Insecticide Resistance In Mosquitoes Research Articles

Chromobacterium biopesticide overcomes insecticide resistance in malaria vector mosquitoes.

Vector mosquito control is an integral part of malaria control. The global emergence of insecticide resistance in malaria-transmitting Anophelines has become an impediment and has created an urgent need for novel mosquito control approaches. Here, we show that a biopesticide derived from the soil-dwelling bacterium Chromobacterium sp. Panama (Csp_P) kills insecticide-resistant Anopheles mosquitoes, regardless of their resistance mechanisms. In addition, sublethal dose of Csp_P acts as a synergist to now used chemical insecticides across multiple classes. Moreover, Csp_P reduces host-seeking behavior and malaria parasite infection in vector mosquitoes in ways that further decrease transmission. Mosquito glutathione S-transferases are essential for Csp_P's mosquito-killing mechanism. Enclosed field trials in Burkina Faso, conducted in diverse ecological settings and supported by a mathematical model, have now demonstrated its potential for malaria control in settings with widespread insecticide resistance.

Target-site mediated insecticide resistance in major mosquito (Diptera: Culicidae) vectors: A systematic review

The use of insecticides remain the most effective vector control approach for mosquito borne diseases like malaria, dengue fever, chikungunya, and Zika virus disease; however, their increasing resistance has complicated the management. Mutations in kdr, ace-1/ace-2, rdl, and nAChR, are involved in target-site mediated resistance and prevent the binding of pyrethroids and dichlorodiph enyltrichloroethane, organophosphorus pesticide, carbamates and cyclodienes, respectively. Here, we review the current knowledge on target-site mediated insecticidal resistance mechanisms in major mosquito vectors and the techniques used to identify these mutations. The results showed that kdr mutations are frequently reported in mosquito species, indicating the overuse of pyrethroid in mosquito control. Report on ace mutations is very limited, primarily detected in Anopheles and Culex, with extremely low detection rate in Aedes, despite the wide application of organophosphates in their control. Notably, reports of rdl mutations and changes in nAChR are rare, which provides an opportunity to exploit these target sites, particularly in the event of disease outbreaks. Among various detection methods such as RFLP, TaqMan, Multiplex PCR and FRET, allele-specific PCR is mostly employed, especially in detecting kdr mutation. However, allele-specific PCR cannot detect novel mutation. As a result, there is an urgent need to develop a scalable, cost-effective tool that can be widely applied especially as these mutations are genetic markers for early detection of insecticide resistance. Robust monitoring methods remain critical to manage insecticide resistance and effective control of mosquito-borne diseases.

The non-inferiority of piperonyl-butoxide Yorkool® G3 insecticide-treated nets compared to Olyset®Plus measured by Anopheles arabiensis mortality in experimental huts in Tanzania

BackgroundNon-inferiority trials are recommended by the World Health Organization (WHO) to demonstrate that health products show comparable efficacy to that of existing standard of care. As part of the WHO Global Malaria Programme (GMP) process of assessment of malaria vector control products, a second-in-class insecticide-treated net (ITN) must be shown to be non-inferior to a first-in-class product based on mosquito mortality. The public health impact of the first-in-class pyrethroid-piperonyl butoxide (PBO) ITN, Olyset® Plus, has been demonstrated in epidemiological trials in areas with insecticide-resistant mosquitoes, but there is a need to determine the efficacy of other pyrethroid-PBO nets to ensure timely market availability of nets in order to increase access to ITNs. The non-inferiority of a deltamethrin-PBO ITN Yorkool® G3 was evaluated entomologically against Olyset® Plus in experimental huts in Tanzania, following WHO guidelines for non-inferiority trials.MethodsThe trial of the two pyrethroid-PBO ITNs was conducted in experimental huts in Lupiro, Tanzania, using a randomized 7 × 7 Latin square block design. The study ran for 49 nights in 14 huts assessing the mosquito mortality and blood-feeding of wild, free-flying, pyrethroid-resistant Anopheles arabiensis. Using the non-inferiority approach, the comparative efficacy (primary endpoint was mosquito mortality at 24 h and secondary endpoint was blood-feeding) of unwashed and 20 times field-washed pyrethroid-PBO Yorkool® G3 ITNs, were compared with the first-in-class product Olyset® Plus and against a pyrethroid-only ITN, PermaNet® 2.0 ITNs, as a standard comparator.ResultsThe experimental hut trial demonstrated non-inferiority and superiority of Yorkool® G3 to Olyset® Plus based on mosquito mortality [51% vs. 39%, OR 1.68 (95% CI 1.50–1.88)], given that lower 95% CI exceeded 0.74 (delta of 39%) and the margin of no difference (1). Blood-feeding inhibition was high for all treated ITNs (> 90%) and Yorkool® G3 was non-inferior to Olyset® Plus [4% vs. 2%, OR 1.81 (95% CI 1.46–2.39)], given that upper 95% CI was less than 4.85 (delta of 4%). The pyrethroid-PBO ITNs were superior to the pyrethroid-only net, PermaNet® 2.0, as determined by both the proportion of mortality and blood-feeding of mosquitoes (p-value < 0.05).ConclusionYorkool® G3 ITNs demonstrated non-inferiority to the first-in-class Olyset® Plus and superiority over the standard pyrethroid-only ITN, PermaNet® 2.0 as measured by mortality and blood-feeding inhibition of wild pyrethroid-resistant An. arabiensis mosquitoes. Yorkool® G3 ITNs are potential tools for the control of metabolic insecticide-resistant malaria vectors, and their market availability will contribute to the cost-effective selection of ITNs by malaria control programmes to improve population access to ITNs.

