Emergence Of Adult Mosquitoes Research Articles

Detection of arboviruses in Aedes aegypti through transovarian analysis: A study in Goiânia, Goiás.

Arboviral diseases are a group of infectious diseases caused by viruses transmitted by arthropods, mainly mosquitoes. These diseases, such as those caused by the dengue (DENV), Zika (ZIKV), chikungunya (CHIKV), and yellow fever (YFV) viruses, have a significant impact worldwide. In this context, entomological surveillance plays a crucial role in the control and prevention of arboviruses by providing essential information on the presence, distribution, and activity of vector mosquitoes. Based on entomological surveillance, transovarian transmission provides information regarding the maintenance and dissemination of arboviruses. The objective of this study was to detect these arboviruses in Goiânia, Goiás, and analyze the occurrence of transovarian transmission. Aedes aegypti eggs were collected from different regions of Goiânia and cultivated under controlled laboratory conditions until the emergence of adult mosquitoes. Adult females were grouped into pools containing their heads and thoraxes. These pools were subsequently evaluated using reverse-transcription quantitative polymerase chain reaction (RT-qPCR) assay. A total of 157 pools (N=1570) were analyzed, with two pools testing positive for CHIKV and one pool testing positive for ZIKV, indicating that the offspring resulting from transovarian transmission are potentially infectious. In summary, the demonstration of the vertical transmission mechanisms of CHIKV and ZIKV in A. aegypti serves as an alert to health authorities, as these diseases are still underreported, and their primary urban vector has likely acquired this capacity, contributing to the dissemination of these infections.

Predation risk effects on larval development and adult life of Aedes aegypti mosquito.

Biological control is one of the methods available for control of Aedes aegypti populations. We used experimental microcosms to evaluate the effects of actual predation and predation risk by dragonfly larvae (Odonata) on larval development, adult longevity, and adult size of Ae. aegypti. We used six treatments: control, removal, variable density cues (Cues VD), fixed density cues (Cues FD), variable density predator (Predator VD), and fixed density predator (Predator FD) (n = 5 each). Predator treatments received one dragonfly larva. Cue treatments were composed of crushed Ae. aegypti larvae released into the microcosm. For the FD treatments, we maintained a larval density of 200 individuals. The average mortality of Ae. aegypti larvae in the Predator VD treatment was used as the standard mortality for the other treatments. Mosquitoes from the Predator VD and Cues VD treatments developed faster, and adults were larger and had greater longevity compared to all other treatments, likely due to the higher food availability from larval density reduction. High larval density negatively affected larval developmental time, adult size, and longevity. Males were less sensitive to density-dependent effects. Results from this study suggest that the presence of predators may lead to the emergence of adult mosquitoes with greater fitness, causing an overall positive effect on Ae. aegypti population growth rates.

Community-Based Control of Malaria Vectors Using Bacillus thuringiensis var. Israelensis (Bti) in Rwanda.

Larval source management (LSM) programs for control of malaria vectors are often vertically organized, while there is much potential for involving local communities in program implementation. To address this, we evaluated the entomological impact of community-based application of Bacillus thuringiensis var. israelensis (Bti) in a rice irrigation scheme in Ruhuha, Rwanda. A non-randomized trial with control compared a Bti implementation program that was supervised by the project team (ES) with a program that was led and carried out by local rice farming communities (CB). One other area served as a control to assess mosquito populations without Bti application. Entomological surveys were carried out every two weeks and assessed the presence and abundance of the larval, pupal, and adult stages of Anopheles mosquitoes. In ES, the per round reduction in Anopheles larval habitats was estimated at 49%. This reduction was less in CB (28%) and control (22%) although the per round reduction in CB was still significantly higher than in control. Pupal production was almost completely prevented from round 5 (out of 10) onwards in both CB (average habitat occupancy 0.43%) and ES intervention arms (average habitat occupancy 0.27%), whereas pupal occupancy rates were on average 12.8% from round 5 onwards in the control. Emergence of adult mosquitoes from rice fields was thus prevented although this was not directly noticeable in adult An. gambiae populations in houses nearby the rice fields. Together with our earlier work on the willingness to financially contribute to the LSM program and the high perceived safety and acceptance of the Bti product, the current study demonstrates that, in an environment with limited resources, communities could become more engaged in LSM program implementation and contribute directly to malaria vector control in their environment.

