Impact of environment on mosquito response to pyrethroid insecticides: facts, evidences and prospects

Restoring functional integrity of the global production ecosystem through biological control

Human society is anchored in the global agroecosystem. For millennia, this system has provided humans with copious supplies of nutrient-rich food. Yet, through chemical intensification and simplification, vast shares of present-day farmland derive insufficient benefits from biodiversity and prove highly vulnerable to biotic stressors. Here, we argue that on-farm action centered on biological control can effectively defuse pest risk by bolstering foundational ecosystem services. By harnessing plant, animal and microbial biodiversity, biological control offers safe, efficacious and economically-sound plant health solutions and coevolved options for invasive species mitigation. In recent years, its scientific foundation has been fortified and solutions have been refined for myriad ecologically brittle systems. Yet, for biological control to be mainstreamed, it needs to be rebooted, intertwined with (on- and off-farm) agroecological tactics and refurbished - from research, policy and regulation, public-private partnerships up to modes of implementation. Misaligned incentives (for chemical pesticides) and adoption barriers further need to be removed, while its scientific underpinnings should become more interdisciplinary, policy-relevant, solution-oriented and linked with market demand. Thus, biological control could ensure human wellbeing in a nature-friendly manner and retain farmland ecological functioning under global change.

Synthesis and larvicidal efficacy of pyrazolopyrimidine derivatives conjugated with selenium nanoparticles against Culex pipiens L. and Musca domestica L. larvae

The synthesized pyrazolopyrimidine derivatives conjugated with selenium nanoparticles were prepared via a reaction of pyrazolone 1 with aryl-aldehyde and malononitrile or 3-oxo-3-phenylpropanenitrile in the presence ammonium acetate or pipridine using an ultrasonic bath as a modified method in the organic synthesis for such materials. The structure of the synthesized compounds was elucidated through various techniques. All the synthesized pyrazolopyrimidines were used in the synthesis of selenium nanoparticles (SeNPs). These nanoparticles were confirmed using UV-spectra, Dynamic Light scattering and (TEM) techniques. The larvicidal efficiency;of the synthesized;compounds; was investigated against some strains such as Culex pipiens;and Musca domestica larvae. Bioassay test showed pyrazolopyrimide derivatives to exhibit an acceptable larvicidal;bio-efficacy. The derivative (3) exhibited;the highest;efficiency for more than; lab strains of both species. Moreover, C. pipiens larvae were more sensitive towards the examined compounds than M. domestica. The field;strain displayed lower affinity for the 2 folds compounds. Some biochemical changes were tracked through analysis of insect main metabolites (protein, lipid and carbohydrate), in addition to measuring the changes in seven enzymes after treatment. Generally, there was a reduction in the protein, lipids and carbohydrates after treatment with all tested compounds. Moreover, a decrement was noticed for acetylcholine esterase and glutathione;S-transferase; enzymes. There was an increment in the acid;phosphatase; and alkaline phosphatase. In addition, there was elevation in Phenoloxidase level but it noticed the declination in both Cytochrome P450 and Ascorbate peroxidase activity after treatment both flies with derivatives of selenium-nanoparticles in both lab and field strain. Generally, the experiments carried out indicate that antioxidant and detoxification enzymes may play a significant role in mechanism of action of our novel nanocompounds. The cytotoxicity of the synthesized compounds and conjugated with SeNPs showed enhanced compatibility with human normal fibroblast cell line (BJ1) with no toxic effect.

Functional analysis of novel cystatins from Haemaphysalis doenitzi and evaluation of their roles in cypermethrin and λ-cyhalothrin resistance

Currently, the primary strategy for tick control relies on chemical agents. Pyrethrins, which are botanically derived compounds, have demonstrated efficacy in controlling ticks without posing a risk to human or animal health. However, research into pyrethrins' metabolic mechanisms remains sparse. Cystatin, as a reversible binding inhibitor of cysteine protease, may be involved in the initiation of pyrethrin detoxification of Haemaphysalis doenitzi. In this study, two novel cystatins were cloned, HDcyst-3 and HDcyst-4, the relative expression of which was highest in the Malpighian tubules compared with the tick midguts, salivary glands, and ovaries. Prokaryotic expression and in vitro studies revealed that cystatins effectively inhibit the enzymatic activities of cathepsins B and S. RNAi results showed that the reduction of cystatins significantly decreased the engorgement weight, egg mass weight, and egg hatching rate of adult female ticks, and prolonged feeding time by two days. The control rate of rHDcyst-3 and rHDcyst-4 protein vaccination against female adults were 55.9% and 63.2%, respectively. In addition, the tick immersion test showed that cypermethrin and λ-cyhalothrin had significant acaricidal effects against adult unfed H. doenitzi. The qPCR result indicated that compared with the control group, the expression of HDcyst-3 and HDcyst-4 was markedly decreased in the sublethal cypermethrin and λ-cyhalothrin group at LC50. Enzyme activity showed that cypermethrin and λ-cyhalothrin could significantly induce the activities of glutathione S-transferase (GST), carboxylesterase (CarE), and acetylcholinesterase (AchE). The aforementioned results provided indirect evidence that cystatin plays an important role in pyrethrin detoxification and provides a theoretical basis for future acaricide experiments and pest management.

Susceptibility status of Aedes aegypti (Diptera: Culicidae) to public health insecticides in Southern Afar Region, Ethiopia

Mosquito-borne viral diseases such as dengue fever, chikungunya, and yellow fever have been documented in Ethiopia since the 1960s. However, the efficacy of public health insecticides against Aedes aegypti that transmits these viruses remains poorly understood in the country, particularly in the Afar Region. Thus, the aim of the study was to assess the susceptibility status of Ae. aegypti to deltamethrin, permethrin, alpha-cypermethrin, pirimiphos-methyl, bendiocarb, and propoxur insecticides. Larvae and pupae of Aedes species were collected from Awash Arba, Awash Sebat, and Werer towns of the Afar Region of Ethiopia during July-October 2022, brought to the Aklilu Lemma Institute of Pathobiology, insectary and reared to adults. Non-blood-fed, 3-5 days-old females Ae. aegypti were exposed to pyrethroid, carbamate, and organophosphate insecticide impregnated papers in tube test following the standard guidelines. Knockdown rates were noted at 10 minutes interval until one hour. The mortality in mosquitoes was recorded 24 hours after 60 minutes of exposure. The mortality rates of Ae. aegypti exposed to propoxur were 87% in all the study towns. Similarly, 88% mortality in Ae. aegypti was recorded when tested with bendiocarb in Awash Sebat and Awash Arba towns. Suspected resistance of Ae. aegypti (95% mortality) to alpha-cypermethrin was observed in Awash Arba town. However, Ae. aegypti collected from all the three sites was observed to be susceptible to deltamethrin, permethrin, and pirimiphos-methyl. Ae. aegypti was resistant to 0.1% bendiocarb and 0.1% propoxur and possibly resistant to 0.05% alpha-cypermethrin. On the other hand, it was susceptible to 0.05% deltamethrin, 0.75% permethrin, and 0.25% pirimiphos-methyl. Thus, vector control products with deltamethrin, permethrin, and pirimiphos-methyl can be used in the control of adult Ae. aegypti in the Afar Region of Ethiopia. However, further studies should be carried out to evaluate the susceptibility status of Ae. aegypti to alpha-cypermethrin in the Awash Arba area.

Longitudinal survey of insecticide resistance in a village of central region of Burkina Faso reveals co-occurrence of 1014F, 1014S and 402L mutations in Anopheles coluzzii and Anopheles arabiensis

BACKGROUND

Pyrethroid resistance is one of the major threats for effectiveness of insecticide-treated bed nets (ITNs) in malaria vector control. Genotyping of mutations in the voltage gated sodium channel (VGSC) gene is widely used to easily assess the evolution and spread of pyrethroid target-site resistance among malaria vectors. L1014F and L1014S substitutions are the most common and best characterized VGSC mutations in major African malaria vector species of the Anopheles gambiae complex. Recently, an additional substitution involved in pyrethroid resistance, i.e. V402L, has been detected in Anopheles coluzzii from West Africa lacking any other resistance alleles at locus 1014. The evolution of target-site resistance mutations L1014F/S and V402L was monitored in An. coluzzii and Anopheles arabiensis specimens from a Burkina Faso village over a 10-year range after the massive ITN scale-up started in 2010.

METHODS

Anopheles coluzzii (N = 300) and An. arabiensis (N = 362) specimens collected both indoors and outdoors by different methods (pyrethrum spray catch, sticky resting box and human landing collections) in 2011, 2015 and 2020 at Goden village were genotyped by TaqMan assays and sequencing for the three target site resistance mutations; allele frequencies were statistically investigated over the years.

RESULTS

A divergent trend in resistant allele frequencies was observed in the two species: 1014F decreased in An. coluzzii (from 0.76 to 0.52) but increased in An. arabiensis (from 0.18 to 0.70); 1014S occurred only in An. arabiensis and slightly decreased over time (from 0.33 to 0.23); 402L increased in An. coluzzii (from 0.15 to 0.48) and was found for the first time in one An. arabiensis specimen. In 2020 the co-occurrence of different resistance alleles reached 43% in An. coluzzii (alleles 410L and 1014F) and 32% in An. arabiensis (alleles 1014F and 1014S).

CONCLUSIONS

Overall, an increasing level of target-site resistance was observed among the populations with only 1% of the two malaria vector species being wild type at both loci, 1014 and 402, in 2020. This, together with the co-occurrence of different mutations in the same specimens, calls for future investigations on the possible synergism between resistance alleles and their phenotype to implement local tailored intervention strategies.

Knockdown resistance (kdr) associated organochlorine resistance in mosquito-borne diseases (Culex quinquefasciatus): Systematic study of reviews and meta-analysis

INTRODUCTION

Culex quinquefasciatus is one of the most important carriers of human pathogens. Using the insecticides is one of the most important methods of combating this vector. But the genetic resistance created in Culex quinquefasciatus led to disruption in the fight against this pest. Consequently, it is necessary to know the level of resistance to fight this vector. Based on this, the present study was conducted to investigate the prevalence of kdr resistance in Culex quinquefasciatus against organochlorine insecticides in the world.

