Survival of Aedes aegypti (Diptera: Culicidae) eggs in surface and subterranean breeding sites during the northern Queensland dry season

Temporal dynamics of the egg bank of Aedes aegypti (Diptera: Culicidae) in the winter-spring transition in a temperate region

In temperate regions, the populations of Aedes aegypti (L.) (Diptera: Culicidae) remain in the egg stage during the winter. In Buenos Aires, Argentina, a temperate region in the southern limit of Ae. aegypti distribution, the start of the next reproductive season and the rate of increase of the adult population depend on the egg bank that remains after the winter. This study aimed to analyze the mortality, field-hatching, and survival of eggs exposed to field conditions representative of those that occur in nature. In addition, the post-exposure hatching response of the eggs was assessed. Four egg batches were exposed to natural conditions starting in mid-winter and were recovered progressively after 3, 6, 9, and 12 weeks. One egg batch (initial control) was not exposed in the field and remained under laboratory conditions. After the exposure period, the recovered intact, collapsed, and hatched eggs were counted. Intact eggs were immersed three times in the laboratory to study their hatching response. Progressive increases in the proportion of lost (presumably by predation), dead, and hatched eggs in successive egg batches were recorded. Field-hatching was recorded from late winter onwards. The first hatchings occurred in conditions probably not favorable to complete development into reproductive adults. A progressive decrease in live eggs was observed, with 51% of the recovered eggs alive after 12 weeks of exposure. In the laboratory, the hatching response in the first immersion was low for the initial control and for the eggs exposed for 3 weeks, and increased for successive cohorts. The results confirm that the survival of Ae. aegypti eggs in the winter-spring transition ensures persistence throughout the next favorable season in Buenos Aires City. The observed inhibition to hatch of the first batches might relate to a photoperiod-induced diapause, as observed in previous studies.

Anti-Insect Properties of Penicillium Secondary Metabolites

In connection with their widespread occurrence in diverse environments and ecosystems, fungi in the genus Penicillium are commonly found in association with insects. In addition to some cases possibly implying a mutualistic relationship, this symbiotic interaction has mainly been investigated to verify the entomopathogenic potential in light of its possible exploitation in ecofriendly strategies for pest control. This perspective relies on the assumption that entomopathogenicity is often mediated by fungal products and that Penicillium species are renowned producers of bioactive secondary metabolites. Indeed, a remarkable number of new compounds have been identified and characterized from these fungi in past decades, the properties and possible applications of which in insect pest management are reviewed in this paper.

The use of drones for mosquito surveillance and control

In recent years, global health security has been threatened by the geographical expansion of vector-borne infectious diseases such as malaria, dengue, yellow fever, Zika and chikungunya. For a range of these vector-borne diseases, an increase in residual (exophagic) transmission together with ecological heterogeneity in everything from weather to local human migration and housing to mosquito species' behaviours presents many challenges to effective mosquito control. The novel use of drones (or uncrewed aerial vehicles) may play a major role in the success of mosquito surveillance and control programmes in the coming decades since the global landscape of mosquito-borne diseases and disease dynamics fluctuates frequently and there could be serious public health consequences if the issues of insecticide resistance and outdoor transmission are not adequately addressed. For controlling both aquatic and adult stages, for several years now remote sensing data have been used together with predictive modelling for risk, incidence and detection of transmission hot spots and landscape profiles in relation to mosquito-borne pathogens. The field of drone-based remote sensing is under continuous change due to new technology development, operation regulations and innovative applications. In this review we outline the opportunities and challenges for integrating drones into vector surveillance (i.e. identification of breeding sites or mapping micro-environmental composition) and control strategies (i.e. applying larval source management activities or deploying genetically modified agents) across the mosquito life-cycle. We present a five-step systematic environmental mapping strategy that we recommend be undertaken in locations where a drone is expected to be used, outline the key considerations for incorporating drone or other Earth Observation data into vector surveillance and provide two case studies of the advantages of using drones equipped with multispectral cameras. In conclusion, recent developments mean that drones can be effective for accurately conducting surveillance, assessing habitat suitability for larval and/or adult mosquitoes and implementing interventions. In addition, we briefly discuss the need to consider permissions, costs, safety/privacy perceptions and community acceptance for deploying drone activities.

Temperature-dependent population dynamics for Aedes aegypti in outdoor, indoor, and enclosed habitats: a mathematical model for five North American cities

A model for the Aedes aegypti lifecycle is developed that takes into account temperature-dependent maturation and death rates for several life stages, wet and dry egg oviposition with flooding, as well as three classes of larval habitat with different temperature profiles: outdoor (subject to external temperature fluctuations, human-inhabited), indoor (temperature moderated, human-inhabited, interior), and enclosed (temperature moderated, human free, exterior). An equilibrium analysis shows that the temperature range of outdoor viable equilibrium populations aligns closely with reported risk levels. Temperature patterns for El Paso, Texas; New York, New York; New Orleans, Louisiana; Orlando, Florida; and Miami, Florida, are considered. In four of these locations (all but New York), enclosed habitats can support mosquito populations even if all outdoor and indoor habitats are removed. In two locations (El Paso and New York) the model shows that in spite of the disappearance of adult mosquitoes during colder temperatures, populations reach seasonal steady state due to the survival of eggs. The results have implications for both vector and disease control.

Could species-focused suppression of Aedes aegypti, the yellow fever mosquito, and Aedes albopictus, the tiger mosquito, affect interacting predators? An evidence synthesis from the literature

The risks of Aedes aegypti and Aedes albopictus nuisance and vector-borne diseases are rising and the adverse effects of broad-spectrum insecticide application have promoted species-specific techniques, such as sterile insect technique (SIT) and other genetic strategies, as contenders in their control operations. When specific vector suppression is proposed, potential effects on predators and wider ecosystem are some of the first stakeholder questions. These are not the only Aedes vectors of human diseases, but are those for which SIT and genetic strategies are of most interest. They vary ecologically and in habitat origin, but both have behaviorally human-adapted forms with expanding ranges. The aquatic life stages are where predation is strongest due to greater resource predictability and limited escape opportunity. These vectors' anthropic forms usually use ephemeral water bodies and man-made containers as larval habitats; predators that occur in these are mobile, opportunistic and generalist. No literature indicates that any predator depends on larvae of either species. As adults, foraging theory predicts these mosquitoes are of low profitability to predators. Energy expended hunting and consuming will mostly outweigh their energetic benefit. Moreover, as adult biomass is mobile and largely disaggregated, any predator is likely to be a generalist and opportunist. This work, which summarizes much of the literature currently available on the predators of Ae. aegypti and Ae. albopictus, indicates it is highly unlikely that any predator species depends on them. Species-specific vector control to reduce nuisance and disease is thus likely to be of negligible or limited impact on nontarget predators. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Winter survival of Aedes aegypti (Diptera: Culicidae) eggs at its southern limit distribution

Aedes aegypti (L.) (Diptera: Culicidae) survives in the egg stage under unfavorable environmental conditions. In this study, we assessed the survival of Ae. aegypti eggs under natural winter conditions as an overwintering mechanism. To address this, field collected eggs (from Buenos Aires city) were exposed for three months during the winter season in three sites of Santa Rosa and General Acha (La Pampa province, Argentina). Eggs survival and hatching response were analyzed considering two factors (site of exposure and time of oviposition). Of the 1397 analyzed eggs, 936 (67%) were viable at the end of the study. Egg survival showed to be high in all sites (between 53% and 84%), except in one site of Santa Rosa. Also, eggs survival was higher in eggs laid in May (94%) (late-fall) as compared to those laid in March (61%) and April (56%) (early- and mid-fall respectively). Eggs hatching response was only affected by the time of oviposition, being lower for eggs laid in May (33%) as compared to March (38%) and April (50%). These results provide information regarding the winter resistance of Ae. aegypti at the limit of its distribution in temperate regions. Given the high percentages of survival found in this study, we consider that the low winter temperatures would not be a limitation for its establishment in southern areas.