Effect of pyriproxyfen on development and survival of Anopheles gambiae sensu stricto under forested and deforested areas

BackgroundThe land cover changes in the form of deforestation are known for their impact on enhancing Anopheline life-history traits. In most cases, these traits depend on environmental parameters such as temperature and light. Pyriproxyfen is an insect growth regulator juvenile hormone (JH) designed to inhibit adult mosquito emergence. It is an effective biolarvicide in controlling immature stages of malaria vectors and many other insects. Despite the known efficiency of pyriproxyfen in malaria vector control, but the understanding of its performance under deforested or afforested areas is not clear. The present study aimed at evaluating the impact of pyriproxyfen on development and survivorship of Anopheles gambiae s.s. in forested and deforested areas. Tests of two dosages (0.03 ppm.ai. and 0.3 ppm.ai.) of pyriproxyfen were done in standardized semi-field conditions under ambient temperature and light in netting screened environment. The plastic artificial microcosms containing 1 kg of soil and 2000 mL of dechlorinated water were used. First instars larvae were distributed in densities of 20, 40, and 60 in six replicates each, to form a total of 18 microcosms per each land cover type. Larvae mortality, development, and survival time were monitored and recorded after every 24 h until pupation. Emerging adults from pupa were recorded, and their sexes were identified.ResultsPyriproxyfen increased Anopheles gambiae larvae mortality rates and larvae developmental time of first instar larvae to pupal at densities of 20, 40 and 60 larvae in forested area (p < 0.05). Also, the larvae survival time was found to be longer in forested area compared to deforested area (p < 0.05) except at the density of 20 larvae. Pyriproxyfen reduced larvae pupation rates by 88% in forested area and it had 100% adult emergence inhibition regardless of land cover type and pyriproxyfen concentration, except at the density of 60 larvae exposed to 0.03 ppm, where adult emergence rate of 6.7% was detected.ConclusionThese findings suggest that, the efficacy of pyriproxyfen against Anopheles gambiae s.s. larvae and pupae is dependent on land cover types and its larvicidal effect can be increased by presence of trees canopy covers. Therefore, reviving forestry schemes and community afforestation programmes could have a positive impact on mosquito larval control by using larvicides. Also, increasing land canopy cover can be opted as a way to discourage the development and survival of potential malaria vectors.

Effects of gamma radiation on the reproductive viability of Aedes aegypti and its descendants (Diptera: Culicidae)

This work evaluated the genetic damage in descendants of male pupae of Aedes (Stegomyia) aegypti (Diptera: Culicidae) separately exposed to 20, 30, and 40 Gy of gamma radiation in the context of Sterile Insect Technique (SIT). Despite the transmission of the dominant lethal mutation, the employed dose levels did not promote a marked reduction in adult mosquito emergence and fertility. This study emphasized that semi-sterilizing doses < 50 Gy for SIT of Aedes aegypti are not recommended.

Insecticidal and Repellent Activity of Citrus aurantium1 Essential Oil against Dengue Mosquito Vector Aedes aegypti2

Indiscriminate use of insecticides to control vector-borne disease contaminates the environment and with time, mosquitoes gradually become resistant, making their control increasingly difficult. An alternative to synthetic insecticides, such as use of essential oils and extracts from plants, is needed for vector control. This study aimed to evaluate Cuban essential oil of Citrus aurantium (Sapindales: Rutaceae) against Aedes aegypti L. mosquito (Diptera: Culicidae), the main vector of arbovirus in Cuban. Calculated mean lethal concentrations (LC) were significantly low (LC50 = 13.5 mg/liter (Rockefeller) and 15.5 mg/liter (Marianao 2013). A developmental inhibitory effect was obtained by exposing each population of mosquito larvae to lethal concentration LC90. The emergence of adult mosquitoes was inhibited by exposing larvae to the LC90 of each population. Neither adulticidal activity was obtained with papers and bottles impregnated at neither 60 mg/ml nor, repellent activity with the evaluated formulations. C. aurantium oil is a promissory candidate for control larvae of Ae. aegypti, although it was not effective against adults nor repellent unless formulations were enhanced.

