Dengue Vector Research Articles

Potential Toxicity of <i>Indigofera tinctoria</i> Synthesized Iron Nanoparticles against <i>Aedes aegypti</i>

Mosquitoes are the most important single category of insects, killing millions of people worldwide each year by spreading a variety of diseases. The principal dengue vector Aedes aegypti, is expected to infect 2.5 billion people worldwide, or more than 40% of the world’s population. According to a WHO survey, 50-100 million cases are reported globally each year. Extensive fumigation of synthetic pesticides to control the mosquito vector in Pakistan during each post-monsoon season greatly increased environmental contamination and the loss of beneficial insects from urban environments. This study looked into the larvicidal and pupicidal efficiency of green synthesized iron nanoparticles against Ae. aegypti. Nanoparticles were subjected to several analyses, including UV-Vis, FTIR, FESEM, EDAX, XRD, Zeta Potential, and DLS. Ae. aegypti, the predominant dengue mosquito, was studied for its larvicidal and pupicidal activities. Indigofera tinctoria produced iron nanoparticles with LC50 values ranging from 4.468 ppm (I instar larvae) to 7.952 ppm (pupae). Laboratory experimental studies on larval body tissues, particularly fat cells, fingernail skin and midgut have been carried out. It has been determined the plant synthesis of iron nanoparticles are harmful to Ae. aegypti larval.

Detection of dengue in German tourists returning from Ibiza, Spain, related to an autochthonous outbreak, August to October 2022.

In February 2023, German public health authorities reported two dengue cases (one confirmed, one probable) and four possible cases who travelled to Ibiza, Spain, in late summer/autumn 2022; the infection was probably acquired through mosquito bites. Case 1 visited Ibiza over 1 week in late August with two familial companions; all three developed symptoms the day after returning home. Only Case 1 was tested; dengue virus (DENV) infection was confirmed by presence of NS1 antigen and IgM antibodies. Case 2 travelled to Ibiza with two familial companions for 1 week in early October, and stayed in the same town as Case 1. Case 2 showed symptoms on the day of return, and the familial companions 1 day before and 3 days after return; Case 2 tested positive for DENV IgM. The most probable source case had symptom onset in mid-August, and travelled to a dengue-endemic country prior to a stay in the same municipality of Ibiza for 20 days, until the end of August. Dengue diagnosis was probable based on positive DENV IgM. Aedes albopictus, a competent vector for dengue, has been present in Ibiza since 2014. This is the first report of a local dengue transmission event on Ibiza.

Nornicotine‐Typed Insecticides: The Potential Insecticides with Strong Activity Against Aedes Albopictus

AbstractAedes albopictus, the main vector of dengue, yellow fever, chikungunya, and Zika, has caused significant public health concerns, but there are still few effective insecticides. Nicotine and nornicotine‐typed compounds are well‐known for their potential as an insecticide, which has potential activity against Ae. albopictus. Here we report the effects of nornicotine‐typed insecticide against larvae of Ae. albopictus. We developed a novel synthetic strategy for nicotine and nornicotine‐typed compounds. Novel compounds A1‐A8 and B1‐B26 were synthesized by the synthesized nornicotine. And bioassays indicated that most of these compounds exhibited good effects against larvae of Ae. albopictus, and compounds A3, B4, B20, and B26 had excellent activity against Ae. albopictus, and they were not toxic to humans according to other reports. After considering the cost, compounds B4, B20, and B26 could be potential lead compounds against Ae. albopictus and other Aedes mosquitoes.

Bamboo stumps that are artificially in use put pressure on dengue and chikungunya vector control in Dhaka city, Bangladesh.

