Insects

Editorial

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10 pages, 250 KiB

Open AccessEditor’s ChoiceEditorial

Insecticides for Mosquito Control: Improving and Validating Methods to Strengthen the Evidence Base

by Rosemary Susan Lees, Christen Fornadel, Janneke Snetselaar, Joe Wagman and Angus Spiers

Insects 2023, 14(2), 116; https://doi.org/10.3390/insects14020116 - 23 Jan 2023

Cited by 6 | Viewed by 4165

Abstract

Efforts to eliminate vector-borne diseases, for example malaria which caused an estimated 619,000 deaths in 2021 [...] Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

Research

Jump to: Editorial, Review, Other

20 pages, 2555 KiB

Open AccessArticle

Modified World Health Organization (WHO) Tunnel Test for Higher Throughput Evaluation of Insecticide-Treated Nets (ITNs) Considering the Effect of Alternative Hosts, Exposure Time, and Mosquito Density

by Dismas S. Kamande, Olukayode G. Odufuwa, Emmanuel Mbuba, Lorenz Hofer and Sarah J. Moore

Insects 2022, 13(7), 562; https://doi.org/10.3390/insects13070562 - 21 Jun 2022

Cited by 4 | Viewed by 3615

Abstract

The standard World Health Organization (WHO) tunnel test is a reliable laboratory bioassay used for “free-flying” testing of insecticide-treated nets (ITNs) bio-efficacy where mosquitoes pass through a ITN sample to reach a live animal bait. Multiple parameters (i.e., bait, exposure time, and mosquito [...] Read more.

The standard World Health Organization (WHO) tunnel test is a reliable laboratory bioassay used for “free-flying” testing of insecticide-treated nets (ITNs) bio-efficacy where mosquitoes pass through a ITN sample to reach a live animal bait. Multiple parameters (i.e., bait, exposure time, and mosquito density) may affect the outcomes measured in tunnel tests. Therefore, a comparison was conducted of alternative hosts, exposure time, and lower mosquito density against the current gold standard test (100 mosquitoes, animal bait, and 12-h exposure) as outlined in the WHO ITN evaluation guideline. This was done with the aim to make the tunnel test cheaper and with higher throughput to meet the large sample sizes needed for bio-efficacy durability monitoring of chlorfenapyr ITNs that must be evaluated in “free-flying” bioassays. Methods: A series of experiments were conducted in the WHO tunnel test to evaluate the impact of the following factors on bio-efficacy endpoints of mosquito mortality at 24-h (M24) and 72-h (M72) and blood-feeding success (BFS): (1) baits (rabbit, membrane, human arm); (2) exposure time in the tunnel (1 h vs. 12 h); and (3) mosquito density (50 vs. 100). Finally, an alternative bioassay using a membrane with 50 mosquitoes (membrane-50) was compared to the gold standard bioassay (rabbit with 100 mosquitoes, rabbit-100). Pyrethroid-resistant Anopheles arabiensis and pyrethroid susceptible Anopheles gambiae were used to evaluate Interceptor^® and Interceptor^® G2 ITNs. Results: Using a human arm as bait gave a very different BFS, which impacted measurements of M24 and M72. The same trends in M24, M72 and BFS were observed for both Interceptor^® ITN and Interceptor^® G2 unwashed and washed 20 times measured using the gold standard WHO tunnel test (rabbit-100) or rabbit with 50 mosquitoes (rabbit-50). M24, M72 and BFS were not statistically different when either 50 or 100 mosquitoes were used with rabbit bait in the tunnel bioassay for either the susceptible or resistant strains. No systematic difference was observed between rabbit-50 and rabbit-100 in the agreement by the Bland and Altman method (B&A). The mean difference was 4.54% (−22.54–31.62) in BFS and 1.71% (−28.71–32.12) in M72 for rabbit-50 versus rabbit-100. Similar M24, M72 and lower BFS was measured by membrane-50 compared to rabbit-100. No systematic difference was observed in the agreement between membrane-50 and rabbit-100, by B&A. The mean difference was 9.06% (−11.42–29.64) for BSF and −5.44% (−50.3–39.45) for M72. Both membrane-50, rabbit-50 and rabbit-100 predicted the superiority of Interceptor^® G2 over Interceptor^® ITN for the resistant strain on M72. Conclusion: These results demonstrate that WHO tunnel tests using rabbit bait may be run with 50 mosquitoes to increase sample sizes needed for bio-efficacy durability monitoring of ITNs in “free-flying” bioassays. Using a membrane feeder with 50 mosquitoes is a potential replacement for the WHO tunnel bioassay with animal bait if control blood feeding rates can be improved to 50% because blood feeding impacts mosquito survival after exposure to insecticides. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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23 pages, 2147 KiB