Myracrodruon urundeuva leaf lectin damages exochorionic cells and binds to the serosal cuticle of Aedes aegypti eggs

In recent years, lectins have been identified as alternative agents against Aedes aegypti during the aquatic phases of its life cycle. For example, chitin-binding lectin from Myracrodruon urundeuva leaf (MuLL) can function as a larvicide. In this study, we investigated whether MuLL can also act as an ovicide against this insect. Aedes aegypti eggs were incubated with MuLL for 72 h to determine the concentration at which the hatching rate reduces by 50% (EC₅₀). The effects of MuLL on the egg surface structure were evaluated using scanning electron microscopy (SEM), and the possible interaction of MuLL with the internal structures of eggs and embryos was investigated using MuLL-fluorescein isothiocyanate (FITC) conjugate. MuLL acted as an ovicidal agent with an EC₅₀ of 0.88 mg/mL. The SEM analysis revealed that eggs treated with MuLL for 24 and 48 h no longer had tubercles and did not show a well-defined exochorionic network. In addition, deformation and degeneration of the surface were observed after 72 h. Fluorescence microscopy showed that MuLL penetrated the eggs 48 h after incubation and was detected in the upper portion of the embryo's gut. After 72 h, MuLL was observed in the serosal cuticle and digestive tract. In conclusion, MuLL can function as an ovicidal agent against A. aegypti through damage to the surface and internal structures of the eggs.

Extensive public health initiatives drive the elimination of Aedes aegypti (Diptera, Culicidae) from a town in regional Queensland: A case study from Gin Gin, Australia

Aedes aegypti is the primary vector of exotic arboviruses (dengue, chikungunya and Zika) in Australia. Once established across much of Australia, this mosquito species remains prevalent in central and northern Queensland. In 2011, Ae. aegypti was re-discovered in the town of Gin Gin, Queensland, by health authorities during routine larval surveillance. This town is situated on a major highway that provides a distribution pathway into the highly vulnerable and populous region of the state where the species was once common. Following the detection, larval habitat and adult control activities were conducted as a public health intervention to eliminate the Ae. aegypti population and reduce the risk of exotic disease transmission. Importantly, genetic analysis revealed a homogenous cluster and small effective population vulnerable to an elimination strategy. By 2015, adult surveillance revealed the population had expanded throughout the centre of the town. In response, a collaboration between research agencies and local stakeholders activated a second control program in 2016 that included extensive community engagement, enhanced entomologic surveillance and vector control activities including the targeting of key containers, such as unsealed rainwater tanks. Here we describe a model of the public health intervention which successfully reduced the Ae. aegypti population below detection thresholds, using source reduction, insecticides and novel, intensive genetic surveillance methods. This outcome has important implications for future elimination work in small towns in regions sub-optimal for Ae. aegypti presence and reinforces the longstanding benefits of a partnership model for public health-based interventions for invasive urban mosquito species.

Larval habitat determines the bacterial and fungal microbiota of the mosquito vector Aedes aegypti

Mosquito larvae are naturally exposed to microbial communities present in a variety of larval development sites. Several earlier studies have highlighted that the larval habitat influences the composition of the larval bacterial microbiota. However, little information is available on their fungal microbiota, i.e. the mycobiota. In this study, we provide the first simultaneous characterization of the bacterial and fungal microbiota in field-collected Aedes aegypti larvae and their respective aquatic habitats. We evaluated whether the microbial communities associated with the breeding site may affect the composition of both the bacterial and fungal communities in Ae. aegypti larvae. Our results show a higher similarity in microbial community structure for both bacteria and fungi between larvae and the water in which larvae develop than between larvae from different breeding sites. This supports the hypothesis that larval habitat is a major factor driving microbial composition in mosquito larvae. Since the microbiota plays an important role in mosquito biology, unravelling the network of interactions that operate between bacteria and fungi is essential to better understand the functioning of the mosquito holobiont.

Efficacy of focal applications of a mycoinsecticide to control Aedes aegypti in Central Brazil

Entomopathogenic fungi can achieve important innovative outcomes for integrated mosquito control especially of Aedes aegypti, the key vector of arboviruses to humans in the tropics and subtropics. This study sought to design and to develop a simple dissemination device to attract and to infect gravid A. aegypti adults with a granular formulation of the ascomycete Metarhizium humberi IP 46, and to validate this device in the laboratory as well as in semi-field and field conditions. Hydrogel (polyacrylamide potassium polyacrylate) was confirmed to be a suitable substitute for water used in the device that attracted gravid females under field conditions. Females laid eggs on black polyethylene terephthalate carpet fixed in the device that also proved to be a suitable substrate for a granular formulation of fungal microsclerotia and/or conidia. The plastic device (29.5 cm high) was divided into a lower closed compartment with a water reservoir and an upper, laterally open but covered compartment with continuously hydrated gel and the fungal formulation attached to the carpet. The uppermost compartment permitted free circulation of mosquito adults. The device attracted both male and female A. aegypti. The fungal formulations of IP 46 propagules tested in the device were effective against adults in laboratory, semi-field, and field settings. Findings in the laboratory, semi-field, and especially in field conditions strengthen the value and utility of this innovative device for focal applications of a mycoinsecticide against this important mosquito vector.Key points• Low-cost and simple disseminating device for focal control of Aedes aegypti.• Granulized Metarhizium humberi IP 46 and hydrogel yield extended control.• Findings in field tests strengthen benefit of the device for focal application.

Choice of nest attributes as a frontline defense against brood parasitism

Breeding- and nest-site choice is a behavioral strategy often used to counter negative interactions. Site choices before breeding prevent costs of predation and competition but have been neglected in the context of brood parasitism. For hosts of brood parasites, the earlier brood parasitism is prevented in the breeding cycle the lower the future costs. Suitable nest-sites for cavity-nesting common redstarts (Phoenicurus phoenicurus), a host of the common cuckoo (Cuculus canorus), are a limited resource, but their cavity-nesting strategy could potentially deter predators and brood parasites. We altered the entrance size of breeding cavities and investigated redstart nest-site choice and its consequences to nest predation and brood parasitism risk, although accounting for potential interspecific competition for nest sites. We set-up paired nest-boxes and let redstarts choose between 7 cm and 5 cm entrance sizes. Additionally, we monitored occupancy rates in nest-boxes with 3 cm, 5 cm, and 7 cm entrance sizes and recorded brood parasitism and predation events. We found that redstarts preferred to breed in 5 cm entrance size cavities, where brood parasitism was eliminated but nest predation rates were comparable to 7 cm entrance size cavities. Only in 3 cm cavities both, brood parasitism and predation rates were reduced. In contrast to the other cavity-nesting species, redstart settlement was lowest in 3 cm entrance size cavities, potentially suggesting interspecific competition for small entrance size cavities. Nest-site choice based on entrance size could be a frontline defense strategy that redstarts use to reduce brood parasitism.