Aedes aegypti and Ae. albopictus mosquitoes breed in natural and artificial containers, and they transmit dengue and chikungunya. A study was conducted to identify the contribution of bamboo stumps to these disease vectors that were used in the flower garden as pillars to hold the bamboo flex fence. Two sizes of whole bamboo were used to hold fences around gardens at Dhaka University, Bangladesh, and were painted red and green. Mosquito larvae and pupae were collected from bamboo stumps between July and August, and vectors were identified up to the species level. The data were analyzed using the STATA/MP 14.2 version. 83.5% and 0.2% were Ae. albopictus and Ae. aegypti, respectively, and the remaining were Culex and Ar-migeres species. Ae. albopictus, Ae. aegypti, and both species-positive bamboo stumps were 46.9, 0.7, and 47.1%, respectively. 54.5% of the bamboo stumps had at least one mosquito species. The average stump depth for Aedes positive stumps (mean=11.7 cm, SE = 0.5) was significantly (p <0.001) higher than the Aedes negative stumps (mean = 9.5 cm, SE = 0.4). 53.8% and 38.0% stumps were found Aedes positive on the ground and upper sides of fences, respectively, and found significant (p<0.01) differences between both sides. A zero-inflated negative binomial count model is significant at a 5% level of significance, χ2(4) = 11.8, p = 0.019 (<0.05) for Ae. albopictus. Stump depth is found to have a significant positive effect on the number of Aedes-positive stumps. Artificially used natural containers are adding pressure to current mosquito control activities as mosquitoes are breeding on them, which needs additional attention.

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

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. 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. 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. 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.

Species composition of larval mosquitoes (Diptera: Culicidae) in bamboo stumps in mid-western Nepal

ABSTRACT Bamboo stumps serve as important phytotelmata in which mosquitoes breed. The physiochemical parameters of water in the bamboo stumps influence the species composition and larval abundance of mosquito species. Bamboo stumps were scanned in monsoon season of 2022 by adopting a larval survey method in mid-western Nepal. Supplementary data such as water volume, temperature and pH were also recorded. The linear relationship between different physiochemical parameters with mosquito larval population and larval abundance of different mosquito species was analysed in RStudio-1.0.44 and Past software version 4.07. Altogether, 120 larval mosquitoes belonging to 7 species and 3 genera were recorded from 26 bamboo stumps. The larval abundance of immature mosquito shows positive correlation with water temperature, pH and volume of the water. The coexistence of larvae of dengue vectors (Aedes aegypti and Aedes albopictus) and vector of Lymphatic Filariasis (Culex quinquefasciatus) as well the coexistence of different larval mosquito species were recorded. This established bamboo stumps as important mosquito breeding habitats including vector species in mid-western Nepal.

Polymer Beads Increase Field Responses to Host Attractants in the Dengue Vector Aedes aegypti.

This study investigates the efficacy of three different olfactory cues - cyclohexanone, linalool oxide (LO), and 6-methyl-5-heptan-2-one (sulcatone) - in attracting Aedes aegypti, the primary vector of dengue, using BG sentinel traps in a dengue-endemic area (urban Ukunda) in coastal Kenya. Two experiments were conducted. Experiment 1 compared solid formulations of the compounds in polymer beads against liquid formulations with hexane as the solvent. CO2-baited traps served as controls. In Experiment 2, traps were baited with each compound in the polymer beads, commercial BG-Lure, and CO2. Our results indicate that CO2-baited traps recorded the greatest Ae. aegypti captures in both Experiment 1 and 2, whereas trap captures with polymer beads and solvent-based treatments were comparable. In experiment 2, polymer bead-based treatments yielded significantly greater female captures, each recording ~ 2-fold more captures than traps baited with the BG-Lure. There was no significant difference, however, between the treatments. Female Ae. aegypti captured in CO2-baited traps were mainly unfed (91%), with fewer gravid mosquitoes (6.4%) compared to traps with test compounds (range; 12.7-21.1%). Male captures were lower in LO and BG-Lure baited traps compared to other treatments. Gravimetric analysis showed LO had a slower release rate compared to other compounds. The findings suggest that host-associated compounds loaded on polymer beads are more effective in trapping Ae. aegypti than commercial BG-Lure and reveal sex-specific differences in mosquito responses. These results have implications for mosquito surveillance and control programs, highlighting the potential for selective trapping strategies.

