Biological Control of Mosquito Vectors: Past, Present, and Future

Semi-field evaluation of aquatic predators for the control of Anopheles funestus in rural south-eastern Tanzania

BACKGROUND

Biological control is a promising alternative or complementary approach for controlling vector populations in response to the spread of insecticide resistance in malaria vectors. This study evaluated the efficacy of three selected potential predators on the density and fitness parameters of Anopheles funestus larvae in rural Tanzania.

METHODS

Common predator families Aeshnidae (dragonflies), Coenagrionidae (damselflies), and Notonectidae (backswimmers) and An. funestus group larvae were collected from natural aquatic habitats in rural south-eastern Tanzania. Predators were starved for 12-h while An. funestus larvae were given fish food before starting the experiment. Anopheles funestus larvae were placed into artificial habitats containing predators, exposing them to potential predation. The number of surviving An. funestus larvae were counted every 24-h. An emergence traps were placed at the top of artificial habitats to capture emerging mosquitoes. Emerged mosquitoes were monitored until they died. Female wings were measured and used as a proxy for body size. Generalized linear mixed models (GLMM) with binomial variates at 95% CI and Cox proportional hazard models were used to assess the proportion of dead mosquitoes and the daily survival determined.

RESULTS

There were significant differences in the number of emerged mosquitoes between the treatment and control groups (P < 0.001). Thus, all predator species played a significant role in reducing the density of An. funestus mosquitoes (P < 0.001). Furthermore, these predators had notable effects on the fitness parameters and survival of emerged mosquitoes (P < 0.001). Among the three predators studied, Coenagrionidae (damselflies) were most efficient followed by Notonectidae (backswimmers), with Aeshnidae (dragonflies) being the least efficient.

CONCLUSION

Selected aquatic predators have the potential to reduce the survival and density of An. funestus larvae. They might eventually be included within an integrated malaria vector control strategy, ultimately leading to a reduction in malaria transmission.

Wolbachia pipientis (Rickettsiales: Rickettsiaceae) mediated effects on the fitness and performance of Aedes aegypti (Diptera: Culicidae) under variable temperatures and initial larval densities

Wolbachia pipientis (Hertig, 1936), also referred as Wolbachia, is a bacterium present across insect taxa, certain strains of which have been demonstrated to impact the fitness and capacity to transmit viruses in mosquitoes, particularly Aedes aegypti (Linnaeus, 1762). Most studies examine these impacts in limited sets of environmental regimes. Here we seek to understand the impacts of environmentally relevant conditions such as larval density, temperature, and their interaction on wAlbB-infected A. aegypti. Using a factorial design, we measured wAlbB stability (relative density, post-emergence in females, and in progeny), the ability for wAlbB to induce cytoplasmic incompatibility, and bacterial effects on mosquito fitness (fecundity, fertility, and body mass) and performance (adult survival and time to pupation) across 2 temperature regimes (fluctuating and constant) and 2 initial larval densities (low and high). Fluctuating daily regimes of temperature (27 to 40 °C) led to decreased post-emergence wAlbB density and increased wAlbB density in eggs compared to constant temperature (27 °C). An increased fecundity was found in wAlbB-carrying females reared at fluctuating temperatures compared to uninfected wild-type females. wAlbB-carrying adult females showed significantly increased survival than wild-type females. Contrarily, wAlbB-carrying adult males exhibited a significantly lower survival than wild-type males. We found differential effects of assessed treatments (Wolbachia infection status, temperature, and larval density) across mosquito sexes and life stages. Taken together, our results indicate that realistic conditions may not impact dramatically the stability of wAlbB infection in A. aegypti. Nonetheless, understanding the ecological consequence of A. aegypti-wAlbB interaction is complex due to life history tradeoffs under conditions faced by natural populations.

Integrated metabolomic analysis and molecular docking: Unveiling the potential of Nephrolepis exaltata (L.) Schott phytocompounds for mosquito control via glutathione-S-transferase targeting

Plants contain a wide range of potential phytochemicals that are target-specific, and less toxic to human health. The present study aims to investigate the metabolomic profile of Nephrolepis exaltata (L.) Schott and its potential for mosquito control by targeting Glutathione-S-Transferase, focusing on the larvicidal activity against Culex pipiens. Crude extracts (CEs) were prepared using ethanol, ethyl acetate and n-hexane. CEs have been used for assessment of mosquitocidal bioassay. The metabolomic analyses for CEs were characterized for each CE by gas chromatography-mass spectrometry (GC-MS). The most efficient CE with the highest larval mortality and the least LC50 was the hexane CE. Then, alkaline phosphatase (ALP) activity, and glutathione-S-transferase (GST) activity were assessed in larvae treated with the hexane CE. The results demonstrated a decline in protein content, induction of ALP activity, and reduction in GST activity. Finally, molecular docking and dynamic simulation techniques were employed to evaluate the interaction between the hexane phytochemicals and the GST protein. D-(+)-Glucuronic acid, 3TMS derivative and Sebacic acid, 2TMS derivative showed best binding affinities to GST protein pointing to their interference with the enzyme detoxification functions, potentially leading to reduced ability to metabolize insecticides.

Characterization of the fragmentation mechanisms in electrospray ionization tandem mass spectrometry of chloroquinoline derivatives with larvicidal activity against Aedes aegypti

RATIONALE

4,7-Dichloroquinoline (DCQ) represents a group of synthetic molecules inspired by natural products with important roles in biological and biomedical areas. This work aimed to characterize DCQ and its derivatives by high-resolution electrospray ionization (ESI) mass spectrometry and tandem mass spectrometry (ESI-MS/MS), supported by theoretical calculations. Biological assays were carried out with DCQ and its derivatives to determine LC50 values against Aedes aegypti larvae.

METHODS

Five DCQ derivatives were synthesized by using previously described protocols. ESI-MS/MS analyses were carried out with a quadrupole/time-of-flight and ion-trap instrument. The proposed gas-phase protonation sites and fragmentation were supported by density functional theory calculations. The larvicidal tests were performed with the Ae. aegypti Rockefeller strain, and the LC50 values were determined by employing five test concentrations. Larval mortality was determined after treatment for 48 h.

RESULTS

DCQ bromides or aldehydes (C-3 or C-8 positions), as well as the trimethylsilyl derivative (C-3 position), were prepared. Detailed ESI-MS/MS data revealed heteroatom elimination through an exception to the even-electron rule, to originate open-shell species. Computational studies were used to define the protonation sites and fragmentation pathways. High activity of DCQ and its derivatives against Ae. aegypti larvae was demonstrated.

CONCLUSION

Our results provided a well-founded characterization of the fragmentation reactions of DCQ and its derivatives, which can be useful for complementary studies of the development of a larvicidal product against Ae. aegypti.

A review of applications and limitations of using aquatic macroinvertebrate predators for biocontrol of the African malaria mosquito, Anopheles gambiae sensu lato

Macroinvertebrate predators such as backswimmers (Heteroptera: Notonectidae), dragonflies (Odonata: Aeshnidae), and predatory diving beetles (Coleoptera: Dytiscidae) naturally inhabit aquatic ecosystems. Some aquatic ecosystems inhabited by these macroinvertebrate predator taxa equally form malaria vector larval habitats. The presence of these predators in malaria vector larval habitats can negatively impact on development, adult body size, fecundity, and longevity of the malaria vectors, which form important determinants of their fitness and future vectorial capacity. These potential negative impacts caused by aquatic macroinvertebrate predators on malaria vectors warrant their consideration as biocontrol agents in an integrated program to combat malaria. However, the use of these macroinvertebrate predators in malaria biocontrol is currently constrained by technical bottlenecks linked to their generalist predatory tendencies and often long life cycles, demanding complex rearing systems. We reviewed the literature on the use of aquatic macroinvertebrate predators for biocontrol of malaria vectors from the An. gambiae s.l. complex. The available information from laboratory and semi-field studies has shown that aquatic macroinvertebrates have the potential to consume large numbers of mosquito larvae and could thus offer an additional approaches in integrated malaria vector management strategies. The growing number of semi-field structures available in East and West Africa provides an opportunity to conduct ecological experimental studies to reconsider the potential of using aquatic macroinvertebrate predators as a biocontrol tool. To achieve a more sustainable approach to controlling malaria vector populations, additional, non-chemical interventions could provide a more sustainable approach, in comparison with the failing chemical control tools, and should be urgently considered for integration with the current mosquito vector control campaigns.