Mosquitoes: The Long-term Effects of Malaria Eradication in West Africa

Malaria has been a critical public health issue in West Africa for centuries, resulting in widespread morbidity and mortality, especially among vulnerable groups like children and pregnant women. Recent eradication efforts, bolstered by insecticide-treated bed nets (ITNs), indoor residual spraying (IRS), and antimalarial drugs, have significantly reduced the disease burden. This review examines the long-term socio-economic impacts of malaria eradication in West Africa, including improved public health, enhanced productivity, economic growth, and better access to healthcare. The reduction of malaria-related healthcare costs has led to increased investments in education, infrastructure, and other essential services. However, challenges persist, such as insecticide resistance among mosquitoes, financial constraints, and emerging public health concerns. Ecological effects of mosquito eradication, including impacts on biodiversity and the evolution of insecticide-resistant mosquitoes, raise important considerations for future control strategies. The role of climate change in shaping mosquito ecology and malaria transmission dynamics is also explored. This review underscores the need for sustained political and financial commitment, regional collaboration, and innovation to ensure the continued success of malaria eradication in West Africa. Integrating these efforts with broader Sustainable Development Goals (SDGs) and addressing ecological sustainability are essential for achieving long-term health and socio-economic benefits. Keywords: Malaria eradication, West Africa, public health, insecticide resistance, socio-economic impact, mosquito ecology.

Challenges in Malaria Control and Prevention in East Africa

Malaria remains a critical public health issue in East Africa, where high transmission rates persist despite extensive control and prevention efforts. This review article explores the multifaceted challenges that hinder effective malaria control and prevention in the region, including the emergence of drug-resistant Plasmodium parasites, insecticide-resistant mosquito vectors, inadequate healthcare infrastructure, socio-economic barriers, and environmental factors. The review methodology involved analyzing recent studies, reports, and data from international health organizations. Drug resistance and vector control are significant issues, with resistance to both anti-malarial drugs and insecticides compromising treatment efficacy and prevention efforts. Additionally, socio-economic factors such as poverty and lack of education, coupled with climate variability and environmental changes, further complicate malaria control. Addressing these challenges requires a coordinated approach that integrates continuous monitoring, healthcare system strengthening, community engagement, and international collaboration. By tackling these issues, East Africa can improve its malaria control efforts and ultimately enhance the health outcomes of its populations. Keywords: Malaria Control, Drug Resistance, Insecticide Resistance, Healthcare Infrastructure, Socio-Economic Barriers.

Mosquito Gut Microbiota: A Review.