Bats actively prey on mosquitoes and other deleterious insects in rice paddies: Potential impact on human health and agriculture.

The fact that bats suppress agricultural pests has been measured for some particular dyads of predator and prey species in both economic and food security terms. The recent emergence of new molecular techniques allows for more precise screenings of bat's diet than the traditional visual identification systems and provides further evidence that bats consume an ample array of agricultural pest species. The main focus of the regulatory services that bats provide in agroecosystems has been on crop pests that cause yield losses. Rice paddies constitute a particular agronomic system with specific challenges, not only related to crop productivity but also to human health. Dipteran density in such ecosystems poses a serious threat to human wellbeing and hinders crop production. Mosquitoes cause direct harm to human populations, transmitting a number of infectious diseases. Non-biting midges (Chironomidae) can consume and weaken rice seedlings and can cause major yield losses. Mosquito populations and bat activity were assessed in rice paddies of Montgrí, Medes i Baix Ter Natural Park (NE Iberian Peninsula). Molecular analyses of bats faeces (6-weekly samples of 15 faeces each between mid-August and September) proved the presence of both mosquitoes and nonbiting midges in all diet samples. Furthermore, bat activity at the sampling locations was related to adult mosquito density. Our results suggest that bats actively exploit the emergence of adult mosquitoes and further prove that they prey on mosquitoes, nonbiting midges and other deleterious insects. Promoting the presence of bats next to human settlements in such agroecosystems may constitute a biological control system with direct impact on both human health and crop yield. © 2020 Society of Chemical Industry.

Relationships between traditional larval indices and meteorological factors with the adult density of Aedes albopictuscaptured by BG-mosquito trap.

ObjectivesLarval indices have been used for Ae. albopictus surveillance for many years, while there is limited use in assessing dengue transmission risk and adult mosquito emergence. This study is aimed to explore the relationships between larval indices and the Ae. albopictus density captured by BG-mosquito trap (BG-trap) method, with considering the meteorological factors.MethodsData on larval density, adult mosquito density and meteorology factors were collected in an entomological survey carried out in Quzhou City, Zhejiang Province of China in 2018. The Spearman’s rank correlation and Pearson correlation were used for the analysis on the correlation of density indices. Generalized additive models were established to analyze the influencing factors of mosquito density.ResultsBreteau index (BI), House index (HI) and Container index (CI) were highly correlated with each other (r>0.7, p<0.05). The Ae. albopictus density was significantly correlated with CI (rs = 0.260, p<0.05), CI pre one week (rs = 0.259, p<0.05), and CI pre three weeks (rs = 0.329, p<0.05). BI was correlated with female Ae. albopictus density pre 4 weeks (r = -0.299, p<0.05). Female Ae. albopictus density was correlated with CI pre 3 weeks (rs = 0.303, p<0.05). The influencing factors of BI were average wind speed pre 1 week, average temperature and female Ae. albopictus density pre 4 weeks. The influencing factors of CI were average humidity pre 3 weeks and average temperature. The influencing factors of HI were average temperature and precipitation pre 4 weeks. The influencing factor of Ae. albopictus density and female Ae. albopictus density was temperature.ConclusionsThe adult Ae. albopictus density had low correlation with certain larval indices. Some of the meteorology factors played significant roles in the density of adult Ae. albopictus and larva with or without a time lag.

Detection of alleles associated with resistance to chemical insecticide in the malaria vector Anopheles arabiensis in Santiago, Cabo Verde