Utilization of herbivore defensive latex from the weed Calotropis procera L in the green synthesis of silver nanoparticles and its potential application in the control of dengue vector Aedes aegypti

Milky latex produced by few and not all the plants are the treasure chest of various bioactive compounds with defensive potential against herbivores, insects and pathogens. Mankind have utilized latices in the preparation of novel plant-based therapies for centuries. Therefore, an attempt has been made to synthesis silver nanoparticles (AgNPs) using AgNO3 as a precursor and latex from C. procera as a reducing agent. The surface plasmon absorption peak at 430 nm confirmed AgNPs formation. The sharp peak with narrow width illustrated the homogenous nature. The face centre cubic structure of AgNPs was confirmed by the XRD pattern. FT-IR analysis deduced that the bio-molecules in the latex of C. procera are responsible for the reduction of AgNO3 to AgNPs. Biosynthesised L-AgNPs possessed well pronounced antibacterial activity against P. aeruginosa and K. pneumoniae. Anti-inflammatory activity of the nanoparticle determined by membrane stabilization and proteinase inhibitory assay was found to be in dose-dependent. LC50 value of L-AgNPs was found to be 63.09 µg/mL against IV instar larvae of A. aegypti. Distinct morphological changes were observed in the mosquito larva on exposure to various concentrations of L-AgNPs.

Wolbachia Infection through Hybridization to Enhance an Incompatible Insect Technique-Based Suppression of Aedes albopictus in Eastern Spain.

The emergence of insecticide resistance in arbovirus vectors is putting the focus on the development of new strategies for control. In this regard, the exploitation of Wolbachia endosymbionts is receiving increasing attention due to its demonstrated effectiveness in reducing the vectorial capacity of Aedes mosquitoes. Here, we describe the establishment of a naïve Wolbachia infection in a wild Aedes albopictus population of eastern Spain through a hybridization approach to obtain males capable of sterilizing wild females. The obtained lines were compared with the Wolbachia donor, Ae. albopictus ARwP, previously artificially infected with Wolbachia wPip, regarding immature and adult survival, female fecundity, egg fertility, and level of induced sterility. Our results did not show significant differences between lines in any of the biological parameters analyzed, indicating the full suitability of the hybrids to be used as a control tool against Ae. albopictus. In particular, hybrid males induced 99.9% sterility in the eggs of wild females without the need for any preliminary treatment. Being harmless to non-target organisms and the environment, the use of this bacterium for the control of Ae. albopictus deserves further exploration. This is especially relevant in areas such as eastern Spain, where this mosquito species has recently spread and may represent a serious threat due to its competence as a vector for dengue, chikungunya, and Zika viruses.

Dengue Vaccines: Current Status and Future Perspectives

Dengue fever (DF), caused by the dengue virus (DENV), is a major public health problem worldwide, with approximately 390 million reported annual infections. The lack of specific antiviral therapies and limited means of vector control has led to the development of a dengue vaccine as a promising strategy to combat this disease. The purpose of this review is to provide a comprehensive analysis of the current status and prospects of dengue vaccines. This review describes different approaches used in dengue vaccine development, including live-attenuated, inactivated, subunit, and viral vector vaccines. Each approach is evaluated for immunogenicity, safety, and efficacy based on preclinical and clinical studies, highlighting the strengths and limitations of each vaccine candidate. Future directions and research priorities in dengue vaccine development are highlighted. In conclusion, dengue vaccines have great potential to reduce the burden of DF worldwide. However, some challenges remain regarding vaccine safety, efficacy, delivery, and availability. By addressing these challenges and leveraging advances in vaccine technology, there can be more effective control and prevention of DF and protection of public health, leading to improvement in the quality of life.

THE INCREASE IN THE NUMBER OF DENGUE CASES IN BRAZIL AND THE CORRELATION WITH DEFORESTATION AND GLOBALIZATION

Brazil has faced a significant increase in the number of dengue cases in recent decades, which represents a challenge for public health authorities. Several factors may contribute to this increase, including deforestation and globalization, which have a direct impact on the proliferation of the Aedes aegypti mosquito, the dengue vector. The aims of this study are to investigate the relationship between increased deforestation and globalization and the increase in dengue cases in Brazil and to analyse the mechanisms by which deforestation and globalization can influence the spread of dengue. The methodology in question is a systematic review, using the narrative method, using quantitative and qualitative factors to reach the expected result. The DataSus/Tabnet, Terrabrasilis, PubMed, Scopus, Web of Science and Virtual Health Library databases were also used, using the health sciences descriptors “Dengue hospitalizations”, “Deforestation and Arboviruses”, “Deforestation and Dengue” and “Globalization and Dengue”, totalling 84 works and 8 works of literature were used in the formulation of this review and 2 references were formulated through the quantitative databases. Deforestation can increase the incidence of dengue, as it creates favorable environments for the reproduction of the transmitting mosquito, such as the accumulation of water in tires, cans and abandoned containers. In addition, deforestation can lead to the migration of populations from rural to urban areas, increasing exposure to endemic areas of the disease. Globalization can also contribute to the increase in dengue cases by facilitating the transport of infected people and the mosquito vector between different regions. Increased international trade and tourism can expand the spread of the dengue virus to new areas. The increase in the number of dengue cases in Brazil is related to deforestation and globalization, which create favourable conditions for the propagation of the mosquito vector and the spread of the dengue virus between different regions. Disease control measures must take these factors into account and include actions to monitor deforestation, vector control and public health education in order to reduce the incidence of dengue in the country.

