Mosquito Control Strategies Research Articles

Studies of the Biological and Physicochemical Contents of Rock Pool Breeding Habitats of Mosquitoes: A Case Study of the University of Abuja Main Campus

Entomological surveys were conducted to determine the biological and physicochemical parameters influencing mosquito breeding in rock pools in University of Abuja Main Campus. A total of 4 study area were sampled for mosquito larvae using soup ladle dipper (0.105L). Three different species of mosquitoes where found during the survey which is Ae.aegypyi, Ae.vittatus, Cx. Ingrami. Ae.aegypti was found abundant in the four study sites. Biota and physicochemical (depth, temperature, pH, total dissolve solid, total suspended solid, turbidity, hardness, dissolve oxygen, biochemical oxygen demand, nitrate and alkalinity) parameters of the pools were determined. ANOVA showed that the abundance of mosquito larvae differed significantly with pH of each study area (p<0.05). The abundance of mosquito larvae did not differ significantly with depth, surface area, total suspended solid, hardness and turbidity of the rock pools (p>0.05). Epidemiologically, the mosquito species encountered are potential vectors of human and animal diseases, hence rock pools should be inspected to incriminate vectors and be incorporated in mosquito control strategies. Keywords: Mosquitoes: Rock Pool Habitat: Temperature: PH; Ae.aegypyi: Ae.vittatus: Cx Ingrami

Eco-Friendly Mosquito-Control Strategies: Advantages and Disadvantages

Eco-Friendly Mosquito-Control Strategies: Advantages and Disadvantages

Plant-Based Bioinsecticides for Mosquito Control: Impact on Insecticide Resistance and Disease Transmission.

Simple SummaryMosquito-borne diseases cause millions of deaths each year. There has been an increase in the use of insecticides to combat disease transmission caused by mosquitoes. Synthetic insecticides have been effectively used to protect humans from mosquito bites through insecticide-treated mosquito nets, fabrics, and indoor sprays. Despite the considerable progress made in reducing mosquito borne diseases, extensive usage of insecticides has caused serious health problems to humans and animals, insecticide resistance or insensitivity in mosquitoes, and environmental damage. A success in the fight with mosquito disease transmission can only be accomplished by adequate and effective implementation of insecticide resistance monitoring and management programs globally. For this purpose, extensive research focuses on exploring insecticide resistance mechanisms in mosquitoes and how they get resistant to chemical applications over time. The search also focuses on novel compounds that are more effective, safer, and eco-friendly for improved management of mosquito vectors. In this review, we provide the current literature on the synthetic insecticides and how mosquitoes develop resistance to them, with further emphasis on bioinsecticides that could replace conventional synthetic insecticides. In this context, plant-based compounds are explained in detail with their potential applications to control mosquitoes.The use of synthetic insecticides has been a solution to reduce mosquito-borne disease transmission for decades. Currently, no single intervention is sufficient to reduce the global disease burden caused by mosquitoes. Problems associated with extensive usage of synthetic compounds have increased substantially which makes mosquito-borne disease elimination and prevention more difficult over the years. Thus, it is crucial that much safer and effective mosquito control strategies are developed. Natural compounds from plants have been efficiently used to fight insect pests for a long time. Plant-based bioinsecticides are now considered a much safer and less toxic alternative to synthetic compounds. Here, we discuss candidate plant-based compounds that show larvicidal, adulticidal, and repellent properties. Our discussion also includes their mode of action and potential impact in mosquito disease transmission and circumvention of resistance. This review improves our knowledge on plant-based bioinsecticides and the potential for the development of state-of-the-art mosquito control strategies.

