Detection and population genetic analysis of Aedes albopictus (Diptera: Culicidae) based on knockdown resistance (kdr) mutations in the Yangtze River basin of China.

BACKGROUND: Aedes albopictus is an important vector of chikungunya, dengue, yellow fever and Zika viruses. Insecticides are often the most effective tools for rapidly decreasing the density of vector populations, especially during arbovirus disease outbreaks. However, the intense use of insecticides, particularly pyrethroids, has led to the selection of resistant mosquito populations worldwide. Mutations in the voltage-gated sodium channel (VGSC) gene are one of the main drivers of insecticide resistance in Ae. albopictus and are also known as "knockdown resistance" (kdr) mutations. Knowledge about genetic mutations associated with insecticide resistance is a prerequisite for developing techniques for rapid resistance diagnosis. Here, we report studies on the origin and dispersion of kdr haplotypes in samples of Ae. albopictus from the Yangtze River Basin, China; METHODS: Here, we report the results of PCR genotyping of kdr mutations in 541 Ae. albopictus specimens from 22 sampling sites in 7 provinces and municipalities in the Yangtze River Basin. Partial DNA sequences of domain II and domain III of the VGSC gene were amplified. These DNA fragments were subsequently sequenced to discover the possible genetic mutations mediating knockdown resistance (kdr) to pyrethroids. The frequency and distribution of kdr mutations were assessed in 22 Ae. albopictus populations. Phylogenetic relationships among the haplotypes were used to infer whether the kdr mutations had a single or multiple origins; RESULTS: The kdr mutation at the 1016 locus had 2 alleles with 3 genotypes: V/V (73.38%), V/G (26.43%) and G/G (0.18%). The 1016G homozygous mutation was found in only one case in the CQSL strain in Chongqing, and no 1016G mutations were detected in the SHJD (Shanghai), NJDX (Jiangsu) or HBQN (Hubei) strains. A total of 1532 locus had two alleles and three genotypes, I/I (88.35%), I/T (8.50%) and T/T (3.14%). A total of 1534 locus had four alleles and six genotypes: F/F (49.35%), F/S (19.96%), F/C (1.48%) and F/L (0.18%); S/S (23.66%); and C/C (5.36%). Haplotypes with the F1534C mutation were found only in Ae. albopictus populations in Chongqing and Hubei, and C1534C was found only in three geographic strains in Chongqing. Haplotypes with the 1534S mutation were found only in Ae. albopictus populations in Sichuan and Shanghai. F1534L was found only in HBYC. The Ae. albopictus populations in Shanghai were more genetically differentiated from those in the other regions (except Sichuan), and the genetic differentiation between the populations in Chongqing and those in the middle-lower reaches of the Yangtze River (Huber, Jiangsu, Jiangxi, and Anhui) was lower. Shanghai and Sichuan displayed low haplotype diversity and low nucleotide diversity. Phylogenetic analysis and sequence comparison revealed that the 1016 locus was divided into three branches, with the Clade A and Clade B branches bearing the 1016 mutation occurring mostly in Jiangsu and the Clade C branch bearing the 1016 mutation occurring mostly in Chongqing, suggesting at least two origins for 1016G. IIIS6 phylogenetic analysis and sequence comparison revealed that F1534S, F1534C and I1532T can be divided into two branches, indicating that IIIS6 has two origins; CONCLUSIONS: Combined with the distribution of kdr mutations and the analysis of population genetics, we infer that besides the local selection of pyrethroid resistance mutations, dispersal and colonization of Ae. albopictus from other regions may explain why kdr mutations are present in some Ae. albopictus populations in the Yangtze River Basin.

Genetic diversity of the Chagas vector Triatoma dimidiata s.l. (Hemiptera: Reduviidae) across geographic scales in a top-priority area for control.

