Adaptation of ELISA detection of Plasmodium falciparum and Plasmodium vivax circumsporozoite proteins in mosquitoes to a multiplex bead-based immunoassay.

BACKGROUND: Plasmodium spp. sporozoite rates in mosquitoes are used to better understand malaria transmission intensity, the relative importance of vector species and the impact of interventions. These rates are typically estimated using an enzyme-linked immunosorbent assay (ELISA) utilizing antibodies against the circumsporozoite protein of Plasmodium falciparum, Plasmodium vivax VK210 (P. vivax210) or P. vivax VK247 (P. vivax247), employing assays that were developed over three decades ago. The ELISA method requires a separate assay plate for each analyte tested and can be time consuming as well as requiring sample volumes not always available. The bead-based multiplex platform allows simultaneous measurement of multiple analytes and may improve the lower limit of detection for sporozoites. METHODS: Recombinant positive controls for P. falciparum, P. vivax210 and P. vivax247 and previously developed circumsporozoite (cs) ELISA antibodies were used to optimize conditions for the circumsporozoite multiplex bead assay (csMBA) and to determine the detection range of the csMBA. After optimizing assay conditions, known amounts of sporozoites were used to determine the lower limit of detection for the csELISA and csMBA and alternate cut-off measures were applied to demonstrate how cut-off criteria can impact lower limits of detection. Sporozoite rates from 1275 mosquitoes collected in Madagascar and 255 mosquitoes collected in Guinea were estimated and compared using the established csELISA and newly optimized csMBA. All mosquitoes were tested (initial test), and those that were positive were retested (retest). When sufficient sample volume remained, an aliquot of homogenate was boiled and retested (boiled retest), to denature any heat-unstable cross-reactive proteins. RESULTS: Following optimization of the csMBA, the lower limit of detection was 25 sporozoites per mosquito equivalent for P. falciparum, P. vivax210 and P. vivax247 whereas the lower limits of detection for csELISA were found to be 1400 sporozoites for P. falciparum, 425 for P. vivax210 and 1650 for P. vivax247. Combined sporozoite rates after re-testing of samples that initially tested positive for Madagascar mosquitoes by csELISA and csMBA were 1.4 and 10.3%, respectively, and for Guinea mosquitoes 2% by both assays. Boiling of samples followed by csMBA resulted in a decrease in the Madagascar sporozoite rate to 2.8-4.4% while the Guinea csMBA sporozoite rate remained at 2.0%. Using an alternative csMBA cut-off value of median fluorescence intensity (MFI) of 100 yielded a sporozoite rate after confirmational testing of 3.7% for Madagascar samples and 2.0% for Guinea samples. Whether using csMBA or csELISA, the following steps may help minimize false positives: specimens are appropriately stored and bisected anterior to the thorax-abdomen junction, aliquots of homogenate are boiled and retested following initial testing, and an appropriate cut-off value is determined. CONCLUSIONS: The csMBA is a cost-comparable and time saving alternative to the csELISA and may help eliminate false negatives due to a lower limit of detection, thus increasing sensitivity over the csELISA. The csMBA expands the potential analyses that can be done with a small volume of sample by allowing multiplex testing where analytes in addition to P. falciparum, P. vivax210 and P. vivax247 can be added following optimization.

Cryoprotectant toxicity and hypothermic sensitivity among Anopheles larvae.

Laboratory rearing of mosquitoes is commonly practiced by researchers studying mosquito-borne infectious diseases and vector control methods. In the absence of cryopreservation methods to stabilize unique or genetically modified strains, mosquito lines must be continuously maintained, a laborious process that risks selection effects, contamination, and genetic drift. Towards the development of a cryopreservation protocol, several commonly used cryoprotectants were systematically characterized here both individually and as cocktails. Among first instar, feeding-stage An. gambiae and An. stephensi larvae, cryoprotectant toxicity followed the order of dimethyl sulfoxide > ethylene glycol > methanol. The resulting LD50 values were used as the basis for the development of cryoprotectant cocktail solutions, where formulation optimization was streamlined using Taguchi methods of experimental design. Sensitivity to hypothermia was further evaluated to determine the feasibility of cryoprotectant loading at reduced temperatures and slow cooling approaches to cryopreservation. The information described here contributes to the knowledge base necessary to inform the development of a cryopreservation protocol for Anopheles larvae.

Physiological responses to cryoprotectant treatment in an early larval stage of the malaria mosquito, Anopheles gambiae.