Meteorological variables associated with the temporal oviposition rate of Aedes aegypti (Diptera: Culicidae) in Resistencia city, Chaco province, Northeastern Argentina

Aedes aegypti is the main vector of dengue virus in South America. In the last fifteen years, Argentina has suffered three large dengue outbreaks: one in 2009, another one in 2016 and the current 2020 outbreak, with 26,000, 66,000 and more than 43,000 confirmed cases, respectively. These outbreaks are associated with the circulation of the virus in neighboring countries due to the constant movement of people across the frontier. In 2009, the main province affected was Chaco province, with 11,037 confirmed cases (50% of total cases). Thus, the aim of this study was to characterize the temporal oviposition rate of Aedes aegypti in Resistencia, the capital city of this province, in relation to meteorological variables. Mosquitoes were sampled weekly, from April 2015 to March 2017, using ovitraps located in houses randomly selected within the urban area. Oviposition rate was evaluated by means of the total number of eggs collected per week and the proportion of positive ovitraps per week. The coefficient of variation for these two indicators was estimated for the whole study period and then compared using the Wilcoxon Pair test. A generalized linear model (GLM) was performed to infer association between meteorological variables and oviposition rate without time lag and with a time lag of 1 to 4 weeks, considering the biology of this mosquito species. Comparisons between the coefficient of variation of egg number versus the proportion of positive ovitraps showed significant differences, being the former more variable than the latter. The most significant time lag was 2 weeks for the minimum temperature. The number of Ae. aegypti eggs increased 4.05 times when the minimum temperature increased 1°C two weeks before, and decreased 0.69 times with an increase of 1 unit in relative humidity. No eggs were collected when the temperature was below 8°C. The oviposition rate was associated with the increase in the critical minimum temperature (over 8°C) and the weekly frequency of precipitation and dissociated with relative humidity. The maximum oviposition rate was recorded between November and January of both years. The GLM could not explain the relation between meteorological variables and the proportion of positive ovitraps. The peaks of Ae. aegypti egg abundance occurred simultaneously with dengue autochthonous cases recorded in Chaco province, resulting in a good indicative of the period of greatest epidemiological risk.

A potential global surveillance tool for effective, low-cost sampling of invasive Aedes mosquito eggs from tyres using adhesive tape

BACKGROUND

The international movement of used tyres is a major factor responsible for global introductions of Aedes invasive mosquitoes (AIMs) (Diptera: Culicidae) that are major disease vectors (e.g. dengue, Zika, chikungunya and yellow fever). Surveillance methods are restricted by expense, availability and efficiency to detect all life stages. Currently, no tested method exists to screen imported used tyres for eggs in diapause, the life stage most at risk from accidental introduction. Here we test the efficiency of adhesive tape as an affordable and readily available material to screen tyres for eggs, testing its effect on hatch rate, larval development, DNA amplification and structural damage on the egg surface.

RESULTS

We demonstrated that the properties of adhesive tape can influence pick up of dormant eggs attached to dry surfaces. Tapes with high levels of adhesion, such as duct tape, removed eggs with high levels of efficiency (97% ± 3.14). Egg numbers collected from cleaned used tyres were found to explain larval hatch rate success well, particularly in subsequent larval to adult emergence experiments. The strength of this relationship decreased when we tested dirty tyres. Damage to the exochorion was observed following scanning electron microscopy (SEM), possibly resulting in the high variance in the observed model. We found that five days was the optimal time for eggs to remain on all tested tapes for maximum return on hatch rate success. Tape type did not inhibit amplification of DNA of eggs from three, five or ten days of exposure. Using this DNA, genotyping of AIMs was possible using species-specific markers.

CONCLUSIONS

We demonstrated for the first time that adhesive tapes are effective at removing AIM eggs from tyres. We propose that this method could be a standardised tool for surveillance to provide public health authorities and researchers with an additional method to screen tyre cargo. We provide a screening protocol for this purpose. This method has a global applicability and in turn can lead to increased predictability of introductions and improve screening methods at high risk entry points.

The Removal of Subterranean Stormwater Drain Sumps as Mosquito Breeding Sites in Darwin, Australia

The Northern Territory Top End Health Service, Medical Entomology Section and the City of Darwin council carry out a joint Mosquito Engineering Program targeting the rectification of mosquito breeding sites in the City of Darwin, Northern Territory, Australia. In 2005, an investigation into potential subterranean stormwater breeding sites in the City of Darwin commenced, specifically targeting roadside stormwater side entry pits. There were 79 side entry pits randomly investigated for mosquito breeding in the Darwin suburbs of Nightcliff and Rapid Creek, with 69.6% of the pits containing water holding sumps, and 45.6% of those water holding sumps breeding endemic mosquitoes. Culex quinquefasciatus was the most common mosquito collected, accounting for 73% of all mosquito identifications, with the potential vector mosquito Aedes notoscriptus also recovered from a small number of sumps. The sumps were also considered potential dry season maintenance breeding sites for important exotic Aedes mosquitoes such as Aedes aegypti and Aedes albopictus, which are potential vectors of dengue, chickungunya and Zika virus. Overall, 1229 side entry pits were inspected in ten Darwin suburbs from 2005 to 2008, with 180 water holding sumps identified and rectified by concrete filling.

The Global Expansion of Dengue: How Aedes aegypti Mosquitoes Enabled the First Pandemic Arbovirus

Dengue is an emerging viral disease principally transmitted by the Aedes (Stegomyia) aegypti mosquito. It is one of the fastest-growing global infectious diseases, with 100-400 million new infections a year, and is now entrenched in a growing number of tropical megacities. Behind this rapid rise is the simple adaptation of Ae. aegypti to a new entomological niche carved out by human habitation. This review describes the expansion of dengue and explores how key changes in the ecology of Ae. aegypti allowed it to become a successful invasive species and highly efficient disease vector. We argue that characterizing geographic heterogeneity in mosquito bionomics will be a key research priority that will enable us to better understand future dengue risk and design control strategies to reverse its global spread.

MVSE: An R-package that estimates a climate-driven mosquito-borne viral suitability index

Viruses, such as dengue, Zika, yellow fever and chikungunya, depend on mosquitoes for transmission. Their epidemics typically present periodic patterns, linked to the underlying mosquito population dynamics, which are known to be driven by natural climate fluctuations. Understanding how climate dictates the timing and potential of viral transmission is essential for preparedness of public health systems and design of control strategies. While various alternative approaches have been proposed to estimate local transmission potential of such viruses, few open-source, ready to use and freely available software tools exist.We developed the Mosquito-borne Viral Suitability Estimator (MVSE) software package for the R programming environment. MVSE estimates the index P, a novel suitability index based on a climate-driven mathematical expression for the basic reproductive number of mosquito-borne viruses. By accounting for local humidity and temperature, as well as viral, vector and human priors, the index P can be estimated for specific host and viral species in different regions of the globe.We describe the background theory, empirical support and biological interpretation of the index P. Using real-world examples spanning multiple epidemiological contexts, we further demonstrate MVSE's basic functionality, research and educational potentials.