Biocidal efficacy of olefinic N-alkylamides against Aedes aegypti and Culex quinquefasciatus larvae

Mosquito-borne diseases are a major public-health concern worldwide. The development of resistance in mosquitoes to the existing larvicides and the associated-risks necessitates the exploration of novel molecules to control vector-borne pathogens. This study demonstrates that N-alkylamides [2E,4E-N-isobutyl-undeca-2,4-diene-8,10-diynamide (1) and 2E,4E,8Z,10E-N-isobutyl-dodeca-2,4,8,10-tetraenamide (2)] of Acmella ciliata exhibit biocidal action against Aedes aegypti and Culex quinquefasciatus larvae. The LC50 for 1 and 2 were 44.19 and 18.28 ppm against Aedes larvae, and 30.89 and 11.75 ppm against Culex larvae, respectively. We further observed that the chain length, degree of unsaturation, and terminal methylation influence the larvicidal efficacy of N-alkylamides. HPLC-assisted quantification revealed that the content of both 1 (19.01 mg/g) and 2 (68.55 mg/g) was maximum in the flowers of A. ciliata. Thus, this study concludes that N-alkylamides are promising alternatives to control mosquito larvae and can be used as standard for quantitation in test samples.

Innate immunity in Aedes mosquitoes: from pathogen resistance to shaping the microbiota

Discussions of host-microbe interactions in mosquito vectors are frequently dominated by a focus on the human pathogens they transmit (e.g. Plasmodium parasites and arboviruses). Underlying the interactions between a vector and its transmissible pathogens, however, is the physiology of an insect living and interacting with a world of bacteria and fungi including commensals, mutualists and primary and opportunistic pathogens. Here we review what is known about the bacteria and fungi associated with mosquitoes, with an emphasis on the members of the Aedes genus. We explore the reciprocal effects of microbe on mosquito, and mosquito on microbe. We analyse the roles of bacterial and fungal symbionts in mosquito development, their effects on vector competence, and their potential uses as biocontrol agents and vectors for paratransgenesis. We explore the compartments of the mosquito gut, uncovering the regionalization of immune effectors and modulators, which create the zones of resistance and immune tolerance with which the mosquito host controls and corrals its microbial symbionts. We examine the anatomical patterning of basally expressed antimicrobial peptides. Finally, we review the relationships between inducible antimicrobial peptides and canonical immune signalling pathways, comparing and contrasting current knowledge on each pathway in mosquitoes to the model insect Drosophila melanogaster. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Influence of insular conditions on wing phenotypic variation in two dominant mosquito vectors, Aedes albopictus and Armigeres subalbatus (Diptera: Culicidae), in the border archipelagos of Thailand

Insects geographically separated into island and mainland populations often exhibit phenotypic variations, a phenomenon known as insular conditions. These conditions can lead to rapid evolutionary changes that affect the morphological characteristics of mosquito vectors. Nevertheless, studies that specifically examine phenotype differences between island and mainland mosquito populations have been limited. In this study, wing variation in size and shape was investigated using the geometric morphometric (GM) technique in two dominant mosquito vectors, Aedes albopictus and Armigeres subalbatus, in the Ranong and Trat archipelagos of Thailand. Significant differences in average wing centroid size (CS) were found in 6 out of 15 population pairs for Ae. albopictus (p < 0.05) and in 5 population pairs for Ar. subalbatus (p < 0.05). After removing the allometric effect, canonical variate analyses (CVA) based on wing shape analysis revealed overlap across all populations for both Ae. albopictus and Ar. subalbatus. However, the statistical analysis indicated that Ar. subalbatus exhibited wing shape differences across all populations (p < 0.05), and most Ae. albopictus populations also displayed distinct wing shapes (p < 0.05), except for the populations from Chang Island and the mainland of Ranong, which showed no significant differences (p > 0.05). These findings enhance our understanding of mosquito adaptability in island regions and provide valuable data for the surveillance and monitoring of vector evolution.

Natural products from Xenorhabdus and Photorhabdus show promise as biolarvicides against Aedes albopictus

BACKGROUND

In the perpetual struggle to manage mosquito populations, there has been increasing demand for the development of biopesticides to supplant/complement current products. The insecticidal potential of Xenorhabdus and Photorhabdus has long been recognized and is of interest for the control of important mosquitoes like Aedes albopictus which vectors over 20 different arboviruses of global public health concern.

RESULTS

The larvicidal effects of cell-free supernatants, cell growth cultures and cell mass of an extensive list of Xenorhabdus and Photorhabdus spp. was investigated. They were quite effective against Ae. albopictus causing larval mortality ranging between 52-100%. Three Photorhabdus spp. and 13 Xenorhabdus spp. release larvicidal compounds in cell-free supernatants. Cell growth culture of all tested species exhibited larvicidal activity, except for Xenorhabdus sp. TS4. Twenty-one Xenorhabdus and Photorhabdus bacterial cells (pellet) exhibited oral toxicity (59-91%) against exposed larvae. The effect of bacterial supernatants on the mosquito eggs were also assessed. Bacterial supernatants inhibited the hatching of mosquito eggs; when unhatched eggs were transferred to clean water, they all hatched. Using the easyPACId approach, the larvicidal compounds in bacterial supernatant were identified as fabclavine from X. szentirmaii and xencoumacin from X. nematophila (causing 98 and 70% mortality, respectively, after 48 h). Xenorhabdus cabanillasii and X. hominickii fabclavines were as effective as commercial Bacillus thuringiensis subsp. israelensis and spinosad products within 5 days post-application (dpa).

CONCLUSION

Fabclavine and xenocoumacin can be developed into novel biolarvicides, can be used as a model to synthesize other compounds or/and can be combined with other commercial biolarvicides. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Upsurge of dengue outbreaks in several WHO regions: Public awareness, vector control activities, and international collaborations are key to prevent spread

Background

Dengue, the world's fastest-growing vector-borne disease, has skyrocketed in the 21st century. Dengue has harmed human health since its first known cases among Spanish soldiers in the Philippines to its 21st-century outbreaks in Southeast Asia, the Pacific, and the Americas. In light of the current circumstances, it is imperative to investigate its origin and prevalence, enabling the implementation of effective interventions to curb the upsurge.

Methods

Our study examines the history of dengue outbreaks, and evolving impact on public health, aiming to offer valuable insights for a more resilient public health response worldwide. In this comprehensive review, we incorporated data from renowned databases such as PubMed, Google Scholar, and Scopus to provide a thorough analysis of dengue outbreaks.

Results

Recent dengue outbreaks are associated with rapid urbanization, international travel, climatic change, and socioeconomic factors. Rapid urbanization and poor urban design and sanitation have created mosquito breeding places for dengue vectors. Also, international travel and trade have spread the pathogen. Climate change in the past two decades has favored mosquito habitats and outbreaks. Socioeconomic differences have also amplified the impact of dengue outbreaks on vulnerable communities. Dengue mitigation requires vector control, community engagement, healthcare strengthening, and international cooperation.

Conclusion

Climate change adaptation and urban planning are crucial. Although problems remain, a comprehensive vector control and community involvement plan may reduce dengue epidemics and improve public health in our interconnected world.

Mosquitoes escape looming threats by actively flying with the bow wave induced by the attacker

To detect and escape looming threats, night-flying insects must rely on other senses than vision alone. Nocturnal mosquitoes can evade looming objects in the dark, but how they achieve this is still unknown. Here, we show how night-active female malaria mosquitoes escape from rapidly looming objects that simulate defensive actions of blood-hosts. First, we quantified the escape performance of flying mosquitoes from an event-triggered mechanical swatter, showing that mosquitoes use swatter-induced airflow to increase their escape success. Secondly, we used high-speed videography and deep-learning-based tracking to analyze escape flights in detail, showing that mosquitoes use banked turns to evade the threat. By combining escape kinematics data with numerical simulations of attacker-induced airflow and a mechanistic movement model, we unraveled how mosquitoes control these banked evasive maneuvers: they actively steer away from the danger, and then passively travel with the bow wave produced by the attacker. Our results demonstrate that night-flying mosquitoes can detect looming objects when visual cues are minimal, suggesting that they use attacker-induced airflow both to detect the danger and as a fluid medium to move with away from the threat. This shows that escape strategies of flying insects are more complex than previous visually induced escape flight studies suggest. As most insects are of similar or smaller sizes than mosquitoes, comparable escape strategies are expected among millions of flying insect species. The here-observed escape maneuvers are distinct from those of mosquitoes escaping from odor-baited traps, thus providing new insights for the development of novel trapping techniques for integrative vector management.

The Perpetual Vector Mosquito Threat and Its Eco-Friendly Nemeses

Mosquitoes are the most notorious arthropod vectors of viral and parasitic diseases for which approximately half the world's population, ~4,000,000,000, is at risk. Integrated pest management programs (IPMPs) have achieved some success in mitigating the regional transmission and persistence of these diseases. However, as many vector-borne diseases remain pervasive, it is obvious that IPMP successes have not been absolute in eradicating the threat imposed by mosquitoes. Moreover, the expanding mosquito geographic ranges caused by factors related to climate change and globalization (travel, trade, and migration), and the evolution of resistance to synthetic pesticides, present ongoing challenges to reducing or eliminating the local and global burden of these diseases, especially in economically and medically disadvantaged societies. Abatement strategies include the control of vector populations with synthetic pesticides and eco-friendly technologies. These "green" technologies include SIT, IIT, RIDL, CRISPR/Cas9 gene drive, and biological control that specifically targets the aquatic larval stages of mosquitoes. Regarding the latter, the most effective continues to be the widespread use of Lysinibacillus sphaericus (Ls) and Bacillus thuringiensis subsp. israelensis (Bti). Here, we present a review of the health issues elicited by vector mosquitoes, control strategies, and lastly, focus on the biology of Ls and Bti, with an emphasis on the latter, to which no resistance has been observed in the field.