METHODS

This study was conducted by systematic review, and meta-analysis on the prevalence of kdr resistance and mortality rate in Culex quinquefasciatus against organochlorine insecticides in the world. All pertinent articles were extracted and analyzed in accordance with this information during an unrestricted search of the scientific databases Web of Science, PubMed, Scopus, biooan.org, Embase, ProQuest, and Google Scholar until the end of November 2023. Statistical analysis of data was done using fixed and random effects model in meta-analysis, I2 index, Cochran's test, and meta-regression by STATA version 17 software.

RESULTS

Seventy articles were included in the meta-analysis process. Based on the findings, the prevalence of Kdr in Culex quinquefasciatus against organochlorine insecticide was estimated at 63.1%. Moreover, the mortality rate against the insecticide deltamethrin was 46%, DDT 18.5%, permethrin 42.6%, malathion 54.4% and lambdacyhalothrin 53%.

CONCLUSION

More than half of Cx. quinquefasciatus had Kdr. This vector was relatively resistant to DDT and permethrin insecticides and sensitive to malathion, deltamethrin and lambdacyhalothrin. In order to prevent the development of resistance to alternative insecticides, it is consequently critical to combat this vector with efficacious insecticides.

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.

Non-contact detection of pyrethroids widely used in vector control by Anopheles mosquitoes

Pyrethroids are the most widely used insecticides to control vector borne diseases including malaria. Physiological resistance mechanisms to these insecticides have been well described, whereas those for behavioral resistance remain overlooked. Field data suggest the presence of spatial sensory detection by Anopheles mosquitoes of the pyrethroid molecules used in insecticide-based control tools, such as long-lasting insecticide nets or insecticide residual spraying. This opens the way to the emergence of a wide range of behavioral adaptations among malaria vectors. However, the spatial sensory detection of these molecules is controversial and needs to be demonstrated. The goal of this study was to behaviorally characterize the non-contact detection of three of the most common pyrethroids used for malaria vector control: permethrin, deltamethrin an ⍺-cypermethrin. To reach this goal, we recorded the behavior (takeoff response) of Anopheles gambiae pyrethroid-sensitive and resistant laboratory strains, as well as field collected mosquitoes from the Gambiae Complex, when exposed to the headspace of bottles containing different doses of the insecticides at 25 and 35°C, in order to represent a range of laboratory and field temperatures. We found the proportion of laboratory susceptible and resistant female mosquitoes that took off was, in all treatments, dose and the temperature dependent. Sensitive mosquitoes were significantly more prone to take off only in the presence of ⍺-cypermethrin, whereas sensitive and resistant mosquitoes showed similar responses to permethrin and deltamethrin. Field-collected mosquitoes of the Gambiae Complex were also responsive to permethrin, independently of the species identity (An. gambiae, An. coluzzii and An. arabiensis) or their genotypes for the kdr mutation, known to confer resistance to pyrethroids. The observed ability of Anopheles spp. mosquitoes to detect insecticides without contact could favor the evolution of behavioral modifications that may allow them to avoid or reduce the adverse effect of insecticides and thus, the development of behavioral resistance.

The P450-Monooxygenase Activity and CYP6D1 Expression in the Chlorfenapyr-Resistant Strain of Musca domestica L

The house fly Musca domestica L. is one of the most common insects of veterinary and medical importance worldwide; its ability to develop resistance to a large number of insecticides is well known. Many studies support the involvement of cytochrome P-450-dependent monooxygenases (P450) in the development of resistance to pyrethroids, neonicotinoids, carbamates, and organophosphates among insects. In this paper, the monooxygenase activity and expression level of CYP6D1 were studied for the first time in a chlorfenapyr-resistant strain of house fly. Our studies demonstrated that P450 activity in adults of the susceptible strain (Lab TY) and chlorfenapyr-resistant strain (ChlA) was 1.56-4.05-fold higher than that in larvae. In females of the Lab TY and ChlA strains, this activity was 1.53- and 1.57-fold higher, respectively (p < 0.05), than that in males, and in contrast, the expression level of CYP6D1 was 21- and 8-fold lower, respectively. The monooxygenase activity did not vary between larvae of the susceptible strain Lab TY and the chlorfenapyr-resistant strain ChlA. Activity in females and males of the ChlA strain exceeded that in the Lab TY strain specimens by 1.54 (p = 0.08) and 1.83 (p < 0.05) times, respectively, with the same level of CYP6D1 expression. PCR-RFLP analysis revealed a previously undescribed mutation in the promoter region of the CYP6D1 gene in adults of the Lab TY and ChlA strains, and it did not affect the gene expression level. The obtained results show that the development of resistance to chlorfenapyr in M. domestica is accompanied by an increase in P450-monooxygenase activity without changes in CYP6D1 expression.

Integrated One Health strategies in Dengue

Zoonoses have rapidly spread globally, necessitating the implementation of vaccination strategies as a control measure. Emerging and re-emerging vector-borne diseases are among the major global public health concerns. Dengue, a zoonotic viral infection transmitted to humans by a vector, the Aedes mosquito, is a severe global health problem. Dengue is a serious tropical infectious disease, second only to malaria, causing around 25,000 deaths each year. The resurgence of Dengue is mainly due to climate change, demographic transitions and evolving social dynamics. The development of an effective vaccine against Dengue has proven to be a complex undertaking due to four different viral serotypes with distinct antigenic profiles. This review highlights the urgent need to address the dengue threat by exploring the application of biotechnological and -OMICS sciences.

Bioactive components in Psidium guajava extracts elicit biotoxic attributes and distinct antioxidant enzyme modulation in the larvae of vectors of lymphatic filariasis and dengue

Control of mosquito vectors, which have caused a global disease burden, has employed various methods. However, the challenges posed by current physical and chemical methods have raised concerns about vector control programs, leading to the search for alternative methods that are less toxic, eco-friendly, and cost-effective. This study investigated the larvicidal potential of aqueous, methanol, and ethylacetate extracts of Guava (Psidium guajava) against Aedes aegypti and Culex quinquefasciatus larvae. Functional group and phytochemical characterization were performed using Fourier-Transform Infrared Spectroscopy (FTIR) and GC-MS analysis to identify the bioactive compounds in the extracts. Larval bioassays were conducted using WHO standard procedures at concentrations of 12.5, 25, 50, 125, and 250 mg/L, and mortality was recorded after 24, 48, and 72 h. Additionally, antioxidant enzyme profiles in the larvae were studied. All of the solvent extracts showed larvicidal activity, with the methanol extract exhibiting the highest mortality against Ae. aegypti and Cx. quinquefasciatus larvae, followed by aqueous and ethylacetate extracts. FTIR spectroscopic analysis revealed the presence of OH, C-H of methyl and methylene, CO and CC. The GC-MS analysis indicated that the methanol, aqueous, and ethylacetate extracts all had 27, 34, and 43 phytoactive compounds that were effective at causing larvicidal effects, respectively. Different concentrations of each extract significantly modulated the levels of superoxide dismutase, catalase, glutathione peroxidase, and reduced glutathione in larvae. This study's findings indicate the potential for developing environmentally friendly vector control products using the bioactive components of extracts from P. guajava leaves.

Insecticide susceptibility status of Anopheles albimanus populations in historical malaria foci in Quintana Roo, Mexico

BACKGROUND

Mexico has experienced a significant reduction in malaria cases over the past two decades. Certification of localities as malaria-free areas (MFAs) has been proposed as a steppingstone before elimination is achieved throughout the country. The Mexican state of Quintana Roo is a candidate for MFA certification. Monitoring the status of insecticide susceptibility of major vectors is crucial for MFA certification. This study describes the susceptibility status of Anopheles albimanus, main malaria vector, from historically important malaria foci in Quintana Roo, using both phenotypic and genotypic approaches.

METHODS

Adult mosquito collections were carried out at three localities: Palmar (Municipality of Othon P. Blanco), Buenavista (Bacalar) and Puerto Morelos (Puerto Morelos). Outdoor human-landing catches were performed by pairs of trained staff from 18:00 to 22:00 during 3-night periods at each locality during the rainy season of 2022. Wild-caught female mosquitoes were exposed to diagnostic doses of deltamethrin, permethrin, malathion, pirimiphos-methyl or bendiocarb using CDC bottle bioassays. Mortality was registered at the diagnostic time and recovery was assessed 24 h after exposure. Molecular analyses targeting the Voltage-Gated Sodium Channel (vgsc) gene and acetylcholinesterase (ace-1) gene were used to screen for target site polymorphisms. An SNP analysis was carried out to identify mutations at position 995 in the vgsc gene and at position 280 in the ace-1 gene.

RESULTS

A total of 2828 anophelines were collected. The main species identified were Anopheles albimanus (82%) and Anopheles vestitipennis (16%). Mortalities in the CDC bottle bioassay ranged from 99% to 100% for all the insecticides and mosquito species. Sequence analysis was performed on 35 An. albimanus across the three localities; of those, 25 were analysed for vgsc and 10 for ace-1 mutations. All individuals showed wild type alleles.

CONCLUSION

The results demonstrated that An. albimanus populations from historical malaria foci in Quintana Roo are susceptible to the main insecticides used by the Ministry of Health.

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

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

An optical system to detect, surveil, and kill flying insect vectors of human and crop pathogens

Sustainable and effective means to control flying insect vectors are critically needed, especially with widespread insecticide resistance and global climate change. Understanding and controlling vectors requires accurate information about their movement and activity, which is often lacking. The Photonic Fence (PF) is an optical system that uses machine vision, infrared light, and lasers to identify, track, and interdict vectors in flight. The PF examines an insect's outline, flight speed, and other flight parameters and if these match those of a targeted vector species, then a low-power, retina-safe laser kills it. We report on proof-of-concept tests of a large, field-sized PF (30 mL × 3 mH) conducted with Aedes aegypti, a mosquito that transmits dangerous arboviruses, and Diaphorina citri, a psyllid which transmits the fatal huanglongbing disease of citrus. In tests with the laser engaged, < 1% and 3% of A. aegypti and D. citri, respectfully, were recovered versus a 38% and 19% recovery when the lacer was silenced. The PF tracked, but did not intercept the orchid bee, Euglossa dilemma. The system effectively intercepted flying vectors, but not bees, at a distance of 30 m, heralding the use of photonic energy, rather than chemicals, to control flying vectors.