Population genetic structure of arthropod disease vectors provides important information on vector movement and climate or other environmental variables that influence their distribution. This information is critical for data-driven vector control. In the first comprehensive study of the genetic structure of T. dimidiata s.l. (Latreille, 1811) we focus on an area of active transmission designated as a top priority for control. We examined a high number of specimens across a broad geographic area along the border of Guatemala and El Salvador including multiple spatial scales using a high number of genome-wide markers. Measuring admixture, pairwise genetic differentiation, and relatedness, we estimated the specimens represented three genetic clusters. We found evidence of movement (migration/gene flow) across all spatial scales with more admixture among locations in El Salvador than in Guatemala. Although there was significant isolation by distance, the 2 close villages in Guatemala showed either the most or least genetic variation indicating an additional role of environmental variables. Further, we found that social factors may be influencing the genetic structure. We demonstrated the power of genomic studies with a large number of specimens across a broad geographic area. The results suggest that for effective vector control movement must be considered on multiple spatial scales along with its contributing factors.

Slow recovery rates and spatial aggregation of Triatoma infestans populations in an area with high pyrethroid resistance in the Argentine Chaco.

BACKGROUND: The emergence of pyrethroid resistance has threatened the elimination of Triatoma infestans from the Gran Chaco ecoregion. We investigated the status and spatial distribution of house infestation with T. infestans and its main determinants in Castelli, a municipality of the Argentine Chaco with record levels of triatomine pyrethroid resistance, persistent infestation over 2005-2014, and limited or no control actions over 2015-2020. METHODS: We conducted a 2-year longitudinal survey to assess triatomine infestation by timed manual searches in a well-defined rural section of Castelli including 14 villages and 234 inhabited houses in 2018 (baseline) and 2020, collected housing and sociodemographic data by on-site inspection and a tailored questionnaire, and synthetized these data into three indices generated by multiple correspondence analysis. RESULTS: The overall prevalence of house infestation in 2018 (33.8%) and 2020 (31.6%) virtually matched the historical estimates for the period 2005-2014 (33.7%) under recurrent pyrethroid sprays. While mean peridomestic infestation remained the same (26.4-26.7%) between 2018 and 2020, domestic infestation slightly decreased from 12.2 to 8.3%. Key triatomine habitats were storerooms, domiciles, kitchens, and structures occupied by chickens. Local spatial analysis showed significant aggregation of infestation and bug abundance in five villages, four of which had very high pyrethroid resistance approximately over 2010-2013, suggesting persistent infestations over space-time. House bug abundance within the hotspots consistently exceeded the estimates recorded in other villages. Multiple regression analysis revealed that the presence and relative abundance of T. infestans in domiciles were strongly and negatively associated with indices for household preventive practices (pesticide use) and housing quality. Questionnaire-derived information showed extensive use of pyrethroids associated with livestock raising and concomitant spillover treatment of dogs and (peri) domestic premises. CONCLUSIONS: Triatoma infestans populations in an area with high pyrethroid resistance showed slow recovery and propagation rates despite limited or marginal control actions over a 5-year period. Consistent with these patterns, independent experiments confirmed the lower fitness of pyrethroid-resistant triatomines in Castelli compared with susceptible conspecifics. Targeting hotspots and pyrethroid-resistant foci with appropriate house modification measures and judicious application of alternative insecticides with adequate toxicity profiles are needed to suppress resistant triatomine populations and prevent their eventual regional spread.

Exploring fine-scale urban landscapes using satellite data to predict the distribution of Aedes mosquito breeding sites.

BACKGROUND: The spread of mosquito-transmitted diseases such as dengue is a major public health issue worldwide. The Aedes aegypti mosquito, a primary vector for dengue, thrives in urban environments and breeds mainly in artificial or natural water containers. While the relationship between urban landscapes and potential breeding sites remains poorly understood, such a knowledge could help mitigate the risks associated with these diseases. This study aimed to analyze the relationships between urban landscape characteristics and potential breeding site abundance and type in cities of French Guiana (South America), and to evaluate the potential of such variables to be used in predictive models. METHODS: We use Multifactorial Analysis to explore the relationship between urban landscape characteristics derived from very high resolution satellite imagery, and potential breeding sites recorded from in-situ surveys. We then applied Random Forest models with different sets of urban variables to predict the number of potential breeding sites where entomological data are not available. RESULTS: Landscape analyses applied to satellite images showed that urban types can be clearly identified using texture indices. The Multiple Factor Analysis helped identify variables related to the distribution of potential breeding sites, such as buildings class area, landscape shape index, building number, and the first component of texture indices. Models predicting the number of potential breeding sites using the entire dataset provided an R² of 0.90, possibly influenced by overfitting, but allowing the prediction over all the study sites. Predictions of potential breeding sites varied highly depending on their type, with better results on breeding sites types commonly found in urban landscapes, such as containers of less than 200 L, large volumes and barrels. The study also outlined the limitation offered by the entomological data, whose sampling was not specifically designed for this study. Model outputs could be used as input to a mosquito dynamics model when no accurate field data are available. CONCLUSION: This study offers a first use of routinely collected data on potential breeding sites in a research study. It highlights the potential benefits of including satellite-based characterizations of the urban environment to improve vector control strategies.

