Selection of cyanobacteria isolated from mosquito breeding sites as a potential food source for mosquito larvae.

One way to increase the persistence of larvicidal toxins in mosquito breeding sites is to clone the corresponding genes in microorganisms, such as cyanobacteria, which could serve as a source of food for the larvae. We isolated and cultured 10 strains of cyanobacteria from three mosquito breeding sites along the French Mediterranean coast. Most of the strains were tolerant to a relatively wide range of salt concentrations, and all of them were totally or partially resistant to at least four of the five biological or chemical larvicides used in the local mosquito control program. Six unicellular strains from these habitats and Synechococcus strain PCC 7942, a strain maintained for more than 10 years under laboratory conditions, were assessed for ingestion and digestion by larvae Culex pipiens and Anopheles gambiae mosquitoes. The numbers of cells ingested and digested were dependent on the cyanobacterial strain and varied with the mosquito species. Three of the new isolates, Synechococcus strain PCC 8905 and Synechocystis strains PCC 8906 and PCC 8912, were ingested and digested rapidly by larvae of both mosquito species. Since these strains are also tolerant to larvicides and relatively resistant to elevated salt concentrations, they meet the basic requirements for potential recipients of bacterial genes that encode endotoxins.     

Selection of cyanobacteria isolated from mosquito breeding sites as a potential food source for mosquito larvae.

One way to increase the persistence of larvicidal toxins in mosquito breeding sites is to clone the corresponding genes in microorganisms, such as cyanobacteria, which could serve as a source of food for the larvae. We isolated and cultured 10 strains of cyanobacteria from three mosquito breeding sites along the French Mediterranean coast. Most of the strains were tolerant to a relatively wide range of salt concentrations, and all of them were totally or partially resistant to at least four of the five biological or chemical larvicides used in the local mosquito control program. Six unicellular strains from these habitats and Synechococcus strain PCC 7942, a strain maintained for more than 10 years under laboratory conditions, were assessed for ingestion and digestion by larvae Culex pipiens and Anopheles gambiae mosquitoes. The numbers of cells ingested and digested were dependent on the cyanobacterial strain and varied with the mosquito species. Three of the new isolates, Synechococcus strain PCC 8905 and Synechocystis strains PCC 8906 and PCC 8912, were ingested and digested rapidly by larvae of both mosquito species. Since these strains are also tolerant to larvicides and relatively resistant to elevated salt concentrations, they meet the basic requirements for potential recipients of bacterial genes that encode endotoxins.     

Effects of global warming on mosquitoes & mosquito‐borne diseases and the new strategies for mosquito control

Global warming has shortened mosquitoes’ lifecycle period and increased the disease transmission rates by mosquito vectors. We reviewed only three mosquito‐borne diseases: malaria, dengue fever, and the Japanese encephalitis. Billions of people get infected with those diseases and millions of people die every year. Although we struggle to find the most effective way to control mosquitoes using various methods (including pesticides), mosquito‐borne diseases are still among the most serious problems being faced. This paper, therefore, reviews the strategies for controlling mosquitoes. The use of pesticides to control mosquitoes might have more negative effects on humans and environments than benefits. Although the development of genetically modified (GM) mosquitoes raises new hopes for effective mosquito control, it will take longer to assess the risks to humans and environments. Furthermore, there has been concern about the possible adverse effects from the release of GM mosquitoes into the environment. The various mosquito traps may not be as effective at controlling only female mosquito populations. Therefore, new strategies for the control of mosquitoes are vital. The smart mosquito counter device was developed by Korean Centre for Disease Control (KCDC) in 2013. The mosquito pest control office is able to set up the appropriate mosquito control strategies by using quantitative mosquito information. The smart device will bring mosquito control in line with modern smart generation technology and the device will also soon be able to identify different mosquito species. This new strategy will change the methods of mosquito control and will provide beneficial effects toward sustainable nature and human health.     