Insecticide paints: a new community strategy for controlling dengue and zika mosquito vectors in Cabo Verde

BackgroundCabo Verde, an island country in West Africa, has been affected since human colonization by epidemics of vector-borne diseases with major epidemics of dengue and zika in recent years. Although there is a national program for integrated vector control, innovative strategies that reinforce routine activities and strengthen vector control are necessary to prevent the emergence or reemergence of arboviruses and new epidemics of dengue and zika. Insecticide paints are evidenced as new technologies for the formulation of insecticides in a more residual and safe way. The TINTAEDES project aimed to assess the efficacy, acceptability, and operational deployment of an insecticide paint for Aedes control.Methodology/Principal findingsLaboratory and small-scale field trials were conducted, assessing mortality through World Health Organization cone bioassays. A community-based intervention study in the neighborhoods of Várzea and Tira Chapéu in the city of Praia, Cabo Verde, was developed. The intervention is a paint self-application model by homeowners and neighborhood volunteers. The intervention was evaluated based on entomological indicators and the responses given by the residents of the painted houses to a questionnaire on the knowledge, satisfaction, and safety of insecticidal paints. A transfluthrin-based insecticide paint was effective against wild Ae. aegypti for one year in the laboratory and semi-field conditions. Residents largely perceived a reduction in mosquito presence in the treated houses (98%).ConclusionInsecticide paints are presented as an effective innovation strategy for mosquito control, which could be implemented as a reinforcement of the measures carried out by the vector control program in the city of Praia and throughout the country.

Insecticide Susceptibility and KDR Mutations in Aedes Albopictus Collected from Seven Districts of Guangyuan city, Northern Sichuan, China.

The Asian tiger mosquito, Aedes albopictus, is an important vector of chikungunya, dengue, yellow fever, and Zika viruses. Vector control remains an important means for the prevention and control of vector-borne diseases. The development of insecticide resistance has become a serious threat to the efficacy of insecticide-based control programs. To understand the resistance status and the underlying genetic mechanism in mosquitoes in Guangyuan City of Sichuan Province, China, we investigated the susceptibility of Ae. albopictus to four commonly used insecticides. We found that all the examined populations were susceptible to malathion and propoxur. However, Ae. albopictus populations in Guangyuan showed a possible resistance to the two tested pyrethroids (beta-cypermethrin and deltamethrin). Notably, phenotypic resistance to deltamethrin was detected in 2 of the 7 populations. The potential of resistance to pyrethroids was confirmed by the presence of knockdown resistance (kdr) related mutations in the voltage-gated sodium channel. Four kdr mutations (V1016G, I1532T, F1534L, and F1534S) were identified to be present alone or in combination, and their distribution displayed significant spatial heterogeneity. These findings are helpful for making evidence-based mosquito control strategies and highlight the need to regularly monitor the dynamics of pyrethroid resistance in this city.

Pelatihan Pengendalian Nyamuk Vektor Demam Berdarah dengan &lt;i&gt;Lethal MosquiTrap Modification&lt;/i&gt; (LMM) di Kecamatan Ampenan, Kota Mataram