[Biological threats to global malaria elimination â £ Emergence of invasive vector species].

Driven by international exchanges and climate changes, the invasion and spread of vector Anopheles mosquitoes posed a new challenge to achieving global malaria elimination. Taking the invasion of An. stephensi to exacerbate the malaria epidemic in Africa as an example, this article summarizes the current situation of global Anopheles invasion, and estimates the potential risk of vector Anopheles mosquitoes to unravel the difficulties and challenges in the global malaria elimination program, so as to provide insights into improved early earning and precision control of vector Anopheles mosquito invasion across the world.

Contextual factors related to vector-control interventions for malaria: a scoping review and evidence and gap map protocol.

Objective: This scoping review will identify existing literature regarding contextual factors relevant to vector-control interventions to prevent malaria. We will use the findings of the scoping review to produce an interactive evidence and gap map. The map will assist in the priority setting, development, and conduct of targeted systematic reviews. These systematic reviews seek to assist the Vector Control and Insecticide Resistance Unit of the World Health Organization's Global Malaria Programme by informing recommendation development by their Guidelines Development Group. Introduction: Malaria contributes substantially to the global burden of disease, with an estimated 247 million cases and 619,000 deaths in 2021. Vector-control is key in reducing malaria transmission. Vector-control interventions directly target the mosquito, reducing the potential for parasite infections. These interventions commonly include insecticides used in indoor residual spraying or insecticide-treated nets and larval source management. Several new vector-control interventions are under evaluation to complement these. In addition to estimating the effects of interventions on health outcomes, it is critical to understand how populations at risk of malaria consider them in terms of their feasibility, acceptability, and values. Inclusion Criteria: Eligible studies will have assessed the contextual factors of feasibility or acceptability of the interventions of interest, or the valuation of the outcomes of interests. These assessments will be from the perspective of people who receive (residents) or deliver (workers or technicians) the vector-control intervention for the purpose of preventing malaria. Methods: We will conduct this scoping review in accordance with the JBI methodology for scoping reviews and report in line with the Preferred Reporting Items for Systematic Reviews and Meta-analyses extension for Scoping Reviews (PRISMA-ScR). We will construct the evidence and gap map following guidance from the Campbell Collaboration.

Essential oil nanoemulsion: An emerging eco-friendly strategy towards mosquito control.

Mosquito borne diseases are impeding to human health due to their uncontrolled proliferation. Various commercial insecticides currently used become ineffective due to the resistance acquired by mosquitoes. It is necessary and a priority to combat mosquito population. Plant-based products are gaining interest over the past few decades due to their environment friendliness and their effectiveness in controlling mosquitoes along with their lack of toxicity. Essential oil nanoemulsions are found to be highly effective when compared to their bulk counterparts. Due to their nano size, they can effectively interact and yield 100 % mortality with the mosquito larvae and encounter with minimal concentrations. This is the main advantage of the nano-sized particles due to which they find application in various disciplines and have also received the attention of researchers globally. There are various components present in essential oils that have been analysed using GC-MS. These findings reflect the challenge to mosquitoes to gain resistance against each component and therefore it requires time. Commercially used repellants are synthesised using materials like DEET are not advisable for topical application on human skin and essential oil nanoemulsions could be an ideal non toxic candidate that can be used against mosquito adults and larvae. However, there are other synthesis, optimisation parameters, and toxicity towards non-target organisms that have to be taken into account when essential oil nanoemulsions are considered for commercial applications. Here we review the strategies used by the nanoemulsions against the mosquito population. Apart from the positive effects, their minor drawbacks also have to be scrutinised in the future.