Redressing the sex imbalance in knowledge of vector biology

The recent development of transgenic mosquitoes that are resistant to infection by the Plasmodium malarial parasite is a promising new tool in the fight against malaria. However, results of large-scale field releases of alternatively modified mosquitoes carried out during the 1970s and 1980s suggest that this approach could be difficult to implement in the field. These past attempts to control mosquito populations largely floundered as a result of our insufficient understanding of the behavioural ecology of released males. In spite of this, contemporary research on genetic control strategies has concentrated predominantly on molecular aspects, with little progress being made toward resolving key ecological uncertainties, male mosquito ecology being the most important. Here, we review the state of knowledge of male mosquito ecology, and highlight priorities for further research. Case studies of two crop pests, the Mediterranean fruit fly and melon fly, are given as examples of how knowledge of male ecology facilitates successful control in other species. Unless similar information becomes available for mosquitoes, any future genetic control strategy will risk failure.     

A review of the role of fish as biological control agents of disease vector mosquitoes in mangrove forests: reducing human health risks while reducing environmental risk

The saltwater mosquito, Aedes vigilax, is prolific in coastal wetlands including mangroves and saltmarshes. Ae. vigilax is a vector for arboviruses such as Ross River and Barmah Forest viruses, with significant consequences for human health and economic productivity. In Australia the dominant form of mosquito control is chemicals. For mangroves, this is because there is a critical lack of knowledge supporting alternative approaches, such as environmental modification or biological control using larvivorous fish. This review examines the potential of fish as biological agents for the control of mosquito larvae in mangroves. We consider two key aspects: how larvivorous fish use mangroves; and can larvivorous fish reduce larval mosquito populations sufficiently to provide effective mosquito control? The link between fish and mangroves is reasonably well established, where mangroves act as refuge habitat for small and juvenile fish. Also, research has established that fish can be significant predators of mosquitoes, and therefore may be effective control agents. However, studies of fish activity within mangroves are limited to study of the fringe of the mangroves and not the internal structure of mangrove basins and as a result, fish populations within these areas remain unstudied. Also, until recently there was little appreciation of the mangrove-mosquito habitat relationship and, as a consequence, the importance of the mangrove basin as the key mosquito habitat has also been overlooked in the literature. Similarly, the predator/prey relationships between fish and mosquitoes within mangrove basin environments also remain unstudied, and therefore the importance of fish for mosquito management in mangrove basins is not known. There are substantial knowledge gaps regarding the potential of fish in controlling larval mosquitoes in mangroves. The gaps include: understanding of how larvivorous fish use mangrove basins; the nature of the fish-mosquito predator/prey relationship in mangrove basins; and whether larvivorous fish are effective as a mosquito control option in mangroves.     

Impact of environment on mosquito response to pyrethroid insecticides: Facts,evidences and prospects

By transmitting major human diseases such as malaria, dengue fever and filariasis, mosquito species represent a serious threat worldwide in terms of public health, and pose a significant economic burden for the African continent and developing tropical regions. Most vector control programmes aiming at controlling life-threatening mosquitoes rely on the use of chemical insecticides, mainly belonging to the pyrethroid class. However, resistance of mosquito populations to pyrethroids is increasing at a dramatic rate, threatening the efficacy of control programmes throughout insecticide-treated areas, where mosquito-borne diseases are still prevalent. In the absence of new insecticides and efficient alternative vector control methods, resistance management strategies are therefore critical, but these require a deep understanding of adaptive mechanisms underlying resistance. Although insecticide resistance mechanisms are intensively studied in mosquitoes, such adaptation is often considered as the unique result of the selection pressure caused by insecticides used for vector control. Indeed, additional environmental parameters, such as insecticides/pesticides usage in agriculture, the presence of anthropogenic or natural xenobiotics, and biotic interactions between vectors and other organisms, may affect both the overall mosquito responses to pyrethroids and the selection of resistance mechanisms. In this context, the present work aims at updating current knowledge on pyrethroid resistance mechanisms in mosquitoes and compiling available data, often from different research fields, on the impact of the environment on mosquito response to pyrethroids. Key environmental factors, such as the presence of urban or agricultural pollutants and biotic interactions between mosquitoes and their microbiome are discussed, and research perspectives to fill in knowledge gaps are suggested.     

