Emergence Of Insecticide Resistance Research Articles

Mapping malaria vectors and insecticide resistance in a high-endemic district of Haryana, India: implications for vector control strategies

BackgroundAchieving effective control and elimination of malaria in endemic regions necessitates a comprehensive understanding of local mosquito species responsible for malaria transmission and their susceptibility to insecticides.MethodsThe study was conducted in the highly malaria prone Ujina Primary Health Center of Nuh (Mewat) district of Haryana state of India. Monthly entomological surveys were carried out for adult mosquito collections via indoor resting collections, light trap collections, and pyrethrum spray collections. Larvae were also collected from different breeding sites prevalent in the region. Insecticide resistance bioassay, vector incrimination, blood meal analysis was done with the collected vector mosquitoes.ResultsA total of 34,974 adult Anopheles mosquitoes were caught during the survey period, out of which Anopheles subpictus was predominant (54.7%). Among vectors, Anopheles stephensi was predominant (15.5%) followed by Anopheles culicifacies (10.1%). The Human Blood Index (HBI) in the case of An. culicifacies and An. stephensi was 6.66 and 9.09, respectively. Vector incrimination results revealed Plasmodium vivax positivity rate of 1.6% for An. culicifacies. Both the vector species were found resistant to DDT, malathion and deltamethrin.ConclusionThe emergence of insecticide resistance in both vector species, compromises the effectiveness of commonly used public health insecticides. Consequently, the implementation of robust insecticide resistance management strategies becomes imperative. To effectively tackle the malaria transmission, a significant shift in vector control strategies is warranted, with careful consideration and adaptation to address specific challenges encountered in malaria elimination efforts.

Study of Mosquito Borne Deasease Found in Yavatmal Region

Abstract: Mosquito-borne diseases are a significant public health concern in the Yavatmal region of Maharashtra, India. Malaria, dengue fever, and Japanese encephalitis are among the prominent diseases transmitted by mosquitoes in this region. Malaria, caused by the Plasmodium parasite, is endemic in Yavatmal, with transmission occurring mainly during the monsoon and post-monsoon seasons. Dengue fever, caused by the dengue virus and transmitted by Aedes mosquitoes, has seen periodic outbreaks in the region, with increased incidence during the rainy season. Japanese encephalitis, caused by the Japanese encephalitis virus and transmitted by Culex mosquitoes, poses a threat to the population, particularly in rural areas. Several factors contribute to the spread of mosquito-borne diseases in the Yavatmal region, including inadequate sanitation, stagnant water bodies, deforestation, and climate change. Socioeconomic factors such as poverty and limited access to healthcare further exacerbate the problem. Control and prevention efforts in the region primarily focus on vector control measures, including insecticide spraying, larval source management, and the use of bed nets. Community education and awareness campaigns play a crucial role in promoting preventive behaviors such as the use of insect repellents and proper waste disposal. Challenges in addressing mosquito-borne diseases in Yavatmal include inadequate healthcare infrastructure, insufficient funding, and the emergence of insecticide resistance among mosquito populations. Collaborative efforts involving government agencies, healthcare providers, researchers, and community organizations are essential to effectively combat these diseases. Strengthening surveillance systems, improving access to diagnostic and treatment facilities, and implementing integrated vector management strategies are necessary steps towards reducing the burden of mosquito-borne diseases in the Yavatmal region and improving public health outcomes.

Evaluating the carnivorous efficacy of Utricularia aurea (Lamiales: Lentibulariaceae) on the larval stages of Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti (Diptera: Culicidae).