Comparison of the Trapping Efficacy of Locally Modified Gravid Aedes Trap and Autocidal Gravid Ovitrap for the Monitoring and Surveillance of Aedes aegypti Mosquitoes in Tanzania.

The study assessed the trapping efficacy of locally modified (1) Gravid Aedes Trap (GAT) lined with insecticide-treated net (ITN) as a killing agent and (2) Autocidal Gravid Ovitrap (AGO) with sticky board in the semi-field system (SFS) and field setting. Fully balanced Latin square experiments were conducted to compare GAT lined with ITN vs. AGO, both with either yeast or grass infusion. Biogent-Sentinel (BGS) with BG-Lure and no CO2 was used as a standard trap for Aedes mosquitoes. In the SFS, GAT outperformed AGO in collecting both nulliparous (65% vs. 49%, OR = 2.22, [95% CI: 1.89-2.60], p < 0.001) and gravid mosquitoes (73% vs. 64%, OR = 1.67, [95% CI: 1.41-1.97], p < 0.001). Similar differences were observed in the field. Yeast and grass infusion did not significantly differ in trapping gravid mosquitoes (OR = 0.91, [95% CI: 0.77-1.07], p = 0.250). The use of ITN improved mosquito recapture from 11% to 70% in the SFS. The same trend was observed in the field. Yeast was chosen for further evaluation in the optimized GAT due to its convenience and bifenthrin net for its resistance management properties. Mosquito density was collected when using 4× GATs relative to BGS-captured gravid mosquitoes 64 vs. 58 (IRR = 0.82, [95% CI: 0.35-1.95], p = 0.658) and showed no density dependence. Deployment of multiple yeast-baited GAT lined with bifenthrin net is cost-effective (single GAT < $8) compared to other traps such as BGS ($160).

Efficacy of Metarhizium anisopliae, Isolate ICIPE 7, against Anopheles arabiensis, Glossina fuscipes, and Rhipicephalus spp.

Arthropod vectors are responsible for a multitude of human and animal diseases affecting poor communities in sub-Saharan Africa. Their control still relies on chemical agents, despite growing evidence of insecticide resistance and environmental health concerns. Biorational agents, such as the entomopathogenic fungus Metarhizium anisopliae, might be an alternative for vector control. Recently, the M. anisopliae isolate ICIPE 7 has been developed into a commercial product in Kenya for control of ticks on cattle. We were interested in assessing the potential of controlling not only ticks but also disease-transmitting mosquitoes and tsetse flies using cattle as blood hosts, with the aim of developing a product for integrated vector management. Laboratory bioassays were carried out with M. anisopliae, isolate ICIPE 7 and isolate ICIPE 30, to compare efficacy against laboratory-reared Anopheles arabiensis. ICIPE 7 was further tested against wild Glossina fuscipes and Rhipicephalus spp. Dose-response tests were implemented, period of mosquito exposure was evaluated for effects on time to death, and the number of spores attached to exposed vectors was assessed. Exposure to 109 spores/mL of ICIPE 7 for 10 min resulted in a similar mortality of An. arabiensis as exposure to ICIPE 30, albeit at a slower rate (12 vs. 8 days). The same ICIPE 7 concentration also resulted in mortalities of tsetse flies (LT50: 16 days), tick nymphs (LT50: 11 days), and adult ticks (LT50: 20 days). Mosquito mortality was dose-dependent, with decreasing LT50 of 8 days at a concentration of 106 spores/mL to 6 days at 1010 spores/mL. Exposure period did not modulate the outcome, 1 min of exposure still resulted in mortality, and spore attachment to vectors was dose-dependent. The laboratory bioassays confirmed that ICIPE 7 has the potential to infect and cause mortality to the three exposed arthropods, though at slower rate, thus requiring further validation under field conditions.

Addressing the Dengue fever challenges in Nigeria: A narrative review and recommendations for control.