The community service was carried out in Ampenan District, Mataram City, West Nusa Tenggara. Larval Monitoring Cadres (Jumantik) as targets or partners for this service activity. The problem faced by partners is the large number of cases of Dengue Hemorrhagic Fever (DBD) in several areas of Ampenan. The solution to conducting outreach and training on the manufacture and use of Lethal MosquiTrap Modification (LMM). Through this activity, it hoped that provide information and skills to target cadres so that they are able to independently make ovitraps as an effort to control the dengue virus vector. The final result of this service is that it is hoped that the community can avoid the dangers of dengue fever. Training activities are carried out in 2 stages, the evaluation is carried out in a separate phase. First, carry out socialization on mosquito traps which was attended by the local RT Head, posyandu cadres and community leaders. Second, training in making mosquito traps called Lethal MosquiTrap Modification (LMM). In this activity, training was provided on making simple mosquito traps and how to apply these traps by the community. The final phase carried out an evaluation process to see the seriousness of residents in using these traps to control the dengue virus vector, namely the Aedes aegypti mosquito.

Nonlinear Robust Adaptive Sliding Mode Control Strategies Involve a Fractional Ordered Approach to Reducing Dengue Vectors

This study presents an innovative approach by integrating adaptive sliding mode control strategies with fractional order modeling to address the challenge of reducing Aedes aegypti mosquito populations, the primary vector of Dengue - a widespread and debilitating disease. By employing the Atangana-Baleanu-Caputo fractional operator to model the dynamics of the mosquito population, we achieve a more precise representation of complex and non-linear behaviors. The motivation behind adopting the Adaptive Sliding Mode Control (ASMC) approach lies in the critical need to efficiently control Aedes aegypti mosquito populations, a key step in combating the prevalence of dengue. The ASMC method dynamically adjusts control parameters based on evolving conditions, enhancing its adaptability to the changing dynamics of mosquito populations.The Lyapunov stability theorem ensures the reliability of tracking convergence and control structure. Additionally, we implement the Toufik Atangana method to solve both state and adjoint fractional differential equations using the ABC derivative operator. This incorporation adds a novel dimension to the study, providing a comprehensive framework for addressing the intricate dynamics inherent in the Aedes aegypti mosquito population. To assess the effectiveness of the proposed strategy, a numerical performance index is introduced at the end of the abstract. This index justifies the controller’s efficacy by comparing it to other conventional controllers. The inclusion of this quantitative measure reinforces the significance of the proposed strategy in the context of dengue prevention and control efforts.

Pyrethroid resistance status and co-occurrence of V1016G, F1534C and S989P mutations in the Aedes aegypti population from two dengue outbreak counties along the China-Myanmar border

BackgroundOver the past two decades, dengue fever (DF) has emerged as a significant arboviral disease in Yunnan province, China, particularly in the China-Myanmar border area. Aedes aegypti, an invasive mosquito species, plays a crucial role in transmitting the dengue virus to the local population. Insecticide-based vector control has been the primary tool employed to combat DF, but the current susceptibility status of Ae. aegypti to commonly used insecticides is unknown. Assessment of Ae. aegypti resistance to pyrethroid insecticides and an understanding of the underlying mechanisms of this resistance in the China-Myanmar border region is of significant strategic importance for effectively controlling the DF epidemic in the area.MethodsAedes aegypti larvae collected from Ruili and Gengma counties in Yunnan Province were reared to adults in the laboratory and tested for susceptibility to three pyrethroid insecticides (3.20% permethrin, 0.08% lambda-cyhalothrin and 0.20% deltamethrin) by the standard WHO susceptibility bioassay. Genotyping of mutations in the knockdown gene (kdr), namely S989P, V1016G and F1534C, that are responsible for resistance to pyrethroid insecticides was performed using allele-specific PCR methods. A possible association between the observed resistant phenotype and mutations in the voltage-gated sodium channel gene (VGSC) was also studied.ResultsAedes aegypti mosquitoes collected from the two counties and reared in the laboratory were resistant to all of the pyrethroids tested, with the exception of Ae. aegypti from Gengma County, which showed sensitivity to 0.20% deltamethrin. The mortality rate of Ae. aegypti from Ruili county exposed to 3.20% permethrin did not differ significantly from that of Ae. aegypti from Gengma County (χ2 = 0.311, P = 0.577). By contrast, the mortality rate of Ae. aegypti from Ruili County exposed to 0.08% lambda-cyhalothrin and 0.20% deltamethrin, respectively, was significantly different from that of Ae. aegypti from Gengma. There was no significant difference in the observed KDT50 of Ae. aegypti from the two counties to various insecticides. Four mutation types and 12 genotypes were detected at three kdr mutation sites. Based on results from all tested Ae. aegypti, the V1016G mutation was the most prevalent kdr mutation (100% prevalence), followed by the S989P mutation (81.6%) and the F1534C mutation (78.9%). The constituent ratio of VGSC gene mutation types was significantly different in Ae. aegypti mosquitoes from Ruili and those Gengma. The triple mutant S989P + V1016G + F1534C was observed in 274 Ae. aegypti mosquitoes (60.8%), with the most common genotype being SP + GG + FC (31.4%). The prevalence of the F1534C mutation was significantly higher in resistant Ae. aegypti from Ruili (odds ratio [OR] 7.43; 95% confidence interval [CI] 1.71–32.29; P = 0.01) and Gengma (OR 9.29; 95% CI 3.38–25.50; P = 0.00) counties than in susceptible Ae. aegypti when exposed to 3.20% permethrin and 0.08% lambda-cyhalothrin, respectively. No significant association was observed in the triple mutation genotypes with the Ae. aegypti population exposed to 3.20% permethrin and 0.20% deltamethrin resistance (P > 0.05), except for Ae. aegypti from Gengma County when exposed to 0.08% lambda-cyhalothrin (OR 2.86; 95% CI 1.20–6.81; P = 0.02).ConclusionsAedes aegypti from Ruili and Gengma counties have developed resistance to various pyrethroid insecticides. The occurrence of multiple mutant sites in VGSC strongly correlated with the high levels of resistance to pyrethroids in the Ae. aegypti populations, highlighting the need for alternative strategies to manage the spread of resistance. A region-specific control strategy for dengue vectors needs to be implemented in the future based on the status of insecticide resistance and kdr mutations.Graphical