The emergence of insecticide resistance in mosquitoes necessitates the exploration and validation of sustainable biological strategies for controlling mosquitoes in their natural habitats. We assessed the predatory effect of Utricularia aurea Lour (Lamiales: Lentibulariaceae), an aquatic carnivorous plant found in the Indian subcontinent, Japan, and Australia, on 4 instars of Anopheles stephensi Liston, Culex quinquefasciatus Say, and Aedes aegypti Linn (Diptera: Culicidae), in the laboratory and field settings. In the laboratory setting, predation of larvae by U. aurea was highest during the first hour when it predated 45%, 61%, and 58% of first instars of An. stephensi, Cx. quinquefasciatus, and, Ae. aegypti, respectively, and, within 12h, U. aurea preyed upon ~95% of the first, second, and third instars of the 3 mosquito species, ~80% of the fourth instars of An. stephensi and Ae. aegypti, and ~60% of fourth instars of Cx. quinquefasciatus. The predatory effect of U. aurea varied with mosquito species and instar. Broadly, predation risk declined with the increase of the instar size. In the field setting, at the end of 16 days, U. aurea predated 76% and 71% of the immature An. stephensi and Ae. aegypti, respectively. Our findings suggest U. aurea can be utilized as a potential biocontrol agent for controlling mosquito larvae in natural habitats; however, the current claim warrants additional investigations in a variety of natural habitats.

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.

Presence of Multiple Genetic Mutations Related to Insecticide Resistance in Chinese Field Samples of Two Phthorimaea Pest Species.

Potatoes hold the distinction of being the largest non-cereal food crop globally. The application of insecticides has been the most common technology for pest control. The repeated use of synthetic insecticides of the same chemical class and frequent applications have resulted in the emergence of insecticide resistance. Two closely related pests that feed on potato crops are the potato tuber moth, Phthorimaea operculella, and the tomato leafminer, Phthorimaea absoluta (syn. Tuta absoluta). Previous studies indicated the existence of insecticide resistance to various classes of insecticides including organophosphates, carbamates, and pyrethroids in field populations of P. operculella and P. absoluta. However, the exact mechanisms of insecticide resistance in P. operculella and to a lesser extent P. absoluta remain still poorly understood. Detecting resistance genotypes is crucial for the prediction and management of insecticide resistance. In this study, we identified multiple genetic mutations related to insecticide resistance in two species of Phthorimaea. An unexpected genetic divergence on target-site mutations was observed between P. operculella and P. absoluta. Three mutations (A201S, L231V, and F290V) in Ace1 (acetylcholinesterase), four mutations (M918T, L925M, T928I, and L1014F) in VGSC (voltage-gated sodium channel), and one mutation (A301S) in RDL (GABA-gated chloride channel) have been detected with varying frequencies in Chinese P. absoluta field populations. In contrast, P. operculella field populations showed three mutations (F158Y, A201S, and L231V) in Ace1, one mutation (L1014F) in VGSC at a lower frequency, and no mutation in RDL. These findings suggest that pyrethroids, organophosphates, and carbamates are likely to be ineffective in controlling P. absoluta, but not P. operculella. These findings contributed to a deeper understanding of the presence of target-site mutations conferring resistance to commonly used (and cheap) classes of insecticides in two closely related potato pests. It is recommended to consider the resistance status of both pests for the implementation of resistance management strategies in potatoes.

Insecticide Resistance and Metabolic Mechanisms in Aedes aegypti from Two Agrosystems (Vegetable and Cotton Crops) in Côte d'Ivoire.

Background: The emergence of insecticide resistance in Aedes vectors mosquitoes poses a real challenge for arboviral-borne disease control. In Côte d'Ivoire, data are available on phenotypic resistance and the presence of kdr mutations in Aedes aegypti. Therefore, information on metabolic resistance in Aedes populations is very scarce. Here, we assessed the insecticide resistance status of Ae. aegypti in periurban and rural areas of Côte d'Ivoire, and we investigated the role of detoxification enzymes as possible resistance mechanisms. Materials and Methods: Aedes mosquito eggs were collected between June 2019 to April 2021 in two agricultural sites. Adults of Ae. aegypti were tested using World Health Organization tube assays, with seven insecticides belonging to pyrethroids, organochlorines, carbamates, and organophosphates classes. We determined the knockdown times (KdT50, KdT95) and resistance ratios of pyrethroids in natural populations. The synergist piperonyl butoxide (PBO) was used to investigate the role of enzymes in resistance. Biochemical assays were performed to detect potential increased activities in mixed-function oxidase levels, nonspecific esterases (NSEs), and glutathione S-transferases. Results: The results showed that Ae. aegypti populations were resistant to five insecticides with mortality of 46% and 89% for 0.75% permethrin, 68% and 92% for 0.05% deltamethrin, 57% and 89% for lambda-cyhalothrin, 41% and 47% for dichlorodiphenyltrichloroethane (DDT), 82% and 91% for chlorpyrifos-methyl in Songon-Agban and Kaforo, respectively. Susceptibility to carbamates was observed in our study sites. After exposure to PBO, the susceptibility of Ae. aegypti to pyrethroids and DDT was partially restored in Songon-Agban. Whereas in Kaforo, none increase of the mortality rates of Ae. aegypti for these four insecticides was observed after exposure to PBO. Increased activity of NSE (α-esterases) was found in Songon-Agban compared with the reference susceptible strain. Conclusion: These findings provide valuable information to support decisions for vector control strategies in Cote d'Ivoire. Also, we highlight the need for the monitoring of insecticide resistance management in Aedes vectors.