Mosquitoes are vectors of many important human diseases. The prolonged and widespread use of insecticides has led to the development of mosquito resistance to these insecticides. The gut microbiota is considered the master of host development and physiology; it influences mosquito biology, disease pathogen transmission, and resistance to insecticides. Understanding the role and mechanisms of mosquito gut microbiota in mosquito insecticide resistance is useful for developing new strategies for tackling mosquito insecticide resistance. We searched online databases, including PubMed, MEDLINE, SciELO, Web of Science, and the Chinese Science Citation Database. We searched all terms, including microbiota and mosquitoes, or any specific genera or species of mosquitoes. We reviewed the relationships between microbiota and mosquito growth, development, survival, reproduction, and disease pathogen transmission, as well as the interactions between microbiota and mosquito insecticide resistance. Overall, 429 studies were included in this review after filtering 8139 search results. Mosquito gut microbiota show a complex community structure with rich species diversity, dynamic changes in the species composition over time (season) and across space (environmental setting), and variation among mosquito species and mosquito developmental stages (larval vs. adult). The community composition of the microbiota plays profound roles in mosquito development, survival, and reproduction. There was a reciprocal interaction between the mosquito midgut microbiota and virus infection in mosquitoes. Wolbachia, Asaia, and Serratia are the three most studied bacteria that influence disease pathogen transmission. The insecticide resistance or exposure led to the enrichment or reduction in certain microorganisms in the resistant mosquitoes while enhancing the abundance of other microorganisms in insect-susceptible mosquitoes, and they involved many different species/genera/families of microorganisms. Conversely, microbiota can promote insecticide resistance in their hosts by isolating and degrading insecticidal compounds or altering the expression of host genes and metabolic detoxification enzymes. Currently, knowledge is scarce about the community structure of mosquito gut microbiota and its functionality in relation to mosquito pathogen transmission and insecticide resistance. The new multi-omics techniques should be adopted to find the links among environment, mosquito, and host and bring mosquito microbiota studies to the next level.

Boric acid toxic sugar bait suppresses male Aedes aegypti (Diptera: Culicidae): wing beat frequency and amplitude, flight activity, fecundity, insemination, and mate-finding Allee effect.

Controlling the spread of arboviral diseases remains a considerable challenge due to the rapid development of insecticide resistance in Aedes mosquitoes. This study evaluated the effects of boric acid-containing toxic sugar bait (TSB) on field populations of resistant Aedes aegypti mosquitoes. In addition, this study examined the flight activity and wing beat frequency and amplitude of males and the flight activity, fecundity, and insemination of females after pairing with males exposed to TSB. The population dynamics of Aedes mosquitoes under imbalanced sex ratios were examined to simulate realistic field conditions for male suppression under the effect of TSB. The mortality of male mosquitoes was consistently high within 24 h after exposure. By contrast, the mortality of female mosquitoes was inconsistent, with over 70% mortality observed at 168 h. The flight activity and wing beat amplitude of treated males were significantly lower than those of controls, but no significant difference in wing beat frequency was detected. The fecundity and insemination of treated female mosquitoes were lower than those of controls. A simulation study indicated that considerably low male population densities led to mating failures, triggering a mate-finding Allee effect and resulting in persistently low population levels. Boric acid-containing TSB could effectively complement current chemical intervention approaches to control resistant mosquito populations. TSB is effective in reducing field male populations and impairing male flight activity and female-seeking behavior, resulting in decreased fecundity and insemination. Male suppression due to TSB potentially results in a small mosquito population. © 2024 Society of Chemical Industry.

The origin and insecticide resistance of Aedes albopictus mosquitoes established in southern Mozambique

BackgroundThe Aedes albopictus mosquito is of medical concern due to its ability to transmit viral diseases, such as dengue and chikungunya. Aedes albopictus originated in Asia and is now present on all continents, with the exception of Antarctica. In Mozambique, Ae. albopictus was first reported in 2015 within the capital city of Maputo, and by 2019, it had become established in the surrounding area. It was suspected that the mosquito population originated in Madagascar or islands of the Western Indian Ocean (IWIO). The aim of this study was to determine its origin. Given the risk of spreading insecticide resistance, we also examined relevant mutations in the voltage-sensitive sodium channel (VSSC).MethodsEggs of Ae. albopictus were collected in Matola-Rio, a municipality adjacent to Maputo, and reared to adults in the laboratory. Cytochrome c oxidase subunit I (COI) sequences and microsatellite loci were analyzed to estimate origins. The presence of knockdown resistance (kdr) mutations within domain II and III of the VSSC were examined using Sanger sequencing.ResultsThe COI network analysis denied the hypothesis that the Ae. albopictus population originated in Madagascar or IWIO; rather both the COI network and microsatellites analyses showed that the population was genetically similar to those in continental Southeast Asia and Hangzhou, China. Sanger sequencing determined the presence of the F1534C knockdown mutation, which is widely distributed among Asian populations, with a high allele frequency (46%).ConclusionsThese results do not support the hypothesis that the Mozambique Ae. albopictus population originated in Madagascar or IWIO. Instead, they suggest that the origin is continental Southeast Asia or a coastal town in China.Graphical