An Efficient Access to Heteroaryl/Aryl-Annulated Pyridine Derivatives and a Study of Their Mosquito Larvicidal Activity Against Dengue Vector

AbstractWe report a convergent synthesis of heteroaryl/aryl-annulated pyridine and quinoline derivatives by a metal-free Povarov reaction. para-Toluene sulfonic acid was used as the catalyst in this reaction, which produced the products in good yields from the corresponding aromatic amines and ethyl vinyl ether. A pyridocoumarin and a pyridopyrimidine product were evaluated for their mosquito larvicidal activity against the third instar larvae of the dengue vector mosquito Aedes aegypti. Examination of morphological changes in the larvae showed damage to the target body part after treatment with both the pyridocoumarin and pyridopyrimidine products at the LC50 concentrations.

Larvicidal properties of terpenoid-based nanoemulsions against the dengue vector Aedes aegypti L. and their potential toxicity against non-target organism.

The development of insecticide resistance in mosquitoes of public health importance has encouraged extensive research into innovative vector control methods. Terpenes are the largest among Plants Secondary Metabolites and have been increasingly studied for their potential as insecticidal control agents. Although promising, terpenes are insoluble in water, and they show low residual life which limits their application for vector control. In this study, we developed and evaluated the performances of terpenoid-based nanoemulsions (TNEs) containing myrcene and p-cymene against the dengue vector Aedes aegypti and investigated their potential toxicity against non-target organisms. Our results showed that myrcene and p-cymene showed moderate larvicidal activity against mosquito larvae compared to temephos an organophosphate widely used for mosquito control. However, we showed similar efficacy of TNEs against both susceptible and highly insecticide-resistant mosquitoes from French Guyana, hence suggesting an absence of cross-resistance with conventional insecticides. We also showed that TNEs remained effective for up to 45 days in laboratory conditions. The exposure of zebrafish to TNEs triggered behavioral changes in the fish at high doses but they did not alter the normal functioning of zebrafish organs, suggesting a good tolerability of non-target organisms to these molecules. Overall, this study provides new insights into the insecticidal properties and toxicity of terpenes and terpenoid-based formulations and confirms that TNE may offer interesting prospects for mosquito control as part of integrated vector management.