Molecular Identification of Malaria Vector in Gusau Township, Nigeria

There about 460 Anopheles species recognized, over 100 can transmit human malaria but only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria. Anopheles gambiae is the principal vector of the most dangerous malaria parasite species in Africa, which is Plasmodium falciparum. Anopheles gambiae are a complex consisting of eight morphologically indistinguishable species and each of the members of the complex having unique biology, ecology and behaviour and should be studied and differentiated. The research objective was to identify the species of malaria vector in Gusau township Nigeria using molecular biological technique to know the exact malaria vector. Knowledge of the exact malaria vector in a given environment enables formulating a carefully designed tailor-made vector control measure. Indoor and outdoor mosquito samples were collected from selected areas in five wards of Gusau township using standard collection methods, for a period of twelve months. The samples were identified using polymerase chain reaction (PCR) technique and the result showed Anopheles gambiae in all sites of sample collection. It is therefore recommended that integrated malaria vector control should be adopted in the mosquito control programme because Anopheles gambiae is rugged and can be difficult to control and/or eradicate because of the emerging insecticide resistance and its close association with human host.

Worldwide Status of Insecticide Resistance of Aedes aegypti and Ae. albopictus, Vectors of Arboviruses of Chikungunya, Dengue, Zika and Yellow Fever.

Controlling of Aedes aegypti and Ae. albopictus, vectors of five important mosquito-borne diseases, is known as the most effective method to prevent the transmission of arboviruses to humans, but the emergence of insecticide resistance is threat for control and prevention of vector borne diseases. A better understanding of mosquito resistance to insecticides will help to develop more effective methods to control insecticide resistance in mosquito vectors. Worldwide geographical distribution of insecticide resistance in Ae. aegypti and Ae. albopictus by the available papers and map of the data for carbamates, organochlorines, organophosphates, pyrethroids, microbial and insect growth regulator insecticides were reviewed. Article data published up to December 2022 were investigated by searching the following databases: "Google Scholar", "PubMed", "Scopus", "SID" and "Web of Knowledge". The results showed that the susceptibility and resistance status of Ae. aegypti and Ae. albopictus to insecticides in the world is very diverse. Due to the importance of Ae. aegypti and Ae. albopictus in the transmission of mosquito-borne arboviruses, resistance management should be given more attention worldwide to prevent insecticide resistance in the arbovirus vector and replace the new approach for vector control.

Two Novel Mosquitocidal Peptides Isolated from the Venom of the Bahia Scarlet Tarantula (Lasiodora klugi).

Effective control of diseases transmitted by Aedes aegypti is primarily achieved through vector control by chemical insecticides. However, the emergence of insecticide resistance in A. aegypti undermines current control efforts. Arachnid venoms are rich in toxins with activity against dipteran insects and we therefore employed a panel of 41 spider and 9 scorpion venoms to screen for mosquitocidal toxins. Using an assay-guided fractionation approach, we isolated two peptides from the venom of the tarantula Lasiodora klugi with activity against adult A. aegypti. The isolated peptides were named U-TRTX-Lk1a and U-TRTX-Lk2a and comprised 41 and 49 residues with monoisotopic masses of 4687.02 Da and 5718.88 Da, respectively. U-TRTX-Lk1a exhibited an LD50 of 38.3 pmol/g when injected into A. aegypti and its modeled structure conformed to the inhibitor cystine knot motif. U-TRTX-Lk2a has an LD50 of 45.4 pmol/g against adult A. aegypti and its predicted structure conforms to the disulfide-directed β-hairpin motif. These spider-venom peptides represent potential leads for the development of novel control agents for A. aegypti.