A Model of Optimal Interval for Anti-Mosquito Campaign Based on Stochastic Process

Mosquito control is very important, in particular, for tropical countries. The purpose of mosquito control is to decrease the number of mosquitos such that the mosquitos transmitted diseases can be reduced. However, mosquito control can be costly, thus there is a trade-off between the cost for mosquito control and the cost for mosquitos transmitted diseases. A model is proposed based on renewal theory in this paper to describe the process of mosquitos’ growth, with consideration of the mosquitos transmitted diseases growth process and the corresponding diseases treatment cost. Through this model, the total mosquitos control cost of different strategies can be estimated. The optimal mosquito control strategy that minimizes the expected total cost is studied. A numerical example and corresponding sensitivity analyses are proposed to illustrate the applications.

Predicting dengue incidence leveraging internet-based data sources. A case study in 20 cities in Brazil.

The dengue virus affects millions of people every year worldwide, causing large epidemic outbreaks that disrupt people’s lives and severely strain healthcare systems. In the absence of a reliable vaccine against dengue or an effective treatment to manage the illness in humans, most efforts to combat dengue infections have focused on preventing its vectors, mainly the Aedes aegypti mosquito, from flourishing across the world. These mosquito-control strategies need reliable disease activity surveillance systems to be deployed. Despite significant efforts to estimate dengue incidence using a variety of data sources and methods, little work has been done to understand the relative contribution of the different data sources to improved prediction. Additionally, scholarship on the topic had initially focused on prediction systems at the national- and state-levels, and much remains to be done at the finer spatial resolutions at which health policy interventions often occur. We develop a methodological framework to assess and compare dengue incidence estimates at the city level, and evaluate the performance of a collection of models on 20 different cities in Brazil. The data sources we use towards this end are weekly incidence counts from prior years (seasonal autoregressive terms), weekly-aggregated weather variables, and real-time internet search data. We find that both random forest-based models and LASSO regression-based models effectively leverage these multiple data sources to produce accurate predictions, and that while the performance between them is comparable on average, the former method produces fewer extreme outliers, and can thus be considered more robust. For real-time predictions that assume long delays (6–8 weeks) in the availability of epidemiological data, we find that real-time internet search data are the strongest predictors of dengue incidence, whereas for predictions that assume short delays (1–3 weeks), in which the error rate is halved (as measured by relative RMSE), short-term and seasonal autocorrelation are the dominant predictors. Despite the difficulties inherent to city-level prediction, our framework achieves meaningful and actionable estimates across cities with different demographic, geographic and epidemic characteristics.

Evaluation of larval toxicity, mode of action and chemical composition of citrus essential oils against Anopheles stephensi and Culex quinquefasciatus

Mosquitoes are the most significant insect vectors and are known for their community health prominences, which causes economic and social disturbances. Almost currently implemented strategies for mosquito control are based on synthetic insecticides, which have several toxic exposures to humans, animals and other non-targets as well as multiplied various environmental pollution. Hence, the mosquito larvicidal impact of essential oils of Citrus limetta (Musambi), C. limon (Lemon) and C. reticulata (Kinnow) was evaluated. The essential oils obtained through hydrodistillation and further characterized by phytochemical and GC-MS examinations. The larvicidal bioassay was performed according to the standard protocol of WHO, 2005 with slide modifications. The results indicated that alkaloids, terpenes, terpenoids, anthraquinones, flavonoids and tannins were present in the leaves and peels. d ‒Limonene, β‒Terpinene, Linalool, Citral, α‒Pinene β‒Caryophyllene, Terpinen‒4‒ol, γ‒Terpinene, 3‒Carene, Sylvestrene, β‒Ocimene, β‒Thujene, Citronellal, Sabinene and β‒Pinene were determined as major phytocompounds. Moreover, C. limetta was found as the most potent larvicide. The essential oil of leaves having LC 50 and LC 90 values 23.77 ± 3.45 and 81.07 ± 15.24 ppm and 35.12 ± 3.55 and 81.30 ± 10.79 ppm and in the case of peels 16.31 ± 3.50 and 77.60 ± 18.17 ppm and 29.20 ± 3.11 and 68.62 ± 9.03 ppm against Anopheles stephensi and Culex quinquefasciatus after 24 h, respectively. Therefore, they can be used as environmental friendly and cheap botanical mosquitocides. • Larvicidal efficacy of essential oils isolated from Citrus leaves and peels against significant mosquito vectors. • Citrus plants selected are economically and widely cultivated species and are waste products of juice industries. • Phytochemical and GC-MS analysis were performed to show the presence of phytocompounds. • Essential oils may have ability to cross the cell membrane of target organism as they have higher LogP values. • Essential oils are biodegradable, eco-friendly and cost effective botanicals of larvicidal nature.