Insights and Challenges for the Development of Mosquito Control Action Thresholds Using Historical Mosquito Surveillance and Climate Datasets

Strategies to advance action threshold development can benefit both civilian and military vector control operations. The Anastasia Mosquito Control District (AMCD) has curated an extensive record database of surveillance programs and operational control activities in St. Johns County, Florida, since 2004. A thorough exploratory data analysis was performed on historical mosquito surveillance and county-wide climate data to identify climate predictors that could be used in constructing proactive threshold models for initiating control of Aedes, Culex, and Anopheles vector mosquitoes. Species counts pulled from Centers for Disease Control and Prevention (CDC) light trap (2004-2019) and BG trap (2014-2019) collection records and climate parameters of temperature (minimum, maximum, average), rainfall, and relative humidity were used in two iterations of generalized linear models. Climate readings were incorporated into models 1) in the form of continuous measurements, or 2) for categorization into number of "hot," "wet," or "humid" days by exceedance of selected biological index threshold values. Models were validated with tests of residual error, comparison of model effects, and predictive capability on testing data from the two recent surveillance seasons 2020 and 2021. Two iterations of negative binomial regression models were constructed for 6 species groups: container Aedes (Ae. aegypti, Ae. albopictus), standing water Culex (Cx. nigripalpus, Cx. quinquefasciatus), floodwater Aedes (Ae. atlanticus, Ae. infirmatus), salt-marsh Aedes (Ae. taeniorhyncus, Ae. sollicitans), swamp water Anopheles (An. crucians), and a combined Total Mosquitoes group. Final significant climate predictors varied substantially between species groups. Validation of models with testing data displayed limited predictive abilities of both model iterations. The most significant climate predictors for floodwater Aedes, the dominant and operationally influential species group in the county, were either total precipitation or frequency of precipitation events (number of "wet" days) at two to four weeks before trap collection week. Challenges hindering the construction of threshold models were discussed. Insights gained from these models provide initial feedback for streamlining the AMCD mosquito control program and analytical recommendations for future modelling efforts of interested mosquito control programs, in addition to generalized guidance for deployed armed forces personnel with needs of mosquito control but lacking active surveillance programs.

Relative importance of VECTRI model parameters in the malaria disease transmission and prevalence

In this study, a sensitivity analysis on a VECTRI dynamical model of malaria transmission is investigated to determine the relative importance of model parameters to disease transmission and prevalence. Apart from being most climatic prone, Odisha is a highly endemic state for malaria in India. The lack in sufficient modeling studies severely impacts the malarial process studies which further hinder the possibility of malaria early warning systems and preventive measures to be undertaken beforehand. Therefore, modeling studies and investigating the relationship between malaria transmission process studies and associated climatic factors are the need of the hour. Environmental conditions have pronounced effects on the malaria transmission dynamics and abundance of the poikilothermic vectors, but the exact relationship of sensitivity for these parameters is not well established. Sensitivity analysis is a useful tool for ascertaining model responses to different input variables. Therefore, in order to perform the requisite study, a dynamical model, VECTRI, is utilized. The study period ranges from 2000 to 2013, where several sensitivity tests are performed using different model parameters such as infiltration and evaporation rate loss of ponds, degree-days for parasite development, threshold temperature for parasite development, threshold temperature for egg development in the vector, and maximum and minimum temperature for larvae survival. The experiments suggest that the lower value of minimum temperature for larvae survival (rlarv_tmin), i.e., 16 °C, provides higher vector density and entomological inoculation rate (EIR) values. EIR reaches its maximum, when the threshold temperature for parasite development (rtsporo) is 22 °C and degree-days for parasite development (dsporo) is 8 degree-days. No change is observed in the vector density; even when rtsporo is 30 °C, values of EIR are close to 0. A successive increment of infiltration and evaporation rate loss of ponds (rwaterfrac evap126) values from 130 to 200 mm/day result in approximately 5% consistent decline in vector density and EIR. The study concludes that the most sensitive parameters are dsporo, rlarv_tmin, and rwaterfrac evap126. The VECTRI model is rather insensitive to maximum temperature for larvae survival (rlarv_tmin) for vector density and EIR variables. Further certain modifications and improvements are required in VECTRI to predict out variables like vector density and EIR more accurately in highly endemic region.

RNAi-Mediated Knockdown of Acidic Ribosomal Stalk Protein P1 Arrests Egg Development in Adult Female Yellow Fever Mosquitoes, Aedes aegypti

After taking a blood meal, the fat body of the adult female yellow fever mosquito, Aedes aegypti, switches from a previtellogenic state of arrest to an active state of synthesizing large quantities of yolk protein precursors (YPPs) that are crucial for egg development. The synthesis of YPPs is regulated at both the transcriptional and translational levels. Previously, we identified the cytoplasmic protein general control nonderepressible 1 (GCN1) as a part of the translational regulatory pathway for YPP synthesis. In the current study, we used the C-terminal end of GCN1 to screen for protein-protein interactions and identified 60S acidic ribosomal protein P1 (P1). An expression analysis and RNAi-mediated knockdown of P1 was performed to further investigate the role of P1 in mosquito reproduction. We showed that in unfed (absence of a blood meal) adult A. aegypti mosquitoes, P1 was expressed ubiquitously in the mosquito organs and tissues tested. We also showed that the RNAi-mediated knockdown of P1 in unfed adult female mosquitoes resulted in a strong, transient knockdown with observable phenotypic changes in ovary length and egg deposition. Our results suggest that 60S acidic ribosomal protein P1 is necessary for mosquito reproduction and is a promising target for mosquito population control.

Wolbachia populations across organs of individual Culex pipiens: highly conserved intra-individual core pangenome with inter-individual polymorphisms

Wolbachia is a maternally inherited intracellular bacterium that infects a wide range of arthropods including mosquitoes. The endosymbiont is widely used in biocontrol strategies due to its capacity to modulate arthropod reproduction and limit pathogen transmission. Wolbachia infections in Culex spp. are generally assumed to be monoclonal but the potential presence of genetically distinct Wolbachia subpopulations within and between individual organs has not been investigated using whole genome sequencing. Here we reconstructed Wolbachia genomes from ovary and midgut metagenomes of single naturally infected Culex pipiens mosquitoes from Southern France to investigate patterns of intra- and inter-individual differences across mosquito organs. Our analyses revealed a remarkable degree of intra-individual conservancy among Wolbachia genomes from distinct organs of the same mosquito both at the level of gene presence-absence signal and single-nucleotide polymorphisms (SNPs). Yet, we identified several synonymous and non-synonymous substitutions between individuals, demonstrating the presence of some level of genomic heterogeneity among Wolbachia that infect the same C. pipiens field population. Overall, the absence of genetic heterogeneity within Wolbachia populations in a single individual confirms the presence of a dominant Wolbachia that is maintained under strong purifying forces of evolution.

Wing geometric morphometrics and DNA barcoding to distinguish three closely related species of Armigeres mosquitoes (Diptera: Culicidae) in Thailand

Armigeres subalbatus, a mosquito species widely found in Thailand and other Asian countries, serves as a vector for filarial parasites, affecting both humans and animals. However, the surveillance of this vector is complicated because of its morphological similarity to two other species, Armigeres dohami and Armigeres kesseli. To differentiate these morphologically similar species, our study employed both wing geometric morphometrics (GM) and DNA barcoding, offering a comprehensive approach to accurately identify these closely related Armigeres species in Thailand. Our GM analyses based on shape demonstrated significant accuracy in differentiating Armigeres species. Specifically, the outline-based GM method focusing on the 3rd posterior cell exhibited an accuracy rate of 82.61%, closely followed by the landmark-based GM method with 81.54%. Both these GM techniques effectively distinguished Ar. subalbatus from Ar. dohami and Ar. kesseli. Regarding DNA barcoding, our investigation of pairwise intra- and interspecific divergences revealed a "barcoding gap". Furthermore, the results of species confirmation using both species delimitation methods including the automatic barcode gap discovery method (ABGD) and the Multi-rate Poisson tree process (mPTP) were consistent with those of morphological identification, sequence comparisons with the GenBank and Barcode of Life Data System (BOLD) databases, and the neighbor-joining tree construction. These consistent results emphasize the efficacy of DNA barcoding in the precise identification of Armigeres species.