Whole transcriptomic analysis reveals overexpression of salivary gland and cuticular proteins genes in insecticide-resistant Anopheles arabiensis from Western Kenya

BACKGROUND

Effective vector control is key to malaria prevention. However, this is now compromised by increased insecticide resistance due to continued reliance on insecticide-based control interventions. In Kenya, we have observed heterogenous resistance to pyrethroids and organophosphates in Anopheles arabiensis which is one of the most widespread malaria vectors in the country. We investigated the gene expression profiles of insecticide resistant An. arabiensis populations from Migori and Siaya counties in Western Kenya using RNA-Sequencing. Centers for Disease Control and Prevention (CDC) bottle assays were conducted using deltamethrin (DELTA), alphacypermethrin (ACYP) and pirimiphos-methyl (PMM) to determine the resistance status in both sites.

RESULTS

Mosquitoes from Migori had average mortalities of 91%, 92% and 58% while those from Siaya had 85%, 86%, and 30% when exposed to DELTA, ACYP and PMM, respectively. RNA-Seq analysis was done on pools of mosquitoes which survived exposure ('resistant'), mosquitoes that were not exposed, and the insecticide-susceptible An. arabiensis Dongola strain. Gene expression profiles of resistant mosquitoes from both Migori and Siaya showed an overexpression mainly of salivary gland proteins belonging to both the short and long form D7 genes, and cuticular proteins (including CPR9, CPR10, CPR15, CPR16). Additionally, the overexpression of detoxification genes including cytochrome P450s (CYP9M1, CYP325H1, CYP4C27, CYP9L1 and CYP307A1), 2 carboxylesterases and a glutathione-S-transferase (GSTE4) were also shared between DELTA, ACYP, and PMM survivors, pointing to potential contribution to cross resistance to both pyrethroid and organophosphate insecticides.

CONCLUSION

This study provides novel insights into the molecular basis of insecticide resistance in An. arabiensis in Western Kenya and suggests that salivary gland proteins and cuticular proteins are associated with resistance to multiple classes of insecticides.

Time of exposure and assessment influence the mortality induced by insecticides against metabolic resistant mosquitoes

BACKGROUND

Increasing metabolic resistance in malaria vector mosquitoes resulted in the development of insecticide-treated nets (ITNs) with active ingredients (AI) that target them. Bioassays that accurately measure the mortality induced by these AIs on ITNs are needed. Mosquito metabolic enzyme expression follows a circadian rhythm. Thus, this study assessed (i) influence of the time of day of mosquito exposure and (ii) timing of assessment of mortality post exposure (24 and 72 h) to ITNs against vectors that are susceptible to pyrethroids and those with metabolic and knockdown resistance mechanisms.

METHODS

Two cone bioassay experiments were conducted following World Health Organization (WHO) guidelines. Firstly, on ITNs incorporated with 2 g AI/kg of deltamethrin (DM) alone, or combined with 8 g AI/kg piperonyl butoxide (PBO) synergist, during the day (9:00-14:00 h) and repeated in the evening (18:00-20:00 h). This was followed by a confirmatory experiment during the afternoon (12:00-14:00 h) and repeated in the night (22:00-24:00 h) using mosquitoes unexposed or pre-exposed to PBO for 1 h before exposure to DM ITNs. Each net piece was tested with a minimum of eight cones per time (N = 24). The outcome was mortality after 24 h (M24) or 72 h (M72) of holding.

RESULTS

The cone bioassays performed using metabolic resistant mosquitoes during the evening showed significantly lower M24 than those performed in the day for DM: odds ratio (OR) 0.14 [95% confidence interval (CI) 0.06-0.30, p < 0.0001] and DM PBO [OR 0.29 (95% CI 0.18-0.49, p < 0.0001). M72 was higher than M24 for metabolic resistant mosquitoes exposed to DM [OR 1.44 (95% CI 1.09-1.88), p = 0.009] and DM PBO [OR 1.82 (95% CI 1.42-2.34), p < 0.0001]. An influence of hour of experiment and time of assessment was not observed for mosquitoes that had knockdown resistance or that were pyrethroid-susceptible.

CONCLUSIONS

Time of day of experiment and hour of assessment of delayed mortality after exposure of mosquitoes are important considerations in evaluating insecticides that interact with mosquito metabolism to counter metabolic resistant mosquitoes. This is important when evaluating field-aged ITNs that may have lower concentrations of AI.

Is Anopheles gambiae (sensu stricto), the principal malaria vector in Africa prone to resistance development against new insecticides? Outcomes from laboratory exposure of An. gambiae (s.s.) to sub-lethal concentrations of chlorfenapyr and clothianidin

Indiscriminate use of pesticides in the public health and agriculture sectors has contributed to the development of resistance in malaria vectors following exposure to sub-lethal concentrations. To preserve the efficacy of vector control tools and prevent resistance from spreading, early resistance detection is urgently needed to inform management strategies. The introduction of new insecticides for controlling malaria vectors such as clothianidin and chlorfenapyr requires research to identify early markers of resistance which could be used in routine surveillance. This study investigated phenotypic resistance of Anopheles gambiae (sensu stricto) Muleba-Kis strain using both WHO bottle and tube assays following chlorfenapyr, clothianidin, and alpha-cypermethrin selection against larvae and adults under laboratory conditions. High mortality rates were recorded for both chlorfenapyr-selected mosquitoes that were consistently maintained for 10 generations (24-h mortality of 92-100% and 72-h mortality of 98-100% for selected larvae; and 24-h mortality of 95-100% and 72-h mortality of 98-100% for selected adults). Selection with clothianidin at larval and adult stages showed a wide range of mortality (18-91%) compared to unselected progeny where mortality was approximately 99%. On the contrary, mosquitoes selected with alpha-cypermethrin from the adult selection maintained low mortality (28% at Generation 2 and 23% at Generation 4) against discrimination concentration compared to unselected progeny where average mortality was 51%. The observed resistance in the clothianidin-selected mosquitoes needs further investigation to determine the underlying resistance mechanism against this insecticide class. Additionally, further investigation is recommended to develop molecular markers for observed clothianidin phenotypic resistance.

Human activities and densities shape insecticide resistance distribution and dynamics in the virus-vector Culex pipiens mosquitoes from Morocco

BACKGROUND

Mosquitoes of the Culex pipiens complex are widely distributed vectors for several arboviruses affecting humans. Consequently, their populations have long been controlled using insecticides, in response to which different resistance mechanisms have been selected. Moreover, their ecological preferences and broad adaptability allow C. pipiens mosquitoes to breed in highly polluted water bodies where they are exposed to many residuals from anthropogenic activities. It has been observed for several mosquito species that anthropization (in particular urbanization and agricultural lands) can lead to increased exposure to insecticides and thus to increased resistance. The main objective of the present study was to investigate whether and how urbanization and/or agricultural lands had a similar impact on C. pipiens resistance to insecticides in Morocco.

METHODS

Breeding sites were sampled along several transects in four regions around major Moroccan cities, following gradients of decreasing anthropization. The imprint of anthropogenic activities was evaluated around each site as the percentage of areas classified in three categories: urban, agricultural and natural. We then assessed the frequencies of four known resistance alleles in these samples and followed their dynamics in five urban breeding sites over 4 years.

RESULTS

The distribution of resistance alleles revealed a strong impact of anthropization, in both agricultural and urbanized lands, although different between resistance mutations and between Moroccan regions; we did not find any clear trend in the dynamics of these resistance alleles during the survey.

CONCLUSIONS

Our study provides further evidence for the role of anthropic activities in the selection and maintenance of mutations selected for resistance to insecticides in mosquitoes. The consequences are worrying as this could decrease vector control capacities and thus result in epizootic and epidemic outbreaks. Consequently, concerted and integrated disease control strategies must be designed that include better management regarding the consequences of our activities.

Insecticide resistance of Miami-Dade Culex quinquefasciatus populations and initial field efficacy of a new resistance-breaking adulticide formulation

Sporadic outbreaks of human cases of West Nile virus (WNV), primarily vectored by Culex quinquefasciatus Say in suburban and urban areas, have been reported since introduction of the virus into Florida in 2001. Miami-Dade County, Florida is part of one of the largest metropolitan areas in the United States, supports Cx. quinquefasciatus year-round, and recently experienced over 60 human cases of WNV during one outbreak. To facilitate more effective integrated vector management and public health protection, we used the Centers for Disease Control and Prevention (CDC) bottle bioassay method to evaluate the susceptibility of adult Cx. quinquefasciatus collected from 29 locations throughout Miami-Dade County to pyrethroid and organophosphate adulticide active ingredients (AIs) used by Miami-Dade County Mosquito Control. We also determined the frequency of the 1014 knockdown resistance (kdr) mutation for Cx. quinquefasciatus from a subset of 17 locations. We detected resistance to two pyrethroid AIs in all tested locations (permethrin: 27 locations, deltamethrin: 28 locations). The 1014F allele was widely distributed throughout all 17 locations sampled; however, 29.4% of these locations lacked 1014F homozygotes even though phenotypic pyrethroid resistance was present. Organophosphate resistance was more variable; 20.7% of the locations tested were susceptible to malathion, and 33.3% of the populations were susceptible to naled. We subsequently conducted a field trial of ReMoa Tri, a recently approved multiple AI adulticide formulation labelled for resistant mosquitoes, against a mixed location field population of Miami-Dade Cx. quinquefasciatus. Average 24-hr mortality was 65.1 ± 7.2% and 48-hr mortality increased to 85.3 ± 9.1%, indicating good control of these resistant Cx. quinquefasciatus. This current study shows that insecticide resistance is common in local Cx. quinquefasciatus but effective options are available to maintain control during active disease transmission in Miami-Dade County.