The development of cryopreservation protocols for Anopheles gambiae could significantly improve research and control efforts. Cryopreservation of any An. gambiae life stage has yet to be successful. The unique properties of embryos have proven to be resistant to any practical cryoprotectant loading. Therefore, we have chosen to investigate early non-feeding first instar larvae as a potential life stage for cryopreservation. In order to determine an appropriate cryoprotective compound, larvae were treated with progressively better glass-forming cryoprotective mixtures. Toxicity evaluation in combination with calorimetry-based water content and supercooling point depression assessments were used to determine the cryoprotectants that could be used for cryostorage of viable larvae. Approximately 35-75% of the larvae were viable after reasonably high osmotic and biochemical challenge. This study provides ample evidence for an active osmoregulatory response in the Anopheles larvae to counter the permeation of cryoprotectants from the surrounding medium. The data show a strong correlation between the larval mortality and water content, indicating an osmoregulatory crisis in the larva due to certain cryoprotectants such as the higher concentrations of ethane diol (ED). The observations also indicate that the ability of the larvae to regulate permeation and water balance ceases at or within 20 min of cryoprotectant exposure, but this is strongly influenced by the treatment temperature. Among the compound cryoprotectants tested, 25% ED + 10% dimethyl sulfoxide (DMSO) and 40% ED + 0.5 M trehalose seem to present a compromise between viability, larval water content, supercooling point depression, and glass forming abilities.

Fluorescent markers rhodamine B and uranine for Anopheles gambiae adults and matings.

BACKGROUND: Marking mosquitoes is vital for mark-release-recapture and many laboratory studies, but their small size precludes the use of methods that are available for larger animals such as unique identifier tags and radio devices. Fluorescent dust is the most commonly used method to distinguish released individuals from the wild population. Numerous colours and combinations can be used, however, dust sometimes affects longevity and behaviour so alternatives that do not have these effects would contribute substantially. Rhodamine B has previously been demonstrated to be useful for marking adult Aedes aegypti males when added to the sugar meal. Unlike dust, this also marked the seminal fluid making it possible to detect matings by marked males in the spermatheca of females. Here, marking of Anopheles gambiae sensu stricto with rhodamine B and uranine was performed to estimate their potential contribution. METHODS: Two fluorescent markers, rhodamine B and uranine, were dissolved in sugar water and fed to adult An. gambiae. Concentrations that are useful for marking individuals and seminal fluid were determined. The effects on adult longevity, the durability of the marking and detection of the marker in mated females was determined. Male mating competitiveness was also evaluated. RESULTS: Rhodamine B marking in adults is detectable for at least 3 weeks, however uranine marking declines with time and at low doses can be confused with auto-fluorescence. Both can be used for marking seminal fluid which can be detected in females mated by marked males, but, again, at low concentrations uranine-marking is more easily confused with the natural fluorescence of seminal fluid. Neither dye affected mating competitiveness. CONCLUSIONS: Both markers tested could be useful for field and laboratory studies. Their use has substantial potential to contribute to a greater understanding of the bio-ecology of this important malaria vector. Rhodamine B has the advantage that it appears to be permanent and is less easily confused with auto-fluorescence. The primary limitation of both methods is that sugar feeding is necessary for marking and adults must be held for at least 2 nights to ensure all individuals are marked whereas dusts provide immediate and thorough marking.

Malaria vector research and control in Haiti: a systematic review.

BACKGROUND: Haiti has a set a target of eliminating malaria by 2020. However, information on malaria vector research in Haiti is not well known. This paper presents results from a systematic review of the literature on malaria vector research, bionomics and control in Haiti. METHODS: A systematic search of literature published in French, Spanish and English languages was conducted in 2015 using Pubmed (MEDLINE), Google Scholar, EMBASE, JSTOR WHOLIS and Web of Science databases as well other grey literature sources such as USAID, and PAHO. The following search terms were used: malaria, Haiti, Anopheles, and vector control. RESULTS: A total of 132 references were identified with 40 high quality references deemed relevant and included in this review. Six references dealt with mosquito distribution, seven with larval mosquito ecology, 16 with adult mosquito ecology, three with entomological indicators of malaria transmission, eight with insecticide resistance, one with sero-epidemiology and 16 with vector control. In the last 15 years (2000-2015), there have only been four published papers and three-scientific meeting abstracts on entomology for malaria in Haiti. Overall, the general literature on malaria vector research in Haiti is limited and dated. DISCUSSION: Entomological information generated from past studies in Haiti will contribute to the development of strategies to achieve malaria elimination on Hispaniola. However it is of paramount importance that malaria vector research in Haiti is updated to inform decision-making for vector control strategies in support of malaria elimination.