MBORS: Mosquito vector Biocontrol Ontology and Recommendation System

BACKGROUND OBJECTIVES

Mosquito vectors are disease-causing insects, responsible for various life-threatening vector-borne diseases such as dengue, Zika, malaria, chikungunya, and lymphatic filariasis. In practice, synthetic insecticides are used to control the mosquito vector, but, the continuous usage of synthetic insecticides is toxic to human health resulting in communicable diseases. Non-toxic biocontrol agents such as bacteria, fungus, plants, and mosquito densoviruses play a vital role in controlling mosquitoes. Community awareness of mosquito biocontrol agents is required to control vector-borne diseases. Mosquito vector-based ontology facilitates mosquito biocontrol by providing information such as species names, pathogen-associated diseases, and biological controlling agents. It helps to explore the associations among the mosquitoes and their biocontrol agents in the form of rules. The Mosquito vector-based Biocontrol Ontology Recommendation System (MBORS) provides the knowledge on mosquito-associated biocontrol agents to control the vector at the early stage of the mosquitoes such as eggs, larvae, pupae, and adults. This paper proposes MBORS for the prevention and effective control of vector-borne diseases. The Mosquito Vector Association ontology (MVAont) suggests the appropriate mosquito vector biocontrol agents (MosqVecRS) for related diseases.

METHODS

Natural Language Processing and Data mining are employed to develop the MBORS. While Tokenization, Part-of-speech Tagging (POS), Named Entity Recognition (NER), and rule-based text mining techniques are used to identify the mosquito ontology concepts, the data mining apriori algorithm is used to predict the associations among them.

RESULTS

The outcome of the MBORS results in MVAont as Web Ontology Language (OWL) representation and MosqVecRS as an Android application. The developed ontology and recommendation system are freely available on the web portal.

INTERPRETATION CONCLUSION

The MVAont predicts harmless biocontrol agents which help to diminish the rate of vector-borne diseases. On the other hand, the MosqVecRS system raises awareness of vectors and vector-borne diseases by recommending suitable biocontrol agents to the vector control community and researchers.

MosChito rafts as a promising biocontrol tool against larvae of the common house mosquito, Culex pipiens

Mosquito control is of paramount importance, in particular, in light of the major environmental alterations associated with human activities, from climate change to the altered distribution of pathogens, including those transmitted by Arthropods. Here, we used the common house mosquito, Culex pipiens to test the efficacy of MosChito raft, a novel tool for mosquito larval control. MosChito raft is a floating hydrogel matrix, composed of chitosan, genipin and yeast cells, as bio-attractants, developed for the delivery of a Bacillus thuringiensis israeliensis (Bti)-based bioinsecticide to mosquito larvae. To this aim, larvae of Cx. pipiens were collected in field in Northern Italy and a novel colony of mosquito species (hereafter: Trescore strain) was established. MosChito rafts, containing the Bti-based formulation, were tested on Cx. pipiens larvae from the Trescore strain to determine the doses to be used in successive experiments. Thus, bioassays with MosChito rafts were carried out under semi-field conditions, both on larvae from the Trescore strain and on pools of larvae collected from the field, at different developmental stages. Our results showed that MosChito raft is effective against Cx. pipiens. In particular, the observed mortality was over 50% after two days exposure of the larvae to MosChito rafts, and over 70-80% at days three to four, in both laboratory and wild larvae. In conclusion, our results point to the MosChito raft as a promising tool for the eco-friendly control of a mosquito species that is not only a nuisance insect but is also an important vector of diseases affecting humans and animals.

A review of knowledge, attitudes and practices regarding mosquitoes and mosquito-borne infectious diseases in nonendemic regions

Mosquito-borne infectious diseases (MBIDs) present significant public health risks within tropical and subtropical regions. However, the rapid spread of MBIDs from these areas to temperate regions increase the risk of their emergence in nonendemic regions, i.e., regions where diseases are still sporadic and not sustained in the population. Raising awareness about preventive measures and protective behaviors is of primary importance to face the risks of vector-borne diseases. In this context, the number of studies on knowledge, attitude, and practice (KAP) about mosquitoes and MBIDs has grown rapidly in response to the need to identify knowledge and practices in nonendemic countries to fight mosquito proliferation. Building upon the recent developments in this field, we conducted the first-ever literature review to examine KAP studies conducted in nonendemic regions. Our aim was to identify the community's knowledge and attitudes that shape practices concerning the prevention of MBIDs. We used specific keywords regarding the scope of this review and then selected studies that were performed in nonendemic regions for MBIDs, including regions located in European countries, the USA or Asia. We identified 32 KAP studies, the oldest from 2003. The findings in the reviewed studies show that survey participants generally possessed a rather good understanding of mosquito breeding sites. However, there were notable variations in knowledge and perception of MBIDs, primarily linked to the geographic location of the survey and the prevalence of infectious outbreaks related to mosquito transmission. These findings highlight the significant influence of knowledge and awareness in fostering effective mosquito control practices. Moreover, socioeconomic status, particularly educational attainment, and respondents' gender emerged as key determinants in explaining the variability of appropriate practices. The survey results thus show the crucial role of knowledge, emphasizing the need for widespread awareness and information campaigns, encompassing both appropriate practices and efficient mosquito control methods. Understanding the interaction between these factors could provide good guidelines for implementing awareness plans and ultimately motivate the population to actively fight against mosquito proliferation and MBIDs development.

Road salt pollution alters sex ratios in emerging mosquito populations

De-icing road salt is a persistent emerging pollutant in temperate freshwater systems, where winter salting is necessary for road and pedestrian safety. Experts argue that road salts may increase salt-tolerant mosquito populations and, potentially, disease transmission in urban areas. Only adult females consume bloodmeals and may carry zoonotic diseases. While there are some species with naturally occurring male-biased sex ratios, it is unclear whether road salt differentially affects male and female mosquitoes to alter sex ratios. We hypothesized that road salts would masculinize emergence sex ratios and decrease female success because females may face higher exposure to stressors during their lengthy juvenile development compared to males. We measured mosquito emergence sex ratios of control (0 g/L added salt) and salt (4.5 g/L added salt) mesocosms in southern Ontario, Canada across the West Nile Virus season (May to October). We found female-biased sex ratios (i.e., <50% male frequency) in both 0 and 4.5 g/L. While mosquito abundance was significantly higher in 4.5 g/L compared to 0 g/L, road salt significantly increased the proportion of emerging males from 32.8% to 40.8% (Negative Binomial Model; Estimate ± SE = 0.283 ± 0.108; P = 0.009); mosquitoes shift their sex ratios from female-biased towards parity (50:50) in response to salt. Our study illustrates the need to evaluate sex-specific abundance in pollution-related mosquito population studies. By showing a shift toward more male mosquitoes emerging in high salinity compared to control treatments, our results suggest that road salts may have the potential to decrease female mosquito success and indirectly reduce disease transmission in cities.

Comparative efficacy of natural aquatic predators for biological control of mosquito larvae: A neglected tool for vector control

Mosquitoes are a dominant fraction of dipteran fauna, occupying a variety of niches. The most common method deployed for their control is the use of insecticides. Throughout their life cycle they are exposed to a wide range of predators in different habitats, thus biological control of mosquitoes by using aquatic predators has been suggested. Therefore, the present study was carried out to explore the type of natural predators coexisting with the mosquito larvae in still water bodies and to determine their efficacy as predators for mosquito larvae. A coexistence of different predators with mosquito larvae was observed in 27 standing water bodies of Chandigarh, India. The predation efficiency of tadpoles of frog was comparable to Gambusia fish, as 97% of the mosquito larvae of all instars of the medically important mosquito genera Anopheles, Aedes, Culex and Armigeres were preyed. The toad tadpoles were found to be least effective and their predation rate was found to be negligible. Further studies on larval source management by frog tadpoles in combination with insecticides or stand-alone would be worthwhile.

Exploring Natural Alkaloids from Brazilian Biodiversity as Potential Inhibitors of the Aedes aegypti Juvenile Hormone Enzyme: A Computational Approach for Vector Mosquito Control

This study explores the potential inhibitory activity of alkaloids, a class of natural compounds isolated from Brazilian biodiversity, against the mJHBP enzyme of the Aedes aegypti mosquito. This mosquito is a significant vector of diseases such as dengue, zika, and chikungunya. The interactions between the ligands and the enzyme at the molecular level were evaluated using computational techniques such as molecular docking, molecular dynamics (MD), and molecular mechanics with generalized Born surface area (MMGBSA) free energy calculation. The findings suggest that these compounds exhibit a high binding affinity with the enzyme, as confirmed by the binding free energies obtained in the simulation. Furthermore, the specific enzyme residues that contribute the most to the stability of the complex with the compounds were identified: specifically, Tyr33, Trp53, Tyr64, and Tyr129. Notably, Tyr129 residues were previously identified as crucial in the enzyme inhibition process. This observation underscores the significance of the research findings and the potential of the evaluated compounds as natural insecticides against Aedes aegypti mosquitoes. These results could stimulate the development of new vector control agents that are more efficient and environmentally friendly.