BackgroundMosquitoes of the Anopheles gambiae complex are the main malaria vectors worldwide. Due to the lack of a vaccine to prevent malaria, the principal way to reduce the impact of this disease relies on the use of chemical insecticides to control its vectors. However, the intensive use of such compounds has led to the emergence of insecticide resistance in several Anopheles populations in Africa. This study aimed to investigate the presence of resistance alleles in an Anopheles arabiensis population from the City of Praia, capital of the Archipelago Cabo Verde, one of the countries on the World Health Organization list of countries that are on a path to eliminate local transmission of malaria.MethodsLarvae from the Anopheles genus were collected using a one-pint dipper in three areas of City of Praia. Larvae were fed and maintained until the emergence of adult mosquitoes, and these were morphologically identified. In addition, molecular identification was performed using IGS markers and all An. arabiensis samples were subjected to PCR to screen for mutations associated to resistance in the Ace-1, Nav and GSTE2 genes.ResultsFrom a total of 440 mosquitoes collected, 52.3% were morphologically identified as An. gambiae sensu lato (s.l.) and 46.7% as Anopheles pretoriensis. The molecular identification showed that 100% of the An. gambiae s.l. were An. arabiensis. The mutations G119S in the Ace-1 gene and L119F in the GSTE2 gene were screened but not found in any sample. However, sequencing analysis for GSTE2 revealed the presence of 37 haplotypes, 16 polymorphic sites and a high genetic diversity (π = 2.67). The L1014S mutation in the Nav (voltage-gated sodium channel gene) was detected at a frequency of 7.3%.ConclusionThis is the first study to investigate the circulation of insecticide resistance alleles in An. arabiensis from Cabo Verde. The circulation of the L1014S allele in the population of An. arabiensis in the city of Praia suggests that pyrethroid resistance may arise, be quickly selected, and may affect the process of malaria elimination in Cabo Verde. Molecular monitoring of resistance should continue in order to guide the development of strategies to be used in vector control in the study region.

Analyzing the control of dengue by releasing Wolbachia-infected male mosquitoes through a delay differential equation model.

To date, an innovative strategy to control dengue is to release Wolbachia-infected male mosquitoes into wild areas to sterilize wild female mosquito vectors by cytoplasmic incompatibility (CI). To investigate the efficacy of Wolbachia in blocking dengue virus transmission, we develop a deterministic mathematical model of human and mosquito populations in which one dengue serotype circulates. The delay differential equation model captures the respective extrinsic and intrinsic incu-bation periods (EIP and IIP) in the mosquito and human, as well as the maturation delay between mating and emergence of adult mosquitoes, which have received relatively little attention. We analyze the existence and stability of disease-free equilibria, and obtain a sufficient and necessary condition on the existence of the disease-endemic equilibrium. We also determine two threshold values of the release ratio $\theta$, denoted by $\theta_1^*$ and $\theta_2^*$ with $\theta_1^*>\theta_2^*$. When $\theta>\theta_1^*$, the mosquito population will be eradicated eventually. When $\theta_2^*<\theta < \theta_1^*$, a complete mosquito eradication becomes impossible, but virus eradication is ensured at the meantime. When $\theta<\theta_2^*$, the disease-endemic equilibrium emerges that allows dengue virus to circulate between humans and mosquitoes. We carry out sensitivity analysis of the threshold values in terms of the model parameters, and simulate several possible control strate-gies with different release ratios, which confirm the public awareness that reducing mosquito bites and killing adult mosquitoes are the most effective strategy to control the epidemic. Our model provides new insights on the effectiveness of Wolbachia in reducing dengue at a population level.

Mosquito-Disseminated Insecticide for Citywide Vector Control and Its Potential to Block Arbovirus Epidemics: Entomological Observations and Modeling Results from Amazonian Brazil.