Dengue fever is a mosquito-borne viral infection that continues to pose a significant public health threat globally, including Nigeria. Here, we provided a review of dengue fever outbreaks in Nigeria from 1972 to 2023, examining the epidemiology, prevention strategies, challenges faced in combating the disease, and recommendations to mitigate its spread and transmission. We utilized scholarly databases such as PubMed and Google Scholar in writing this paper. The search keywords like, "dengue fever", "break-bone fever", "dengue fever virus" "outbreak", "Nigeria", "prevalence", and "epidemiology", were used to get appropriate published articles about the subject areas. Over the past five decades, Nigeria has experienced intermittent outbreaks of dengue fever, with varying degrees of severity and geographic distribution. Factors such as urbanization, climate change, and inadequate healthcare infrastructure have contributed to the resurgence and spread of the disease in the country. Despite efforts to control dengue transmission through vector control measures and public health interventions, challenges persist, including limited surveillance capacity, diagnostic delays, and gaps in vector control strategies. The emergence of new dengue virus serotypes and the potential for co-circulation with other arboviruses further complicate control efforts. This review highlights the importance of strengthening surveillance systems, enhancing vector control measures, improving diagnostic capabilities, and increasing public awareness to effectively mitigate the burden of dengue fever in Nigeria. Collaboration between government agencies, healthcare providers, researchers, and international partners is crucial in addressing the growing threat of dengue fever and reducing its impact on public health in Nigeria.

A hybrid Lagrangian-Eulerian model for vector-borne diseases.

In this paper, a multi-patch and multi-group vector-borne disease model is proposed to study the effects of host commuting (Lagrangian approach) and/or vector migration (Eulerian approach) on disease spread. We first define the basic reproduction number of the model, R 0 , which completely determines the global dynamics of the model system. Namely, if R 0 ≤ 1 , then the disease-free equilibrium is globally asymptotically stable, and if R 0 > 1 , then there exists a unique endemic equilibrium which is globally asymptotically stable. Then, we show that the basic reproduction number has lower and upper bounds which are independent of the host residence times matrix and the vector migration matrix. In particular, nonhomogeneous mixing of hosts and vectors in a homogeneous environment generally increases disease persistence and the basic reproduction number of the model attains its minimum when the distributions of hosts and vectors are proportional. Moreover, R 0 can also be estimated by the basic reproduction numbers of disconnected patches if the environment is homogeneous. The optimal vector control strategy is obtained for a special scenario. In the two-patch and two-group case, we numerically analyze the dependence of the basic reproduction number and the total number of infected people on the host residence times matrix and illustrate the optimal vector control strategy in homogeneous and heterogeneous environments.

Severe coinfection of dengue and malaria: A case report.

Key Clinical Message: In countries like Sudan, where several infectious diseases are prevalent, health care providers should not be satisfied with initial detection of a single pathogen and whenever it is feasible, they should investigate coinfections. Infections with high mortality or severe morbidity should be prioritized during the differential diagnosis particularly for diseases with similar clinical manifestations to reduce the death and disability rates. However, this requires substantial improvement in the diagnostic capacity. Abstract: Here we report a case of dengue and malaria coinfection from the southeast region of Sudan, bordering Ethiopia and Eritrea. A 25-year-old male from Sudan presented with symptoms of fever, chills, vomiting, and muscle and joint pain. Laboratory investigations confirmed a coinfection of dengue and malaria, which is assumingly not uncommon in areas heavily syndemic with several diseases but it is severely under-detected, underreported, and underestimated. The case has fully recovered after the supportive care for dengue and chemotherapy treatment for malaria. In such a case, it was important to monitor the patient's recovery and the treatment outcome through clinical indicators and laboratory parameters to update the treatment course whenever needed, according to response. The increasing burden and outbreaks of vector-borne diseases including dengue and malaria in Sudan, indicates the need for improving the implementation of the global vector control response that established by the World Health Organization. Additionally, the increasing prevalent of coinfections is urging substantial improvement in the diagnostic capacity in endemic countries.

Glaucarubinone from Simarouba glauca DC. as a potential biocontrol agent for mosquito vector management.