Will a lack of fabric durability be their downfall? Impact of textile durability on the efficacy of three types of dual-active-ingredient long-lasting insecticidal nets: a secondary analysis on malaria prevalence and incidence from a cluster-randomized trial in north-west Tanzania

BackgroundThe Dual-Active Ingredient long-lasting insecticidal nets (Dual-AI LLIN) have been developed to counteract the reduced efficacy of pyrethroid (PY)-only nets due to widespread pyrethroid insecticide resistance in malaria vector mosquitoes. They constitute half of the nets distributed in sub-Saharan Africa between 2022 and 2024. However, their effectiveness once they develop holes is unclear, particularly in pyrethroid-resistant settings. This study evaluates the textile integrity of three dual- AI LLINs compared to standard PY LLN, over 3 years of use in a community in Tanzania and the associated impact on malaria prevalence and incidence.MethodsA secondary analysis of data from a randomized controlled trial (RCT) in North-western Tanzania was conducted to evaluate the effectiveness of α-cypermethrin only; pyriproxyfen and α-cypermethrin (PPF-PY); chlorfenapyr and α-cypermethrin (chlorfenapyr-PY); and the synergist piperonyl butoxide and permethrin (PBO-PY) LLINs on malaria infection prevalence and case incidence. The association between the net textile condition and 1/malaria prevalence over 3 years of use between 2019 and 2022, and 2/malaria case incidence in a cohort of children over 2 years of follow-up was assessed between 2019 and 2021.ResultsThere was no significant association between damaged (OR 0.98, 95% CI 0.71–1.37, p-value = 0.655) and too-torn (OR 1.07, 95% CI 0.77–1.47, p-value = 0.694) compared to intact nets on malaria prevalence for all net types. However, there were reduced rates of malaria case incidence in children sleeping under a net in good condition compared to too-torn nets (incidence rate ratio (IRR) 0.76 [95% CI 0.63–0.92], p = 0.005). Malaria incidence was also consistently lower in too-torn PBO-PY LLIN (IRR = 0.37 [95% CI 0.19–0.72], p = 0.003) and chlorfenapyr-PY LLIN (IRR = 0.45 [95% CI 0.33–0.97], p = 0.053) compared to an intact PY-only LLIN during the first year of follow up. In year 2, the incidence was only significantly lower in intact chlorfenapyr-PY LLIN (IRR = 0.49 [95% CI 0.29–0.81], p = 0.006) compared to intact PY LLIN.ConclusionThe study confirmed that sleeping under a chlorfenapyr-PY LLIN or PBO-PY LLIN offered superior protection to pyrethroid-only nets even when torn. Preventing the development of holes is essential as they impact the level of protection offered against malaria infection.Trial registration: ClinicalTrials.gov, number (NCT03554616)

Efficacy of Pirikool® 300 CS used for indoor residual spraying on three different substrates in semi-field experimental conditions

BackgroundVector control using insecticides is a key prevention strategy against malaria. Unfortunately, insecticide resistance in mosquitoes threatens all progress in malaria control. In the perspective of managing this resistance, new insecticide formulations are being tested to improve the effectiveness of vector control tools.MethodsThe efficacy and residual activity of Pirikool® 300 CS was evaluated in comparison with Actellic® 300 CS in experimental huts at the Tiassalé experimental station on three substrates including cement, wood and mud. The mortality, blood-feeding inhibition, exiting behaviour and deterrency of free-flying wild mosquitoes was evaluated. Cone bioassay tests with susceptible and resistant mosquito strains were conducted in the huts to determine residual efficacy.ResultsA total of 20,505 mosquitoes of which 10,979 (53%) wild female Anopheles gambiae were collected for 112 nights. Residual efficacy obtained from monthly cone bioassay was higher than 80% with the susceptible, laboratory-maintained An. gambiae Kisumu strain, from the first to the tenth study period on all three types of treated substrate for both Actellic® 300CS and Pirikool® 300CS. This residual efficacy on the wild Tiassalé strain was over 80% until the 4th month of study on Pirikool® 300CS S treated substrates. Overall 24-h mortalities of wild free-flying An. gambiae sensu lato which entered in the experimental huts over the 8-months trial on Pirikool® 300CS treatment was 50.5%, 75.9% and 52.7%, respectively, on cement wall, wood wall and mud wall. The positive reference product Actellic® 300CS treatment induced mortalities of 42.0%, 51.8% and 41.8% on cement wall, wood wall and mud wall.ConclusionPirikool® 300CS has performed really well against resistant strains of An. gambiae using indoor residual spraying method in experimental huts. It could be an alternative product for indoor residual spraying in response to the vectors' resistance to insecticides.