A Review on Mosquitocidal Activity of the Genus Solanum

As a vector, mosquitoes are responsible for transmitting deadly diseases such as Chikungunya fever, filariasis, encephalitis, West Nile Virus infection, malaria, yellow fever, dengue fever, etc. To combat this problem, various techniques and strategies had been adopted to control the mosquito population. An alternative mosquito control strategy was available from ancient times that is the application of active toxic agents from plant extracts. This preference has several advantages over the consistent application of synthetic insecticides which cause resistance in vector species, harmful effects on environment and non-target organisms, including human health. From ancient times, plants have been used to control the vector mosquitoes, and still now, in many parts of the world, many researchers are looking for plant substances to kill the mosquitoes or cause repellency in mosquitoes. The phytochemicals that originate from the plant showed various activities such as larval mortality, disrupt insect growth, and act as a repellent and also effect as an ovipositional attractant/deterrent. Several plant species have been stated so far possessing mosquitocidal activities. The present review discussed the larvicidal activities of different solvent extracts (viz. hexane, petroleum ether, chloroform, ethyl acetate, acetone, and methanol) of thirteen species of Genus Solanum. Different plant parts of various species such as the leaf, berry, flower, rhizome, bulb, stem and root bark, whole plant, and essential oil demonstrated for significant larvicidal activities against different mosquito vectors viz., Anopheles stephensi, Aedes aegypti, Culex quinquefasciatus, Anopheles subpictus, Anopheles culicifacies species A, Anopheles culicifacies species C, Culex vishnui group and Anopheles labranchiae. This review may open the opportunity for further explorations of the efficacy of larvicidal properties of another species under Genus Solanum for their natural product.

Silencing of Aedes aegypti (Diptera: Culicidae) Doublesex Gene (Dsx) Using iRNAs by Oral Delivery

The Aedes aegypti (Linnaeus 1762) mosquito is the most important vector transmitting dengue virus and other pathogens in Latin America. There are several control programs, many of which are ineffective, and therefore, new control alternatives need to be developed. Small interference RNAs (dsiRNA) are mediators of the interference of gene expression. Silencing RNA is a very conserved mechanism in nature in which small double-stranded siRNA (dsiRNA) regulates gene translation. The aim of this study was to use antisense RNA (dsiRNA and siRNA) by oral administration in stage-I mosquito larvae and evaluate the effect of inhibition of the translation of exon 5 of gene DSX. The exon is removed specifically in males (alternative splicing in exon 5 encodes a protein version of females in dipteran species). The dsiRNA molecule had greater impact on individuals treated, obtaining 25.45% of emerged females, in contrast to the siRNA molecule that had 35.80%, compared with the check in which the emergence ratio was 1:1. This might have been due to the chemical structure of the molecule, because dsiRNA is folded on itself, providing greater stability, compared to single-chain siRNA. Silencing with iRNA of exon 5 in the DSX gene produced changes in sexual differentiation of Ae. aegypti, which could lead to a new mosquito control strategy.