Anopheles Pupa Collection and Sex Identification.

For most Anopheles species, larval-pupal metamorphosis commences ∼1 wk after egg hatching. However, depending on the amount of food provided, H2O temperature, and larval density, the pupation process can be accelerated or delayed. Synchronous pupation is difficult to accomplish consistently, and, thus, pupae need to be separated from larvae daily. Adult emergence will take place 24-48 h after pupation. Most adults will eclose before the next morning (light cycle) in many species. Here, we provide information on some methods available to collect pupae and to sort pupae by sex. Notably, pupa collection and sorting are some of the most time-consuming procedures of the overall mosquito rearing process. Some methods mentioned here attempt to help reduce work effort and time required.

Anopheles Egg Collection, Disinfection, and Hatching.

Gravid (i.e., with fully developed eggs), mated Anopheles females typically lay their eggs directly on water ∼48-72 h after a blood meal. Unlike some other mosquito species, Anopheles eggs cannot be desiccated and stored for long durations, and, hence, colonies must be reared continuously. In this protocol, we discuss methods for egg collection, including individual and en masse oviposition; egg disinfection to avoid the transmission of infectious agents to the next generation; and egg hatching for colony maintenance or experimentation. We also include optional methods for estimating life history traits such as fecundity, fertility, and larval mortality rates from egg counts.

Considerations for Rearing and Maintaining Anopheles in the Laboratory.

Anopheles mosquitoes can transmit several human pathogens, including viruses such as o'nyong-nyong and parasites including Plasmodium spp. and Wuchereria spp., which cause malaria and filariasis, respectively. Rearing Anopheles species of medical importance under laboratory conditions allows researchers to carry out experiments to better understand their genetics, physiology, and behavior. However, Anopheles species vary in how easily they can be reared in the laboratory, and some species have been difficult to colonize. Once established, members of the important African Anopheles gambiae complex thrive following a standard protocol and are predictable in growth and development rates. Here, we provide useful basic information and guidance to successfully maintain colonies of A. gambiae and other species of Anopheles in a laboratory setting. We also provide an example of a 3-wk rearing schedule that produces sufficient numbers of mosquitoes while minimizing the work required during weekends. In the accompanying protocols, we detail efficient methods and techniques suitable for several species of this genus at the egg, larva, pupae, and adult stages; however, it will be necessary for researchers to adjust methods as needed based on site-specific rearing observations of their particular strains.

Anopheles Adult Anesthesia, Feeding, and Sex Separation.

The adult stage is the only nonaquatic stage of the Anopheles mosquito. Both male and female Anopheles mosquitoes require access to a source of sugar to survive. In the insectary, a temperature of ∼27°C and 80% relative humidity and a cycle of 12 h light:12 h dark light, ideally with a sunrise and sunset period, are necessary minimum conditions to mimic their natural environment. Laboratory-reared Anopheles can survive for over a month; however, decreased activity and increased mortality may be observed ∼2 wk postemergence depending on the species and health of the colony. Details on how to maintain adults Anopheles are discussed here. Information and considerations on blood and sugar feeding are described. This protocol also provides instructions on how to differentiate male and female adult mosquitoes.

Anopheles Larval Rearing.

Mosquito larvae are aquatic and go through four development stages (larval instars L1-L4) before pupation. Species vary in the duration of larval development, and a variety of external factors affect the development rate (e.g., water temperature, food type, and larval density), which are discussed more thoroughly elsewhere. Here, we detail how to rear Anopheles larvae. This protocol describes appropriate distribution of larvae into rearing pans, feeding of larvae, cleaning of pans, and care until pupation.

Juvenile Hormone as a contributing factor in establishing midgut microbiota for fecundity and fitness enhancement in adult female Aedes aegypti.

Understanding the factors influencing mosquitoes' fecundity and longevity is important for designing better and more sustainable vector control strategies, as these parameters can impact their vectorial capacity. Here, we address how mating affects midgut growth in Aedes aegypti, what role Juvenile Hormone (JH) plays in this process, and how it impacts the mosquito's immune response and microbiota. Our findings reveal that mating and JH induce midgut growth. Additionally, the establishment of a native bacterial population in the midgut due to JH-dependent suppression of the immune response has important reproductive outcomes. Specific downregulation of AMPs with an increase in bacteria abundance in the gut results in increased egg counts and longer lifespans. Overall, these findings provide evidence of a cross-talk between JH response, gut epithelial tissue, cell cycle regulation, and the mechanisms governing the trade-offs between nutrition, immunity, and reproduction at the cellular level in the mosquito gut.

