by previously trained Hygiene and Epidemiology second-year residents. The participants accepted to take part in this study. Results: Most of the statements by the interviewed people were classified into unfavourable for all categories and typologies from the interviews of the two studied groups, in terms of organization and functioning, care to the workers, suitable qualification of the staff, work with the community and support by the different sectors. Conclusions: The solution to detected problems based on the criteria of the supporting staff is necessary and important to achieve higher effectiveness and efficiency and sustainability in daily work by different social actors involved in Aedes aegypti control. The achieved results confirmed and supplemented those of the research work in 2006. It was recommended to communicate the results of this study to the relevant authorities.

Potential control of Aedes aegypti (Diptera: Culicidae) with Piper aduncum L. (Piperaceae) extracts demonstrated by chromosomal biomarkers and toxic effects on interphase nuclei

Dillapiol, a phenylpropanoid isolate from essential oils of leaves of Piper aduncum (Piperaceae), has insecticidal, fungicidal and antimicrobial activities. The insecticidal activity of dillapiol was tested in vivo on the larvae and pupae of Aedes aegypti, the mosquito vector of dengue. Specifically, the effect of dillapiol on the formation of micronuclei and chromosome aberrations was analyzed. Dillapiol treatments comprised two concentrations of 200 and 400 micro dissolved in well water, and a pure well water control used to rear four generations of mosquitoes. Micronuclei occurred in mitotic diploid and tetraploid chromosomes of larvae; nuclear abnormalities also occurred in interphase, metaphase, telophase, and single nucleus cells of pupae. Mortality, oviposition, chromosome breakage, and anaphase bridges were significantly greater in the extract treatments than in controls. The genotoxic effects of dillapiol described here suggest that this natural product may be a useful alternative for the control of A. aegypti.