Plastic pellets make Excirolana armata more aggressive: Intraspecific interactions and isopod mortality differences between populations

Plastic pellets represent a significant component of microplastic (< 5 mm) pollution. Impacts caused by plastic pellets involve physical harm and toxicity related to ingestion and non-ingestion (such as the release of chemicals in leachates). The latter is the main route of exposure for invertebrate macrobenthic populations. This study aimed to compare the toxicity of plastic pellets in distinct marine macrobenthic populations, considering the influence of sediment characteristics (organic matter and grain size) and quality (contamination by hydrophobic chemicals) on ecotoxicological effects, as well as the influence of color on the toxicity of beach-stranded plastic pellets. We performed three experiments on plastic pellet exposure using Excirolana armata from beaches with high and low pellet density. When exposed to pellets, populations that inhabit beaches without pellets demonstrate higher mortality than those inhabiting beaches with high pellet densities. The mortality of E. armata to pellets was higher when the exposure occurred in sediment with high organic matter (OM), suggesting that chemicals were transferred from pellets to OM. Yellowish beach-stranded pellets induced higher mortality of E. armata than the white tones did. We also observed lethargic (near-dead) and dead individuals being preyed upon by healthy individuals, a cannibalistic behavior that raises an ecological concern regarding the negative effects of this exposure on intraspecific interactions in marine macrobenthic populations.

Odor-evoked transcriptomics of Aedes aegypti mosquitoes

Modulation of odorant receptors mRNA induced by prolonged odor exposure is highly correlated with ligand-receptor interactions in Drosophila as well as mammals of the Muridae family. If this response feature is conserved in other organisms, this presents an intriguing initial screening tool when searching for novel receptor-ligand interactions in species with predominantly orphan olfactory receptors. We demonstrate that mRNA modulation in response to 1-octen-3-ol odor exposure occurs in a time- and concentration-dependent manner in Aedes aegypti mosquitoes. To investigate gene expression patterns at a global level, we generated an odor-evoked transcriptome associated with 1-octen-3-ol odor exposure. Transcriptomic data revealed that ORs and OBPs were transcriptionally responsive whereas other chemosensory gene families showed little to no differential expression. Alongside chemosensory gene expression changes, transcriptomic analysis found that prolonged exposure to 1-octen-3-ol modulated xenobiotic response genes, primarily members of the cytochrome P450, insect cuticle proteins, and glucuronosyltransferases families. Together, these findings suggest that mRNA transcriptional modulation of olfactory receptors caused by prolonged odor exposure is pervasive across taxa and can be accompanied by the activation of xenobiotic responses.

Deltamethrin and transfluthrin select for distinct transcriptomic responses in the malaria vector Anopheles gambiae

BACKGROUND

The widespread use of pyrethroid insecticides in Africa has led to the development of strong resistance in Anopheles mosquitoes. Introducing new active ingredients can contribute to overcome this phenomenon and ensure the effectiveness of vector control strategies. Transfluthrin is a polyfluorinated pyrethroid whose structural conformation was thought to prevent its metabolism by cytochrome P450 monooxygenases in malaria vectors, thus representing a potential alternative for managing P450-mediated resistance occurring in the field. In this study, a controlled selection was used to compare the dynamics of resistance between transfluthrin and the widely used pyrethroid deltamethrin in the mosquito Anopheles gambiae. Then, the associated molecular mechanisms were investigated using target-site mutation genotyping and RNA-seq.

METHODS

A field-derived line of An. gambiae carrying resistance alleles at low frequencies was used as starting material for a controlled selection experiment. Adult females were selected across 33 generations with deltamethrin or transfluthrin, resulting in three distinct lines: the Delta-R line (selected with deltamethrin), the Transflu-R line (selected with transfluthrin) and the Tiassale-S line (maintained without selection). Deltamethrin and transfluthrin resistance levels were monitored in each selected line throughout the selection process, as well as the frequency of the L1014F kdr mutation. At generation 17, cross-resistance to other public health insecticides was investigated and transcriptomes were sequenced to compare gene transcription variations and polymorphisms associated with adaptation to each insecticide.

RESULTS

A rapid increase in resistance to deltamethrin and transfluthrin was observed throughout the selection process in each selected line in association with an increased frequency of the L1014F kdr mutation. Transcriptomic data support a broader response to transfluthrin selection as compared to deltamethrin selection. For instance, multiple detoxification enzymes and cuticle proteins were specifically over-transcribed in the Transflu-R line including the known pyrethroid metabolizers CYP6M2, CYP9K1 and CYP6AA1 together with other genes previously associated with resistance in An. gambiae.

CONCLUSION

This study confirms that recurrent exposure of adult mosquitoes to pyrethroids in a public health context can rapidly select for various resistance mechanisms. In particular, it indicates that in addition to target site mutations, the polyfluorinated pyrethroid transfluthrin can select for a broad metabolic response, which includes some P450s previously associated to resistance to classical pyrethroids. This unexpected finding highlights the need for an in-depth study on the adaptive response of mosquitoes to newly introduced active ingredients in order to effectively guide and support decision-making programmes in malaria control.

Inference of selection pressures that drive insecticide resistance in Anopheles and Culex mosquitoes in Korea

Pyrethroids are primarily used for mosquito control in Korea. However, high frequencies of mutations conferring resistance to not only pyrethroids but also to other insecticides have been found in mosquito populations. This study aimed to examine the hypothesis that insecticides used outside of public health may play a role in selection. Briefly, the resistance mutation frequencies to three insecticide groups (pyrethroids, organophosphates, and cyclodienes) were estimated in two representative groups of mosquito species (Anopheles Hyrcanus Group and Culex pipiens complex). The relationship between these frequencies and the land-use status of the collection sites was investigated through multiple regression analysis. In the Anopheles Hyrcanus Group, the frequencies of both ace1 (organophosphate resistance) and rdl (cyclodiene resistance) mutations were positively correlated with 'proximity to golf course', possibly be due to the insecticides used for turf maintenance. They also showed positive correlations with field area and rice paddy area, respectively, suggesting the role of agricultural insecticides in the selection of these resistance traits. For the Cx. pipiens complex, the kdr (pyrethroid resistance), ace1, and rdl mutations were positively correlated with the residential area, field, and rice paddy, respectively. Therefore, pyrethroids used for public health could serve as a direct source of resistance selection pressure against kdr, whereas non-public health insecticides may pose primary selection pressure against the ace1 and rdl traits. The current findings suggest that the insecticides used in agriculture and the golf industry play a significant role in mosquito selection, despite variations in the extent of indirect selection pressure according to the mosquito groups and insecticide classes.

Identification of two insecticide resistance markers in Ethiopian Anopheles stephensi mosquitoes using a multiplex amplicon sequencing assay

Since its first detection in 2012 in Djibouti, Anopheles stephensi has invaded and established in the Horn of Africa, and more recently Nigeria. The expansion of this vector poses a significant threat to malaria control and elimination efforts. Integrated vector management is the primary strategy used to interrupt disease transmission; however, growing insecticide resistance is threatening to reverse gains in global malaria control. We present a next-generation amplicon-sequencing approach, for high-throughput monitoring of insecticide resistance genes (ace1, GSTe2, vgsc and rdl), species identification and characterization of genetic diversity (its2 and cox1) in An. stephensi. Ninety-five An. stephensi mosquitoes, collected in Ethiopia, were screened, identifying 104 SNPs, including the knock-down mutation L958F (L1014F in Musca domestica), and for the first time in this vector species, the A296S substitution (A301S in Drosophila melanogaster) in the rdl locus. Two other amino acid substitutions (ace1-N177D, GSTe2-V189L) were also identified but have not been previously implicated in insecticide resistance. Genetic diversity in the mitochondrial cox1 gene revealed shared haplotypes between Ethiopian An. stephensi with samples from Pakistan, Sudan, and Djibouti. Overall, we present a reliable, cost-effective strategy using amplicon-sequencing to monitor known insecticide resistance mutations, with the potential to identify new genetic variants, to assist in the high-throughput surveillance of insecticide resistance in An. stephensi populations.

Odor-evoked transcriptomics of Aedes aegypti mosquitoes

Modulation of odorant receptors mRNA induced by prolonged odor exposure is highly correlated with ligand-receptor interactions in Drosophila as well as mammals of the Muridae family. If this response feature is conserved in other organisms, this presents a potentially potent initial screening tool when searching for novel receptor-ligand interactions in species with predominantly orphan olfactory receptors. We demonstrate that mRNA modulation in response to 1-octen-3-ol odor exposure occurs in a time- and concentration-dependent manner in Aedes aegypti mosquitoes. To investigate gene expression patterns at a global level, we generated an odor-evoked transcriptome associated with 1-octen-3-ol odor exposure. Transcriptomic data revealed that ORs and OBPs were transcriptionally responsive whereas other chemosensory gene families showed little to no differential expression. Alongside chemosensory gene expression changes, transcriptomic analysis found that prolonged exposure to 1-octen-3-ol modulated xenobiotic response genes, primarily members of the cytochrome P450, insect cuticle proteins, and glucuronosyltransferases families. Together, these findings suggest that mRNA transcriptional modulation caused by prolonged odor exposure is pervasive across taxa and accompanied by the activation of xenobiotic responses. Furthermore, odor-evoked transcriptomics create a potential screening tool for filtering and identification of chemosensory and xenobiotic targets of interest.

The interplay between malaria vectors and human activity accounts for high residual malaria transmission in a Burkina Faso village with universal ITN coverage

BACKGROUND

Mosquito and human behaviour interaction is a key determinant of the maximum level of protection against malaria that can be provided by insecticide-treated nets (ITNs). Nevertheless, scant literature focuses on this interaction, overlooking a fundamental factor for efficient malaria control. This study aims to estimate malaria transmission risk in a Burkina Faso village by integrating vector biting rhythms with some key information about human habits.