A review of the impact of maize-legume intercrops on the diversity and abundance of entomophagous and phytophagous insects.

In many parts of the world, chemical pesticides are the primary method of pest control in maize (Zea mays L.) crops. Concerns about the negative consequences of chemical pesticide use on people's health and the environment, as well as the emergence of insecticide resistance, have accelerated attempts to discover alternatives that are effective, low-risk, and cost-effective. Maize-legume intercropping systems are known to have multiple benefits to agroecosystem functioning, including pest regulation. This review focuses on the influence of maize-legume intercropping systems on insect diversity and abundance as a mechanism for insect pest regulation in maize crops. First, this review combines knowledge of maize-legume intercrops, with a particular emphasis on the mechanism by which this practice attracts beneficial insects (e.g., predators, parasitoids) to reduce pest damage in intercropping systems. In addition, the pairings of specific legume species with the greatest potential to attract more beneficial insects and therefore reduce maize pests are also discussed. Finally, future research needs are also recommended. Findings are reviewed in the context of looking for long-term management strategies that can increase the adoption of integrated pest management programs in maize-based production systems.

Phytochemical screening and larvicidal effects of methanolic leave extract of Ocimum gratissimum on Anopheles species larva in Gombe, Gombe State Nigeria

Mosquito vectors are among the well-known group of insect that transmit a number of deleterious human diseases, which has pose a major public health challenges affecting development of poorest countries in the world. Vector control is therefore an essential requirement in the control of these diseases. The emergence of insecticide resistance and their effects on non-target population and the environment has necessitated an urgent search for development of new and improved vector control methods that are ecofriendly, economical and effective as well as safe for non-target organisms and the environment. The present study aims to access the larvicidal efficacy of Ocimum gratissimum extracts against Anopheles species larvae. The Ocimum (scent) leaf methanolic extract was obtained using a cold method of extraction, the phytochemical investigation was studied using a simple qualitative analysis and a biological test to determine it larvicidal properties as per the WHO standard protocol. The percent yield of the methanolic extract from leaves of Occimum gratissimum was 8.14%. Presence of alkaloids, flavonoids, tannins, steroids, saponins, antraquinones, phenolics and glycosides have been observed. The biological test revealed that the methanolic extract from Occimum gratissimum has remarkable larvicidal properties with an LC50 and LC90 values of 4.28 and 24.40 mg/ml after a period of 72 hours respectively. This may offer great prospective as new control agents against Anopheles spp which is considered a threat to human health in the World especially Nigeria. The Ocimum gratissimum plant extracts tested in our study showed potent larvicidal properties that have potential to be developed as a natural insecticides.

Preventive residual insecticide applications successfully controlled Aedes aegypti in Yucatan, Mexico

Insecticide-based approaches remain a key pillar for Aedes-borne virus (ABV, dengue, chikungunya, Zika) control, yet they are challenged by the limited effect of traditional outdoor insecticide campaigns responding to reported arboviral cases and by the emergence of insecticide resistance in mosquitoes. A three-arm Phase II unblinded entomological cluster randomized trial was conducted in Merida, Yucatan State, Mexico, to quantify the entomological impact of targeted indoor residual spraying (TIRS, application of residual insecticides in Ae. aegypti indoor resting sites) applied preventively 2 months before the beginning of the arbovirus transmission season. Trial arms involved the use of two insecticides with unrelated modes of action (Actellic 300CS, pirimiphos-methyl, and SumiShield 50WG, clothianidin) and a control arm where TIRS was not applied. Entomological impact was quantified by Prokopack adult collections performed indoors during 10 min per house. Regardless of the insecticide, conducting a preventive TIRS application led to significant reductions in indoor Ae. aegypti densities, which were maintained at the same levels as in the low arbovirus transmission period (Actellic 300CS reduced Ae. aegypti density up to 8 months, whereas SumiShield 50WG up to 6 months). The proportional reduction in Ae. aegypti abundance in treatment houses compared to control houses was 50–70% for Actellic 300CS and 43–63% for SumiShield 50WG. Total operational costs including insecticide ranged from US$4.2 to US$10.5 per house, depending on the insecticide cost. Conducting preventive residual insecticide applications can maintain Ae. aegypti densities at low levels year-round with important implications for preventing ABVs in the Americas and beyond.