Open AccessEditor’s ChoiceArticle

Reviewing the WHO Tube Bioassay Methodology: Accurate Method Reporting and Numbers of Mosquitoes Are Key to Producing Robust Results

by Giorgio Praulins, Daniel P. McDermott, Angus Spiers and Rosemary Susan Lees

Insects 2022, 13(6), 544; https://doi.org/10.3390/insects13060544 - 14 Jun 2022

Cited by 11 | Viewed by 4348

Abstract

Accurately monitoring insecticide resistance in target mosquito populations is important for combating malaria and other vector-borne diseases, and robust methods are key. The “WHO susceptibility bioassay” has been available from the World Health Organization for 60+ years: mosquitoes of known physiological status are [...] Read more.

Accurately monitoring insecticide resistance in target mosquito populations is important for combating malaria and other vector-borne diseases, and robust methods are key. The “WHO susceptibility bioassay” has been available from the World Health Organization for 60+ years: mosquitoes of known physiological status are exposed to a discriminating concentration of insecticide. Several changes to the test procedures have been made historically, which may seem minor but could impact bioassay results. The published test procedures and literature for this method were reviewed for methodological details. Areas where there was room for interpretation in the test procedures or where the test procedures were not being followed were assessed experimentally for their impact on bioassay results: covering or uncovering of the tube end during exposure; the number of mosquitoes per test unit; and mosquito age. Many publications do not cite the most recent test procedures; methodological details are reported which contradict the test procedures referenced, or methodological details are not fully reported. As a result, the precise methodology is unclear. Experimental testing showed that using fewer than the recommended 15–30 mosquitoes per test unit significantly reduced mortality, covering the exposure tube had no significant effect, and using mosquitoes older than 2–5 days old increased mortality, particularly in the resistant strain. Recommendations are made for improved reporting of experimental parameters Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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15 pages, 2049 KiB

Open AccessArticle

Enhancing the Quality of Spray Application in IRS: Evaluation of the Micron Track Sprayer

by Janneke Snetselaar, Rosemary S. Lees, Geraldine M. Foster, Kyle J. Walker, Baltazari J. Manunda, David J. Malone, Franklin W. Mosha, Mark W. Rowland and Matthew J. Kirby

Insects 2022, 13(6), 523; https://doi.org/10.3390/insects13060523 - 6 Jun 2022

Cited by 3 | Viewed by 2789

Abstract

Indoor residual spraying (IRS) has changed little since its introduction in the 1940s. Manual spraying is still prone to variation in insecticide dose. To improve the application of IRS in experimental hut trials, an automated track sprayer was developed, which regulates the speed [...] Read more.