The study explored Simarouba glauca DC. for mosquito larvicidal potential by performing bioactivity-guided chemical investigation of its root extract resulting in isolation of the known bioactive metabolite glaucarubinone (1). Mosquito larvicidal activity of glaucarubinone (1) against the three vector species viz. Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus was determined using a modified WHO 2005 protocol. It was observed that Culex quinquefasciatus larvae were the most susceptible species with LC50 13.88 ppm and LC90 70.01 ppm followed by Aedes aegypti and Anopheles stephensi at 24 h of exposure. The mode of action as observed microscopically is the lysis of midgut and thorax cells of the third instar larvae. The crystal structure of the glaucarubinone (1) is reported for the first time using X-ray crystallography. This phytochemical product has the potential to act as a green alternative to existing chemical-based insecticides for integrated vector management.

Chagas Disease across the Ages: A Historical View and Commentary on Navigating Future Challenges.

Chagas disease, discovered over a century ago, continues to pose a global health challenge, affecting millions mainly in Latin America. This historical review with commentary outlines the disease's discovery, its evolution into a global concern due to migration, and highlights significant advances in diagnostics and treatment strategies. Despite these advancements, the paper discusses ongoing challenges in eradication, including vector control, congenital transmission, the disease's asymptomatic nature, and socioeconomic barriers to effective management. It calls for a multidisciplinary approach, enhanced diagnostics, improved treatment accessibility, and sustained vector control efforts. The review emphasizes the importance of global collaboration and increased funding to reduce Chagas disease's impact.

Genetic surveillance of insecticide resistance in African Anopheles populations to inform malaria vector control.

Insecticide resistance in malaria vector populations poses a major threat to malaria control, which relies largely on insecticidal interventions. Contemporary vector-control strategies focus on combatting resistance using multiple insecticides with differing modes of action within the mosquito. However, diverse genetic resistance mechanisms are present in vector populations, and continue to evolve. Knowledge of the spatial distribution of these genetic mechanisms, and how they impact the efficacy of different insecticidal products, is critical to inform intervention deployment decisions. We developed a catalogue of genetic-resistance mechanisms in African malaria vectors that could guide molecular surveillance. We highlight situations where intervention deployment has led to resistance evolution and spread, and identify challenges in understanding and mitigating the epidemiological impacts of resistance.

Combined use of long-lasting insecticidal nets and Bacillus thuringiensis israelensis larviciding, a promising integrated approach against malaria transmission in northern Côte d'Ivoire.

BACKGROUND: The recent reduction in malaria burden in Côte d'Ivoire is largely attributable to the use of long-lasting insecticidal nets (LLINs). However, this progress is threatened by insecticide resistance and behavioral changes in Anopheles gambiae sensu lato (s.l.) populations and residual malaria transmission, and complementary tools are required. Thus, this study aimed to assess the efficacy of the combined use of LLINs and Bacillus thuringiensis israelensis (Bti), in comparison with LLINs. METHODS: This study was conducted in the health district of Korhogo, northern Côte d'Ivoire, within two study arms (LLIN + Bti arm and LLIN-only arm) from March 2019 to February 2020. In the LLIN + Bti arm, Anopheles larval habitats were treated every fortnight with Bti in addition to the use of LLINs. Mosquito larvae and adults were sampled and identified morphologically to genus and species using standard methods. The members of the An. gambiae complex were determined using a polymerase chain reaction technique. Plasmodium infection in An. gambiae s.l. and malaria incidence in local people was also assessed. RESULTS: Overall, Anopheles spp. larval density was lower in the LLIN + Bti arm 0.61 [95% CI 0.41-0.81] larva/dip (l/dip) compared with the LLIN-only arm 3.97 [95% CI 3.56-4.38] l/dip (RR = 6.50; 95% CI 5.81-7.29; P < 0.001). The overall biting rate of An. gambiae s.l. was 0.59 [95% CI 0.43-0.75] biting/person/night in the LLIN + Bti arm against 2.97 [95% CI 2.02-3.93] biting/person/night in LLIN-only arm (P < 0.001). Anopheles gambiae s.l. was predominantly identified as An. gambiae sensu stricto (s.s.) (95.1%, n = 293), followed by Anopheles coluzzii (4.9%; n = 15). The human-blood index was 80.5% (n = 389) in study area. EIR was 1.36 infected bites/person/year (ib/p/y) in the LLIN + Bti arm against 47.71 ib/p/y in the LLIN-only arm. Malaria incidence dramatically declined from 291.8‰ (n = 765) to 111.4‰ (n = 292) in LLIN + Bti arm (P < 0.001). CONCLUSIONS: The combined use of LLINs with Bti significantly reduced the incidence of malaria. The LLINs and Bti duo could be a promising integrated approach for effective vector control of An. gambiae for elimination of malaria.