Spatial distribution and insecticide resistance profile of Aedes aegypti and Aedes albopictus in Douala, the most important city of Cameroon.

Prevention and control of Aedes-borne viral diseases such as dengue rely on vector control, including the use of insecticides and reduction of larval sources. However, this is threatened by the emergence of insecticide resistance. This study aimed to update the spatial distribution, the insecticide resistance profile of A. aegypti and A. albopictus and the potential resistant mechanisms implicated in the city of Douala. Immature stages of Aedes were collected in August 2020 in eight neighbourhoods in Douala and reared to adult stages. Adult bioassays, and piperonyl butoxide (PBO) synergist assays were carried out according to World Health Organization recommendations. Expression of some candidate metabolic genes including Cyp9M6F88/87, Cyp9J28a, Cyp9J10 and Cyp9J32 in A. aegypti, and Cyp6P12 in A. albopictus were assessed using qPCR. A. aegypti adults G0 were screened using real time melting curve qPCR analyses to genotype the F1534C, V1016I and V410L Aedes kdr mutations. Overall, A. aegypti is the predominant Aedes species, but analyses revealed that both A. albopictus and A. aegypti coexist in all the prospected neighbourhoods of Douala. High level of resistance was observed to three pyrethroids tested in both Aedes species. In A. aegypti a lower mortality rate was reported to permethrin (5.83%) and a higher mortality rate to deltamethrin (63.74%). Meanwhile, for A. albopictus, lower (6.72%) and higher (84.11%) mortality rates were reported to deltamethrin. Similar analysis with bendiocarb, revealed for A. aegypti a loss of susceptibility. However, in A. albopictus samples, analyses revealed a susceptibility in Logbessou, and confirmed resistance in Kotto (59.78%). A partial recovery of mortality was found to insecticides after pre-exposure to PBO. Cyp6P12 was found significantly overexpressed in A. albopictus permethrin resistant and Cyp9M6F88/87 for A. aegypti deltamethrin resistant. F1534C, V1016I and V410L mutations were detected in A. aegypti from different neighbourhoods and by considering the combination of these three kdr 14 genotypes were found. These findings provide relevant information which should be capitalised in the implementation of arbovirus vector control strategies and insecticide resistance management.

Malaria vector feeding, peak biting time and resting place preference behaviors in line with Indoor based intervention tools and its implication: scenario from selected sentinel sites of Ethiopia

In Ethiopia, malaria incidence has significantly reduced in the past decade through the combined use of conventional vector control approaches and treatment using antimalarial drugs. However, the sustainability of this achievement is threatened by the shift in biting and resting behaviors and emergence of insecticide resistance by the primary malaria vector. Therefore, continuous monitoring of the behaviour of malaria mosquitoes in different sentinel sites is crucial to design effective prevention and control methods in the local context. Entomological investigations were conducted in three sentinel sites for five consecutive months during the major malaria transmission season. The species composition, population dynamics, biting and resting behaviours of malaria vectors were determined using center for disease control and prevention (CDC) light trap, human landing catch (HLC), pyrethrum spray catch (PSC) and Pitfall shelter collection (PFS). Accordingly, 10 households for CDC, 10 households for PSC, 10 households for PFS and 5 households for HLC from each site were randomly enrolled for mosquito collection. A total of 8,297 anopheline mosquitoes were collected from the three sites, out of which 4,525 (54.5 %) were An. gambiae, s.l. 2,028 (24.4 %) were An. pharoensis, 160 (1.9 %) were An. funestus and the rest 1,584 (19 %) were other anophelines (An. coustani, An. cinerus and An. tenebrosus). No significant variation (P = 0.476) was observed between indoor (25.2/trap-night and outdoor collections (20.1/trap-night). Six hundred seventy six (43.3%) of An. gambiae s.l. (primary vector) were collected between 18:00 and 22:00 h. Biting activity declined between 00:00 and 02:00 h. The national malaria control program should pay close attention to the shifting behavior of vector mosquitoes as the observed outdoor feeding tendency of the vector population could pose challenges to the indoor intervention tools IRS and LLINs.