Three Togolese aromatic plants' essential oils diurnal variations and their insecticidal activities against the dengue vector Aedesaegypti

The present reported work deals with the ability of Togolese plants’ essential oils (EOs) to act as repellents for Aedes aegypti mosquitoes in order to use them as personal protective requirements or actions against mosquito bites and therefore to drastically reduce the risk of contracting dengue or yellow fever. EOs studied here were extracted from dry leaves of Ageratum conyzoides L., Eucalyptus citriodora Hook, and Lantana camara Linn, three plants that were collected at different daytimes (7 a.m., 1 p.m., and 7 p.m.) at various locations in Togo. Using a Clevenger-type device, EOs were obtained by the hydrodistillation method (Clevenger, 1928). The physical parameters of the EOs such as density, refractive index, rotatory power, and organoleptic properties were determined. Then, the characterization of EOs using gas chromatography equipped with a flame ionization detector (GC/FID) and gas chromatography coupled to mass spectrometry (GC/MS) was conducted. Chemical analyses showed the presence of several main compounds from EO samples of the three plants. The major compounds were characterized and identified as: (i) precocene I (67.7, 70.6, and 66.9%) and β-caryophyllene (17.4, 12.1, and 16.5%) for the EO of A. conyzoïdes; (ii) citronellal (63.3, 67.2, and 75.4%) and citronellol (24.5, 21.4, and 14.3%) for E. citriodora and (iii) β-caryophyllene (15.3, 11.7, and 12.4%), sabinene (28.4, 35, and 33.3%) and eucalyptol (11.5, 14.1, and 15.6%) for L. camara at 7 a.m., 1 p.m., and 7 p.m., respectively. The yield and the chemical composition of the oils vary according to harvesting time and sunlight.The insecticidal activity of EOs was evaluated following the CDC bottle method on Aedes aegypti females. All the EOs tested on the female adults of Aedes aegypti showed significant insecticidal activity. The EO of A. conyzoïdes at 1 p.m. and 7 p.m. resulted in 100% mortality after 8 min of exposure time at the lowest concentration (0.0025%). At the same concentration for the EO of E. citriodora, the mortality rates were 83%, 38.8%, and 30.80% at 7 a.m., 1 p.m., and 7 p.m., respectively for an exposure time of 8 min. The EO extracted from the leaves of L. camara harvested at 7 a.m. was effective after an exposure time of 15 min for a concentration of 0.02%. For the same concentration, the mortality rates of the EO of L. camara harvested at 1 p.m. and 7 p.m., after 8 min were 62.9% and 52%, respectively.From these interesting results reported for the first time in Togo, EOs from leaves of three Togolese plants harvested at different times of the day appear to be a valuable alternative for mosquito vector control in Togo or abroad countries in which dengue and yellow fever constitute a terrible scourge.

Microsatellite-based analysis reveals Aedes aegypti populations in the Kingdom of Saudi Arabia result from colonization by both the ancestral African and the global domestic forms.

The Aedes aegypti (Linnaeus, 1762) mosquito is the main vector of dengue, chikungunya and Zika and is well established today all over the world. The species comprises two forms: the ancestral form found throughout Africa and a global domestic form that spread to the rest of the tropics and subtropics. In Saudi Arabia, A. aegypti has been known in the southwest since 1956, and previous genetic studies clustered A. aegypti from Saudi Arabia with the global domestic form. The purpose of this study was to assess the genetic structure of A. aegypti in Saudi Arabia and determine their geographic origin. Genetic data for 17 microsatellites were collected for A. aegypti ranging from the southwestern highlands of Saudi Arabia on the border of Yemen to the north-west in Madinah region as well as from Thailand and Uganda populations (as representatives of the ancestral African and global domestic forms, respectively). The low but significant level of genetic structuring in Saudi Arabia was consistent with long-distance dispersal capability possibly through road connectivity and human activities, that is, passive dispersal. There are two main genetic groupings in Saudi Arabia, one of which clusters with the Ugandan population and the other with the Thailand population with many Saudi Arabian individuals having mixed ancestry. The hypothesis of genetic admixture of the ancestral African and global domestic forms in Saudi Arabia was supported by approximate Bayesian computational analyses. The extent of admixture varied across Saudi Arabia. African ancestry was highest in the highland area of the Jazan region followed by the lowland Jazan and Sahil regions. Conversely, the western (Makkah, Jeddah and Madinah) and Najran populations corresponded to the global domesticated form. Given potential differences between the forms in transmission capability, ecology and behaviour, the findings here should be taken into account in vector control efforts in Saudi Arabia.