Life on the margin: Rainwater tanks facilitate overwintering of the dengue vector, Aedes aegypti, in a sub-tropical climate

A key determinant of insect persistence in marginal habitats is the ability to tolerate environmental extremes such as temperature. Aedes aegypti is highly invasive and little is known about the physiological sensitivity of the species to fluctuating temperature regimes at the lower critical threshold for development. A temperature that may limit the establishment and persistence of the species in sub-optimal regions. Daily winter temperatures were measured in common Australian larval habitats, replicated in environmental chambers and used to investigate the effect of fluctuating temperatures on the development and survival of tropical and subtropical strains of Australian Ae. aegypti. Development was slow for all treatments but both strains were able to complete development to the adult stage, suggesting previous models underestimate the potential for the species to persist in eastern Australia. Results suggested that thermal buffering in large volume habitats, and water that persists for greater than 32 days, will facilitate completion of the life cycle during sub-tropical winters. Furthermore, we provide a non-linear estimate of the lower critical temperature for Ae. aegypti development that suggests the current threshold may be incorrect. Our study demonstrates that the current re-introduction of water storage containers such as rainwater tanks, into major Australian population centres will increase the risk of Ae. aegypti establishment by permitting year-round development in locations south of its current distribution.

Predation on Eggs of Aedes aegypti (Diptera: Culicidae): Temporal Dynamics and Identification of Potential Predators During the Winter Season in a Temperate Region

In temperate regions, the populations of Aedes aegypti (L.) remain in the egg stage during the cold season. The ability of these eggs to survive until the next favorable season is affected by several mortality factors, including the action of predators. In the present study, we analyzed the temporal dynamics of the loss of eggs and identified predators of Ae. aegypti eggs along the unfavorable season in a temperate region of Argentina. To this end, eggs were exposed in field conditions in pitfall traps, where walking arthropod taxa were captured during 1-wk periods from early June to early September (Austral winter). The association of arthropod taxa with the loss of eggs was analyzed to identify potential predators. Based on the results obtained, two taxa were chosen to confirm their capacity to consume eggs in a laboratory study. The proportion of lost eggs and the abundance of predators were significantly higher in the winter-spring transition, although results were heterogeneous among traps in all exposure periods. Ants of the genus Strumigenys, isopods of the species Armadillidium vulgare (Isopoda: Armadilloidea), and dermapterans of the species Euborellia annulipes (Dermaptera: Anisolabidae) were positively associated with a high proportion of lost eggs. In laboratory conditions, A. vulgare and E. annulipes consumed the offered eggs, thus confirming their predator capacity. This study represents the first record of predation of Ae. aegypti eggs in temperate South America and the first evidence of dermapterans consuming mosquito eggs.

Extremely Long Viability of Aedes aegypti (Diptera: Culicidae) Eggs Stored Under Normal Room Condition

The viability of Aedes aegypti (Linnaeus) eggs was determined by storing the eggs for long period of up to 1,889 d. The viability of eggs declined over time from 88.54 to 4.89% for the storage period of 1-1,883 d (5.15 yr). The percentage of collapsed eggs was inversely proportional to the hatching rate of eggs. In the first day of storage, the eggs remained healthy and intact, and except a few, the eggs were deformed and boat shaped with cleft due to inward shrinkage during long storage of 1,883 d.

The impact of Anopheles gambiae egg storage for mass rearing and production success

BACKGROUND

Mass rearing requires a large colony from which male individuals can be harvested for sterilization and release. Attention is needed when monitoring life parameters of the reared population, knowing that any variations within the target population would lead to mismatching between two populations. The aim of this study was to assess the impact of Anopheles gambiae sensu stricto (s.s.) egg storage on hatchability and life history traits. For each parameter, comparison was made between freshly laid and stored eggs in three densities (40, 80, 120 eggs).

METHODS

Anopheles gambiae s.s. freshly laid eggs were collected from the Tropical Pesticide Research Institute (TPRI) insectary. Eggs to be stored were kept at - 20 °C for 10 min and then transferred to refrigerators at 4 °C for intervals of 5, 10, 15, 20, and 25 days. After respective storage days, the eggs were transferred from refrigerators to ambient temperature of (25 ± 2) °C for 24 h and then placed in incubators for 24 h. Thereafter eggs were hatched. The egg hatchability, emerged larvae development, larvae survival and emerged adult sex ratios were monitored.

RESULTS

This study found that hatching rates decreased with increase in storage time. The difference was significant in eggs stored for 10 and 15 days (P < 0.05). There were no significant differences in hatching rates between An. gambiae eggs stored for 5 days and freshly hatched eggs (P > 0.05). Anopheles larvae development (L1 to pupae) was not significantly affected by storage time across all hatching densities. The study also found that larvae survival decreased with increase in egg storage time. However, there was no significant difference between larvae from freshly hatched eggs and those from eggs at 5 and 10 storage days (P > 0.05) but not for eggs stored for 15 days. Furthermore, there was a decrease in emerged adult males and increase in females relative to increased time of egg storage. The difference was significant (P < 0.05) at 15 storage days but not for eggs stored for 5 and 10 days (in triplicate densities).

CONCLUSION

From this study it was concluded that storing An. gambiae eggs at 4 °C and 48 ± 2% relative humidity (RH) for 5 days is the optimal condition and time that did not affect egg hatching rates, larval development and survivorship and emerged adult mosquito sex ratio.

Mosquito-borne arboviruses of African origin: review of key viruses and vectors

Key aspects of 36 mosquito-borne arboviruses indigenous to Africa are summarized, including lesser or poorly-known viruses which, like Zika, may have the potential to escape current sylvatic cycling to achieve greater geographical distribution and medical importance. Major vectors are indicated as well as reservoir hosts, where known. A series of current and future risk factors is addressed. It is apparent that Africa has been the source of most of the major mosquito-borne viruses of medical importance that currently constitute serious global public health threats, but that there are several other viruses with potential for international challenge. The conclusion reached is that increased human population growth in decades ahead coupled with increased international travel and trade is likely to sustain and increase the threat of further geographical spread of current and new arboviral disease.

Aedes aegypti breeding site in an underground rainwater reservoir: a warning

We describe the discovery of Aedes aegypti underground breeding site in the Pinheiros neighborhood of São Paulo, SP, during an entomological survey program performed in 2016. Even with intense surveillance and vector control, large numbers of mosquitoes were present in this area. A detailed investigation allowed for the detection of Ae. aegypti in an underground reservoir used for rainwater storage. After the implementation of protection screens in the accesses, the presence of the vector was no longer detected. In this study, we discuss the frequent use of this type of reservoir structure and its risk for mosquito production.

Scaling Up of an Innovative Intervention to Reduce Risk of Dengue, Chikungunya, and Zika Transmission in Uruguay in the Framework of an Intersectoral Approach with and without Community Participation

To contribute to the prevention of dengue, chikungunya, and Zika, a process of scaling up an innovative intervention to reduce Aedes aegypti habitats, was carried out in the city of Salto (Uruguay) based on a transdisciplinary analysis of the eco-bio-social determinants. The intervention in one-third of the city included the distributions of plastic bags for all households to collect all discarded water containers that were recollected by the Ministry of Health and the Municipality vector control services. The results were evaluated in 20 randomly assigned clusters of 100 households each, in the intervention and control arm. The intervention resulted in a significantly larger decrease in the number of pupae per person index (as a proxy for adult vector abundance) than the corresponding decrease in the control areas (both areas decreased by winter effects). The reduction of intervention costs ("incremental costs") in relation to routine vector control activities was 46%. Community participation increased the collaboration with the intervention program considerably (from 48% of bags handed back out of the total of bags delivered to 59% of bags handed back). Although the costs increased by 26% compared with intervention without community participation, the acceptability of actions by residents increased from 66% to 78%.