Identification of bloodmeal sources and Trypanosoma cruzi infection in triatomine bugs (Hemiptera: Reduviidae) from residential settings in Texas, the United States.

The host-vector-parasite interactions in Chagas disease peridomestic transmission cycles in the United States are not yet well understood. Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) infection prevalence and bloodmeal sources were determined for adult and immature triatomine (Hemiptera: Reduviidae) specimens collected from residential settings in central Texas. Sequenced cytochrome b DNA segments obtained from triatomine digestive tract identified nine vertebrate hosts and one invertebrate host in four triatomine species (Triatoma gerstaeckeri, Triatoma indictiva, Triatoma protracta, and Triatoma sanguisuga). The broad range of wild and domestic host species detected in triatomine specimens collected from residential sites indicates high host diversity and potential movement between the sylvatic and peridomestic settings. Domestic dogs appear to be key in the maintenance of the peridomestic transmission cycle as both a blood host for the triatomine vectors and a potential reservoir for the parasite. The high rate of T. cruzi infection among triatomine specimens that were collected from inside houses, outside houses, and dog kennels (69, 81, and 82%, respectively) suggests a current risk for Chagas disease vector-borne transmission for humans and domestic animals in residential settings in Texas because of overlap with the sylvatic cycle.

Assessment of Bio-Based Materials as a Sustainable and Scalable Alternative for Detection of Plasmodium spp. (Haemospororida: Plasmodiidae) Sporozoites in Field Deployable Testing.

Malaria is responsible for over 435,000 deaths annually, mostly occurring in sub-Saharan Africa. Detecting Plasmodium spp. sporozoites (spzs) in the salivary glands of Anopheles (Diptera: Culicidae) vectors with circumsporozoite enzyme-linked immunosorbent assay (csELISA) is an important surveillance method. However, current technological advances are intellectual property and often require of distribution and highly trained users. The transition into paper-based rapid plataforms would allow for decentralization of survillance, especially in areas where it was virtually eliminated. The addition of bio-based materials have shown the potential to improve binding of target antigens, while being widely available. Here, we evaluate the use of chitosan and cellulose nanocrystals (CNC) as antibody carriers and substrate coatings on 96-well plates and on wax hydrophobized paper plates for the detection of Plasmodium falciparum (Pf), P. vivax VK210 (Pv210), and P. vivax VK247 (Pv247). To further improve the user-friendliness of the paper plates a quantitative photograph image-based color analysis was done. Interactions between the materials and the assay antibodies were studied by quartz crystal microbalance with dissipation monitoring (QCM-D). Overall, the addition of chitosan increased the interaction with antibodies and enhanced signaling in all tests. This work demonstrated that the adaptation of a PcsELISA shows potential as a cost-effective alternative assay platform easily adaptable in deployable testing sites that also showed reduction in reagent volumes by 80% and assay run time by seventh. While dipstick assays were previously developed, paper-based assays are a cost-effective and field-deployable alternative, reducing volumes of reagents that could be used in malaria control and elimination settings.

Delivery of Double-Stranded RNAs (dsRNAs) Produced by Escherichia coli HT115(DE3) for Nontransgenic RNAi-Based Insect Pest Management.

RNA interference (RNAi) is a powerful mechanism that can be exploited not only for physiology research but also for designing insect pest management approaches. Some insects cause harm by vectoring diseases dangerous to humans, livestock, or plants or by damaging crops. For at least a decade now, different insect control strategies that induce RNAi by delivering double stranded RNA (dsRNA) targeting essential genes have been proposed. Here, we focus on nontransgenic RNAi-based approaches that use oral delivery of dsRNA through feeding of inactivated bacteria to produce RNAi in disease vectors and in a crop pest. This potential pest management method could be easily adapted to target different genes or similar organisms.

Surviving the Journey: Comparisons of Temperature-Stabilizing Materials for Living Arthropod Shipments.

Shipments of living mosquitoes and other arthropods require temperatures that are within a range that is compatible with their health and survival. In addition to express shipping and insulated containers, shipments often include materials that either store heat (i.e., have thermal mass) or otherwise stabilize the temperature. In this paper, we present the results of comparisons of thermal mass and phase change materials to stabilize the temperature under various conditions. We compared a rigid foam refrigerant and a number of phase change materials to bubble wrap for their capacity to moderate temperature change by measuring the temperatures in standard uninsulated shipping containers during exposure to high (37°C), cold (4°C), and freezing (-20°C) temperatures. We make recommendations for shipments depending on the ambient conditions that are expected to be experienced en route.