Mapping the spatial distribution of the dengue vector Aedes aegypti and predicting its abundance in northeastern Thailand using machine-learning approach

BackgroundMapping the spatial distribution of the dengue vector Aedes (Ae.) aegypti and accurately predicting its abundance are crucial for designing effective vector control strategies and early warning tools for dengue epidemic prevention. Socio-ecological and landscape factors influence Ae. aegypti abundance. Therefore, we aimed to map the spatial distribution of female adult Ae. aegypti and predict its abundance in northeastern Thailand based on socioeconomic, climate change, and dengue knowledge, attitude and practices (KAP) and/or landscape factors using machine learning (ML)-based system. MethodA total of 1066 females adult Ae. aegypti were collected from four villages in northeastern Thailand during January–December 2019. Information on household socioeconomics, KAP regarding climate change and dengue, and satellite-based landscape data were also acquired. Geographic information systems (GIS) were used to map the household-based spatial distribution of female adult Ae. aegypti abundance (high/low). Five popular supervised learning models, logistic regression (LR), support vector machine (SVM), k-nearest neighbor (kNN), artificial neural network (ANN), and random forest (RF), were used to predict females adult Ae. aegypti abundance (high/low). The predictive accuracy of each modeling technique was calculated and evaluated. Important variables for predicting female adult Ae. aegypti abundance were also identified using the best-fitted model. ResultsUrban areas had higher abundance of female adult Ae. aegypti compared to rural areas. Overall, study respondents in both urban and rural areas had inadequate KAP regarding climate change and dengue. The average landscape factors per household in urban areas were rice crop (47.4%), natural tree cover (17.8%), built-up area (13.2%), permanent wetlands (21.2%), and rubber plantation (0%), and the corresponding figures for rural areas were 12.1, 2.0, 38.7, 40.1 and 0.1% respectively. Among all assessed models, RF showed the best prediction performance (socioeconomics: area under curve, AUC = 0.93, classification accuracy, CA = 0.86, F1 score = 0.85; KAP: AUC = 0.95, CA = 0.92, F1 = 0.90; landscape: AUC = 0.96, CA = 0.89, F1 = 0.87) for female adult Ae. aegypti abundance. The combined influences of all factors further improved the predictive accuracy in RF model (socioeconomics + KAP + landscape: AUC = 0.99, CA = 0.96 and F1 = 0.95). Dengue prevention practices were shown to be the most important predictor in the RF model for female adult Ae. aegypti abundance in northeastern Thailand. ConclusionThe RF model is more suitable for the prediction of Ae. aegypti abundance in northeastern Thailand. Our study exemplifies that the application of GIS and machine learning systems has significant potential for understanding the spatial distribution of dengue vectors and predicting its abundance. The study findings might help optimize vector control strategies, future mosquito suppression, prediction and control strategies of epidemic arboviral diseases (dengue, chikungunya, and Zika). Such strategies can be incorporated into One Health approaches applying transdisciplinary approaches considering human-vector and agro-environmental interrelationships.

The essential oil of Schinus terebinthifolius and its nanoemulsion and isolated monoterpenes: investigation of their activity against Culex pipiens with insights into the adverse effects on non-target organisms.

The house mosquito, Culex pipiens L. is a harmful species, widespread in urban areas, and considered the primary enzootic vector of West Nile arbovirus. Widespread insecticide resistance in mosquito populations and the environmental risks and toxicity hazards of chemical pesticides make insecticides an inadequate mosquito control strategy. Seeking ecofriendly tools for mosquito control tools has become necessary. Essential oil (EO) was hydrodistilled from the fruits of Brazilian pepper, Schinus terebinthifolius Raddi and analyzed using gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. An oil-in-water nanoemulsion (particle size 41.3nm) was developed and characterized from EO using a green low-energy approach. EO, its nanoemulsion and monoterpenes showed mosquitocidal, repellent and acetylcholinesterase inhibitory activities against Cx. pipiens. A nanoemulsion concentration of 30 μl L-1 caused 100% larval mortality after 24 h of exposure, whereas EO, d-limonene and α-phellandrene at 60 μl L-1 caused 100%, 92.4% and 88.2% larval mortality, respectively. The concentration that killed 50% of organisms (LC50 ) for larvae after 24 h ranged between 6.8 and 40.6μl L-1 . Upon fumigation, 15.0μl L-1 of nanoemulsion killed 94.5% of adults after 24 h of exposure. LC50 values against adults ranged between 5.3 and 31.2μl L-1 . EO products exhibited repellence activity at concentrations between 0.5 and 4.0μl cm-2 . Test materials effectively inhibited the acetylcholinesterase activity of mosquito and were safe toward the non-target organisms Gambusia affinis and Eisenia fetida. There is a potential for using S. terebinthifolius EO, its nanoemulsion and monoterpenes as ecofriendly natural mosquitocides.