Habitat and Density of Oviposition Opportunity Influences Aedes aegypti (Diptera: Culicidae) Flight Distance

Understanding the dispersal of Aedes (aegypti (L.) Diptera: Culicidae) after consuming a potentially infectious bloodmeal is an important part of controlling the spread of the arboviruses it transmits. Because of the impact on abundance, removal of oviposition sites is a key component of vector control. However, source reduction around a case may encourage dispersal of potentially infected vectors. We compare the effect of oviposition site availability on Ae. aegypti dispersal behavior within 30-m linear cages in three model ecosystems at the University of Arizona's Biosphere 2 research facility. We found a significant interaction effect in which, when oviposition site density was sparse, dispersal was greater in the highly vegetated humid rainforest and limited in the low vegetation, arid desert model ecosystem. When oviposition site density was dense, no significant effect on dispersal was observed. These analyses support the idea that source reduction has an important influence on the distance that gravid, potentially infected, females will travel.

Effect of an intervention in storm drains to prevent Aedes aegypti reproduction in Salvador, Brazil

BACKGROUND

Aedes aegypti, the principal vector for dengue, chikungunya and Zika viruses, is a synanthropic species that uses stagnant water to complete its reproductive cycle. In urban settings, rainfall water draining structures, such as storm drains, may retain water and serve as a larval development site for Aedes spp. reproduction. Herein, we describe the effect of a community-based intervention on preventing standing water accumulation in storm drains and their consequent infestation by adult and immature Ae. aegypti and other mosquitoes.

METHODS

Between April and May of 2016, local residents association of Salvador, Brazil, after being informed of water accumulation and Ae. aegypti infestation in the storm drains in their area, performed an intervention on 52 storm drains. The intervention consisted of placing concrete at the bottom of the storm drains to elevate their base to the level of the outflow tube, avoiding water accumulation, and placement of a metal mesh covering the outflow tube to avoid its clogging with debris. To determine the impact of the intervention, we compared the frequency at which the 52 storm drains contained water, as well as adult and immature mosquitoes using data from two surveys performed before and two surveys performed after the intervention.

RESULTS

During the pre-intervention period, water accumulated in 48 (92.3%) of the storm drains, and immature Ae. aegypti were found in 11 (21.2%) and adults in 10 (19.2%). After the intervention, water accumulated in 5 (9.6%) of the storm drains (P < 0.001), none (0.0%) had immatures (P < 0.001), and 3 (5.8%) contained adults (P = 0.039). The total number of Ae. aegypti immatures collected decreased from 109 to 0 (P < 0.001) and adults decreased from 37 to 8 (P = 0.011) after the intervention. Collection of immature and adult non-Aedes mosquitoes (mainly Culex spp.) in the storm drains also decreased after the intervention.

CONCLUSION

This study exemplifies how a simple intervention targeting storm drains can result in a major reduction of water retention, and, consequently, impact Ae. aegypti larval populations. Larger and multi-center evaluations are needed to confirm the potential of citywide structural modifications of storm drains to reduce Aedes spp. infestation level.

Microfungi Associated with Pteroptyx bearni (Coleoptera: Lampyridae) Eggs and Larvae from Kawang River, Sabah (Northern Borneo)

Overlooking the importance of insect disease can have disastrous effects on insect conservation. This study reported the microfungi that infect Pteroptyx bearni eggs and larvae during ex-situ rearing project. Two different species of microfungi that infected the firefly's immature life stages were isolated and identified. Penicillium citrinum infected the firefly's eggs while Trichoderma harzianum infected the firefly during the larval stage. Both microfungi species caused absolute mortality once infection was observed; out of 244 individual eggs collected, 75 eggs (32.5%) were infected by Penicillium citrinum. All 13 larvae that hatched from the uninfected eggs were infected by Trichoderma harzianum. This study was the first to document the infection of Pteroptyx bearni's eggs and larvae by Penicillium citrinum and Trichoderma harzianum.

Influence of the Length of Storage on Aedes aegypti (Diptera: Culicidae) Egg Viability

Aedes aegypti (L.) is one of the most important arboviral vectors worldwide. Vector control is targeted at immature and adult stages; however, eggs are resistant to desiccation and may repopulate treated areas long after treatment ceases. We investigated the effect of age on Ae. aegypti egg hatching rates using newly colonized populations (F2) from an arid region. We found a strongly negative association where older eggs had lower hatch rates. The capacity of eggs to survive for long periods of time has implications on mosquito control. In addition, the accumulation of eggs in containers should be accounted for in abundance modeling efforts where populations may grow rapidly early in the season.

Eggs viability of Aedes aegypti Linnaeus (Diptera, Culicidae) under different environmental and storage conditions in Manaus, Amazonas, Brazil

Abstract The viability of Aedes aegypti eggs was assessed in the Amazon region. The eggs were maintained under different conditions: indoors (insectarium) and outdoors (natural environment), as well as in different storage types (plastic cup, paper envelope, plastic bag) for different days. Egg viability was measured as the mean of hatchings observed from egg-bearing sheets of filter paper immersed in water, using three sheets randomly selected from each storage type and at both sites. There were significant differences in the viability of Ae. aegypti eggs with respect to the location (F=30.40; DF=1; P<0.0001), storage type (F=17.66; DF=2; P<0.0001), and time of storage (F=49.56; DF=9; P<0.0001). The interaction between storage site versus storage type was also significant (F=15.96; DF=2; P<0.0001). A higher hatching mean was observed for the eggs kept in the insectarium than for those outdoors (32.38 versus 7.46). Hatching rates of egg batches stored for 12 to 61 days ranged between 84 and 90%. A reduction was observed between 89 and 118 days, with values of 63 and 48%, respectively. With respect to type of storage, mean egg hatching was higher for the eggs in plastic cups (44.46). It was concluded that the viability of the eggs of Ae. aegypti in the Amazon region remains high up to 4 months, after which it declines drastically, although in this study hatching occurred for up to 8 months in very low percentages.

Storm drains as larval development and adult resting sites for Aedes aegypti and Aedes albopictus in Salvador, Brazil

Background

Dengue (DENV), Chikungunya (CHIKV), Zika (ZIKV), as well as yellow fever (YFV) viruses are transmitted to humans by Aedes spp. females. In Salvador, the largest urban center in north-eastern Brazil, the four DENV types have been circulating, and more recently, CHIKV and ZIKV have also become common. We studied the role of storm drains as Aedes larval development and adult resting sites in four neighbourhoods of Salvador, representing different socioeconomic, infrastructure and topographic conditions.

Results

A sample of 122 storm drains in the four study sites were surveyed twice during a 4-month period in 2015; in 49.0 % of the visits, the storm drains contained water. Adults and immatures of Aedes aegypti were captured in two of the four sites, and adults and immatures of Aedes albopictus were captured in one of these two sites. A total of 468 specimens were collected: 148 Ae. aegypti (38 adults and 110 immatures), 79 Ae. albopictus (48 adults and 31 immatures), and 241 non-Aedes (mainly Culex spp.) mosquitoes (42 adults and 199 immatures). The presence of adults or immatures of Ae. aegypti in storm drains was independently associated with the presence of non-Aedes mosquitoes and with rainfall of ≤ 50 mm during the preceding week.