BackgroundMosquito-borne viruses threaten public health worldwide. When the ratio of competent vectors to susceptible humans is low enough, the virus’s basic reproductive number (R0) falls below 1.0 (each case generating, on average, <1.0 additional case) and the infection fades out from the population. Conventional mosquito control tactics, however, seldom yield R0 < 1.0. A promising alternative uses mosquitoes to disseminate a potent growth-regulator larvicide, pyriproxyfen (PPF), to aquatic larval habitats; this kills most mosquito juveniles and substantially reduces adult mosquito emergence. We tested mosquito-disseminated PPF in Manacapuru, a 60,000-inhabitant city (~650 ha) in Amazonian Brazil.Methods and FindingsWe sampled juvenile mosquitoes monthly in 100 dwellings over four periods in February 2014–January 2016: 12 baseline months, 5 mo of citywide PPF dissemination, 3 mo of focal PPF dissemination around Aedes-infested dwellings, and 3 mo after dissemination ended. We caught 19,434 juvenile mosquitoes (66% Aedes albopictus, 28% Ae. aegypti) in 8,271 trap-months. Using generalized linear mixed models, we estimated intervention effects on juvenile catch and adult emergence while adjusting for dwelling-level clustering, unequal sampling effort, and weather-related confounders. Following PPF dissemination, Aedes juvenile catch decreased by 79%–92% and juvenile mortality increased from 2%–7% to 80%–90%. Mean adult Aedes emergence fell from 1,077 per month (range 653–1,635) at baseline to 50.4 per month during PPF dissemination (range 2–117). Female Aedes emergence dropped by 96%–98%, such that the number of females emerging per person decreased to 0.06 females per person-month (range 0.002–0.129). Deterministic models predict, under plausible biological-epidemiological scenarios, that the R0 of typical Aedes-borne viruses would fall from 3–45 at baseline to 0.004–0.06 during PPF dissemination. The main limitations of our study were that it was a before–after trial lacking truly independent replicates and that we did not measure mosquito-borne virus transmission empirically.ConclusionsMosquito-disseminated PPF has potential to block mosquito-borne virus transmission citywide, even under adverse scenarios. Our results signal new avenues for mosquito-borne disease prevention, likely including the effective control of Aedes-borne dengue, Zika, and chikungunya epidemics. Cluster-randomized controlled trials will help determine whether mosquito-disseminated PPF can, as our findings suggest, develop into a major tool for improving global public health.

Larvicidal and Growth-Inhibitory Activity of Entomopathogenic Bacteria Culture Fluids AgainstAedes aegypti(Diptera: Culicidae)

Dengue, Chikungunya, and Zika are important vector-borne diseases, and Aedes aegypti L. is their main transmitter. As the disease management is mainly based on mosquito control strategies, the search for alternative and cost-effective approaches is ongoing. The Gram-negative bacteria Xenorhabdus nematophila and Photorhabdus luminescens are symbiotically associated with entomopathogenic nematodes and are highly pathogenic for insect larvae. After we have recently confirmed the toxicity of these bacteria in Ae. aegypti larvae, we here evaluated the toxic activity of culture fluids on the development of this mosquito species. Larval susceptibility was assessed by exposing larvae to different concentrations of P. luminescens or X. nematophila culture fluids to confirm whether secondary metabolites might cause the mosquitos' death. Xenorhabdus nematophila culture fluid was more effective and stable during the mosquito pathogenicity bioassays compared to that of P. luminescens. Larval mortality started a few hours after exposure of the insects to the fluids. Furthermore, the residual effect of larvicidal activity of X. nematophila fluid persisted at full efficiency for 4 d. Particularly, larval mortality was still higher than 50% for up to 8 d. Exposure of larvae to a sublethal dose of X. nematophila fluid delayed pupation as well as emergence of adult mosquitoes and caused cumulative larval mortality higher than 90% by day 14. Here, we describe for the first time the use of stable culture fluids and therefore secondary metabolites of P. luminescens and X. nematophila as a promising basis for the use as biopesticide for control of Ae. aegypti in the future.

Modeling the Response of Anopheles gambiae (Diptera: Culicidae) Populations in the Kenya Highlands to a Rise in Mean Annual Temperature.

A dynamical model of Anopheles gambiae larval and adult populations is constructed that matches temperature-dependent maturation times and mortality measured experimentally as well as larval instar and adult mosquito emergence data from field studies in the Kenya Highlands. Spectral classification of high-resolution satellite imagery is used to estimate household density. Indoor resting densities collected over a period of one year combined with predictions of the dynamical model give estimates of both aquatic habitat and total adult mosquito densities. Temperature and precipitation patterns are derived from monthly records. Precipitation patterns are compared with average and extreme habitat estimates to estimate available aquatic habitat in an annual cycle. These estimates are coupled with the original model to produce estimates of adult and larval populations dependent on changing aquatic carrying capacity for larvae and changing maturation and mortality dependent on temperature. This paper offers a general method for estimating the total area of aquatic habitat in a given region, based on larval counts, emergence rates, indoor resting density data, and number of households.Altering the average daily temperature and the average daily rainfall simulates the effect of climate change on annual cycles of prevalence of An. gambiae adults. We show that small increases in average annual temperature have a large impact on adult mosquito density, whether measured at model equilibrium values for a single square meter of habitat or tracked over the course of a year of varying habitat availability and temperature.