Urbanization favors the proliferation of Aedesaegypti and Culexquinquefasciatus in urban areas of Miami-Dade County, Florida

Urbanization processes are increasing globally. Anthropogenic alterations in the environment have profound effects on biodiversity. Decreased biodiversity due to biotic homogenization processes as a consequence of urbanization often result in increased levels of mosquito vector species and vector-borne pathogen transmission. Understanding how anthropogenic alterations in the environment will affect the abundance, richness, and composition of vector mosquito species is crucial for the implementation of effective and targeted mosquito control strategies. We hypothesized that anthropogenic alterations in the environment are responsible for increasing the abundance of mosquito species that are adapted to urban environments such as Aedesaegypti and Culexquinquefasciatus. Therefore, our objective was to survey mosquito relative abundance, richness, and community composition in Miami-Dade County, Florida, in areas with different levels of urbanization. We selected 24 areas, 16 remote areas comprised of natural and rural areas, and 8 urban areas comprised of residential and touristic areas in Miami-Dade County, Florida. Mosquitoes were collected weekly in each area for 24 h for 5 consecutive weeks from August to October 2020 using BG-Sentinel traps baited with dry ice. A total of 36,645 mosquitoes were collected, from which 34,048 were collected in the remote areas and 2,597 in the urban areas. Our results show a clear and well-defined pattern of abundance, richness, and community composition according to anthropogenic modifications in land use and land cover. The more urbanized a given area the fewer species were found and those were primary vectors of arboviruses, Ae.aegypti and Cx.quinquefasciatus.

Bioallethrin activates specific olfactory sensory neurons and elicits spatial repellency in Aedes aegypti.

Use of pyrethroid insecticides is a pivotal strategy for mosquito control globally. Commonly known for their insecticidal activity by acting on voltage-gated sodium channels, pyrethroids, such as bioallethrin and transfluthrin, are used in mosquito coils, emanators and other vaporizers to repel mosquitoes and other biting arthropods. However, whether specific olfactory receptor neurons are activated by pyrethroids to trigger spatial repellency remains unknown. We used behavioral and electrophysiological approaches to elucidate the mechanism of bioallethrin repellency in Aedes aegypti, a major vector of dengue, yellow fever, Zika and chikungunya viruses. We found that bioallethrin elicits spatial (i.e. non-contact) repellency and activates a specific type of olfactory receptor neuron in mosquito antennae. Furthermore, bioallethrin repellency is significantly reduced in a mosquito mutant of Orco, an obligate olfactory co-receptor that is essential for the function of odorant receptors (Ors). These results indicate that activation of specific Or(s) by bioallethrin contributes to bioallethrin repellency. In addition, bioallethrin repellency was reduced in a pyrethroid-resistant strain that carries two mutations in the sodium channel gene that are responsible for knockdown resistance (kdr) to pyrethroids, indicating a role of activation of sodium channels in bioallethrin repellency. Results from this study show that bioallethrin repellency is likely to be the result of co-activation of Or(s) and sodium channels. These findings not only contribute to our understanding of the modes of action of volatile pyrethroids in spatial repellency, but also provide a framework for developing new repellents based on the dual-target mechanism revealed. © 2021 Society of Chemical Industry.