Assessing the impact of low-technology emanators alongside long-lasting insecticidal nets to control malaria

Malaria control in sub-Saharan Africa relies on the widespread use of long-lasting insecticidal nets (LLINs) or the indoor residual spraying of insecticide. Disease transmission may be maintained even when these indoor interventions are universally used as some mosquitoes will bite in the early morning and evening when people are outside. As countries seek to eliminate malaria, they can target outdoor biting using new vector control tools such as spatial repellent emanators, which emit airborne insecticide to form a protective area around the user. Field data are used to incorporate a low-technology emanator into a mathematical model of malaria transmission to predict its public health impact across a range of scenarios. Targeting outdoor biting by repeatedly distributing emanators alongside LLINs increases the chance of elimination, but the additional benefit depends on the level of anthropophagy in the local mosquito population, emanator effectiveness and the pre-intervention proportion of mosquitoes biting outdoors. High proportions of pyrethroid-resistant mosquitoes diminish LLIN impact because of reduced mosquito mortality. When mosquitoes are highly anthropophagic, this reduced mortality leads to more outdoor biting and a reduced additional benefit of emanators, even if emanators are assumed to retain their effectiveness in the presence of pyrethroid resistance. Different target product profiles are examined, which show the extra epidemiological benefits of spatial repellents that induce mosquito mortality.This article is part of the theme issue ‘Novel control strategies for mosquito-borne diseases’.     

Effect of anti-mosquito antibodies on the infectivity of the rodent malaria parasite Plasmodium berghei to Anopheles farauti

The effect of mouse anti-mosquito antibodies, present in the bloodmeal, on the infectivity of Plasmodium berghei Vincke to Anopheles farauti Laveran was investigated. Significantly fewer oocysts developed in mosquitoes feeding on mice immunized with sugar-fed mosquito midgut antigens than in mosquitoes feeding on control mice. Mosquitoes feeding on mice immunized with the midgut antigens derived from sugar-fed mosquitoes also showed reduced mortality and had lower infection rates than those fed on unimmunized mice. Blood-fed midgut antigen was less effective in producing these effects than sugar-fed midgut antigen.     

High-throughput sorting of mosquito larvae for laboratory studies and for future vector control interventions

ABSTRACT: BACKGROUND: Mosquito transgenesis offers new promises for the genetic control of vector-borne infectious diseases such as malaria and dengue fever. Genetic control strategies require the release of large number of male mosquitoes into field populations, whether they are based on the use of sterile males (sterile insect technique, SIT) or on introducing genetic traits conferring refractoriness to disease transmission (population replacement). However, the current absence of high-throughput techniques for sorting different mosquito populations impairs the application of these control measures. METHODS: A method was developed to generate large mosquito populations of the desired sex and genotype. This method combines flow cytometry and the use of Anopheles gambiae transgenic lines that differentially express fluorescent markers in males and females. RESULTS: Fluorescence-assisted sorting allowed single-step isolation of homozygous transgenic mosquitoes from a mixed population. This method was also used to select wild-type males only with high efficiency and accuracy, a highly desirable tool for genetic control strategies where the release of transgenic individuals may be problematic. Importantly, sorted males showed normal mating ability compared to their unsorted brothers. CONCLUSIONS: The developed method will greatly facilitate both laboratory studies of mosquito vectorial capacity requiring high-throughput approaches and future field interventions in the fight against infectious disease vectors.     

Hemolymph of Anopheles stephensi from noninfected and Plasmodium berghei-infected mosquitoes. 1. Collection procedure and physical characteristics.