Field effectiveness of microbial larvicides on mosquito larvae in malaria areas of Botswana and Zimbabwe

BackgroundThe successful control of malaria vectors requires the control of both the larval and adult stages. The adult control methods through indoor residual spraying (IRS) and use of long-lasting insecticidal nets (LLINs) continue to be widely used with some high measure of success. Larval control methods are also being used by a number of National Malaria Control Programmes (NMCPs) with limited understanding of its contribution. Larval control might be needed in some areas to move from malaria control to elimination. This experimental study was conducted to assess the field effectiveness of winter larviciding on the larval stages of the mosquito in Botswana and Zimbabwe.MethodsTwo villages were selected in each of the two countries, one as an intervention and the other as the control. Water bodies in the intervention villages were treated using the commercial product VectoBac® WG (Valent BioSciences Corporation, IL, USA) containing the active ingredient Bacillus thuringiensis var. israelensis (Bti), a WHO recommended bio-larvicide, applied at a rate of 300 g per hectare. Random-effects Poisson regression was employed during data analysis to compare intervention with control sites with respect to larval counts.ResultsThe average marginal effect of larviciding on the mosquito larvae taking interaction with time (period) into account, was −1.94 (95% CI −2.42 to −1.46) with incidence rate ratio of 0.14, thus an 86% larval reduction attributable to the intervention for both countries combined. There was a 92% and 65% effect for Botswana and Zimbabwe respectively. The effect on the early larval and late stages was 77% (P < 0.001) and 91% (P < 0.001), respectively. Overall, intervention larval sampling points had five more larvae than the control at baseline and 26 less after 16 weeks. The effect on the different species also showed similar trends.Discussion/conclusionLarval control using Bti showed a high effect on the population of the mosquito larvae. The reduction of the early and late larval stages can lead to reduced adult mosquito emergence and low adult mosquito densities. Larviciding can be used to control mosquito vector population by suppressing the larval stages thereby reducing adult emergence and malaria risk.

Mosquito-disseminated pyriproxyfen yields high breeding-site coverage and boosts juvenile mosquito mortality at the neighborhood scale.

BackgroundMosquito-borne pathogens pose major public health challenges worldwide. With vaccines or effective drugs still unavailable for most such pathogens, disease prevention heavily relies on vector control. To date, however, mosquito control has proven difficult, with low breeding-site coverage during control campaigns identified as a major drawback. A novel tactic exploits the egg-laying behavior of mosquitoes to have them disseminate tiny particles of a potent larvicide, pyriproxyfen (PPF), from resting to breeding sites, thus improving coverage. This approach has yielded promising results at small spatial scales, but its wider applicability remains unclear.Methodology/Principal FindingsWe conducted a four-month trial within a 20-month study to investigate mosquito-driven dissemination of PPF dust-particles from 100 ‘dissemination stations’ (DSs) deployed in a 7-ha sub-area to surveillance dwellings and sentinel breeding sites (SBSs) distributed over an urban neighborhood of about 50 ha. We assessed the impact of the trial by measuring juvenile mosquito mortality and adult mosquito emergence in each SBS-month. Using data from 1,075 dwelling-months, 2,988 SBS-months, and 29,922 individual mosquitoes, we show that mosquito-disseminated PPF yielded high coverage of dwellings (up to 100%) and SBSs (up to 94.3%). Juvenile mosquito mortality in SBSs (about 4% at baseline) increased by over one order of magnitude during PPF dissemination (about 75%). This led to a >10-fold decrease of adult mosquito emergence from SBSs, from approximately 1,000–3,000 adults/month before to about 100 adults/month during PPF dissemination.Conclusions/SignificanceBy expanding breeding-site coverage and boosting juvenile mosquito mortality, a strategy based on mosquito-disseminated PPF has potential to substantially enhance mosquito control. Sharp declines in adult mosquito emergence can lower vector/host ratios, reducing the risk of disease outbreaks. This approach is a very promising complement to current and novel mosquito control strategies; it will probably be especially relevant for the control of urban disease vectors, such as Aedes and Culex species, that often cause large epidemics.