Potential of MALDI-TOF MS biotyping to detect deltamethrin resistance in the dengue vector Aedes aegypti.

Insecticide resistance in mosquitoes is spreading worldwide and represents a growing threat to vector control. Insecticide resistance is caused by different mechanisms including higher metabolic detoxication, target-site modification, reduced penetration and behavioral changes that are not easily detectable with simple diagnostic methods. Indeed, most molecular resistance diagnostic tools are costly and labor intensive and then difficult to use for routine monitoring of insecticide resistance. The present study aims to determine whether mosquito susceptibility status against the pyrethroid insecticides (mostly used for mosquito control) could be established by the protein signatures of legs and/or thoraxes submitted to MALDI-TOF Mass Spectrometry (MS). The quality of MS spectra for both body parts was controlled to avoid any bias due to unconformity protein profiling. The comparison of MS profiles from three inbreeds Ae. aegypti lines from French Guiana (IRF, IR03, IR13), with distinct deltamethrin resistance genotype / phenotype and the susceptible reference laboratory line BORA (French Polynesia), showed different protein signatures. On both body parts, the analysis of whole protein profiles revealed a singularity of BORA line compared to the three inbreeding lines from French Guiana origin, suggesting that the first criteria of differentiation is the geographical origin and/or the breeding history rather than the insecticide susceptibility profile. However, a deeper analysis of the protein profiles allowed to identify 10 and 11 discriminating peaks from leg and thorax spectra, respectively. Among them, a specific peak around 4870 Da was detected in legs and thoraxes of pyrethroid resistant lines compared to the susceptible counterparts hence suggesting that MS profiling may be promising to rapidly distinguish resistant and susceptible phenotypes. Further work is needed to confirm the nature of this peak as a deltamethrin resistant marker and to validate the routine use of MS profiling to track insecticide resistance in Ae. aegypti field populations.

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 12 h, 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.

INSECTICIDE TOXICITY TO HONEY BEES: LESSONS LEARNED FROM STUDIES BY THE UNIVERSITY OF FLORIDA URBAN ENTOMOLOGY LABORATORY

Laboratory and field studies comparing the relative tolerance of mosquitoes (Aedes aegypti and Aedes albopictus) and non-target species, including the honey bee (Apis mellifera), and other non-target insects have shown that the non-target species can tolerate fairly well when exposed to insecticides used in mosquito control operations. Tolerance levels of non-target species vary due to factors such as the development of insecticide resistance in mosquitoes which require higher insecticide doses to reduce populations to adequate levels. However, well-planned mosquito control programs, can lower risks to honey bees and other non-target species. This review discusses the toxicity of mosquito control insecticides to the honey bee and other non-target insects.

Measuring insecticide resistance in a vacuum: exploring next steps to link resistance data with mosquito control efficacy.

Insecticide resistance is a great challenge facing mosquito operational control agencies across the United States, where few active ingredients with unique modes of action are available for use, increasing resistance pressure and further hampering resistance management strategies. Emergence and expansion of insecticide resistance in mosquitoes can be detected by resistance monitoring programs; however, there are gaps in our knowledge regarding the link between resistance bioassay results and operational control outcomes. Here, we review both public health and agricultural studies on pesticide resistance bioassays and control outcomes. A discussion on the main gaps in our knowledge of insecticide resistance and a review of resistance management practices is also presented. We conclude with research questions that can advance our understanding of resistance monitoring and control.

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.

Resistance of mosquitoes to Lambda-Cyhalothrin and DDT in a Niger Delta Region of Nigeria.