Hemolymph was collected from adult female Anopheles stephensi by centrifugation of incised mosquitoes. Approximately 0.1 muliter was collected from each recently emerged mosquito, although smaller amounts were recovered with increasing age of the mosquito. Determinations were made of the pH, osmotic pressure, and specific gravity of this hemolymph at various times during the life of the adult mosquito. The values obtained were within the ranges found for other insects. Hemolymph collected from mosquitoes fed on hamsters infected with Plasmodium berghei had different values than hemolymph from mosquitoes fed on noninfected hamsters. This probably was due to differences between the quality of these 2 types of blood meals, rather than to the direct effects of the malaria parasite on the infected mosquito itself.     

Manipulating,managing and rehabilitating mangrove-dominated wetlands along Florida’s east coast (USA): balancing mosquito control and ecological values

In Florida, mangrove-dominated wetlands have been manipulated and managed largely for control of mosquitoes or to make way for human development since the late 1800s. More recently, many wetlands have been rehabilitated as their contributions to estuarine ecosystems became apparent and techniques that restored valuable contributions without compromising control of mosquitoes became available. This paper documents the history of manipulations largely used to control mosquito production in wetlands on the east coast of Florida, which have included ditching, filling, and impounding. It describes the management of these environmentally sensitive habitats since World War II and approximately 40 years of effort to rehabilitate these systems and improve their management. Improvements have been accomplished via adaptive management, science-based decision making and engagement of diverse groups of resource managers and stakeholders. Interagency efforts to provide balanced management of these wetlands are discussed, and work is presented to demonstrate the outcomes from rehabilitating impoundments in the Indian River Lagoon. These strategies for management and rehabilitation should provide guidance for restoring and conserving critical ecosystem services delivered by mangrove-dominated wetlands elsewhere, including survival in the face of future environmental changes.

     

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

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

Mosquito-borne Diseases as a Consequence of Land Use Change

Human modification of the natural environment continues to create habitats in which mosquitoes, vectors of a wide variety of human and animal pathogens, thrive if unabated with an enormous potential to negatively affect public health. Historic examples of these modifications include of impoundments, dams, and irrigation systems that create havens for the mosquitoes that transmit malaria, dengue, and filariasis. Additionally, contemporary deforestation appears to be associated with the expansion of mosquito distributions and the increase in mosquito-borne disease transmission. These observations are not unique to the developing world, as urban sprawl also contributes significantly to mosquito habitats and offers a sanctuary to some vector populations. With foresight and planning, most of these systems can be appropriately managed to control vector populations and pathogen transmission. The key to disease control is developing an understanding of the contribution of human landscape modification to vector-borne pathogen transmission and how a balance may be achieved between human development, public health, and responsible land use.     

Inhibition of Malaria Infection in Transgenic Anopheline Mosquitoes Lacking Salivary Gland Cells

Malaria is an important global public health challenge, and is transmitted by anopheline mosquitoes during blood feeding. Mosquito vector control is one of the most effective methods to control malaria, and population replacement with genetically engineered mosquitoes to block its transmission is expected to become a new vector control strategy. The salivary glands are an effective target tissue for the expression of molecules that kill or inactivate malaria parasites. Moreover, salivary gland cells express a large number of molecules that facilitate blood feeding and parasite transmission to hosts. In the present study, we adapted a functional deficiency system in specific tissues by inducing cell death using the mouse Bcl-2-associated X protein (Bax) to the Asian malaria vector mosquito, Anopheles stephensi. We applied this technique to salivary gland cells, and produced a transgenic strain containing extremely low amounts of saliva. Although probing times for feeding on mice were longer in transgenic mosquitoes than in wild-type mosquitoes, transgenic mosquitoes still successfully ingested blood. Transgenic mosquitoes also exhibited a significant reduction in oocyst formation in the midgut in a rodent malaria model. These results indicate that mosquito saliva plays an important role in malaria infection in the midgut of anopheline mosquitoes. The dysfunction in the salivary glands enabled the inhibition of malaria transmission from hosts to mosquito midguts. Therefore, salivary components have potential in the development of new drugs or genetically engineered mosquitoes for malaria control.     