A synthetic lure for Anopheles gambiae (Diptera: Culicidae) based on the attractive plant Parthenium hysterophorus

Sugar is the sole diet for male mosquitoes and a complementary meal for females. Searching for natural sources of sugar is mediated by semiochemicals. Floral nectars, extra floral nectaries, damaged tissues of plants and rotten fruits are the most common sources of sugar in nature. I provide laboratory evidence of the high attraction of Parthenium hysterophorus L., a weed that grows in tropical climates, to Anopheles gambiae Giles. This study has tried to identify the chemicals which might be involved in the chemical attraction of A. gambiae to this plant. Using quantitative GC-MS analysis, α-pinene, camphene, 1-octen-3-ol, β-pinene, cis-β-ocimene, bornyl acetate, α-caryophyllene, hexadecanoic acid, and α-linolenic acid were identified as the main constituents of P. hysterophorus volatiles. Successive olfactory assays helped a better understanding of the more attractive chemicals of P. hysterophorus to A. gambiae which was the basis for testing a possible synthetic blend. Olfactory experiments proved this synthetic blend to be as attractive as Parthenium intact plants for A. gambiae. A minimal blend, consisting of only α-pinene, camphene, and cis-β-ocimene, was also produced and laboratory experiments indicated its relative attraction for A. gambiae. This blend can be tested in the attractive toxic sugar bait stations for sampling, surveillance, or control programs of mosquitoes in tropical Africa, where A. gambiae sensu stricto transfer malaria among residents.

Effect of age on wingbeat frequency of Aedes aegypti and potential application for age estimation of mosquitoes

To combat mosquito-borne diseases, a variety of vector control tools have been implemented. Estimating age structure in populations of vector species is important for understanding transmission potential. Age-grading techniques have been used as critical methods for evaluating the efficacy of vector control tools. However, methods like mark-release-recapture and ovarian dissection are laborious and require a high level of training. For decades, scientists have discussed the wide array of acoustic signatures of different mosquito species. These distinguishable wingbeat signatures with spatiotemporal classification allow mosquitoes of the same species to locate one another for mating. In recent years, the use of sensitive acoustic devices like mobile phones have proved effective. Wingbeat signatures can be used to identify mosquito species without the challenge of intensive field collections and morphological and molecular identifications. In this study, laboratory Aedes aegypti (L.) female and male wingbeats were recorded using mobile phones to determine whether sex and age differences with chronological time, and across different physiological stages, can be detected. Our results indicate significantly different wingbeat signatures between male and female Ae. aegypti, and a change of wingbeat frequencies with age and reproduction stage in females.

Common predators and factors influencing their abundance in Anopheles funestus aquatic habitats in rural south-eastern Tanzania

BACKGROUND

The role of larval predators in regulating the Anopheles funestus population in various malaria-endemic countries remains relatively unknown. This study aimed to investigate the common predators that co-exist with Anopheles funestus group larvae and evaluate factors that influence their abundance in rural south-eastern Tanzania.

METHODS

Mosquito larvae and predators were sampled concurrently using standard dipper (350 ml) or 10 L bucket in previously identified aquatic habitats in selected villages in southern Tanzania. Predators and mosquito larvae were identified using standard identification keys. All positive habitats were geo-located and their physical features characterized. Water physicochemical parameters such as dissolved oxygen (DO), pH, electrical conductivity (EC), total dissolved solids (TDS) and temperature were also recorded.

RESULTS

A total of 85 previously identified An. funestus aquatic habitats in nine villages were sampled for larvae and potential predators. A total of 8,295 predators were sampled. Of these Coenagrionidae 57.7% (n = 4785), Corixidae 12.8% (n = 1,060), Notonectidae 9.9% (n = 822), Aeshnidae 4.9% (n = 405), Amphibian 4.5% (n = 370), Dytiscidae 3.8% (n = 313) were common. A total of 5,260 mosquito larvae were sampled, whereby Anopheles funestus group were 60.3% (n = 3,170), Culex spp. 24.3% (n = 1,279), An. gambie s.l. 8.3% (n = 438) and other anophelines 7.1% (n = 373). Permanent and aquatic habitats larger than 100m2 were positively associated with An. funestus group larvae (P<0.05) and predator abundance (P<0.05). Habitats with submerged vegetation were negatively associated with An. funestus group larvae (P<0.05). Only dissolved oxygen (DO) was positively and significantly affect the abundance of An. funestus group larvae (P<0.05). While predators' abundance was not impacted by all physicochemical parameters.

CONCLUSION

Six potential predator families were common in aquatic habitats of An. funestus group larvae. Additional studies are needed to demonstrate the efficacy of different predators on larval density and adult fitness traits. Interventions leveraging the interaction between mosquitoes and predators can be established to disrupt the transmission potential and survival of the An. funestus mosquitoes.

Mosquito gene targeted RNAi studies for vector control

Vector-borne diseases are serious public health concern. Mosquito is one of the major vectors responsible for the transmission of a number of diseases like malaria, Zika, chikungunya, dengue, West Nile fever, Japanese encephalitis, St. Louis encephalitis, and yellow fever. Various strategies have been used for mosquito control, but the breeding potential of mosquitoes is such tremendous that most of the strategies failed to control the mosquito population. In 2020, outbreaks of dengue, yellow fever, and Japanese encephalitis have occurred worldwide. Continuous insecticide use resulted in strong resistance and disturbed the ecosystem. RNA interference is one of the strategies opted for mosquito control. There are a number of mosquito genes whose inhibition affected mosquito survival and reproduction. Such kind of genes could be used as bioinsecticides for vector control without disturbing the natural ecosystem. Several studies have targeted mosquito genes at different developmental stages by the RNAi mechanism and result in vector control. In the present review, we included RNAi studies conducted for vector control by targeting mosquito genes at different developmental stages using different delivery methods. The review could help the researcher to find out novel genes of mosquitoes for vector control.

RNA interference to combat the Asian tiger mosquito in Europe: A pathway from design of an innovative vector control tool to its application

The Asian tiger mosquito Aedes albopictus is currently spreading across Europe, facilitated by climate change and global transportation. It is a vector of arboviruses causing human diseases such as chikungunya, dengue hemorrhagic fever and Zika fever. For the majority of these diseases, no vaccines or therapeutics are available. Options for the control of Ae. albopictus are limited by European regulations introduced to protect biodiversity by restricting or phasing out the use of pesticides, genetically modified organisms (GMOs) or products of genome editing. Alternative solutions are thus urgently needed to avoid a future scenario in which Europe faces a choice between prioritizing human health or biodiversity when it comes to Aedes-vectored pathogens. To ensure regulatory compliance and public acceptance, these solutions should preferably not be based on chemicals or GMOs and must be cost-efficient and specific. The present review aims to synthesize available evidence on RNAi-based mosquito vector control and its potential for application in the European Union. The recent literature has identified some potential target sites in Ae. albopictus and formulations for delivery. However, we found little information concerning non-target effects on the environment or human health, on social aspects, regulatory frameworks, or on management perspectives. We propose optimal designs for RNAi-based vector control tools against Ae. albopictus (target product profiles), discuss their efficacy and reflect on potential risks to environmental health and the importance of societal aspects. The roadmap from design to application will provide readers with a comprehensive perspective on the application of emerging RNAi-based vector control tools for the suppression of Ae. albopictus populations with special focus on Europe.

Discovery and structure-activity relationship of Morita-Baylis-Hillman adducts as larvicides against dengue mosquito vector, Aedes aegypti (Diptera: Culicidae)

Neglected tropical diseases (NTDs) have become a significant public health problem worldwide, notably the life-threatening dengue hemorrhagic fever borne by the Aedes aegypti mosquito. Thus, mosquito vector control measures remain essential in public health vector surveillance and control to combat Aedes-borne infections. Therefore, a series of MBH adducts were synthesized and assessed towards the fourth instar mosquito larvae, Aedes aegypti, along with the preliminary structure-activity relationship (SAR). Noteworthy, this compound class might be synthetized by an efficient eco-friendly synthesismethod and a rapid route for the synthesis of commercial larvicide through a single synthetic step. The bioassays showed that this compound class is a promising larvicide to control Aedes aegypti mosquito larvae, mainly 3g, with an LC₅₀ of 41.35 µg/mL, which was higher than evaluated positive controls. Nevertheless, it is a viable larvicidalhit candidate for further hit-to-leadproperties optimization of its biphenyl backbone scaffold with enhanced insecticidalbioactivity. Moreover, scanning electron microscopy analysis suggested a disruption of the osmoregulatory/ionoregulatory functions by the complete deterioration of the terminal exoskeleton hindgut and anal papillae. Therefore, this new study shows the larvicidal efficacy of the tested compounds against the Aedes aegypti larvae.