Conclusions

We found that in Salvador, one of the epicentres of the 2015 ZIKV outbreak, storm drains often accumulate water and serve as larval development sites and adult resting areas for both Ae. aegypti and Ae. albopictus. Vector control campaigns usually overlook storm drains, as most of the effort to prevent Ae. agypti reproduction is directed towards containers in the domicile environment. While further studies are needed to determine the added contribution of storm drains for the maintenance of Aedes spp. populations, we advocate that vector control programs incorporate actions directed at storm drains, including regular inspections and use of larvicides, and that human and capital resources are mobilized to modify storm drains, so that they do not serves as larval development sites for Aedes (and other) mosquitoes.

Mapping global environmental suitability for Zika virus

Zika virus was discovered in Uganda in 1947 and is transmitted by Aedes mosquitoes, which also act as vectors for dengue and chikungunya viruses throughout much of the tropical world. In 2007, an outbreak in the Federated States of Micronesia sparked public health concern. In 2013, the virus began to spread across other parts of Oceania and in 2015, a large outbreak in Latin America began in Brazil. Possible associations with microcephaly and Guillain-Barré syndrome observed in this outbreak have raised concerns about continued global spread of Zika virus, prompting its declaration as a Public Health Emergency of International Concern by the World Health Organization. We conducted species distribution modelling to map environmental suitability for Zika. We show a large portion of tropical and sub-tropical regions globally have suitable environmental conditions with over 2.17 billion people inhabiting these areas.

DOI:http://dx.doi.org/10.7554/eLife.15272.001

Zika virus is transmitted between humans by mosquitoes. The majority of infections cause mild flu-like symptoms, but neurological complications in adults and infants have been found in recent outbreaks.

Although it was discovered in Uganda in 1947, Zika only caused sporadic infections in humans until 2007, when it caused a large outbreak in the Federated States of Micronesia. The virus later spread across Oceania, was first reported in Brazil in 2015 and has since rapidly spread across Latin America. This has led many people to question how far it will continue to spread. There was therefore a need to define the areas where the virus could be transmitted, including the human populations that might be risk in these areas.

Messina et al. have now mapped the areas that provide conditions that are highly suitable for the spread of the Zika virus. These areas occur in many tropical and sub-tropical regions around the globe. The largest areas of risk in the Americas lie in Brazil, Colombia and Venezuela. Although Zika has yet to be reported in the USA, a large portion of the southeast region from Texas through to Florida is highly suitable for transmission. Much of sub-Saharan Africa (where several sporadic cases have been reported since the 1950s) also presents an environment that is highly suitable for the Zika virus. While no cases have yet been reported in India, a large portion of the subcontinent is also suitable for Zika transmission.

Over 2 billion people live in Zika-suitable areas globally, and in the Americas alone, over 5.4 million births occurred in 2015 within such areas. It is important, however, to recognize that not all individuals living in suitable areas will necessarily be exposed to Zika.

We still lack a great deal of basic epidemiological information about Zika. More needs to be known about the species of mosquito that spreads the disease and how the Zika virus interacts with related viruses such as dengue. As such information becomes available and clinical cases become routinely diagnosed, the global evidence base will be strengthened, which will improve the accuracy of future maps.

DOI:http://dx.doi.org/10.7554/eLife.15272.002

Establishment of a Wolbachia Superinfection in Aedes aegypti Mosquitoes as a Potential Approach for Future Resistance Management

Wolbachia pipientis is an endosymbiotic bacterium estimated to chronically infect between 40-75% of all arthropod species. Aedes aegypti, the principle mosquito vector of dengue virus (DENV), is not a natural host of Wolbachia. The transinfection of Wolbachia strains such as wAlbB, wMel and wMelPop-CLA into Ae. aegypti has been shown to significantly reduce the vector competence of this mosquito for a range of human pathogens in the laboratory. This has led to wMel-transinfected Ae. aegypti currently being released in five countries to evaluate its effectiveness to control dengue disease in human populations. Here we describe the generation of a superinfected Ae. aegypti mosquito line simultaneously infected with two avirulent Wolbachia strains, wMel and wAlbB. The line carries a high overall Wolbachia density and tissue localisation of the individual strains is very similar to each respective single infected parental line. The superinfected line induces unidirectional cytoplasmic incompatibility (CI) when crossed to each single infected parental line, suggesting that the superinfection would have the capacity to replace either of the single constituent infections already present in a mosquito population. No significant differences in fitness parameters were observed between the superinfected line and the parental lines under the experimental conditions tested. Finally, the superinfected line blocks DENV replication more efficiently than the single wMel strain when challenged with blood meals from viremic dengue patients. These results suggest that the deployment of superinfections could be used to replace single infections and may represent an effective strategy to help manage potential resistance by DENV to field deployments of single infected strains.

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.

The global distribution of the arbovirus vectors Aedes aegypti and Ae. albopictus

Dengue and chikungunya are increasing global public health concerns due to their rapid geographical spread and increasing disease burden. Knowledge of the contemporary distribution of their shared vectors, Aedes aegypti and Aedes albopictus remains incomplete and is complicated by an ongoing range expansion fuelled by increased global trade and travel. Mapping the global distribution of these vectors and the geographical determinants of their ranges is essential for public health planning. Here we compile the largest contemporary database for both species and pair it with relevant environmental variables predicting their global distribution. We show Aedes distributions to be the widest ever recorded; now extensive in all continents, including North America and Europe. These maps will help define the spatial limits of current autochthonous transmission of dengue and chikungunya viruses. It is only with this kind of rigorous entomological baseline that we can hope to project future health impacts of these viruses.

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 (52.5 ppt 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 (10 ppt), rubber (20 ppt) and concrete (20 ppt) surfaces. Addition of smectite clay reduced the minimum effective concentration to 10 ppt NaOCl for all 3 substrates. A minimum exposure period of 24 h was required to completely eliminate egg viability on concrete surfaces, even at the highest NaOCl concentration (52.5 ppt). 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.

The 2012 Madeira dengue outbreak: epidemiological determinants and future epidemic potential

Dengue, a vector-borne viral disease of increasing global importance, is classically associated with tropical and sub-tropical regions around the world. Urbanisation, globalisation and climate trends, however, are facilitating the geographic spread of its mosquito vectors, thereby increasing the risk of the virus establishing itself in previously unaffected areas and causing large-scale epidemics. On 3 October 2012, two autochthonous dengue infections were reported within the Autonomous Region of Madeira, Portugal. During the following seven months, this first 'European' dengue outbreak caused more than 2000 local cases and 81 exported cases to mainland Europe. Here, using an ento-epidemiological mathematical framework, we estimate that the introduction of dengue to Madeira occurred around a month before the first official cases, during the period of maximum influx of airline travel, and that the naturally declining temperatures of autumn were the determining factor for the outbreak's demise in early December 2012. Using key estimates, together with local climate data, we further propose that there is little support for dengue endemicity on this island, but a high potential for future epidemic outbreaks when seeded between May and August-a period when detection of imported cases is crucial for Madeira's public health planning.

An assessment of the importance of subsurface catch basins for Aedes aegypti adult production during the dry season in a neighborhood of Merida, Mexico

We compared the number of adult Aedes aegypti emerging from subsurface catch basins located in the streets against the number of pupae (as a proxy of adults emerging) from the entire container larval habitats found at residential premises within 1 ha of a neighborhood in the Mexican city of Merida during 8 days in the dry season of 2012. Aedes aegypti adults were collected from 60% of the subsurface catch basins. They produced 12 adults/day/ha (95% confidence interval [CI], 6.4 to 17.9), 5 females (95% CI, 2.1 to 7.7), and 7 males (95% CI, 3.8 to 10.7). In contrast, only 7 containers holding water were identified in 30 premises inspected, 1 bucket was positive for Ae. aegypti larvae, but no pupae-positive containers were found. No other mosquito species were found. This study revealed the importance of this type of nonresidential and subterranean aquatic habitat for Ae. aegypti adult production in this neighborhood of Merida during the dry season.