The escalation of insecticide resistance across the World Health Organization (WHO) African region calls for the routine monitoring of insecticide resistance in mosquitoes. While pyrethroids are recommended for use and dichlorodiphenyltrichloroethane (DDT) has been prescribed, it is imperative to reevaluate their efficacy across diverse geographical settings. The extent of resistance among mosquitoes to DDT and lambda-cyhalothrin remains understudied in Ika North East, Delta State, Nigeria, where the yellow fever virus was reported in 2019. We investigated the susceptibility of female mosquitoes to DDT (4%) and lambda-cyhalothrin (0.05%) in this specific study area. Adult female mosquitoes of Anopheles gambiae, Culex quinquefasciatus, and Aedes albopictus, aged between 2 and 4 days, were subjected to these insecticides utilizing the WHO bioassay method. The assessment of knockdown was done between 10 and 60 min, then mortality after 24 h. C. quinquefasciatus and A. albopictus mosquitoes exposed to DDT and lambda-cyhalothrin exhibited high susceptibility, resulting in complete mortality (100%); however, A. gambiae displayed resistance, with mortality rates of 19% and 76%, respectively . Notably, A. gambiae mosquitoes exposed to piperonyl butoxide (PBO)-DDT and PBO-lambda-cyhalothrin exhibited enhanced mortality, reaching 95% (indicating suspected resistance) and 100% (indicating susceptibility), respectively. Knockdown time (KDT) for 50% in mosquitoes exposed to lambda-cyhalothrin ranged from 3.94 to 33.51 min. Similarly, KDT model for 95% ranged from 19.04 to 84.15 min. Among the tested mosquito species, Culex mosquitoes exhibited the shortest knockdown resistance time for lambda-cyhalothrin, recorded at 3.94 min. Similarly, the KDT for DDT ranged from 24.97 to 187.06 min for 50% mortality and from 61.04 to 431.03 min for 95% mortality, respectively. Anopheles mosquitoes exposed to PBO + DDT recorded the lowest KDT. Our study underscores the potential of exercising caution in the use of DDT and lambda-cyhalothrin insecticides for the control of mosquitoes due to emerging resistance.

Heat shock proteins, thermotolerance, and insecticide resistance in mosquitoes.

Mosquitoes transmit pathogens that pose a threat to millions of people globally. Unfortunately, widespread insecticide resistance makes it difficult to control these public health pests. General mechanisms of resistance, such as target site mutations or increased metabolic activity, are well established. However, many questions regarding the dynamics of these adaptations in the context of developmental and environmental conditions require additional exploration. One aspect of resistance that deserves further study is the role of heat shock proteins (HSPs) in insecticide tolerance. Studies show that mosquitoes experiencing heat stress before insecticide exposure demonstrate decreased mortality. This is similar to the observed reciprocal reduction in mortality in mosquitoes exposed to insecticide prior to heat stress. The environmental shifts associated with climate change will result in mosquitoes occupying environments with higher ambient temperatures, which could enhance existing insecticide resistance phenotypes. This physiological relationship adds a new dimension to the problem of insecticide resistance and further complicates the challenges that vector control and public health personnel face. This article reviews studies illustrating the relationship between insecticide resistance and HSPs or hsp genes as well as the intersection of thermotolerance and insecticide resistance. Further study of HSPs and insecticide resistance could lead to a deeper understanding of how environmental factors modulate the physiology of these important disease vectors to prepare for changing climatic conditions and the development of novel strategies to prevent vector-borne disease transmission.

Susceptibility status and synergistic activity of DDT and Lambda-cyhalothrin on Anopheles gambiae and Aedes aegypti in Delta State, Nigeria.