A conserved female-specific larval requirement for MtnB function facilitates sex separation in multiple species of disease vector mosquitoes

BackgroundClusters of sex-specific loci are predicted to shape the boundaries of the M/m sex-determination locus of the dengue vector mosquito Aedes aegypti, but the identities of these genes are not known. Identification and characterization of these loci could promote a better understanding of mosquito sex chromosome evolution and lead to the elucidation of new strategies for male mosquito sex separation, a requirement for several emerging mosquito population control strategies that are dependent on the mass rearing and release of male mosquitoes. This investigation revealed that the methylthioribulose-1-phosphate dehydratase (MtnB) gene, which resides adjacent to the M/m locus and encodes an evolutionarily conserved component of the methionine salvage pathway, is required for survival of female larvae.ResultsLarval consumption of Saccharomyces cerevisiae (yeast) strains engineered to express interfering RNA corresponding to MtnB resulted in target gene silencing and significant female death, yet had no impact on A. aegypti male survival or fitness. Integration of the yeast larvicides into mass culturing protocols permitted scaled production of fit adult male mosquitoes. Moreover, silencing MtnB orthologs in Aedes albopictus, Anopheles gambiae, and Culex quinquefasciatus revealed a conserved female-specific larval requirement for MtnB among different species of mosquitoes.ConclusionsThe results of this investigation, which may have important implications for the study of mosquito sex chromosome evolution, indicate that silencing MtnB can facilitate sex separation in multiple species of disease vector insects.Graphical

Fat and Happy: Profiling Mosquito Fat Body Lipid Storage and Composition Post-blood Meal.

The fat body is considered the insect analog of vertebrate liver and fat tissue. In mosquitoes, a blood meal triggers a series of processes in the fat body that culminate in vitellogenesis, the process of yolk formation. Lipids are stored in the fat body in specialized organelles called lipid droplets that change in size depending on the nutritional and metabolic status of the insect. We surveyed lipid droplets in female Aedes aegypti fat body during a reproductive cycle using confocal microscopy and analyzed the dynamic changes in the fat body lipidome during this process using LC/MS. We found that lipid droplets underwent dynamic changes in volume after the mosquito took a blood meal. The lipid composition found in the fat body is quite complex with 117 distinct lipids that fall into 19 classes and sublcasses. Our results demonstrate that the lipid composition of the fat body is complex as most lipid classes underwent significant changes over the course of the vitellogenic cycle. This study lays the foundation for identifying unknown biochemical pathways active in the mosquito fat body, that are high-value targets for the development of novel mosquito control strategies.

Re-emergence of dengue virus in regional Queensland: 2019 dengue virus outbreak in Rockhampton, Central Queensland, Australia.

To describe an autochthonous dengue virus type 2 (DENV-2) outbreak in Central Queensland from May 2019 and subsequent public health actions. Public health outbreak investigation of locally acquired DENV-2 cases in Rockhampton, Central Queensland. This included laboratory investigations, associated mosquito vector surveillance, and control measures implemented in response to the outbreak. Twenty-one locally-acquired DENV-2 cases were identified during the Rockhampton outbreak (from 23 May to 7 October 2019): 13 laboratory-confirmed and eight probable cases. Clinical symptoms included lethargy (100%); fever (95%); headache (95%); and aches and pains (90%). Inspections of premises demonstrated that Aedes aegypti was present in 9.5% of those investigated which was more than half of the premises identified as containing mosquitoes. Nucleotide sequencing of a DENV-2 isolate recovered from the first confirmed case and DENV-2 RNA from an additional 5 patients indicated a single DENV-2 strain was responsible for the outbreak which was most closely related to DENV-2 strains from Southeast Asia. The 2019 DENV-2 outbreak in Rockhampton, Central Queensland, Australia, likely resulted from the importation of a strain, most closely related to DENV-2 strains from Southeast Asia and is the first reported outbreak in the region specifically implicating DENV-2. Given the presence of Aedes aegypti in Rockhampton, appropriate medical and mosquito avoidance advice; ongoing surveillance; and deployment of mosquito control strategies for the prevention of dengue and other mosquito-borne diseases should be priorities for this region.