Highly sensitive droplet digital PCR-based diagnostics for the surveillance of malaria vector populations in low transmission and incipient resistance settings

ABSTRACT Background Sensitive monitoring of Plasmodium infective mosquitoes in low malaria transmission settings is of high priority for disease control. Early detection of insecticide resistance at low frequencies is also key for vector monitoring nowadays, when new insecticides are launched to control vector populations. Research design and methods An. gambiae mosquitoes with predetermined infection and resistance status were used to produce populations with various malaria infection rates and mutant allelic frequencies (MAFs) of target site insecticide resistance traits. Total RNA and gDNA were isolated and used in droplet Digital PCR (ddPCR) and Reverse Transcription (RT) ddPCR performed in the QX200 ddPCR System. Results We developed a novel ddPCR for detecting P. falciparum DNA in pooled mosquito head-thoraces with infective rate as low as 1.0%. A dissection-free RT-ddPCR assay for specific infective-stage detection was additionally developed and validated (accuracy = 100%) in mosquito pools with infective rates down to 1.0%. A novel ddPCR assay for insecticide resistant alleles, which was able to reliably quantify MAFs as low as 0.050% in pooled mosquito specimens, is also reported. Conclusions We developed highly sensitive and efficient (RT-) ddPCR assays for contemporary operational needs that require monitoring of low malaria transmission and emerging insecticide resistance.

Transcriptional Response of Wolbachia to Dengue Virus Infection in Cells of the Mosquito Aedes aegypti.

ABSTRACTAedes aegypti transmits one of the most significant mosquito‐borne viruses, dengue virus (DENV). The absence of effective vaccines and clinical treatments and the emergence of insecticide resistance in A. aegypti necessitate novel vector control strategies. A new approach uses the endosymbiotic bacterium Wolbachia pipientis to reduce the spread of arboviruses. However, the Wolbachia-mediated antiviral mechanism is not well understood. To shed light on this mechanism, we investigated an unexplored aspect of Wolbachia-virus-mosquito interaction. We used RNA sequencing to examine the transcriptional response of Wolbachia to DENV infection in A. aegypti Aag2 cells transinfected with the wAlbB strain of Wolbachia. Our results suggest that genes encoding an endoribonuclease (RNase HI), a regulator of sigma 70-dependent gene transcription (6S RNA), essential cellular, transmembrane, and stress response functions and primary type I and IV secretion systems were upregulated, while a number of transport and binding proteins of Wolbachia, ribosome structure, and elongation factor-associated genes were downregulated due to DENV infection. Furthermore, bacterial retrotransposon, transposable, and phage-related elements were found among the up- and downregulated genes. We show that Wolbachia elicits a transcriptional response to virus infection and identify differentially expressed Wolbachia genes mostly at the early stages of virus infection. These findings highlight Wolbachia’s ability to alter its gene expression in response to DENV infection of the host cell.IMPORTANCE Aedes aegypti is a vector of several pathogenic viruses, including dengue, Zika, chikungunya, and yellow fever viruses, which are of importance to human health. Wolbachia is an endosymbiotic bacterium currently used in transinfected mosquitoes to suppress replication and transmission of dengue viruses. However, the mechanism of Wolbachia-mediated virus inhibition is not fully understood. While several studies have shown mosquitoes’ transcriptional responses to dengue virus infection, none have investigated these responses in Wolbachia, which may provide clues to the inhibition mechanism. Our results suggest changes in the expression of a number of functionally important Wolbachia genes upon dengue virus infection, including those involved in stress responses, providing insights into the endosymbiont’s reaction to virus infection.