Impact of population age structure on Wolbachia transgene driver efficacy: ecologically complex factors and release of genetically modified mosquitoes

Wolbachia symbionts hold theoretical promise as a way to drive transgenes into insect vector populations for disease prevention. For simplicity, current models of Wolbachia dynamics and spread ignore ecologically complex factors such as the age structure of vector populations and overlapping vector generations. We developed a model including these factors to assess their impact on the process of Wolbachia spread into populations of three mosquito species (Anopheles gambiae, Aedes aegypti and Culex pipiens). Depending on the mosquito species, Wolbachia parameters, released mosquito life stage and initial age structure of the target population, the number of Wolbachia-infected mosquitoes that we predict would need to be released ranged from less than the threshold calculated by the simple model to a 10-30-fold increase. Transgenic releases into age-structured populations, which is an expectation for wild mosquitoes, will be difficult and depending on the circumstances may not be economically or logistically feasible due to the large number of infected mosquitoes that must be released. Our results support the perspective that understanding ecological factors is critical for designing transgenic vector-borne disease control strategies.     

Biosynthesis of 130-kilodalton mosquito larvicide in the cyanobacterium Agmenellum quadruplicatum PR-6

The 130-kilodalton mosquito larvicidal gene, cloned from Bacillus thuringiensis var. israelensis, was introduced into the cyanobacterium Agmenellum quadruplicatum PR-6 by plasmid transformation. Transformed cells synthesized 130-kilodalton delta-endotoxin protein and showed mosquito larvicidal activity. Results demonstrate a potential use of a cyanobacterium for biological control of mosquitoes.     

Biosynthesis of 130-kilodalton mosquito larvicide in the cyanobacterium Agmenellum quadruplicatum PR-6.

The 130-kilodalton mosquito larvicidal gene, cloned from Bacillus thuringiensis var. israelensis, was introduced into the cyanobacterium Agmenellum quadruplicatum PR-6 by plasmid transformation. Transformed cells synthesized 130-kilodalton delta-endotoxin protein and showed mosquito larvicidal activity. Results demonstrate a potential use of a cyanobacterium for biological control of mosquitoes.     

Combining two teaching techniques for young children on Aedes aegypti control: effects on entomological indices in western Mexico

A study of the effect of educating four- to six-year-old children in mosquito control was recently conducted in a city in the state of Jalisco, western Mexico. Four neighborhood districts were selected. Children attending one kindergarten in each of two experimental districts were taught mosquito control with a video from the American Mosquito Control Association (AMCA), joined to the use of the AMCA Touch Table Technique. The entomological indices monitored in the study decreased significantly (P<0.05) in houses in the experimental districts, apparently because parents acted on the comments and suggestions of the children and eliminated or monitored containers used as oviposition sites by mosquitoes. Based on these results, combining both techniques for teaching children mosquito control is a potentially useful tool for control efforts in Mexico and other places in Latin America.     

Wetlands and mosquitoes: a review

This review brings together information on mosquitoes, the diseases they transmit and the wetlands that provide habitats for the immature stages (eggs and larvae). Wetland values are mentioned, though the main literature on this does not generally overlap the mosquito issue. Mosquito management is overviewed to include: the use of larvicides, source reduction in intertidal wetlands and management in freshwater systems. There is not a great deal of information on mosquitoes and freshwater systems, except for constructed wetlands and they are considered separately. We then consider restoration mainly in the context of wetlands that have been the subject of habitat modification for mosquito control. Land use and climate change, as they affect mosquitoes and the diseases they transmit, are also reviewed, as this will affect wetlands via management activities. Finally the review addresses the critical issue of balancing health, both human and environmental, in an adaptive framework. It concludes that there is a need to ensure that both mosquito and wetland management communicate and integrate to sustain wetland and human health.