METHODS

Indoor/outdoor human landing catches were conducted for 16 h (16:00-08:00) during 8 nights (September 2020) in Goden village. A survey about net usage and sleeping patterns was submitted to half the households (October-December 2020). A subsample of collected specimens of Anopheles gambiae sensu lato was molecularly processed for species identification, Plasmodium detection from heads-thoraxes and L1014F pyrethroid-resistance allele genotyping. Hourly mosquito abundance was statistically assessed by GLM/GAM, and the entomological inoculation rate (EIR) was corrected for the actual ITN usage retrieved from the questionnaire.

RESULTS

Malaria transmission was mainly driven by Anopheles coluzzii (68.7%) followed by A. arabiensis (26.2%). The overall sporozoite rate was 2% with L1014F estimated frequency of 0.68 (N = 1070 out of 15,201 A. gambiae s.l. collected). No major shift in mosquito biting rhythms in response to ITN or differences between indoor and outdoor catches were detected. Impressive high biting pressure (mean 30.3 mosquitoes/person/hour) was exerted from 20:00 to 06:00 with a peak at 4:00. Human survey revealed that nearly all inhabitants were awake before 20:00 and after 7:00 and at least 8.7% had no access to bednets. Adjusting for anthropological data, the EIR dropped from 6.7 to 1.2 infective bites/person/16 h. In a scenario of full net coverage and accounting only for the human sleeping patterns, the daily malaria transmission risk not targetable by ITNs was 0.69 infective bites.

CONCLUSIONS

The high mosquito densities and interplay between human/vector activities means that an estimated 10% of residual malaria transmission cannot be prevented by ITNs in the village. Locally tailored studies, like the current one, are essential to explore the heterogeneity of human exposure to infective bites and, consequently, to instruct the adoption of new vector control tools strengthening individual and community protection.

Bioactivity of brassica seed meals and its compounds as ecofriendly larvicides against mosquitoes

Strategic, sustainable, and ecofriendly alternatives to chemical pesticides are needed to effectively control mosquitoes and reduce the incidence of their vectored diseases. We evaluated several Brassicaceae (mustard family) seed meals as sources of plant derived isothiocyanates produced from the enzymatic hydrolysis of biologically inactive glucosinolates for the control of Aedes aegypti (L., 1762). Five defatted seed meals (Brassica juncea (L) Czern., 1859, Lepidium sativum L., 1753, Sinapis alba L., 1753, Thlaspi arvense L., 1753, and Thlaspi arvense-heat inactivated and three major chemical products of enzymatic degradation (allyl isothiocyanate, benzyl isothiocyanate and 4-hydroxybenzyl isothiocyanate) were assayed to determine toxicity (LC₅₀) to Ae. aegypti larvae. All seed meals except the heat inactivated T. arvense were toxic to mosquito larvae. L. sativum seed meal was the most toxic treatment to larvae (LC₅₀ = 0.04 g/120 mL dH₂O) at the 24-h exposure. At the 72-h evaluation, the LC₅₀ values for B. juncea, S. alba and T. arvense seed meals were 0.05, 0.08 and 0.1 g/120 mL dH₂O, respectively. Synthetic benzyl isothiocyanate was more toxic to larvae 24-h post treatment (LC₅₀ = 5.29 ppm) compared with allyl isothiocyanate (LC₅₀ = 19.35 ppm) and 4-hydroxybenzyl isothiocyanate (LC₅₀ = 55.41 ppm). These results were consistent with the higher performance of the benzyl isothiocyanate producing L. sativum seed meal. Isothiocyanates produced from seed meals were more effective than the pure chemical compounds, based on calculated LC₅₀ rates. Using seed meal may provide an effective method of delivery for mosquito control. This is the first report evaluating the efficacy of five Brassicaceae seed meals and their major chemical constituent against mosquito larvae and demonstrates how natural compounds from Brassicaceae seed meals can serve as a promising ecofriendly larvicides to control mosquitoes.

Larval habitat stability and productivity in two sites in Southern Ghana

BACKGROUND

Mosquito larval source management (LSM) is a valuable additional tool for malaria vector control. Understanding the characteristics of mosquito larval habitats and its ecology in different land use types can give valuable insight for an effective larval control strategy. This study determined the stability and productivity of potential anopheline larval habitats in two different ecological sites: Anyakpor and Dodowa in southern Ghana.

METHODS

A total of 59 aquatic habitats positive for anopheline larvae were identified, and sampled every two weeks for a period of 30 weeks using a standard dipping method. Larvae were collected using standard dippers and were raised in the insectary for identification. Sibling species of the Anopheles gambiae sensu lato (s.l.) were further identified by polymerase chain reaction. The presence of larval habitats, their stability and larvae positive habitats were compared between the two sites using Mann-Whitney U and the Kruskal-Wallis test. Factors affecting the presence of An. gambiae larvae and physicochemical properties at the sites were determined using multiple logistic regression analysis and Spearman's correlation.

RESULTS

Out of a total of 13,681 mosquito immatures collected, 22.6% (3095) were anophelines and 77.38% (10,586) were culicines. Out of the 3095 anophelines collected, An. gambiae s.l. was predominant (99.48%, n = 3079), followed by Anopheles rufipes (0.45%, n = 14), and Anopheles pharoensis (0.064%, n = 2). Sibling species of the An. gambiae consisted of Anopheles coluzzii (71%), followed by An. gambiae s.s. (23%), and Anopheles melas (6%). Anopheles mean larval density was highest in wells [6.44 (95% CI 5.0-8.31) larvae/dip], lowest in furrows [4.18 (95% CI 2.75-6.36) larvae/dip] and man-made ponds [1.20 (95% CI 0.671-2.131) larvae/dip].The results also revealed habitat stability was highly dependent on rainfall intensity, and Anopheles larval densities were also dependent on elevated levels of pH, conductivity and TDS.

CONCLUSION

The presence of larvae in the habitats was dependent on rainfall intensity and proximity to human settlements. To optimize the vector control measures of malaria interventions in southern Ghana, larval control should be focused on larval habitats that are fed by underground water, as these are more productive habitats.

Biogenic Synthesis of Silver Nanoparticles Using Pantoea stewartii and Priestia aryabhattai and Their Antimicrobial, Larvicidal, Histopathological, and Biotoxicity Potential

In recent years, green nanotechnology has gained considerable importance for the synthesis of nanoparticles due to its economic viability and biosafety. In the current study, silver nanoparticles were synthesized using two bacterial isolates, H2 and H3, which were isolated from soil samples collected from the Western Ghats, Tamil Nadu, and identified at the species level as Pantoeastewartii (H2) and Priestiaaryabhattai (H3) by sequencing their 16s rRNA genes. Intracellularly synthesized silver nanoparticles were characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and particle size analysis. AFM studies show that both of the bacterial synthesized Ag NPs were circular-shaped and disaggregated, with an average size distribution of 4 nm for Pantoeastewartii and 3.6 nm for Priestiaaryabhattai. Furthermore, their larvicidal activity, antimicrobial, histopathological, and biotoxicity effects were determined. The synthesized Ag NPs exhibited potent larvicidal activity against fourth instars of Ae.aegypti, An.stephensi, and Cx.quinquefasciatus exposed to a 50 µg/mL concentration for 24 h based on their LC₅₀ and LC₉₀ values. Histopathological studies of the affected mosquito larvae clearly show damage to the epithelial cells, food bolus, basement membrane, muscles, and midgut parts. The maximum antimicrobial activity of Priestiaaryabhattai-synthesized Ag NPs was observed for Streptomyces varsoviensis MTCC-1537, and that of Pantoea stewartii-synthesized Ag NPs was against Escherichia coli MTCC-43. The toxicity test on non-target organisms such as Artemia nauplii and zebrafish embryos indicates no visible abnormalities or mortality after their exposure for 48h. It is concluded that silver nanoparticles can easily be synthesized using Pantoea stewartii (H2) and Priestia aryabhattai (H3) as capping and reducing agents. Silver nanoparticles showed potent larvicidal activities and could potentially be used in integrated vector control programs because they are safe for other inhabitants of the same aquatic environment as mosquito larvae.

Natural plant diet impacts phenotypic expression of pyrethroid resistance in Anopheles mosquitoes

Success in reducing malaria transmission through vector control is threatened by insecticide resistance in mosquitoes. Although the proximal molecular mechanisms and genetic determinants involved are well documented, little is known about the influence of the environment on mosquito resistance to insecticides. The aim of this study was to assess the effect of plant sugar feeding on the response of Anopheles gambiae sensu lato to insecticides. Adults were fed with one of four treatments, namely a 5% glucose control solution, nectariferous flowers of Barleria lupulina, of Cascabela thevetia and a combination of both B. lupulina + C. thevetia. WHO tube tests were performed with 0.05% and 0.5% deltamethrin, and knockdown rate (KD) and the 24 h mosquito mortality were measured. Plant diet significantly influenced mosquito KD rate at both concentrations of deltamethrin. Following exposure to 0.05% deltamethrin, the B. lupulina diet induced a 2.5 fold-increase in mosquito mortality compared to 5% glucose. Species molecular identification confirmed the predominance of An. gambiae (60% of the samples) over An. coluzzii and An. arabiensis in our study area. The kdr mutation L1014F displayed an allelic frequency of 0.75 and was positively associated with increased phenotypic resistance to deltamethrin. Plant diet, particularly B. lupulina, increased the susceptibility of mosquitoes to insecticides. The finding that B. lupulina-fed control individuals (i.e. not exposed to deltamethrin) also displayed increased 24 h mortality suggests that plant-mediated effects may be driven by a direct effect of plant diet on mosquito survival rather than indirect effects through interference with insecticide-resistance mechanisms. Thus, some plant species may weaken mosquitoes, making them less vigorous and more vulnerable to the insecticide. There is a need for further investigation, using a wider range of plant species and insecticides, in combination with other relevant environmental factors, to better understand the expression and evolution of insecticide resistance.