Mesocosm Experiments to Quantify Predation of Mosquito Larvae by Aquatic Predators to Determine Potential of Ecological Control of Malaria Vectors in Ethiopia.

Malaria parasites are transmitted to humans by infectious female Anopheles mosquitoes. Chemical-insecticide-based mosquito control has been successful in reducing the burden of malaria. However, the emergence of insecticide resistance in malaria vectors and concerns about the effect of the chemicals on the environment, human health, and non-target organisms present a need for new or alternative vector control intervention tools. Biocontrol methods using aquatic invertebrate predators have emerged as a potential alternative and additional tool to control mosquito populations. Ecological control specifically makes use of species insights for improving the physical habitat conditions of competitors and predators of vectors. A first step towards this is to gain knowledge on the predation potential of several typically present macroinvertebrates. Hence, this study aimed at (1) examining the influence of the predation of hemipterans on the number of emerging adult mosquitoes and (2) detecting Anopheles mosquito DNA in the gut of those predators. The prey and predators were collected from a range of water bodies located in the Gilgel Gibe watershed, southwest Ethiopia. A semi-field study was carried out using mesocosms which were constructed using plastic containers mimicking the natural aquatic habitat of immature Anopheles mosquitoes. Adult mosquitoes that emerged from the mesocosms were collected using a mechanical aspirator. At the end of the experiment, predators were withdrawn from the mesocosms and identified to genus level. Polymerase Chain Reaction (PCR) was employed to identify sibling species of Anopheles gambiae s.l. and to detect Anopheles mosquito DNA in the gut of the predators. Data were analysed using R software. Giant water bugs (belostomatids) were the most aggressive predators of Anopheles larvae, followed by backswimmers (notonectids) and water boatmen (corixids). All female Anopheles gambiae s.l. emerged from the mesocosms were identified as Anopheles arabiensis. Anopheles arabiensis DNA was detected in the gut content of hemipteran specimens analysed from the three families. The number of the adult mosquitoes emerging from the mesocosms was affected by the presence of predators. The findings of this study provide evidence of the potential use of aquatic macroinvertebrate predators as biocontrol agents against immature Anopheles mosquitoes and their potential to be considered as a component of integrated vector management for insecticide resistance and the combined restoration of aquatic ecosystems via smart ecological engineering.

Analyses of Insecticide Resistance Genes in Aedes aegypti and Aedes albopictus Mosquito Populations from Cameroon.

The emergence of insecticide resistance in Aedes mosquitoes could pose major challenges for arboviral-borne disease control. In this paper, insecticide susceptibility level and resistance mechanisms were assessed in Aedes aegypti (Linnaeus, 1762) and Aedes albopictus (Skuse, 1894) from urban settings of Cameroon. The F1 progeny of Aedes aegypti and Aedes albopictus collected in Douala, Yaoundé and Dschang from August to December 2020 was tested using WHO tube assays with four insecticides: deltamethrin 0.05%, permethrin 0.75%, DDT 4% and bendiocarb 0.1%. TaqMan, qPCR and RT-qPCR assays were used to detect kdr mutations and the expression profiles of eight detoxification genes. Aedes aegypti mosquitoes from Douala were found to be resistant to DDT, permethrin and deltamethrin. Three kdr mutations, F1534C, V1016G and V1016I were detected in Aedes aegypti populations from Douala and Dschang. The kdr allele F1534C was predominant (90%) in Aedes aegypti and was detected for the first time in Aedes albopictus (2.08%). P450s genes, Cyp9J28 (2.23–7.03 folds), Cyp9M6 (1.49–2.59 folds), Cyp9J32 (1.29–3.75 folds) and GSTD4 (1.34–55.3 folds) were found overexpressed in the Douala and Yaoundé Aedes aegypti populations. The emergence of insecticide resistance in Aedes aegypti and Aedes albopictus calls for alternative strategies towards the control and prevention of arboviral vector-borne diseases in Cameroon.