Lethal and sublethal impacts of membrane-fed ivermectin are concentration dependent in Anopheles coluzzii.

BACKGROUND: Ivermectin is a well-tolerated anthelminthic drug with wide clinical and veterinary applications. It also has lethal and sublethal effects on mosquitoes. Mass drug administration with ivermectin has therefore been suggested as an innovative vector control tool in efforts to curb emerging insecticide resistance and reduce residual malaria transition. To support assessments of the feasibility and efficacy of current and future formulations of ivermectin for vector control, we sought to establish the relationship between ivermectin concentration and its lethal and sublethal impacts in a primary malaria vector. METHODS: The in vitro effects of ivermectin on daily mortality and fecundity, measured by egg production, were assessed up to 14 days post-blood feed in a laboratory colony of Anopheles coluzzii. Mosquitoes were fed ivermectin in blood meals delivered by membrane feeding at one of six concentrations: 0 ng/ml (control), 10 ng/ml, 15 ng/ml, 25 ng/ml, 50 ng/ml, 75 ng/ml, and 100 ng/ml. RESULTS: Ivermectin had a significant effect on mosquito survival in a concentration-dependent manner. The LC50 at 7 days was 19.7 ng/ml. The time to median mortality at ≥ 50 ng/ml was ≤ 4 days, compared to 9.6 days for control, and 6.3-7.6 days for ivermectin concentrations between 10 and 25 ng/ml. Fecundity was also affected; no oviposition was observed in surviving females from the two highest concentration treatment groups. While females exposed to 10 to 50 ng/ml of ivermectin did oviposit, significantly fewer did so in the 50 ng/ml treatment group compared to the control, and they also produced significantly fewer eggs. CONCLUSIONS: Our results showed ivermectin reduced mosquito survival in a concentration-dependent manner and at ≥ 50 ng/ml significantly reduced fecundity in An. coluzzii. Results indicate that levels of ivermectin found in human blood following ingestion of a single 150-200 µg/kg dose would be sufficient to achieve 50% mortality across 7 days; however, fecundity in survivors is unlikely to be affected. At higher doses, a substantial impact on both survival and fecundity is likely. Treating human populations with ivermectin could be used as a supplementary malaria vector control method to kill mosquito populations and supress their reproduction; however strategies to safely maintain mosquitocidal blood levels of ivermectin against all Anopheles species require development.

Development of a sterile insect technique as a control strategy for the Asian citrus psyllid: establishing the effect of sterilizing X-rays on fecundity, fertility, and survival.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is a major pest of citrus due to its role as the vector of the bacterium that causes huanglongbing. In commercial citrus, ACP control currently relies on the application of insecticides, which may not be sustainable long-term, nor practical in urban areas. The sterile insect technique (SIT) is an alternative strategy in which large numbers of pests are reared, sterilized using radiation, and then released into the field to compete with wild individuals for matings, suppressing population growth. As a fundamental step toward the development of SIT for ACP, this study sought to identify the optimum radiation dose required to sterilize ACP without affecting their survival and mating capacity. Virgin adult ACP of both sexes were subjected to doses of X-ray irradiation ranging from 40 to 480 Gy, then paired with a nonirradiated mate and allowed to produce offspring. Fecundity was estimated as the number of eggs laid, and fertility as the proportion of those eggs that hatched. Females were more radio-sensitive than males, exhibiting a major drop in fecundity at even the lowest dose and 100% sterility at 80 Gy. In contrast, a fivefold higher dose (400 Gy) did not achieve complete sterility in males, with around 5% offspring survival. However, F1 progeny of males exposed to 320 Gy or higher were subsequently found to be 100% sterile. This confirmation of inherited sterility suggests that balancing the sterilizing effects of radiation against its mortality-inducing effects may warrant further evaluation.