Phenotypic insecticide resistance status of the Culex pipiens complex: a European perspective

Background

The common house mosquito Culex pipiens is known to be a major vector for West Nile virus. In order to decrease risks of West Nile virus outbreaks in Europe, insecticides and the bio-larvicide Bacillus thuringiensis israelensis (Bti) are commonly used for vector control. Alarmingly, insecticide resistance has been reported in Cx. pipiens populations from Southern Europe and several countries neighbouring Europe. For Central and Northern Europe, however, the phenotypic insecticide resistance status of Cx. pipiens has not yet been investigated.

Methods

A literature review was performed to assess the geographical distribution of insecticide resistance in Cx. pipiens. To fill the gap of knowledge for Central and Northern Europe, WHO susceptibility tests with permethrin, deltamethrin, malathion, bendiocarb and DDT and a larval toxicity test with Bti were performed with a Cx. pipiens population from Belgium, a country in Central Europe.

Results

This research provides the first evidence of widespread phenotypic insecticide resistance in Cx. pipiens. In general, Cx. pipiens developed resistance against multiple insecticides in several countries. Another Cx. pipiens population from Belgium was tested and showed insecticide resistance against deltamethrin, permethrin, DDT and possibly against bendiocarb. The bio-larvicide Bti caused lower mortality than reported for other Cx. pipiens populations in the literature.

Conclusions

These results indicate the urgent need for insecticide resistance monitoring against commonly used adulticides and larvicides in Europe, for the translation of knowledge gained regarding the limited efficiency and availability of insecticide into EU legislation and the need for innovative non-chemical vector control tools in order to counter the widespread insecticide resistance in Culex populations.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05542-x.

Participatory approaches for raising awareness among subsistence farmers in Tanzania about the spread of insecticide resistance in malaria vectors and the possible link to improper agricultural pesticide use

Background

Insecticide resistance is a key barrier to long-term malaria control, and it may be exacerbated by poor agricultural pesticide use. Current practices, however, do not link public health and agricultural pesticide use. This study investigated the perspectives of farmers and other stakeholders regarding the integration of agricultural and public health measures to address resistance. Additionally, the feasibility of participatory workshops to increase the farmers’ understanding and participation in pesticide stewardship was assessed.

Methods

Four themes were investigated: pesticide awareness, practices, and opinions of; insecticide resistance in malaria vectors; the effectiveness of current malaria prevention tools; and the links between agricultural and public health pesticide usage. Participatory workshops and field training were held with entomologists, farmers, and agricultural specialists, focusing on agro-ecosystem practices related to pest control; and local farmers were involved in live-testing for insecticides resistance of local Anopheles mosquitoes.

Results

Most farmers (94%) considered pesticides effective, and nearly half of them (n = 198, 46.4%) could identify and name crop pests and diseases, mostly using local names. Three quarters were unaware of mosquito larvae in their fields, and only 7% considered their fields as potential sources of mosquitoes. Two thirds were uninformed of any effects that agricultural pesticides may have on mosquitoes, and three quarters had never heard of resistance in malaria mosquitoes. Experts from various sectors acknowledged that agricultural pesticides might impact malaria control through increasing resistance. They did, however, emphasize the importance of crop protection and advocated for the use of pesticides sparingly and non-chemical approaches. Farmers learnt how to discriminate between malaria vectors and non-vectors, identify agricultural pests and diseases, choose and use pesticides effectively, and conduct resistance tests during the participatory workshops.

Conclusion

This study emphasizes the significance of enhancing subsistence farmers’ awareness of mosquito ecology as well as merging public health and agricultural pest management measures. Participatory techniques have the potential to raise stakeholder awareness and engagement, resulting in more effective resistance management.

Detection and Co-occurrence of kdr (F1534C and S989P) Mutations in Multiple Insecticides Resistant Aedes aegypti (Diptera: Culicidae) in Nigeria

The outbreak of yellow fever virus transmitted by Aedes aegypti has been of major concern in Nigeria, this mosquito also transmits several other arboviruses globally. The control of many vectors of mosquito-borne diseases relies heavily on the use of insecticides. Therefore, constant monitoring of insecticide resistance status and associated mechanisms is crucial within the local mosquito population. Here, we determined the resistance profile of adult Ae. aegypti from Majidun and Oke Ota communities, Ikorodu Local Government Area of Lagos State, Nigeria to different classes of insecticides using WHO procedures. The resistant phenotypes of Ae. aegypti were screened for the presence of kdr mutations F1534C, S989P, and V1016G, which have been implicated in insecticide resistance in yellow fever vectors. A high level of resistance to DDT and pyrethroids was recorded in Ae. aegypti in this study, although possible resistance to deltamethrin, one of the pyrethroids was reported in one of the locations. Resistance to bendiocarb was recorded in the Majidun community while Ae. aegypti in both locations were susceptible to malathion. The presence of F1534C mutation associated with DDT and deltamethrin resistance in Ae. aegypti population, and the presence of S989P mutation were detected singly and in co-occurrence with F1534C for the first time in Africa, while V1016G mutation was not detected in this study. The role of these mutations in resistance phenotype expressed in Ae. aegypti in larger populations needs to be established.

An Ethical Overview of the CRISPR-Based Elimination of Anopheles gambiae to Combat Malaria

Approximately a quarter of a billion people around the world suffer from malaria each year. Most cases are located in sub-Saharan Africa where Anopheles gambiae mosquitoes are the principal vectors of this public health problem. With the use of CRISPR-based gene drives, the population of mosquitoes can be modified, eventually causing their extinction. First, we discuss the moral status of the organism and argue that using genetically modified mosquitoes to combat malaria should not be abandoned based on some moral value of A. gambiae. Secondly, we argue that environmental impact studies should be performed to obtain an accurate account of the possible effects of a potential eradication of the organism. However, the risks from the purposeful extinction of A. gambiae should not overtake the benefits of eradicating malaria and risk assessments should be used to determine acceptable risks. Thirdly, we argue that the eventual release of the genetically modified mosquitoes will depend on transparency, community involvement, and cooperation between different nations.

Quantitative reverse transcription PCR assay to detect a genetic marker of pyrethroid resistance in Culex mosquitoes

Pyrethroid insecticides are widely used to control mosquitoes that transmit pathogens such as West Nile virus (WNV) to people. Single nucleotide polymorphisms (SNP) in the knockdown resistance locus (kdr) of the voltage gated sodium channel (Vgsc) gene in Culex mosquitoes are associated with knockdown resistance to pyrethroids. RNAseq was used to sequence the coding region of Vgsc for Culex tarsalis Coquillett and Culex erythrothorax Dyar, two WNV vectors. The cDNA sequences were used to develop a quantitative reverse transcriptase PCR assay that detects the L1014F kdr mutation in the Vgsc. Because this locus is conserved, the assay was used successfully in six Culex spp. The resulting Culex RTkdr assay was validated using quantitative PCR and sequencing of PCR products. The accuracy of the Culex RTkdr assay was 99%. The L1014F kdr mutation associated with pyrethroid resistance was more common among Cx. pipiens than other Culex spp. and was more prevalent in mosquitoes collected near farmland. The Culex RTkdr assay takes advantage of the RNA that vector control agencies routinely isolate to assess arbovirus prevalence in mosquitoes. We anticipate that public health and vector control agencies may employ the Culex RTkdr assay to define the geographic distribution of the L1014F kdr mutation in Culex species and improve the monitoring of insecticide resistance that will ultimately contribute to effective control of Culex mosquitoes.

Pyrethroid Susceptibility in Stomoxys calcitrans and Stomoxys indicus (Diptera: Muscidae) Collected from Cattle Farms in Southern Thailand

The susceptibility to six pyrethroid insecticides (permethrin, deltamethrin, alpha-cypermethrin, cypermethrin, lambda-cyhalothrin, and bifenthrin), each at the recommended concentration, was evaluated for two stable fly species-Stomoxys calcitrans (Linnaeus, 1758) and Stomoxys indicus Picard, 1908 (Diptera: Muscidae)-through tarsal contact using a World Health Organization (WHO) cone bioassay procedure. The field populations of S. calcitrans were collected from the Songkhla and Phattalung provinces, while S. indicus were collected from the Phattalung and Satun provinces in Thailand. The stable flies were exposed to insecticide-treated filter paper for 30 min, and their knockdown counts at 30 min and 60 min and mortality counts at 12 h and 24 h were recorded. The S. calcitrans and S. indicus Songkhla and Phattalung populations were moderately susceptible to pyrethroids, as indicated by the 24 h mortality. Nonetheless, the Satun population of S. indicus was completely susceptible to permethrin, with 100% mortality, and showed the lowest susceptibility to deltamethrin and bifenthrin. The results indicate the generally low susceptibility of stable flies to pyrethroids in the southern provinces of Thailand.

Suppression of Midgut Microbiota Impact Pyrethroid Susceptibility in Aedes aegypti

Aedes aegypti is a mosquito that transmits viral diseases such as dengue, chikungunya, Zika, and yellow fever. The insect’s microbiota is recognized for regulating several biological processes, including digestion, metabolism, egg production, development, and immune response. However, the role of the bacteria involved in insecticide susceptibility has not been established. Therefore, the objective of this study was to characterize the resident microbiota in a field population of A. aegypti to evaluate its role associated with susceptibility to the insecticides permethrin and deltamethrin. Mosquitoes were fed 10% sucrose mixed with antibiotics and then exposed to insecticides using a diagnostic dose. DNA was extracted, and sequencing of bacterial 16S rRNA was carried out on Illumina^® MiSeq™. Proteobacteria (92.4%) and Bacteroidetes (7.6%) were the phyla, which are most abundant in mosquitoes fed with sucrose 10%. After exposure to permethrin, the most abundant bacterial species were Pantoea agglomerans (38.4%) and Pseudomonas azotoformans-fluorescens-synxantha (14.2%). Elizabethkingia meningoseptica (38.4%) and Ps. azotoformans-fluorescens-synxantha (26.1%) were the most abundant after exposure to deltamethrin. Our results showed a decrease in mosquitoes’ survival when exposed to permethrin, while no difference in survival when exposed to deltamethrin when the microbiota was modified. We found that the change in microbiota modifies the response of mosquitoes to permethrin. These results are essential for a better understanding of mosquito physiology in response to insecticides.