Evaluation of Bacillus thuringiensis israelensis as toxic sugar bait against adult Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus mosquitoes.

Attractive toxic sugar baits (ATSB) are a novel and effective mosquito control tool based on sugar-feeding behaviors and oral ingestion. In general, there is a demand from consumers for more novel control products with more effective active ingredients. Bacillus thuringiensis israelensis (BTi) is a major larvicide for control of mosquito larvae. This study evaluated BTi as an active ingredient of toxic sugar baits (TSB) against adult Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus, compared with a positive control of 1% boric acid toxic sugar bait. Ingestion of BTi TSB by female mosquitoes resulted in an average mortality at 48 h of 97% for Ae. aegypti, 98% for Ae. albopictus, and 100% for Cx. quinquefasciatus. The study findings suggest ingestible BTi TSBs could be a viable alternative to current mosquito control strategies and programs against adults of these three species of mosquitoes.

Evidence of Wing Shape Sexual Dimorphism in Aedes (Stegomyia) albopictus in Mallorca, Spain

The Asian tiger mosquito Aedes albopictus (Skuse, 1894) is a highly invasive species widely distributed on the Spanish Mediterranean coast and the Balearic archipelago. Most studies involving this species in Spain have been focused on surveillance and control methods. However, micro-evolutionary studies for Ae. albopictus in Spain have been traditionally neglected. Morphological diversity could be the result of long-term evolutionary diversification in responses to selective pressures such as temperature, precipitation, food availability, predation, or competition that may influence flight activity, host-seeking, and blood-feeding behavior. Wing geometric morphometric have been used not only to study micro- and macro-evolution in mosquitoes but also in studies of population structuring and sexual dimorphism. Therefore, the main goal of this study was to investigate the wing shape patterns of Ae. albopictus populations to unveil sexual dimorphism that could provide information about their ecology and behavior. Mosquito eggs were collected using oviposition traps at the main campus of the University of the Balearic Islands (Palma de Mallorca, Spain) and reared under laboratory conditions. In order to study wing shape variation patterns in Ae. albopictus males and females, the left wing of each adult mosquito was removed and analyzed based on 18 landmarks. Our results indicated strong levels of sexual dimorphism between Ae. albopictus males and females. Furthermore, according to the cross-validated reclassification test, males were correctly distinguished from females with an accuracy of 84% and females from males 75%. We observed a significant sexual dimorphism in the wing shape patterns of Ae. albopictus when considering different seasonal patterns (spring vs. autumn). Our results suggested that selective pressures may affect males differently to females. Host-seeking, blood-feeding, and oviposition behavior of females may act as a major driver for wing shape sexual dimorphism. These results should be considered for the development of more effective and targeted mosquito control strategies.

A functional requirement for sex-determination M/m locus region lncRNA genes in Aedes aegypti female larvae

Although many putative long non-coding RNA (lncRNA) genes have been identified in insect genomes, few of these genes have been functionally validated. A screen for female-specific larvicides that facilitate Aedes aegypti male sex separation uncovered multiple interfering RNAs with target sites in lncRNA genes located in the M/m locus region, including loci within or tightly linked to the sex determination locus. Larval consumption of a Saccharomyces cerevisiae (yeast) strain engineered to express interfering RNA corresponding to lncRNA transcripts resulted in significant female death, yet had no impact on male survival or fitness. Incorporation of the yeast larvicides into mass culturing protocols facilitated scaled production and separation of fit adult males, indicating that yeast larvicides could benefit mosquito population control strategies that rely on mass releases of male mosquitoes. These studies functionally verified a female-specific developmental requirement for M/m locus region lncRNA genes, suggesting that sexually antagonistic lncRNA genes found within this highly repetitive pericentromeric DNA sequence may be contributing to the evolution of A. aegypti sex chromosomes.