Prevention of a dengue outbreak via the large-scale deployment of Sterile Insect Technology in a Brazilian city: a prospective study

Background

Dengue is a global problem that seems to be worsening, as hyper-urbanization associated with climate change has led to a significant increase in the abundance and geographical spread of its principal vector, the Aedes aegypti mosquito. Currently available solutions have not been able to stop the spread of dengue which shows the urgent need to implement alternative technologies as practical solutions. In a previous pilot trial, we demonstrated the efficacy and safety of the method 'Natural Vector Control' (NVC) in suppressing the Ae. aegypti vector population and in blocking the occurrence of an outbreak of dengue in the treated areas. Here, we expand the use of the NVC program in a large-scale 20 months intervention period in an entire city in southern Brazil.

Methods

Sterile male mosquitoes were produced from locally sourced Ae. aegypti mosquitoes by using a treatment that includes double-stranded RNA and thiotepa. Weekly massive releases of sterile male mosquitoes were performed in predefined areas of Ortigueira city from November 2020 to July 2022. Mosquito monitoring was performed by using ovitraps during the entire intervention period. Dengue incidence data was obtained from the Brazilian National Disease Surveillance System.

Findings

During the two epidemiological seasons, the intervention in Ortigueira resulted in up to 98.7% suppression of live progeny of field Ae. aegypti mosquitoes recorded over time. More importantly, when comparing the 2020 and 2022 dengue outbreaks that occurred in the region, the post-intervention dengue incidence in Ortigueira was 97% lower compared to the control cities.

Interpretation

The NVC method was confirmed to be a safe and efficient way to suppress Ae. aegypti field populations and prevent the occurrence of a dengue outbreak. Importantly, it has been shown to be applicable in large-scale, real-world conditions.

Funding

This study was funded by Klabin S/A and Forrest Innovations Ltd.

CRISPR/Cas advancements for genome editing, diagnosis, therapeutics, and vaccine development for Plasmodium parasites, and genetic engineering of Anopheles mosquito vector

Malaria as vector-borne disease remains important health concern with over 200 million cases globally. Novel antimalarial medicines and more effective vaccines must be developed to eliminate and eradicate malaria. Appraisal of preceding genome editing approaches confirmed the CRISPR/Cas nuclease system as a novel proficient genome editing system and a tool for species-specific diagnosis, and drug resistance researches for Plasmodium species, and gene drive to control Anopheles population. CRISPR/Cas technology, as a handy tool for genome editing can be justified for the production of transgenic malaria parasites like Plasmodium transgenic lines expressing Cas9, chimeric Plasmodium transgenic lines, knockdown and knockout transgenic parasites, and transgenic parasites expressing alternative alleles, and also mutant strains of Anopheles such as only male mosquito populations, generation of wingless mosquitoes, and creation of knock-out/ knock-in mutants. Though, the incorporation of traditional methods and novel molecular techniques could noticeably enhance the quality of results. The striking development of a CRISPR/Cas-based diagnostic kit that can specifically diagnose the Plasmodium species or drug resistance markers is highly required in malaria settings with affordable cost and high-speed detection. Furthermore, the advancement of genome modifications by CRISPR/Cas technologies resolves contemporary restrictions to culturing, maintaining, and analyzing these parasites, and the aptitude to investigate parasite genome functions opens up new vistas in the better understanding of pathogenesis.

Old Meets New: Mass Spectrometry-Based Untargeted Metabolomics Reveals Unusual Larvicidal Nitropropanoyl Glycosides from the Leaves of Heteropterys umbellata

The Aedes aegypti (Diptera: Culicidae) mosquito is the vector of several arboviruses in tropical and subtropical areas of the globe, and synthetic pesticides remain the most widely used combat strategy. This study describes the investigation of secondary metabolites with larvicidal activity from the Malpighiaceae taxon using a metabolomic and bioactivity-based approach. The workflow initially consisted of a larvicidal screening of 394 extracts from the leaves of 197 Malpighiaceae samples, which were extracted using solvents of different polarity, leading to the selection of Heteropterys umbellata for the identification of active compounds. By employing untargeted mass spectrometry-based metabolomics and multivariate analyses (PCA and PLS-DA), it was possible to determine that the metabolic profiles of different plant organs and collection sites differed significantly. A bioguided approach led to the isolation of isochlorogenic acid A (1) and the nitropropanoyl glucosides karakin (2) and 1,2,3,6-tetrakis-O-[3-nitropropanoyl]-beta-glucopyranose (3). These nitro compounds exhibited larvicidal activity, possibly potentialized by synergistic effects of their isomers in chromatographic fractions. Additionally, targeted quantification of the isolated compounds in different extracts corroborated the untargeted results from the statistical analyses. These results support a metabolomic-guided approach in combination with classical phytochemical techniques to search for natural larvicidal compounds for arboviral vector control.

The diversity of Plasmodium falciparum isolates from asymptomatic and symptomatic school-age children in Kinshasa Province, Democratic Republic of Congo

BACKGROUND

Understanding Plasmodium falciparum population diversity and transmission dynamics provides information on the intensity of malaria transmission, which is needed for assessing malaria control interventions. This study aimed to determine P. falciparum allelic diversity and multiplicity of infection (MOI) among asymptomatic and symptomatic school-age children in Kinshasa Province, Democratic Republic of Congo (DRC).

METHODS

A total of 438 DNA samples (248 asymptomatic and 190 symptomatic) were characterized by nested PCR and genotyping the polymorphic regions of pfmsp1 block 2 and pfmsp2 block 3.

RESULTS

Nine allele types were observed in pfmsp1 block2. The K1-type allele was predominant with 78% (229/293) prevalence, followed by the MAD20-type allele (52%, 152/293) and RO33-type allele (44%, 129/293). Twelve alleles were detected in pfmsp2, and the 3D7-type allele was the most frequent with 84% (256/304) prevalence, followed by the FC27-type allele (66%, 201/304). Polyclonal infections were detected in 63% (95% CI 56, 69) of the samples, and the MOI (SD) was 1.99 (0.97) in P. falciparum single-species infections. MOIs significantly increased in P. falciparum isolates from symptomatic parasite carriers compared with asymptomatic carriers (2.24 versus 1.69, adjusted b: 0.36, (95% CI 0.01, 0.72), p = 0.046) and parasitaemia > 10,000 parasites/µL compared to parasitaemia < 5000 parasites/µL (2.68 versus 1.63, adjusted b: 0.89, (95% CI 0.46, 1.25), p < 0.001).

CONCLUSION

This survey showed low allelic diversity and MOI of P. falciparum, which reflects a moderate intensity of malaria transmission in the study areas. MOIs were more likely to be common in symptomatic infections and increased with the parasitaemia level. Further studies in different transmission zones are needed to understand the epidemiology and parasite complexity in the DRC.

Invasive mosquito vectors in Europe: From bioecology to surveillance and management

Invasive mosquitoes (Diptera: Culicidae) play a key role in the spread of a number of mosquito-borne diseases worldwide. Anthropogenic changes play a significant role in affecting their distribution. Invasive mosquitoes usually take advantage from biotic homogenization and biodiversity reduction, therefore expanding in their distribution range and abundance. In Europe, climate warming and increasing urbanization are boosting the spread of several mosquito species of high public health importance. The present article contains a literature review focused on the biology and ecology of Aedes albopictus, Ae. aegypti, Ae. japonicus japonicus, Ae. koreicus, Ae. atropalpus and Ae. triseriatus, outlining their distribution and public health relevance in Europe. Bioecology insights were tightly connected with vector surveillance and control programs targeting these species. In the final section, a research agenda aiming for the effective and sustainable monitoring and control of invasive mosquitoes in the framework of Integrated Vector Management and One Health is presented. The WHO Vector Control Advisory Group recommends priority should be given to vector control tools with proven epidemiological impact.

Mosquito-Borne Diseases and Their Control Strategies: An Overview Focused on Green Synthesized Plant-Based Metallic Nanoparticles

Mosquitoes act as vectors of pathogens that cause most life-threatening diseases, such as malaria, Dengue, Chikungunya, Yellow fever, Zika, West Nile, Lymphatic filariasis, etc. To reduce the transmission of these mosquito-borne diseases in humans, several chemical, biological, mechanical, and pharmaceutical methods of control are used. However, these different strategies are facing important and timely challenges that include the rapid spread of highly invasive mosquitoes worldwide, the development of resistance in several mosquito species, and the recent outbreaks of novel arthropod-borne viruses (e.g., Dengue, Rift Valley fever, tick-borne encephalitis, West Nile, yellow fever, etc.). Therefore, the development of novel and effective methods of control is urgently needed to manage mosquito vectors. Adapting the principles of nanobiotechnology to mosquito vector control is one of the current approaches. As a single-step, eco-friendly, and biodegradable method that does not require the use of toxic chemicals, the green synthesis of nanoparticles using active toxic agents from plant extracts available since ancient times exhibits antagonistic responses and broad-spectrum target-specific activities against different species of vector mosquitoes. In this article, the current state of knowledge on the different mosquito control strategies in general, and on repellent and mosquitocidal plant-mediated synthesis of nanoparticles in particular, has been reviewed. By doing so, this review may open new doors for research on mosquito-borne diseases.