Water quality assessment in mosquito breeding habitats based on dissolved organic matter and chlorophyll measurements by laser-induced fluorescence spectroscopy

Rapid urbanization and its associated pollution can affect water quality in mosquito breeding habitats and, as a result, the ecology and control of mosquito vectors. To understand the effects of pollution on mosquito vectors, an accurate assessment of water quality in breeding habitats is needed. Presently, water quality assessment of mosquito breeding habitats is usually based on the measurement of individual physicochemical parameters. However, several parameters are sometimes difficult to interpret or may not give a clear picture of the overall water quality of the breeding habitats, especially when the pollutants are in complex mixtures. This study employed the use of Laser-Induced Fluorescence (LIF) spectroscopy to assess water quality in breeding habitats of Anopheles, Aedes, and Culex mosquitoes in urban areas in Cape Coast, Ghana. The LIF spectra, using a 445-nm diode laser, were measured from field-collected water samples in the laboratory. The LIF spectra showed the presence of dissolved organic matter (DOM) and chlorophyll in the breeding habitats. The DOM and chlorophyll fluorescence signals were normalised by the Raman vibrational signals to determine water quality in each habitat. The overall water quality was better in Aedes breeding habitats than in Anopheles and Culex breeding habitats. The poor water quality in Anopheles and Culex breeding habitats was due to the presence of high fulvic acid and chlorophyll content, which often reflect pollutants from anthropogenic sources. Anopheles and Aedes habitats were made up of mainly An. coluzzii and Ae. aegypti respectively while Culex species were identified to genus level. The results add up to the growing concern about the breeding of Anopheles in polluted habitats. The study demonstrated for the first time the ability of LIF spectroscopy to assess water quality in mosquito breeding habitats.

Population genetic structure and evolutionary genetics of Anopheles sinensis based on knockdown resistance (kdr) mutations and mtDNA-COII gene in China-Laos, Thailand-Laos, and Cambodia-Laos borders

BACKGROUND

Vector control is still a pivotal method for preventing malaria, and its potency is weakened by the increasing resistance of vectors to chemical insecticides. As the most abundant and vital malaria vector in Southeast Asia, the chemical insecticide resistance status in Anopheles sinensis remains elusive in Laos, which makes it imperative to evaluate the true nature of chemical insecticide resistance-associated genetic mutations in An. sinensis in Laos.

METHODS

Adult An. sinensis were collected from three border regions in Laos. DNA was extracted from individual mosquitoes. PCR amplification and DNA sequencing of a fragment containing codon 1014 of the voltage-gated sodium channel (vgsc) gene were completed to study the kdr allele frequency distribution, kdr intron polymorphism, population genetic diversity, and the evolutionary status of the kdr codon. The mitochondrial cytochrome c oxidase subunit II gene (COII) was amplified and sequenced to examine population variations, genetic differentiation, spatial population structure, population expansion, and gene flow patterns.

RESULTS

Nine wild kdr haplotypes of the vgsc gene were detected in this study, and eight of them, namely 1014L1, 1014L2, 1014L4, 1014L7, 1014L9, 1014L10, 1014L11, and 1014L21, were discovered in the China-Laos border (northern Laos), while 1014L3 was only detected in the Thailand-Laos border (northwestern Laos) and Cambodia-Laos border (southern Laos). The newly identified haplotype, 1014L21, was uniquely distributed in the China-Laos border and was not identified in other countries. Based on sequence analysis of the mitochondrial COII genes, significant genetic differentiation and limited gene flow were detected between the China-Laos and Cambodia-Laos An. sinensis populations, which suggested that those two regions were genetically isolated. The distinct distribution of the kdr haplotype frequencies is probably the result of geographical isolation in mosquito populations.

CONCLUSIONS

Lack of kdr mutations in the vgsc gene was probably due to genetic isolation and the absence of intense selection pressure in the three border regions of Laos. This study reveals that pyrethroid-based chemical insecticides are still appropriate for battling An. sinensis in parts of Laos, and routine monitoring of chemical insecticide resistance should be continuously implemented and focused on more restricted areas as part of chemical insecticide resistance management.

Effects of agricultural pesticides on the susceptibility and fitness of malaria vectors in rural south-eastern Tanzania

BACKGROUND

Agricultural pesticides may exert strong selection pressures on malaria vectors during the aquatic life stages and may contribute to resistance in adult mosquitoes. This could reduce the performance of key vector control interventions such as indoor-residual spraying and insecticide-treated nets. The aim of this study was to investigate effects of agrochemicals on susceptibility and fitness of the malaria vectors across farming areas in Tanzania.

METHODS

An exploratory mixed-methods study was conducted to assess pesticide use in four villages (V1-V4) in south-eastern Tanzania. Anopheles gambiae (s.l.) larvae were collected from agricultural fields in the same villages and their emergent adults examined for insecticide susceptibility, egg-laying and wing lengths (as proxy for body size). These tests were repeated using two groups of laboratory-reared An. arabiensis, one of which was pre-exposed for 48 h to sub-lethal aquatic doses of agricultural pesticides found in the villages.

RESULTS

Farmers lacked awareness about the linkages between the public health and agriculture sectors but were interested in being more informed. Agrochemical usage was reported as extensive in V1, V2 and V3 but minimal in V4. Similarly, mosquitoes from V1 to V3 but not V4 were resistant to pyrethroids and either pirimiphos-methyl or bendiocarb, or both. Adding the synergist piperonyl butoxide restored potency of the pyrethroids. Pre-exposure of laboratory-reared mosquitoes to pesticides during aquatic stages did not affect insecticide susceptibility in emergent adults of the same filial generation. There was also no effect on fecundity, except after pre-exposure to organophosphates, which were associated with fewer eggs and smaller mosquitoes. Wild mosquitoes were smaller than laboratory-reared ones, but fecundity was similar.

CONCLUSIONS

Safeguarding the potential of insecticide-based interventions requires improved understanding of how agricultural pesticides influence important life cycle processes and transmission potential of mosquito vectors. In this study, susceptibility of mosquitoes to public health insecticides was lower in villages reporting frequent use of pesticides compared to villages with little or no pesticide use. Variations in the fitness parameters, fecundity and wing length marginally reflected the differences in exposure to agrochemicals and should be investigated further. Pesticide use may exert additional life cycle constraints on mosquito vectors, but this likely occurs after multi-generational exposures.

Rapid evolution of insecticide resistance and patterns of pesticides usage in agriculture in the city of Yaoundé, Cameroon

BACKGROUND

The practice of agriculture in urban settings contributes to the rapid expansion of insecticide resistance in malaria vectors. However, there is still not enough information on pesticide usage in most urban settings. The present study aims to assess the evolution of Anopheles gambiae (s.l.) population susceptibility to insecticides and patterns of pesticide usage in agriculture in the city of Yaoundé, Cameroon.

METHODS

WHO susceptibility tests and synergist PBO bioassays were conducted on adult An. gambiae (s.l.) mosquitoes aged 3 to 5 days emerging from larvae collected from the field. Seven insecticides (deltamethrin, permethrin, DDT, bendiocarb, propoxur, fenitrothion and malathion) were evaluated. The presence of target site mutation conferring knockdown (kdr) resistance was investigated using TaqMan assay, and mosquito species were identified using SINE-PCR. Surveys on 81 retailers and 232 farmers were conducted to assess general knowledge and practices regarding agricultural pesticide usage.

RESULTS

High resistance intensity to pyrethroids was observed with a high frequency of the kdr allele 1014F and low frequency of the kdr 1014S allele. The level of susceptibility of An. gambiae (s.l.) to pyrethroids and carbamates was found to decrease with time (from > 34% in 2017 to < 23% in 2019 for deltamethrin and permethrin and from 97% in 2017 to < 86% in 2019 for bendiocarb). Both An. gambiae (s.s.) and An. coluzzii were recorded. Over 150 pesticides and fertilizers were sold by retailers for agricultural purposes in the city of Yaoundé. Most farmers do not respect safety practices. Poor practices including extensive and inappropriate application of pesticides as well as poor management of perished pesticides and empty pesticide containers were also documented.

CONCLUSIONS

The study indicated rapid evolution of insecticide resistance and uncontrolled usage of pesticides by farmers in agriculture. There is an urgent need to address these gaps to improve the management of insecticide resistance.

Crop protection practices and risks associated with infectious tropical parasitic diseases

Two recent literature reviews have shown that: i) agroecological crop protection (ACP) practices generally reduce risks of viral zoonoses, unlike conventional (agrochemical-based) practices which tend to increase them; ii) substitution-based crop protection (CP) practices (mainly biocontrol-based) could result in fewer health risks from bacterial infectious diseases. Here, we present an analysis of the scientific literature to determine to what extent the conclusions regarding viruses or bacteria can be extended to infectious diseases caused by protozoan or helminthic parasites. This analysis of cases of both vector-transmitted and water- or food-borne parasitic diseases, shows, in terms of reduction of health risks: i) an overall negative effect arising from the use of synthetic plant protection products; ii) the relevance of substitution CP practices not strictly under the ACP banner. On the other hand, the public and veterinary health issue of antiparasitic resistance is not affected by CP practices. The positive effects at the large spatio-temporal scales of ACP approaches remain valid, although to a slightly lesser extent than for bacterial diseases and viral zoonoses, in particular through biodiversity conservation which fosters natural regulations and control, preventing the undesirable effects of synthetic pesticides.

Fitness Cost of Sequential Selection with Deltamethrin in Aedes aegypti (Diptera: Culicidae)

In Mexico, Aedes aegypti (L.) is the primary dengue vector, chikungunya, and Zika viruses. The continued use of synthetic pyrethroids has led to the development of resistance in target populations, which has diminished the effectiveness of vector control programs. Resistance has been associated with disadvantages that affect the biological parameters of resistant mosquitoes compared to susceptible ones. In the present study, the disadvantages were evaluated by parameters related to survival and reproduction ('fitness cost') after selection with deltamethrin for five generations. The parameters analyzed were the length of the development cycle, sex ratio, survival, longevity, fecundity, egg viability, preoviposition, oviposition and postoviposition periods, and growth parameters. In the deltamethrin-selected strain, there was a decrease in the development cycle duration, the percentage of pupae, the oviposition period, and eggs viability. Although mean daily fecundity was not affected after the selection process, this, together with the decrease in the survival and fecundity levels by specific age, significantly affected the gross reproductive rate (GRR), net reproductive rate (Ro), and intrinsic growth rate (rm) of the group selected for five generations with deltamethrin compared to the group without selection. Identifying the 'cost' of resistance in biological fitness represents an advantage if it is desired to limit the spread of resistant populations since the fitness cost is the less likely that resistant individuals will spread in the population. This represents an important factor to consider in designing integrated vector management programs.