The detection of insecticide resistance in male mosquitoes has been treated with less importance in monitoring insecticide resistance spread in mosquitoes. There are no studies on the susceptibility and synergistic activity of DDT and lambda-cyhalothrin on male Anopheles gambiae and Aedes aegypti in Delta State, Nigeria. Even though studies have extensively reported resistance in female mosquitoes, the susceptibility of male mosquitoes to insecticide classes should be ascertained. In this study, we tested the susceptibility status and synergistic activity of DDT and Lambda-cyhalothrin on An. gambiae and Ae. aegypti in Delta State, Nigeria, in order to ascertain the level of resistance and knockdown. In addition, we modelled the knockdown time using Probit analysis model. WHO bioassay method was used to expose two days old adult mosquitoes to 4% DDT and 0.05% lambda-cyhalothrin. The results showed that An. gambiae mosquitoes exposed to DDT and lambda-cyhalothrin were confirmed resistant (61% and 53% respectively). However, pre-exposing the resistant mosquito population to piperonyl butoxide (4%) showed an increase in mortality to 90% (possible resistance) in DDT and 98% (susceptible) in lambda-cyhalothrin. Ae. aegypti mosquitoes exposed to DDT were susceptible (98%) while those exposed to lambda-cyhalothrin were confirmed resistant (87%) and this increased to complete mortality (100%) in PBO+lambda-cyhalothrin population. Furthermore, the results showed that the knockdown time (KDT50 and KDT95) in An. gambiae exposed to DDT was 39.5-71.2 minutes and 124.5-146.4 minutes respectively, while that of lambda-cyhalothrin was 33.0-81.8 minutes and 64.0-124.4 minutes respectively. In Ae. aegypti, KDT50 and KDT95 was 23.9 and 61.7minutes for DDT exposure whereas it was 5.6-15.3 minutes and 36.1-72.3 minutes for lambda-cyhalothrin exposure. It can be concluded that male An. gambiae mosquitoes exposed to the insecticides were resistant and the causes may be linked to certain resistant genes in the mosquitoes. The chances of transferring resistance are possible in wild species and molecular-based studies on the resistant gene in male mosquitoes as well as the tendencies of transfer are required to establish this focus.

Mosquito Control Strategies and Insecticide Resistance of the Malaria Vector in Urbanized Land Use Types in Suame Municipality, Ghana.

Modified landscapes could create breeding habitats for mosquitoes and affect their community structure and susceptibility with implications for their management. Hence, in this study, household mosquito control methods in two urbanized landscapes; industrial and residential human settlements, in Ghana and insecticide susceptibility of the inhabiting Anopheles populations were assessed. Household knowledge and usage pattern of mosquito control methods in the modified landscapes were obtained using a questionnaire. Female adult Anopheles mosquitoes were also subjected to susceptibility tests using mosquito coils (0.08% meperfluthrin, 0.03% dimefluthrin, and 0.3% transfluthrin) and World Health Organization (WHO) insecticide test papers (0.05% deltamethrin, 4% DDT, 0.1% bendiocarb, 0.25% pirimiphos-methyl, and 5% malathion). Although insecticide-treated nets and aerosols were used for mosquito control, mosquito coils were the most common and widely preferred household method. The Anopheles mosquitoes were resistant to all the insecticides (mosquito coils and WHO test papers) except pirimiphos-methyl. Land use type did not affect insecticide resistance, but the insecticide type did. The findings indicate the effect of household insecticide usage practices on local mosquito populations and their implications for effective vector management and disease control in modified landscapes.

Larvicidal potential of silver nanoparticles synthesized from Ocimum gratissimum leaf extracts against anopheles’ mosquito

Despite recent improvements in the methods used to eradicate and minimize mosquito populations, they still pose severe threats to human health. This study aimed to investigate the Larvicidal potentials of silver nanoparticles of Ocimum gratissimum on wild Anopheles larvae from Lagos. The plant used in this study was collected from the southeastern part of Nigeria, Ibite-Olo in Ezeagu Local Government Area of Enugu State. Wild Anopheles mosquito larvae were collected from a field at Kosofe Local Government Area of Lagos State, Nigeria where resistant Anopheline populations have been reported in and around Lagos State were brought to the laboratory and kept under standard insectary conditions (25–29 ℃;78–82% relative humidity). Aqueous extract of Ocimum gratissimum was made and subsequently into the silver nanoparticles. A bioassay test was performed according to WHO guidelines, with six different concentrations to assess the larvicidal activity and values obtained were subjected to log prohibit regression analysis to obtain LC50 and values with 95% confidence limit. The results of the larvicidal activities of the silver nanoparticles of Ocimum gratissimum showed that the mortality rate was dose-dependent with the percentage mortality increasing at a direct proportional rate as with dose and time of exposure. Ocimum gratissimum gave LC50 at 0.5 ppm and LC95 at 2.5 ppm respectively. The biosynthesized silver nanoparticles augmented the larvicidal activity of the silver nanoparticles of Ocimum gratissimum on wild Anopheles larvae from Lagos. Therefore, this study showed that the silver nanoparticles of Ocimum gratissimum have the potency to be used against an insecticide-resistant mosquito vector and are a suitable candidate for the development of novel natural insecticides.