Effects of thermal heterogeneity and egg mortality on differences in the population dynamics of Aedes aegypti (Diptera: Culicidae) over short distances in temperate Argentina

In temperate regions, the seasonal dynamics of Aedes aegypti (L.) (Diptera: Culicidae) is mainly influenced by temperature, whereas the probability of local extinction depends on the egg mortality during the cold season. The aim of the current study was to assess the importance of temperature and egg mortality in determining the differences in the oviposition dynamics of Ae. aegypti between favorable and less favorable areas in Buenos Aires City (Argentina). Year-round temperature dynamics were monitored, and oviposition dynamics were experimentally studied with ovitraps at two sites. Daily egg mortality values were calculated from a previous study performed at the same sites. The relative contribution of the differences in temperature and egg mortality between sites to the oviposition dynamics was assessed by means of a mathematical stochastic population dynamics model for Ae. aegypti. The results showed higher temperature and lower daily egg mortality at the site where higher oviposition activity was recorded. A larger influence of temperature than of egg mortality on population abundance during most of the activity season was detected in the results of the simulations. Our results showed a temperature gradient that relates to the distance to the Río de la Plata river and contributes to explaining the spatial heterogeneity in Ae. aegypti population abundances previously reported. The hypothesis of local extinctions because of egg mortality during the winter was not supported by the present analysis. The differences between field oviposition dynamics and simulation results suggest that rainfall might also be an important variable under extremely dry conditions.

Seasonal population dynamics and the genetic structure of the mosquito vector Aedes aegypti in São Paulo, Brazil

Population genetic studies of insect vectors can generate knowledge to improve epidemiological studies focused on the decrease of pathogen transmission. In this study, we used nine SNPs across the Aedes aegypti genome to characterize seasonal population variations of this important dengue vector. Mosquito samples were obtained by ovitraps placed over Botucatu SP from 2005 to 2010. Our data show that, regardless of the large variation in mosquito abundance (deduced from the number of eggs obtained from ovitraps), the effective population size remained stable over the years. These results suggest that Ae. aegypti is able to maintain a sufficiently large active breeding population during the dry season to keep genetic frequencies stable. These results open new perspectives on mosquito survey and control methods.

Oviposition-stimulant and ovicidal activities of Moringa oleifera lectin on Aedes aegypti

Background

Natural insecticides against the vector mosquito Aedes aegypti have been the object of research due to their high level of eco-safety. The water-soluble Moringa oleifera lectin (WSMoL) is a larvicidal agent against A. aegypti. This work reports the effects of WSMoL on oviposition and egg hatching of A. aegypti.

Methodology/Principal Findings

WSMoL crude preparations (seed extract and 0–60 protein fraction), at 0.1 mg/mL protein concentration, did not affect oviposition, while A. aegypti gravid females laid their eggs preferentially (73%) in vessels containing isolated WSMoL (0.1 mg/mL), compared with vessels containing only distilled water (control). Volatile compounds were not detected in WSMoL preparation. The hatchability of fresh eggs deposited in the solutions in the oviposition assay was evaluated. The numbers of hatched larvae in seed extract, 0–60 protein fraction and WSMoL were 45±8.7 %, 20±11 % and 55±7.5 %, respectively, significantly (p<0.05) lower than in controls containing only distilled water (75–95%). Embryos were visualized inside fresh control eggs, but not within eggs that were laid and maintained in WSMoL solution. Ovicidal activity was also assessed using stored A. aegypti eggs. The protein concentrations able to reduce the hatching rate by 50% (EC50) were 0.32, 0.16 and 0.1 mg/mL for seed extract, 0–60 protein fraction and WSMoL, respectively. The absence of hatching of stored eggs treated with WSMoL at 0.3 mg/mL (EC99) after transfer to medium without lectin indicates that embryos within the eggs were killed by WSMoL. The reduction in hatching rate of A. aegypti was not linked to decrease in bacteria population.

Conclusions/Significance

WSMoL acted both as a chemical stimulant cue for ovipositing females and ovicidal agent at a given concentration. The oviposition-stimulant and ovicidal activities, combined with the previously reported larvicidal activity, make WSMoL a very interesting candidate in integrated A. aegypti control.

Bacteria stimulate hatching of yellow fever mosquito eggs

BACKGROUND

Aedes aegypti Linnaeus is a peridomestic mosquito that lays desiccation-resistant eggs in water-filled human-made containers. Previous investigations connected egg hatching with declining dissolved oxygen (DO) that is associated with bacterial growth. However, past studies failed to uncouple DO from other potential stimulatory factors and they contained little quantitative information about the microbial community; consequently, a direct role for bacteria or compounds associated with bacteria in stimulating egg hatching cannot be dismissed.

METHODOLOGY/PRINCIPAL FINDINGS

Environmental factors stimulating hatch of Ae. aegypti eggs were investigated using non-sterile and sterile white oak leaf (WOL) infusions and a bacterial culture composed of a mix of 14 species originally isolated from bamboo leaf infusion. In WOL infusion with active microbes, 92.4% of eggs hatched in 2-h at an average DO concentration of 2.4 ppm. A 24-h old bacterial culture with a DO concentration of 0.73 ppm also stimulated 95.2% of eggs hatch within 1-h. In contrast, only 4.0% of eggs hatched in sterile infusion, whose DO averaged 7.4 ppm. Effects of bacteria were uncoupled from DO by exposing eggs to bacterial cells suspended in NaCl solution. Over a 4-h exposure period, 93.8% of eggs hatched while DO concentration changed minimally from 7.62 to 7.50 ppm. Removal of bacteria by ultra-filtration and cell-free filtrate resulted in only 52.0% of eggs hatching after 4-h at an average DO concentration of 5.5 ppm.

CONCLUSIONS/SIGNIFICANCE

Collectively, the results provide compelling evidence that bacteria or water-soluble compounds secreted by bacteria, not just low DO concentration, stimulate hatching of Ae. aegypti eggs. However, the specific cues involved remain to be identified. These research findings contribute new insight into an important aspect of the oviposition biology of Ae. aegypti, a virus vector of global importance, providing the basis for a new paradigm of environmental factors involved in egg hatching.

Cold season mortality and hatching behavior of Aedes aegypti L. (Diptera: Culicidae) eggs in Buenos Aires City, Argentina

In temperate regions, populations of Aedes aegypti survive the cold season in the egg stage. In the present work, we studied the cold-season mortality of Ae. aegypti eggs and their subsequent hatching pattern in Buenos Aires city. Eggs were exposed during the winter season (three months) in three neighborhoods located along a gradient of distance toward the Río de la Plata River, coincident with a gradient of activity of Ae. aegypti. Results showed mortalities lower (30.6%) than those from tropical regions during the dry season. Significant differences were detected among the egg mortalities of each site with a maximum value at the site nearest the Río de la Plata River (50%), and a minimum value at the most continental site (9%). Post-experimental hatching response of eggs differed between sites, with the highest proportion of hatched eggs during the first immersion in the site nearest to the river and the lowest proportion in the most continental site. The hatching proportion also differed between age classes, with older (early-laid) eggs hatching later than new (late-laid) ones. Our results provide the first information of Ae. aegypti egg mortality in temperate South America and support the hypothesis that differences in egg mortality are associated with abundance patterns of Ae. aegypti in Buenos Aires city.