A generic weather-driven model to predict mosquito population dynamics applied to species of Anopheles, Culex and Aedes genera of southern France

An accurate understanding and prediction of mosquito population dynamics are needed to identify areas where there is a high risk of mosquito-borne disease spread and persistence. Simulation tools are relevant for supporting decision-makers in the surveillance of vector populations, as models of vector population dynamics provide predictions of the greatest risk periods for vector abundance, which can be particularly helpful in areas with a highly variable environment. We present a generic weather-driven model of mosquito population dynamics, which was applied to one species of each of the genera Anopheles, Culex, and Aedes, located in the same area and thus affected by similar weather conditions. The predicted population dynamics of Anopheles hyrcanus, Culex pipiens, and Aedes caspius were not similar. An. hyrcanus was abundant in late summer. Cx. pipiens was less abundant but throughout the summer. The abundance of both species showed a single large peak with few variations between years. The population dynamics of Ae. caspius showed large intra- and inter-annual variations due to pulsed egg hatching. Predictions of the model were compared to longitudinal data on host-seeking adult females. Data were previously obtained using CDC-light traps baited with carbon dioxide dry ice in 2005 at two sites (Marais du Viguerat and Tour Carbonnière) in a favourable temperate wetland of southern France (Camargue). The observed and predicted periods of maximal abundance for An. hyrcanus and Cx. pipiens tallied very well. Pearson's coefficients for these two species were over 75% for both species. The model also reproduced the major trends in the intra-annual fluctuations of Ae. caspius population dynamics, with peaks occurring in early summer and following the autumn rainfall events. Few individuals of this species were trapped so the comparison of predicted and observed dynamics was not relevant. A global sensitivity analysis of the species-specific models enabled us to identify the parameters most influencing the maximal abundance of mosquitoes. These key parameters were almost similar between species, but not with the same contributions. The emergence of adult mosquitoes was identified as a key process in the population dynamics of all of the three species considered here. Parameters associated with adult emergence therefore need to be precisely known to achieve accurate predictions. Our model is a flexible and efficient tool that predicts mosquito abundance based on local environmental factors. It is useful to and already used by a mosquito surveillance manager in France.

Evaluation of Storm-Water Impacts on Larviciding Chemicals at Catch Basins for West Nile Virus Control

Methoprene larvicide is a biochemical insect growth regulator used in North America to control the mosquito population. It can be incorporated in clay pellets or chalks and dropped into a catch basin sump. The slow release mechanism of methoprene has the potential to inhibit the growth of mosquito larvae into pupae in the sump and reduce the emergence of adult mosquitoes. As a result, the vector transport of the West Nile virus can be minimized. The main concern is whether or not the methoprene pellets or ingots will remain in a catch basin sump or be flushed during storm events, resulting in ecological impacts on the receiving waters. A full-scale physical model was constructed to investigate the flushing characteristics of methoprene pellets and chalks in a catch basin. It was found that (1) the sump water could provide a cushion against the hydraulic turbulence of inflows and trap the pellets and ingots; (2) flushing of pellets or ingots was more sensitive to the critical inflow magnitude than the time to reach this flow; (3) ingots would require a higher inflow to be flushed than would pellets; and (4) sediments and leaves at the sump might inhibit the flushing of pellets. Using the measured critical inflow rate at which pellets and ingots were flushed in the experiments, it was found that a 3-month storm and 1.4-year storm in Toronto might have the potential to flush out pellets and ingots respectively in a catch basin filled with sediments. Additionally, the risk of flushing pellets over the summer months may be high when the sump water depth of a catch basin is shallow. On the other hand, the risk of flushing ingots over the summer months is low. As a result, ingots should be used in larviciding catch basins.