Synthesis, SAR studies, and insecticidal activities of certain N-heterocycles derived from 3-((2-chloroquinolin-3-yl)methylene)-5-phenylfuran-2(3H)-one against Culex pipiens L. larvae

An acid hydrazide derivative was synthesized and transformed into a variety of valuable N-heterocycles such as pyridazinone, oxadiazole, triazolopyridazinone, and triazole derivatives via reactions with certain carbon electrophiles such as 4-methoxybenzaldehyde, indole-3-carbaldehyde, pentan-2,4-dione, and carbon disulfide. The chemical structures of all prepared compounds were verified via their analytical and spectroscopic data. The insecticidal activity of the N-heterocycles was evaluated against field and lab strains of the third larval instar of Culex pipiens. All tested compounds exhibited higher larvicidal activity against the lab strains compared to the field strains, with dissimilar ratios. The obtained results demonstrate that the high toxicity achieved by oxadiazole followed the order of furanone, pyridazinone and hydrazide, with lower LC₅₀ values of the hydrazone and N-acetylpyridazinone derivatives compared to that of imidacloprid. Interestingly, these compounds are promising agents for insect pest control, especially since they are insoluble in water and can overcome the disadvantages of neonicotinoid applications in pest management programs.

A new series of N-heterocycles including pyridazinone, oxadiazole, triazolopyridazinone, and triazole derivatives were synthesized from the acid hydrazide via its reaction with certain carbon electrophiles.

Spatio-Temporal Dynamics of a Dieldrin Resistance Gene in Aedes albopictus and Culex quinquefasciatus Populations From Reunion Island

The control of mosquito populations using insecticides is increasingly threatened by the spread of resistance mechanisms. Dieldrin resistance, conferred by point mutations in the Rdl gene encoding the γ-aminobutyric acid receptor, has been reported at high prevalence in mosquito populations in response to selective pressures. In this study, we monitored spatio-temporal dynamics of the resistance-conferring RdlR allele in Aedes (Stegomyia) albopictus (Skuse, 1895) and Culex (Culex) quinquefasciatus (Say, 1823) populations from Reunion Island. Specimens of both mosquito species were sampled over a 12-month period in three cities and in sites located at lower (<61 m) and higher (between 503 and 564 m) altitudes. Mosquitoes were genotyped using a molecular test detecting the alanine to serine substitution (A302S) in the Rdl gene. Overall, the RdlR frequencies were higher in Cx. quinquefasciatus than Ae. albopictus. For both mosquito species, the RdlR frequencies were significantly influenced by location and altitude with higher RdlR frequencies in the most urbanized areas and at lower altitudes. This study highlights environmental factors that influence the dynamics of insecticide resistance genes, which is critical for the management of insecticide resistance and the implementation of alternative and efficient vector control strategies.

Influence of testing modality on bioefficacy for the evaluation of Interceptor® G2 mosquito nets to combat malaria mosquitoes in Tanzania

Background

Insecticide-treated net (ITN) durability is evaluated using longitudinal bioefficacy and fabric integrity sampling post-distribution. Interceptor^® G2 was developed for resistance management and contains two adulticides: alpha-cypermethrin and chlorfenapyr; it is a pro-insecticide that is metabolized into its active form by mosquito-detoxifying enzymes and may be enhanced when the mosquito is physiologically active. To elucidate the impact of bioassay modality, mosquito exposures of the alphacypermethrin ITN Interceptor^® and dual adulticide Interceptor^® G2 were investigated.

Methods

This study evaluated the performance of Interceptor^® G2 compared to Interceptor^® against local strains of mosquitoes in Tanzania. Unwashed and 20× times washed nets were tested. Efficacy of ITNs was measured by four bioassay types: (1) World Health Organisation (WHO) cone test (cone), (2) WHO tunnel test (tunnel), (3) Ifakara ambient chamber test (I-ACT) and (4) the WHO gold standard experimental hut test (hut). Hut tests were conducted against free-flying wild pyrethroid metabolically resistant Anopheles arabiensis and Culex quinquefasciatus. Cone, tunnel and I-ACT bioassays used laboratory-reared metabolically resistant An. arabiensis and Cx. quinquefasciatus and pyrethroid susceptible Anopheles gambiae sensu stricto and Aedes aegypti.

Results

Against resistant strains, superiority of Interceptor^® G2 over Interceptor^® was observed in all “free-flying bioassays”. In cone tests (which restrict mosquito flight), superiority of Interceptor^® over Interceptor^® G2 was recorded. Mortality of unwashed Interceptor^® G2 among An. arabiensis was lowest in hut tests at 42.9% (95% CI: 37.3–48.5), although this increased to 66.7% (95% CI: 47.1–86.3) by blocking hut exit traps so mosquitoes presumably increased frequencies of contact with ITNs. Higher odds of mortality were consistently observed in Interceptor^® G2 compared to Interceptor^® in “free-flying” bioassays using An. arabiensis: tunnel (OR = 1.42 [95% CI:1.19–1.70], p < 0.001), I-ACT (OR = 1.61 [95% CI: 1.05–2.49], p = 0.031) and hut (OR = 2.53 [95% CI: 1.96–3.26], p < 0.001). Interceptor^® and Interceptor^® G2 showed high blood-feeding inhibition against all strains.

Conclusion

Both free-flying laboratory bioassays (WHO Tunnel and I-ACT) consistently measured similarly, and both predicted the results of the experimental hut test. For bioefficacy monitoring and upstream product evaluation of ITNs in situ, the I-ACT may provide an alternative bioassay modality with improved statistical power. Interceptor G2^® outperformed Interceptor ^® against pyrethroid-resistant strains, demonstrating the usefulness of chlorfenapyr in mitigation of malaria.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05207-9.

Mosquito larvicidal activity of pyrrolidine-2,4-dione derivatives: An investigation against Culex quinquefasciatus and molecular docking studies

The pyrrolidine-2,4-dione derivatives were used to conduct a larvicidal test on Culex quinquefasciatus larvae of the second instar. Mannich base condensation method was used to synthesis the pyrrolidine-2,4-dione derivatives by grindstone method. The reaction conditions were mild, resulting in high yields. An analysis of the synthesized compounds was carried out using FTIR, ¹H NMR, ¹³C NMR, mass spectrometry, and elemental analysis. Synthesized compounds (1a-h) were evaluated for larvicidal activities. Compound 1e (LD₅₀: 26.06 µg/mL), and 1f (LD₅₀: 26.89 µg/mL), and were notably more active against Culex quinquefasciatus than permethrin (LD₅₀: 26.14 µg/mL). The docking studies also demonstrated that 1e, and 1f are potent larvicides with higher binding energy (−12.6 kcal/mol) than the control in the mosquito odorant binding protein (PDB ID: 3OGN). The larvicidal properties of lead molecules have made them important for use as insecticides.

A symbiotic gut bacterium enhances Aedes albopictus resistance to insecticide

BACKGROUND

The increasing insecticide resistance of Aedes albopictus puts many countries in Asia and Africa, including China, at great risk of a mosquito-borne virus epidemic. To date, a growing number of researches have focused on the relationship between intestinal symbiotic bacteria and their hosts' resistance to insecticides. This provides a novel aspect to the study of resistant mechanisms.

METHODS/FINDINGS

This study reveals significant composition and dynamic changes in the intestinal symbiotic bacteria of Ae. albopictus between the resistant and susceptible strains based on full-length sequencing technology. The relative abundance of Serratia oryzae was significantly higher in the resistance strain than in the susceptible strains; also, the relative abundance of S. oryzae was significantly higher in deltamethrin-induced Ae. albopictus than in their counterpart. These suggested that S. oryzae may be involved in the development of insecticide resistance in Ae. albopictus. To explore the insecticide resistance mechanism, adult mosquitoes were fed with GFP-tagged S. oryzae, which resulted in stable bacterial enrichment in the mosquito gut without affecting the normal physiology, longevity, oviposition, and hatching rates of the host. The resistance measurements were made based on bioassays as per the WHO guidelines. The results showed that the survival rate of S. oryzae-enriched Ae. albopictus was significantly higher than the untreated mosquitoes, indicating the enhanced resistance of S. oryzae-enriched Ae. albopictus. Also, the activities of three metabolic detoxification enzymes in S. oryzae-enriched mosquitoes were increased to varying degrees. Meanwhile, the activity of extracellular enzymes released by S. oryzae was measured, but only carboxylesterase activity was detected. HPLC and UHPLC were respectively used to measure deltamethrin residue concentration and metabolite qualitative analysis, showing that the deltamethrin degradation efficiency of S. oryzae was positively correlated with time and bacterial amount. Deltamethrin was broken down into 1-Oleoyl-2-hydroxy-sn-glycero-3-PE and 2',2'-Dibromo-2'-deoxyguanosine. Transcriptome analysis revealed that 9 cytochrome P450s, 8 GSTs and 7 CarEs genes were significantly upregulated.

CONCLUSIONS

S. oryzae can be accumulated into adult Ae. albopictus by artificial feeding, which enhances deltamethrin resistance by inducing the metabolic detoxification genes and autocrine metabolic enzymes. S. oryzae is vertically transmitted in Ae. albopictus population. Importantly, S. oryzae can degrade deltamethrin in vitro, and use deltamethrin as the sole carbon source for their growths. Therefore, in the future, S. oryzae may also be commercially used to break down the residual insecticides in the farmland and lakes to protect the environment.