The dengue vector Aedes aegypti: what comes next

Aedes aegypti is the urban vector of dengue viruses worldwide. While climate influences the geographical distribution of this mosquito species, other factors also determine the suitability of the physical environment. Importantly, the close association of A. aegypti with humans and the domestic environment allows this species to persist in regions that may otherwise be unsuitable based on climatic factors alone. We highlight the need to incorporate the impact of the urban environment in attempts to model the potential distribution of A. aegypti and we briefly discuss the potential for future technology to aid management and control of this widespread vector species.

Dynamics of Aedes aegypti and Culex quinquefasciatus in septic tanks

Aedes aegypti and Culex quinquefasciatus were found in large numbers emerging from septic tanks in southern Puerto Rico during the dry season. Previous studies suggested that Ae. aegypti uses subterranean aquatic habitats only during dry periods when surface containers do not have water. This research investigated whether septic tanks are alternative aquatic habitats that this mosquito uses during unfavorable times of the year, or whether Ae. aegypti uses this aquatic habitat throughout the year. To assess temporal change, exit traps were used to collect mosquitoes emerging from septic tanks in Playa/Playita, southern Puerto Rico, from November 2006 to October 2007. We also investigated the hypotheses that (1) the production of Ae. aegypti in septic tanks was larger than in surface containers and (2) adult mosquitoes emerging from septic tanks were larger than those emerging from surface containers. This study demonstrated that unsealed septic tanks produced large numbers of Ae. aegypti and Cx. quinquefasciatus throughout the year, without any significant relationship with rainfall. The number of adult Ae. aegypti emerging per day from septic tanks in each community was 3 to 9 times larger than those produced in surface containers. It was also demonstrated that Ae. aegypti emerging from septic tanks were significantly larger than those emerging from surface container habitats. It is recommended that dengue prevention programs include regular inspection and maintenance of septic tanks in communities lacking sewerage.

Enhanced ovicidal activity of an oil formulation of the fungus Metarhizium anisopliae on the mosquito Aedes aegypti

The effect of humidity on the activity of Metarhizium anisopliae IP 46 (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) formulated in sunflower oil against Aedes aegypti (L.) (Diptera: Culicidae) eggs was examined. After exposure of eggs at 75% relative humidity (RH) for <or= 25 days, ovicidal activity was not increased by oil-in-water formulated conidia, hyphal bodies or pure-oil formulated conidia, compared with conidia or hyphal bodies prepared in water only. At optimal > 98% RH, eclosion was <or= 13.7% after treatment with oil-in-water formulated propagules in <or= 10% oil, and it was completely inhibited when conidia were applied in pure oil. At 86-100% RH, new conidia were found on eggs treated with oil-formulated conidia and incubated down to 91% RH. Ovicidal activity was still detected at 93% RH and was augmented with increasing humidity and time of exposure of eggs. Eclosion of larvae was distinctly reduced by IP 46 pure-oil formulated conidia after a minimal initial exposure of 3 days at > 98% RH, followed by: (a) a 12-day exposure at 75% RH before submersion in water; (b) a minimal 5-day exposure at > 98% RH and direct subsequent transfer of treated eggs to water, or (c) a minimal daily 20-h exposure at > 98% RH alternating with 4 h at 75% RH for 10 days. We demonstrate that oil-based formulations of conidia of M. anisopliae enhance ovicidal activity at high humidities and conclude that these formulations have potential in the integrated control of Ae. aegypti.

Impact of moisture on survival of Aedes aegypti eggs and ovicidal activity of Metarhizium anisopliae under laboratory conditions

The effect of relative humidity (43%, 75%, 86% and > 98%) on Aedes aegypti eggs treated with Metarhizium anisopliae or water only was tested for up to a six months exposure at 25 degrees C. Survival of larvae inside eggs was clearly affected by the lowest humidity (43%) tested, and eclosion diminished at all humidities after increasing periods of exposure. M. anisopliae showed to have a strong ovicidal activity only at humidity close to saturation. No difference of activity was found between conidia and hyphal bodies tested. This fungus affected larvae inside eggs and has potential as a control agent of this important vector in breeding sites with high moisture.

Unusual productivity of Aedes aegypti in septic tanks and its implications for dengue control

Increased DEN-2 virus transmission in Puerto Rico during 2005 prompted the implementation of a rapid intervention programme to suppress Aedes aegypti (L.) (Diptera: Culicidae) emergence, which in turn lead to the discovery of previously unknown breeding sites underground. Initially, the following control measures were applied in Playa/Playita (PP), a town of 1,400 households, to all areas where the number of pupae per person exceeded the expected threshold for dengue transmission; all containers likely to be aquatic habitats were turned over and containers too large to turn were treated with 1 p.p.m. methoprene. The impact of these interventions was evaluated by comparing the number of resting adult mosquitoes (by backpack aspiration and sweepnetting in bedrooms) pre-intervention, with numbers at 3 and 5 weeks post-intervention, and by evaluating pupal density at 4 weeks post-intervention in PP and in a nearby town, Coqui (CO; 1500 households), which was not treated. The pre-intervention and post-intervention densities of resting Ae. aegypti adults were significantly larger in the intervention town, although the density of pupae in surface containers was low and similar in both towns at 4 weeks post-intervention. At 3 weeks post-intervention, the density of resting adults decreased by only 18% of pre-intervention levels, but returned to pre-intervention levels 5 weeks after treatment. By contrast, the density of resting adults in CO steadily decreased to 48% and 61%, at 3 and 5 weeks after the initial surveys, respectively. Geographical Information Systems identified significant clustering of adult mosquitoes, which led to the discovery of underground aquatic habitats (septic tanks) that were producing large numbers of Ae. aegypti and Culex quinquefasciatus (Say) in the treated town. We calculated that septic tanks could produce > 18 000 Ae. aegypti and approximately 170 000 Cx quinquefasciatus adults per day. Septic tanks are likely to be common and widespread in suburban and rural Puerto Rico, where, apparently, they can contribute significantly to the maintenance of island-wide dengue virus endemicity.

Effects of climate and different management strategies on Aedes aegypti breeding sites: a longitudinal survey in Brasilia (DF, Brazil)

OBJECTIVE

To determine the influence of climate and of environmental vector control with or without insecticide on Aedes aegypti larval indices and pupae density.

METHODS

An 18-month longitudinal survey of infestation of Ae. aegypti immature stages was conducted for the 1015 residences (premises) of Vila Planalto, an area of Brasilia where the Breteau Index was about 40 before the study. This area was divided into five zones: a control zone with environmental management alone and four zones with insecticide treatment (methoprene, Bti, temephos). We tested for significant differences between infestation levels in the control and insecticide-treated areas, for relationships between climatic variables and larval indices, and to determine risk factors of infestation for certain types of premises and containers.

RESULTS

Environmental vector control strategies dramatically decreased infestation in the five areas. No significant differences could be detected between control strategies with insecticide and without. Some premises and container types were particularly suitable for breeding. The influence of climate on the emergence of Ae. aegypti adults for the area is described.

CONCLUSION

In a moderately infested area such as Brasilia, insecticides do not improve environmental vector control. Rather, infestations could be further reduced by focusing on residences and containers particularly at risk. The nature of the link between climate and larval population should be investigated in larger-scale studies before being used in forecasting models.