Delimiting cryptic morphological variation among human malaria vector species using convolutional neural networks.

Deep learning is a powerful approach for distinguishing classes of images, and there is a growing interest in applying these methods to delimit species, particularly in the identification of mosquito vectors. Visual identification of mosquito species is the foundation of mosquito-borne disease surveillance and management, but can be hindered by cryptic morphological variation in mosquito vector species complexes such as the malaria-transmitting Anopheles gambiae complex. We sought to apply Convolutional Neural Networks (CNNs) to images of mosquitoes as a proof-of-concept to determine the feasibility of automatic classification of mosquito sex, genus, species, and strains using whole-body, 2D images of mosquitoes. We introduce a library of 1, 709 images of adult mosquitoes collected from 16 colonies of mosquito vector species and strains originating from five geographic regions, with 4 cryptic species not readily distinguishable morphologically even by trained medical entomologists. We present a methodology for image processing, data augmentation, and training and validation of a CNN. Our best CNN configuration achieved high prediction accuracies of 96.96% for species identification and 98.48% for sex. Our results demonstrate that CNNs can delimit species with cryptic morphological variation, 2 strains of a single species, and specimens from a single colony stored using two different methods. We present visualizations of the CNN feature space and predictions for interpretation of our results, and we further discuss applications of our findings for future applications in malaria mosquito surveillance.

Trials of the Automated Particle Counter for laboratory rearing of mosquito larvae.

As a means of obtaining reproducible and accurate numbers of larvae for laboratory rearing, we tested a large-particle flow-cytometer type device called the 'Automated Particle Counter' (APC). The APC is a gravity-fed, self-contained unit that detects changes in light intensity caused by larvae passing the detector in a water stream and controls dispensing by stopping the flow when the desired number has been reached. We determined the accuracy (number dispensed compared to the target value) and precision (distribution of number dispensed) of dispensing at a variety of counting sensitivity thresholds and larva throughput rates (larvae per second) using < 1-day old Anopheles gambiae and Aedes aegypti larvae. All measures were made using an APC algorithm called the 'Smoothed Z-Score' which allows the user to define how many standard deviations (Z scores) from the baseline light intensity a particle's absorbance must exceed to register a count. We dispensed a target number of 100 An. gambiae larvae using Z scores from 2.5-8 and observed no difference among them in the numbers dispensed for scores from 2.5-6, however, scores of 7 and 8 under-counted (over-dispensed) larvae. Using a Z score ≤ 6, we determined the effect of throughput rate on the accuracy of the device to dispense An. gambiae larvae. For rates ≤ 98 larvae per second, the accuracy of dispensing a target of 100 larvae was - 2.29% ± 0.72 (95% CI of the mean) with a mode of 99 (49 of 348 samples). When using a Z score of 3.5 and rates ≤ 100 larvae per second, the accuracy of dispensing a target of 100 Ae. aegypti was - 2.43% ± 1.26 (95% CI of the mean) with a mode of 100 (6 of 42 samples). No effect on survival was observed on the number of An. gambiae first stage larvae that reached adulthood as a function of dispensing.

Pragmatic selection of larval mosquito diets for insectary rearing of Anopheles gambiae and Aedes aegypti.

Larval mosquitoes are aquatic omnivorous scavengers which scrape food from submerged surfaces and collect suspended food particles with their mouth brushes. The composition of diets that have been used in insectaries varies widely though necessarily provides sufficient nutrition to allow colonies to be maintained. Issues such as cost, availability and experience influence which diet is selected. One component of larval diets, essential fatty acids, appears to be necessary for normal flight though deficiencies may not be evident in laboratory cages and are likely more important when mosquitoes are reared for release into the field in e.g. mark-release-recapture and genetic control activities. In this study, four diets were compared for rearing Anopheles gambiae and Aedes aegypti, all of which provide these essential fatty acids. Two diets were custom formulations specifically designed for mosquitoes (Damiens) and two were commercially available fish foods: Doctors Foster and Smith Koi Staple Diet and TetraMin Plus Flakes. Development rate, survival, dry weight and adult longevity of mosquitoes reared with these four diets were measured. The method of presentation of one diet, Koi pellets, was additionally fed in two forms, pellets or a slurry, to determine any effect of food presentation on survival and development rate. While various criteria might be selected to choose 'the best' food, the readily-available Koi pellets resulted in development rates and adult longevity equal to the other diets, high survival to the adult stage and, additionally, this is available at low cost.