Control of Aedes mosquito populations using recombinant microalgae expressing short hairpin RNAs and their effect on plankton

New biocontrol strategies are urgently needed to combat vector-borne infectious diseases. This study presents a low-cost method to produce a potential mosquito insecticide that utilizes the microalgae released into suburban water sources to control mosquito populations. Chlorella microalgae are ubiquitous in local waters, which were chosen as the host for genetic transfection. This species facilitated the recombinant algae to adapt to the prevailing environmental conditions with rapid growth and high relative abundance. The procedure involved microalgae RNAi-based insecticides developed using short hairpin RNAs targeting the Aedes aegypti chitin synthase A (chsa) gene in Chlorella. These insecticides effectively silenced the chsa gene, inhibiting Aedes metamorphosis in the laboratory and simulated-field trials. This study explored the impact of recombinant microalgae on the phytoplankton and zooplankton in suburban waters. High-throughput sequencing revealed that rapid reproduction of recombinant Chlorella indirectly caused the disappearance of some phytoplankton and reduced the protozoan species. This study demonstrated that a recombinant microalgae-based insecticide could effectively reduce the population of Aedes mosquitoes in the laboratory and simulated field trials. However, the impact of this technology on the environment and ecology requires further investigation.

Insecticidal activities of Streptomyces sp. KSF103 ethyl acetate extract against medically important mosquitoes and non-target organisms

A potentially novel actinobacterium isolated from forest soil, Streptomyces sp. KSF103 was evaluated for its insecticidal effect against several mosquito species namely Aedes aegypti, Aedes albopictus, Anopheles cracens and Culex quinquefasciatus. Mosquito larvae and adults were exposed to various concentrations of the ethyl acetate (EA) extract for 24 h. Considerable mortality was evident after the EA extract treatment for all four important vector mosquitoes. Larvicidal activity of the EA extract resulted in LC₅₀ at 0.045 mg/mL and LC₉₀ at 0.080 mg/mL for Ae. aegypti; LC₅₀ at 0.060 mg/mL and LC₉₀ at 0.247 mg/mL for Ae. albopictus; LC₅₀ at 2.141 mg/mL and LC₉₀ at 6.345 mg/mL for An. cracens; and LC₅₀ at 0.272 mg/mL and LC₉₀ at 0.980 mg/mL for Cx. quinquefasciatus. In adulticidal tests, the EA extract was the most toxic to Ae. albopictus adults (LD₅₀ = 2.445 mg/mL; LD₉₀ = 20.004 mg/mL), followed by An. cracens (LD₅₀ = 5.121 mg/mL; LD₉₀ = 147.854 mg/mL) and then Ae. aegypti (LD₅₀ = 28.873 mg/mL; LD₉₀ = 274.823 mg/mL). Additionally, the EA extract exhibited ovicidal activity against Ae. aegypti (LC₅₀ = 0.715 mg/mL; LC₉₀ = 6.956 mg/mL), Ae. albopictus (LC₅₀ = 0.715 mg/mL; LC₉₀ = 6.956 mg/mL), and An. cracens (LC₅₀ = 0.715 mg/mL; LC₉₀ = 6.956 mg/mL), evaluated up to 168 h post-treatment. It displayed no toxicity on the freshwater microalga Chlorella sp. Beijerinck UMACC 313, marine microalga Chlorella sp. Beijerinck UMACC 258 and the ant Odontoponera denticulata. In conclusion, the EA extract showed promising larvicidal, adulticidal and ovicidal activity against Ae. aegypti, Ae. albopictus, An. cracens, and Cx. quinquefasciatus (larvae only). The results suggest that the EA extract of Streptomyces sp. KSF103 has the potential to be used as an environmental-friendly approach in mosquito control. The current study would serve as an initial step toward complementing microbe-based bioinsecticides for synthetic insecticides against medically important mosquitoes.

The bioprospecting potential of Clusia fluminensis Planch. & Triana: a scoping review

Many biological activities are described for the Clusiaceae family. Clusia fluminensis, a species from Brazilian flora, is mainly employed for ornamental purposes. This review aimed to depict the current knowledge of C. fluminensis from a bioprospecting standpoint. "Clusia fluminensis" search term was applied in Scopus, Web of Science, PubMed and Bireme databases according to PRISMA-ScR statement. Selected papers on Phytochemistry or Bioactivity followed hand searching procedures. Bioactivity preclinical studies considered in vitro or in vivo biological systems, treated with plant extracts or isolated compounds. The outcomes were compared with standard or no treatment control groups. Critical appraisal of individual trials considered completeness in the research fields. Our results showed that 81% of the selected papers presented high level of completeness, 69% revealed phytochemical parameters and 31% biological applications of plant extracts and isolated compounds. Polyisoprenylated benzophenones, terpenoids, sterols and phenolic compounds were identified. Antiviral, insecticidal and snake antivenom activities were reported. In conclusion, the phytochemical data reinforce the reported activities. Potential applications in personal care, nutritional supplementation and pharmaceutical, food, chemical or textile industries were also identified. Toxicological and phytochemical complementary studies may be required.

Perspectives of vector management in the control and elimination of vector-borne zoonoses

The complex transmission profiles of vector-borne zoonoses (VZB) and vector-borne infections with animal reservoirs (VBIAR) complicate efforts to break the transmission circuit of these infections. To control and eliminate VZB and VBIAR, insecticide application may not be conducted easily in all circumstances, particularly for infections with sylvatic transmission cycle. As a result, alternative approaches have been considered in the vector management against these infections. In this review, we highlighted differences among the environmental, chemical, and biological control approaches in vector management, from the perspectives of VZB and VBIAR. Concerns and knowledge gaps pertaining to the available control approaches were discussed to better understand the prospects of integrating these vector control approaches to synergistically break the transmission of VZB and VBIAR in humans, in line with the integrated vector management (IVM) developed by the World Health Organization (WHO) since 2004.

First comprehensive report of the resistance of Culex quinquefasciatus Say (Diptera: Culicidae) to commonly used insecticides in Riyadh, Saudi Arabia

The mosquito Culex quinquefasciatus is a vector of various pathogens including West Nile virus, Saint Louis encephalitis virus, and Western equine encephalitis virus. Insecticides are the main tools for Cx. quinquefasciatus control, but this overreliance on chemical tools has led to the development of resistance to many insecticides in this important insect vector. The resistance of eight field populations of Cx. quinquefasciatus to 10 commonly used insecticides was evaluated. Based on the resistance ratios (RRs), the adults of Cx. quinquefasciatus field populations displayed susceptibility to the organophosphates (OPs) except Al-Masanie adults which exhibited low resistance to fenitrothion (RR₅₀ = 3.62). Conversely, the mosquitoes exhibited susceptibility, low resistance, and moderate resistance to the pyrethroids alpha-cypermethrin (RR = 0.59-2.56), bifenthrin (RR = 0.59-2.19), deltamethrin (RR = 0.60-7.07), cypermethrin (RR = 0.60-2.66), and cyfluthrin (RR = 0.58-2.39). At the larval stage, Cx. quinquefasciatus field populations displayed susceptibility to low resistance to the OPs chlorpyrifos (RR = 0.03-1.75), malathion (RR = 0.19-3.42), fenitrothion (RR = 0.11-2.78), and pirimiphos-methyl (RR = 0.08-1.15). Although these results in Cx. quinquefasciatus field populations indicated that the OPs and pyrethroids maintained high efficacy in controlling this species in the geographical area of this study, these findings should be utilized wisely to avoid any potential negative effects on human health and environmental safety attributable to the application of these broad-spectrum conventional insecticides. However, these findings provide a solid basis for decision-making for Cx. quinquefasciatus integrated vector management programs.

Cladophialophora bantiana metabolites are efficient in the larvicidal and ovicidal control of Aedes aegypti, and Culex quinquefasciatus and have low toxicity in zebrafish embryo

Mosquitoes' current insecticide resistance status in available public health insecticides is a serious threat to mosquito control initiatives. Microbe-based control agents provide an alternative to conventional pesticides and insecticides, as they can be more targeted than synthetic insecticides. The present study was focused on identifying and investigating the mosquitocidal potential of Cladophialophora bantiana, an endophytic fungus isolated from Opuntia ficus-indica. The Cladophialophora species was identified through phylogenetic analysis of the rDNA sequence. The isolated fungus was first evaluated for its potential to produce metabolites against Aedes aegpti and Culex quinquefasciatus larvae in the 1-4th instar. The secondary metabolites of mycelium extract were assessed at various test doses (100, 200, 300, 400, and 500 μg/mL) in independent bioassays for each instar of selected mosquito larvae. After 48 h of exposure, A. aegypti expressed LC₅₀ values of 13.069, 18.085, 9.554, and 11.717 μg/mL and LC₉₀ = 25.702, 30.860, 17.275, and 19.601 μg/mL; followed by C. quinquefasciatus LC₅₀ = 14.467, 11.766, 5.934, and 7.589 μg/mL, and LC₉₀ = 29.529, 20.767, 11.192, and 13.296 μg/mL. The mean % of ovicidal bioassay was recorded 120 h after exposure. The hatchability (%) was proportional to mycelia metabolite concentration. The enzymatic level of acetylcholinesterase in fungal mycelial metabolite treated 4th instar larvae indicated a dose-dependent pattern. The GC-MS profile of C. bantiana extracts identified five of the most abundant compounds, namely cyclobutane, trans-3-undecene-1,5-diyne, 1-bromo-2-chloro, propane, 1,2,3-trichloro-2-methyl-, 5,5,10,10-tetrachlorotricyclo, and phenol, which had the killing effect in mosquitoes. Furthermore, the C. bantiana fungus ethyl acetate extracts had a strong larvicidal action on A. aegypti and C. quinquefasciatus. Finally, the toxicity test on zebrafish embryos revealed the induction of malformations only at concentrations above 1 mg/mL. Therefore, our study pioneered evidence that C. bantiana fungal metabolites effectively control A. aegypti and C. qunquefasciastus and show less lethality in zebrafish embryos at concentrations up to 500 μg/mL.