Genetic variation at the Cyp6m2 putative insecticide resistance locus in Anopheles gambiae and Anopheles coluzzii

BackgroundThe emergence of insecticide resistance is a major threat to malaria control programmes in Africa, with many different factors contributing to insecticide resistance in its vectors, Anopheles mosquitoes. CYP6M2 has previously been recognized as an important candidate in cytochrome P450-mediated detoxification in Anopheles. As it has been implicated in resistance against pyrethroids, organochlorines and carbamates, its broad metabolic activity makes it a potential agent in insecticide cross-resistance. Currently, allelic variation within the Cyp6m2 gene remains unknown.MethodsHere, Illumina whole-genome sequence data from Phase 2 of the Anopheles gambiae 1000 Genomes Project (Ag1000G) was used to examine genetic variation in the Cyp6m2 gene across 16 populations in 13 countries comprising Anopheles gambiae and Anopheles coluzzii mosquitoes. To identify whether these alleles show evidence of selection either through potentially modified enzymatic function or by being linked to variants that change the transcriptional profile of the gene, hierarchical clustering of haplotypes, linkage disequilibrium, median joining networks and extended haplotype homozygosity analyses were performed.ResultsFifteen missense biallelic substitutions at high frequency (defined as > 5% frequency in one or more populations) are found, which fall into five distinct haplotype groups that carry the main high frequency variants: A13T, D65A, E328Q, Y347F, I359V and A468S. Despite consistent reports of Cyp6m2 upregulation and metabolic activity in insecticide resistant Anophelines, no evidence of directional selection is found occurring on these variants or on the haplotype clusters in which they are found.ConclusionThese results imply that emerging resistance associated with Cyp6m2 is potentially driven by distant regulatory loci such as transcriptional factors rather than by its missense variants, or that other genes are playing a more significant role in conferring metabolic resistance.

Assessment of Malaria Vector Behavior in Selected Sentinel Sites of Ethiopia

In Ethiopia, malaria incidence has significantly reduced in the past decade through the combined use of conventional vector control approaches and antimalarial drugs. However, the sustainability of this achievement is threatened by the shift in biting and resting behaviors and emergence of insecticide resistance by the primary malaria vector. Therefore, continuous monitoring of the behaviour of malaria mosquitoes in different sentinel sites is crucial to design effective prevention and control methods in the local context. Entomological investigations were conducted in three sentinel sites for five consecutive months during the major malaria transmission season. The species composition, population dynamics, biting and resting behaviours of malaria vectors were determined using center for disease control and prevention (CDC) light trap, human landing catch (HLC), pyrethrum spray catch (PSC) and Pit shelter collection (PFS). Accordingly, 10 households for CDC, 10 households for PSC, 10 households for PFS and 5 households for HLC from each site were randomly enrolled for mosquito collection. A total of 8,297 anopheline mosquitoes were collected from the three sites, out of which 4,525 (54.5%) were An. gambiae, s.l. 2,028 (24.4%) were An. pharoensis, 160 (1.9%) were An. funestus and the rest 1,584 (19%) were other Anophelines (An. coustani, An. cinerus and An. tenebrosus). No significant variation (P = 0.476) was observed between indoor (25.2/trap-night and outdoor collections (20.1/trap-night). Six hundred seventy six (43.3%) of An. gamiabiae s.l. (primary vector) were collected between 18:00 and 22:00 hours. Biting activity declined between 00:00 and 02:00 hours. The national malaria control program should pay close attention to the shifting behavior of vector mosquitoes as the observed outdoor feeding tendency of the vector population could pose challenges to the indoor intervention tools IRS and LLINs. Funding Information: This work was supported by the Ministry of health (Global fund). Declaration of Interests: The authors declare that they have no conflicts of interest. Ethics Approval Statement: This study was issued ethical clearance by the Scientific and Ethical Review Committee (SERC) in Ethiopia Public Health Institute with reference number EPHI 6.13/976. Verbal consent was obtained from the heads of households before commencing mosquito collection in houses. The heads of households surveyed were informed that participation in the study was absolutely voluntary and that even after consenting they would be free to withdraw from the study at any time.