An Atypical Case of Autochthonous Cutaneous Leishmaniasis Associated with Naturally Infected Phlebotomine Sand Flies in Texas, United States.

In the United States, phlebotomine sand flies carrying Leishmania (Leishmania) mexicana are endemic along the southern border. However, relatively little is known about the enzootic and zoonotic transmission of L. (L.) mexicana within the United States, and autochthonous cases of the consequent disease are rarely reported. We investigated an atypical case of cutaneous leishmaniasis (CL) caused by L. (L.) mexicana in a patient from central Texas which did not respond to a typical antileishmanial chemotherapy. We also investigated sand fly vectors around the patient's residence. PCR followed by DNA sequencing was used for determination of Leishmania spp., sand fly species, and host blood meal source. The L. (L.) mexicana genotype from the patient was identical to one found in a positive sand fly. Moreover, this genotype presented the same single-nucleotide polymorphisms as other historical CL cases acquired in Texas over the last 10 years, but distinct from those originating in Mexico and Central America. Three sand fly species were identified among the samples analyzed (n = 194), the majority of which were Lutzomyia (Dampfomyia) anthophora (n = 190), of which four specimens tested positive for Leishmania and two blood-fed specimens showed the presence of a human blood meal. This study highlights the complexity of clinical management of CL in a setting where the disease is infrequently encountered. The detection of human blood in Lu. (D.) anthophora is the first documentation of anthropophagy in this species. This is the first report of wild-caught, naturally infected sand flies found in association with an autochthonous case of human leishmaniasis and the specific strain of Leishmania (Leishmania) mexicana in the United States.

Downregulation of female doublesex expression by oral-mediated RNA interference reduces number and fitness of Anopheles gambiae adult females.

BACKGROUND: Mosquito-borne diseases affect millions worldwide, with malaria alone killing over 400 thousand people per year and affecting hundreds of millions. To date, the best strategy to prevent the disease remains insecticide-based mosquito control. However, insecticide resistance as well as economic and social factors reduce the effectiveness of the current methodologies. Alternative control technologies are in development, including genetic control such as the sterile insect technique (SIT). The SIT is a pivotal tool in integrated agricultural pest management and could be used to improve malaria vector control. To apply the SIT and most other newer technologies against disease transmitting mosquitoes, it is essential that releases are composed of males with minimal female contamination. The removal of females is an essential requirement because released females can themselves contribute towards nuisance biting and disease transmission. Thus, females need to be eliminated from the cohorts prior to release. Manual separation of Anopheles gambiae pupae or adult mosquitoes based on morphology is time consuming, is not feasible on a large scale and has limited the implementation of the SIT technique. The doublesex (dsx) gene is one of the effector switches of sex determination in the process of sex differentiation in insects. Both males and females have specific splicing variants that are expressed across the different life stages. Using RNA interference (RNAi) to reduce expression of the female specific (dsxF) variant of this gene has proven to have detrimental effects to the females in other mosquito species, such as Aedes aegypti. We tested oral RNAi on dsx (AgdsxF) in An. gambiae. METHODS: We studied the expression pattern of the dsx gene in the An. gambiae G3 strain. We knocked down AgdsxF expression in larvae through oral delivery of double stranded RNA (dsRNA) produced by bacteria and observed its effects in adults. RESULTS: Our results show that feeding of AgdsxF dsRNA can effectively reduce (> 66%) the mRNA of female dsx transcript and that there is a concomitant reduction in the number of female larvae that achieve adulthood. Control groups produced 52% (± 3.9% SE) of adult males and 48% (± 4.0% SE) females, while AgdsxF dsRNA treated groups had 72.1% (± 4.0% SE) males vs 27.8% females (± 3.3% SE). In addition, the female adults produce fewer progeny, 37.1% (± 8.2% SE) less than the controls. The knockdown was sex-specific and had no impact on total numbers of viable male adults, in the male dsx transcripts or male fitness parameters such as longevity or body size. CONCLUSIONS: These findings indicate that RNAi could be used to improve novel mosquito control strategies that require efficient sex separation and male-only release of An. gambiae by targeting sex determination genes such as AgdsxF. The advantages of using RNAi in a controlled setting for mosquito rearing are numerous, as the dose and time of exposure are controlled, and the possibility of off-target effects and the waste of female production would be significantly reduced.