Efficacy of Aquatain, a Monomolecular Film, for the Control of Malaria Vectors in Rice Paddies

BackgroundRice paddies harbour a large variety of organisms including larvae of malaria mosquitoes. These paddies are challenging for mosquito control because their large size, slurry and vegetation make it difficult to effectively apply a control agent. Aquatain, a monomolecular surface film, can be considered a suitable mosquito control agent for such breeding habitats due to its physical properties. The properties allow Aquatain to self-spread over a water surface and affect multiple stages of the mosquito life cycle.Methodology/Principal FindingsA trial based on a pre-test/post-test control group design evaluated the potential of Aquatain as a mosquito control agent at Ahero rice irrigation scheme in Kenya. After Aquatain application at a dose of 2 ml/m2 on rice paddies, early stage anopheline larvae were reduced by 36%, and late stage anopheline larvae by 16%. However, even at a lower dose of 1 ml/m2 there was a 93.2% reduction in emergence of anopheline adults and 69.5% reduction in emergence of culicine adults. No pupation was observed in treated buckets that were part of a field bio-assay carried out parallel to the trial. Aquatain application saved nearly 1.7 L of water in six days from a water surface of 0.2 m2 under field conditions. Aquatain had no negative effect on rice plants as well as on a variety of non-target organisms, except backswimmers.Conclusions/SignificanceWe demonstrated that Aquatain is an effective agent for the control of anopheline and culicine mosquitoes in irrigated rice paddies. The agent reduced densities of aquatic larval stages and, more importantly, strongly impacted the emergence of adult mosquitoes. Aquatain also reduced water loss due to evaporation. No negative impacts were found on either abundance of non-target organisms, or growth and development of rice plants. Aquatain, therefore, appears a suitable mosquito control tool for use in rice agro-ecosystems.

Oviposition Site Selection by the Dengue Vector Aedes aegypti and Its Implications for Dengue Control

BackgroundBecause no dengue vaccine or antiviral therapy is commercially available, controlling the primary mosquito vector, Aedes aegypti, is currently the only means to prevent dengue outbreaks. Traditional models of Ae. aegypti assume that population dynamics are regulated by density-dependent larval competition for food and little affected by oviposition behavior. Due to direct impacts on offspring survival and development, however, mosquito choice in oviposition site can have important consequences for population regulation that should be taken into account when designing vector control programs.Methodology/Principal FindingsWe examined oviposition patterns by Ae. aegypti among 591 naturally occurring containers and a set of experimental containers in Iquitos, Peru. Using larval starvation bioassays as an indirect measure of container food content, we assessed whether females select containers with the most food for their offspring. Our data indicate that choice of egg-laying site is influenced by conspecific larvae and pupae, container fill method, container size, lid, and sun exposure. Although larval food positively influenced oviposition, our results did not support the hypothesis that females act primarily to maximize food for larvae. Females were most strongly attracted to sites containing immature conspecifics, even when potential competitors for their progeny were present in abundance.Conclusion/SignificanceDue to strong conspecific attraction, egg-laying behavior may contribute more to regulating Ae. aegypti populations than previously thought. If highly infested containers are targeted for removal or larvicide application, females that would have preferentially oviposited in those sites may instead distribute their eggs among other suitable, previously unoccupied containers. Strategies that kill mosquitoes late in their development (i.e., insect growth regulators that kill pupae rather than larvae) will enhance vector control by creating “egg sinks,” treated sites that exploit conspecific attraction of ovipositing females, but reduce emergence of adult mosquitoes via density-dependent larval competition and late acting insecticide.

Agent-based modelling of mosquito foraging behaviour for malaria control

Traditional environmental management programmes require extensive coverage of larval habitats to reduce drastically the emergence of adult mosquitoes. Recent studies have highlighted the impact of reduced availability of aquatic habitats on mosquito foraging for hosts and oviposition sites. In this study, we developed an agent-based model to track the status and movement of mosquitoes individually. Mosquito foraging was represented as a two-stage process: random flight when the resource was not within the mosquito's perception range and directional flight to the resource when it was detected. Three scenarios of targeted source reduction were devised to eliminate all aquatic habitats within certain distances of human habitations. For comparison, three non-targeted source reductions randomly eliminated the same numbers of aquatic habitats as their corresponding targeted scenarios. Our results show that the elimination of habitats within 100m, 200m and 300m of surrounding houses resulted in 13%, 91% and 94% reductions in malaria incidence, respectively; compared with -3%, 19% and 44%, respectively, for the corresponding conventional interventions. These findings indicate that source reduction might not require coverage of extensive areas, as previously thought, and that the distance to human habitations can be used for habitat targeting.