Larvicidal Efficacy and GC-MS Analysis of Hyptis suaveolens Leaf Extracts against Anopheles Species

Mosquitoes are the most important group of insects in terms of public health importance, which transmit serious human diseases. The continuous application of synthetic insecticides to control these mosquitoes causes development of resistance in vector species, and an adverse effect on environmental quality and non-target organisms including human health. Therefore, the use of active toxic agents from plant extracts as alternative mosquito control strategy cannot be over emphasized, as these are non-toxic, easily available at affordable prices, biodegradable and show target - specific activities against different species of vector mosquitoes. The aim of the present study was to evaluate the larvicidal efficacy of the aqueous and methanol leaf extracts of H. suaveolens against the fourth instars larvae of Anopheles species. Standard WHO protocols was adopted for the larvicidal bioassay. Larvicidal activity was evaluated at concentrations of 200, 400, 600, 800 and 1000 mg/L. The larval mortality was observed after 24 and 48hours bioassay. The results are mean of three replicates and the mortalities recorded were subjected to chi-square test and probit analysis to determine median lethal concentrations (LC50). TheGC-MS analysis ofthe methanolic leaf extract of the plantrevealed the presence of twelve compounds on the chromatogram. Among the major compounds areOleic Acid (33.33%), Octadecanoic acid (13.52%), 1,3-Cyclohexadiene-1-methanol,alpha.,2,6,6-(10.42%), 1,3-Cyclopentanediol, trans (9.60%), n-Hexadecanoic acid (9.01%) and 4-Hepten-3-one, 4-methyl (7.0%).The phytochemical screening of the aqueous and methanol leaf extracts of the plant revealed the presence of Tannins, Terpenoids, Flavonoids, Steroids, Carbohydrates, Cardiac glycoside and resins. The LC50 values estimated were 316.22mg/Lfor methanol extract and 323.59 mg/L for aqueous extract. The differences between the two extracts were however not significantly different at P>0.05. The findings also revealed that mortality was concentration dependent and both extracts showed promising larvicidal activity against Anopheles species larvae. Therefore, the crude leaf extract of the plant is recommended to be used as alternative to synthetic larvicides and further research is needed to test the activity of the plant on non-target organisms.

Mosquito responses to lethal and nonlethal effects of predation and an insect growth regulator

AbstractLethal and nonlethal effects of predation are likely to impact phenotypic traits of potential prey that elude capture. Nonlethal effects of predation on prey can include alterations in behavior or morphology in response to predation risk which may impair prey growth and fitness. The application of pesticide in mosquito control during aquatic stages can interact with predation stress and alter density and phenotypic traits of prey. Insect growth regulator (IGR) pyriproxyfen is a pesticide that mainly prevents pupal‐adult metamorphosis by mimicking juvenile hormone, whereas the larval stage is not targeted. The use of IGR can therefore act in conjunction with natural aquatic predators that target the larval stage to affect population of prey. In this study, we assessed the invasive mosquito prey Aedes aegypti responses to lethal and nonlethal effects of a combination of IGR and predatory mosquito larvae of Toxorhynchites rutilus. The combination of IGR and Tx. rutilus heavily lowered Ae. aegypti metamorphosis to adulthood more than the independent effects of IGR or Tx. rutilus. Exposing Ae. aegypti larvae to the combination shortened life span of adults after metamorphosis for both males and females, whereas control and numerical density reduction “removals” treatments lengthened life span. Our results show strong lethal and nonlethal outcomes of the combination on Ae. aegypti. These findings suggest an additional benefit, decreases adult life span, of the use of an IGR when combined with a natural predator of mosquitoes that may be exploited to improve mosquito control strategies to reduce the risk of disease transmission.