Pyrethroid resistance and gene expression profile of a new resistant An. gambiae colony from Uganda reveals multiple resistance mechanisms and overexpression of Glutathione-S-Transferases linked to survival of PBO-pyrethroid combination.

Background: The effectiveness of long-lasting insecticidal nets (LLINs) are being threatened by growing resistance to pyrethroids. To restore their efficacy, a synergist, piperonyl butoxide (PBO) which inhibits cytochrome P450s has been incorporated into pyrethroid treated nets. A trial of PBO-LLINs was conducted in Uganda from 2017 and we attempted to characterize mechanisms of resistance that could impact intervention efficacy. Methods: We established an Anopheles gambiae s.s colony in 2018 using female mosquitoes collected from Busia district in eastern Uganda. We first assessed the phenotypic resistance profile of this colony using WHO tube and net assays using a deltamethrin dose-response approach. The Busia colony was screened for known resistance markers and RT-qPCR targeting 15 genes previously associated with insecticide resistance was performed. Results: The Busia colony had very high resistance to deltamethrin, permethrin and DDT. In addition, the colony had moderate resistance to alpha-cypermethrin and lambda-cyhalothrin but were fully susceptible to bendiocarb and fenitrothion. Exposure to PBO in combination with permethrin and deltamethrin resulted in higher mortality rates in both net and tube assays, with a higher mortality observed in net assays than tube assays. The kdr marker, Vgsc-995S was at very high frequency (91.7-98.9%) whilst the metabolic markers Coeae1d and Cyp4j5-L43F were at very low (1.3% - 11.5%) and moderate (39.5% - 44.7%) frequencies respectively. Our analysis showed that gene expression pattern in mosquitoes exposed to deltamethrin, permethrin or DDT only were similar in comparison to the susceptible strain and there was significant overexpression of cytochrome P450s, glutathione-s-transferases (GSTs) and carboxyl esterases (COEs). However, mosquitoes exposed to both PBO and pyrethroid strikingly and significantly only overexpressed closely related GSTs compared to unexposed mosquitoes while major cytochrome P450s were underexpressed. Conclusions: The high levels of pyrethroid resistance observed in Busia appears associated with a wide range of metabolic gene families.

Impact of the exposure of sublethal dose of mosquito coil on the development of insecticide resistance in Aedes aegypti (L.) (Diptera: Culicidae).

Mosquito coil is commonly used in many African households for protection against mosquito bites. The coil usually has semi-volatile pyrethroids as an active ingredient, which usually diffuse across open space, and the cloud either kills mosquitoes that are exposed, or mosquitoes can be exposed to sublethal doses of the insecticides. This study was conducted to assess the impact of sublethal doses of mosquito coil on the development of insecticide resistance in Aedes aegypti, a major vector for dengue fever and several other arboviral diseases. A laboratory colony of Ae. aegypti was exposed to sublethal doses of a meperfluthrin-based mosquito coil in a Peet-Grady chamber once per generation for 16 generations. The susceptibility of the exposed colony to a diagnostic dose of the mosquito coil as well as to three other insecticides was determined. Three different kdr mutations and five enzyme activities were evaluated in both the exposed and control colonies. After 16 generations of sublethal exposure to mosquito coils, the full diagnostic dose of the coil caused 68% mortality to the exposed colony compared to 100% mortality in the control colony. Mortality caused by deltamethrin (0.05%) was also significantly lower in the exposed colony. The frequency of 1016I kdr mutation as well as MFO and alpha esterase activities were higher in the exposed colony compared to the control colony. This study provides evidence of the development of pyrethroid resistance in an Ae. aegypti population due to sublethal exposure to mosquito coil for 16 generations. Given the large-scale use of mosquito coils in many African households, its role as a pyrethroid resistance selection source should be taken into consideration when designing resistance management strategies.