Role of the predaceous mosquito Toxorhynchites christophi (Diptera: Culicidae) in treehole ecosystems in a Korean forest

Toxorhynchites mosquitoes have been studied as potential biological mosquito control agents because they consume other mosquito larvae. As a top predator, Toxorhynchites species are also considered keystone predators in phytotelmata. However, limited information is available regarding Toxorhynchites christophi, which is found in northeast Asia. The present study investigated whether Tx. christophi could reduce mosquito populations and increase species diversity by functioning as a mosquito control agent and keystone predator, respectively. During the study, aquatic insects were collected every three weeks (May-October, 2018) from tire habitats, which resemble treehole ecosystems, at the Korean National Arboretum in the central region of the Korean Peninsula. The samples were separated into the surface- and the substrate-groups based on their behavior, and the communities were compared based on the density of Tx. christophi. As a result, the communities with a higher density of the predators showed a higher diversity and evenness, and the communities also had a lower mosquito ratio, dominance, and density of the surface-group. The results of both non-metric multi-dimensional scaling and one-way analysis of similarities also indicated that the communities were affected by the density of Tx. christophi larvae. Similarity percentage analysis results revealed the effects of this predator on the communities could mainly be attributed to reductions in the densities of the three dominant mosquito species (Aedes koreicus, Ae. flavopictus, and Tripteroides bambusa). Thus, Tx. christophi may be valuable as both a biological mosquito control agent and keystone species of treehole ecosystems by reducing dominant mosquito species and improving species diversity.

A Review of the Chemistry and Biological Activities of Acmella oleracea ("jambù", Asteraceae), with a View to the Development of Bioinsecticides and Acaricides

Human pathologies, environmental pollution, and resistance phenomena caused by the intensive use of chemical pesticides have shifted the attention of the agrochemical industries towards eco-friendly insecticides and acaricides. Acmella oleracea (L.) R. K. Jansen (jambù) is a plant native to South America, widely distributed and cultivated in many countries due to its numerous pharmacological properties. This review analyzes literature about the plant, its uses, and current knowledge regarding insecticidal and acaricidal activity. Acmella oleracea has proven to be a potential pesticide candidate against several key arthropod pest and vector species. This property is inherent to its essential oil and plant extract, which contain spilanthol, the main representative of N-alkylamides. As a result, there is a scientific basis for the industrial exploitation of jambù in the preparation of green insecticides. However, studies related to its toxicity towards non-target species and those aimed at formulating and developing marketable products are lacking.

Biodegradable floating hydrogel baits as larvicide delivery systems against mosquitoes

Biological methods for mosquito larvae control are completely biodegradable and have null or limited effects on nontarget organisms. However, commercially available products have a low residual activity, with the consequent need for multiple applications that inevitably increase costs and the risk of resistance phenomena insurgence. Smart delivery systems made of hydrogels proved their efficacy in increasing the action duration of biolarvicides up to several months, but the lack of an efficient baiting mechanism to strongly attract the target pest remains a problem in practical applications. In this work, we investigated two novel hydrogel-based formulations of completely natural composition for baiting and killing larvae of Aedes albopictus mosquitos. The proposed materials consist of charged crosslinked polysaccharides (chitosan and cellulose) and are specifically manufactured to float in water, simulating organic matter usually present at breeding sites. Within the hydrogels' matrix, yeast colonies of Saccharomyces cerevisiae were embedded as phagostimulants alongside a biolarvicide (Bacillus thuringiensis var. israelensis (Bti)). Despite the similar chemical nature and structure, chitosan-based hydrogels exhibited a markedly superior baiting potential compared to those made of cellulose and also succeeded in efficiently killing mosquito larvae just after a few hours from administration. We are confident that the proposed smart delivery hydrogel made of chitosan can be an enabling tool to attract mosquito larvae towards biopesticides of different nature without delocalizing active ingredients away from the breeding site and to simultaneously increase their residual activity, thus holding the potential of minimizing environmental pollution related to pest control and vector-borne disease prevention.

In Silico Study and Excito-Repellent Activity of Vitex negundo L. Essential Oil against Anopheles gambiae

(1) Background: Essential oil from Vitex negundo is known to have repellent and insecticidal properties toward the Anopheles gambiae and this is linked to its monoterpene and sesquiterpene content. In this work, an effort is made to delineate the constitution of V. negundo essential oil (VNEO) and their interaction with odorant-binding proteins (OBPs) of A. gambiae and hence access its repellent efficiency as cost-effective and safer malaria vector control alternatives. (2) Methods: Anopheles species authentication was performed by genomic DNA analysis and was subjected to behavioral analysis. GC-MS profiling was used to identify individual components of VNEO. Anopheles OBPs were obtained from the RCSB protein data bank and used for docking studies. Determination of ligand efficiency metrics and QSAR studies were performed using Hyper Chem Professional 8.0.3, and molecular dynamics simulations were performed using the Desmond module. (3) Results: GC-MS analysis of VNEO showed 28 compounds (monoterpenes, 80.16%; sesquiterpenes, 7.63%; and unknown constituents, 10.88%). The ligand efficiency metrics of all four ligands against the OBP 7 were within acceptable ranges. β-selinene (−12.2 kcal/mol), β-caryophellene (−9.5 kcal/mol), sulcatone (−10.9 kcal/mol), and α-ylangene (−9.3 kcal/mol) showed the strongest binding affinities for the target proteins. The most stable hydrophobic interactions were observed between β-selinene (Phe111 and Phe120), Sulcatone (Phe54 and Phe120), and α-ylangene (Phe111), while only sulcatone (Tyr49) presented H-bond interactions in the simulated environment. (4) Conclusions: Sulcatone and β-caryophyllene presented the best log p values, 6.45 and 5.20, respectively. These lead phytocompounds can be used in their purest as repellent supplement or as a natural anti-mosquito agent in product formulations.

Attractive Sugar Bait Formulation for Development of Attractive Toxic Sugar Bait for Control of Aedes aegypti (Linnaeus)

Background

Attractive toxic sugar bait (ATSB), based on “attract and kill” approach, is a novel and promising strategy for mosquito control. Formulation of an attractive sugar bait (ASB) solution by selecting an efficient olfaction stimulant and preparation of an optimized sugar-attractant dosage is a significant component for the success of the approach.

Methods

Current study evaluated relative potential of nine ASBs, formulated by combination of sugar and fresh fruit juices (guava, mango, muskmelon, orange, papaya, pineapple, plum, sweet lemon, and watermelon) in attracting Aedes aegypti adults. Freshly extracted and 48-hour-fermented juices were combined with 10% sucrose solution (w/v) in 1 : 1 ratio. Cage bioassays were conducted against two laboratory strains (susceptible: AND-Aedes aegypti; deltamethrin-selected: AND-Aedes aegypti-DL10) and two field-collected strains (Shahdara strain of Aedes aegypti: SHD-Delhi; Govindpuri strain of Aedes aegypti: GVD-Delhi). Each of the nine ASBs was assayed, individually or in groups of three, for its attraction potential based on the relative number of mosquito landings. The data were analysed for statistical significance using PASW (SPSS) software 19.0 program.

Results

The prescreening bioassay with individual ASB revealed significantly higher efficacy of ASB containing guava/plum/mango juice than that containing six other juices (p < 0.05) against both the laboratory and field strains. The bioassay with three ASBs kept in one cage, one of the effective ASBs and two others randomly selected ASBs, also showed good attractancy of the guava/plum/mango juice-ASB (p < 0.05). The postscreening assays with these three ASBs revealed maximum attractant potential of guava juice-sucrose combination for all the four strains of Ae. aegypti. Conclusion. Guava juice-ASB showed the highest attractancy against both laboratory and field-collected strains of Ae. aegypti and can be used to formulate ATSB by combining with a toxicant. The field studies with these formulations will ascertain their efficacy and possible use in mosquito management programs.