Indoor residual spraying (IRS) has changed little since its introduction in the 1940s. Manual spraying is still prone to variation in insecticide dose. To improve the application of IRS in experimental hut trials, an automated track sprayer was developed, which regulates the speed of application and the distance of the nozzle from the wall, two key sources of variation. The automated track sprayer was compared to manual spraying, firstly using fluorescein solution in controlled indoor settings, and secondly in experimental huts in Tanzania using several IRS products. Manual spraying produced greater variation with both fluorescein and insecticide applications. Both manual and automated spray methods under-dosed the actual dose sprayed compared to the target dose. Overall, the track sprayer treats surfaces more consistently, offering a potential improvement over manual spraying for experimental hut evaluation of new IRS formulations. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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14 pages, 3472 KiB

Open AccessEditor’s ChoiceArticle

A Practical Insecticide Resistance Monitoring Bioassay for Orally Ingested Dinotefuran in Anopheles Malaria Vectors

by George John Ian Parsons, Rosemary Susan Lees, Sofia Balaska and John Vontas

Insects 2022, 13(4), 311; https://doi.org/10.3390/insects13040311 - 22 Mar 2022

Cited by 5 | Viewed by 3489

Abstract

Attractive Toxic Sugar Baits (ATSB) deployed outdoors are likely to be particularly effective against outdoor biting mosquitoes and, if they contain insecticides with a different mode of action, mosquitoes resistant to pyrethroids. One such ATSB based on the neonicotinoid dinotefuran is currently under [...] Read more.

Attractive Toxic Sugar Baits (ATSB) deployed outdoors are likely to be particularly effective against outdoor biting mosquitoes and, if they contain insecticides with a different mode of action, mosquitoes resistant to pyrethroids. One such ATSB based on the neonicotinoid dinotefuran is currently under evaluation in Africa. As with any insecticide-based intervention, it will be important to monitor for the possible emergence of vector resistance. While methods for detecting resistance to insecticides via tarsal contact are recommended by the World Health Organization (WHO), these may not be applicable for orally ingested insecticides. Here, a new ingestion assay, appropriate for a controlled laboratory setting, is described using fluorescein sodium salt (uranine) as a feeding marker. Conventional topical application bioassays, more appropriate for routine deployment, have also been used to apply dinotefuran to the thorax of adult Anopheles mosquitoes with an organic carrier to bypass lipid cuticle barriers. The two methods were compared by establishing lethal doses (LD) in several Anopheles strains. The similarity of the ratios of susceptibility to dinotefuran between pairs of pyrethroid susceptible and resistant strains validates topical application as a suitable, more practical and field applicable method for monitoring for the emergence of resistance to orally ingested dinotefuran. A discriminating dose is proposed, which will be further validated against field populations and used to routinely monitor for the emergence of resistance alongside ATSB trials. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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9 pages, 4038 KiB

Open AccessArticle

Crystallography of Contemporary Contact Insecticides

by Bryan Erriah, Xiaolong Zhu, Chunhua T. Hu, Bart E. Kahr, Alexander Shtukenberg and Michael D. Ward

Insects 2022, 13(3), 292; https://doi.org/10.3390/insects13030292 - 15 Mar 2022

Cited by 6 | Viewed by 3439

Abstract

The active forms of contact insecticides used for combatting mosquito-borne infectious diseases are typically crystalline solids. Numerous molecular crystals are polymorphic, crystallizing in several solid forms characterized by different physicochemical properties, including bioavailability. Our laboratory recently found that the activity of crystalline contact [...] Read more.

The active forms of contact insecticides used for combatting mosquito-borne infectious diseases are typically crystalline solids. Numerous molecular crystals are polymorphic, crystallizing in several solid forms characterized by different physicochemical properties, including bioavailability. Our laboratory recently found that the activity of crystalline contact insecticides is inversely dependent on the thermodynamic stability of their polymorphs, suggesting that efficacy can be enhanced by the manipulation of the solid-state structure. This paper argues that crystallography should be central to the development of contact insecticides, particularly because their efficacy continues to be compromised by insecticide resistance, especially among Anopheles mosquito populations that spread malaria. Although insecticidal compounds with new modes of action have been introduced to overcome resistance, new insecticides are expensive to develop and implement. The repurposing of existing chemical agents in metastable, more active crystalline forms provides an inexpensive and efficient method for ‘evergreening’ compounds whose risks are already well-established. We report herein seven new single-crystal structures of insecticides used for controlling infectious disease vectors. The structures reported herein include pyrethroid insecticides recommended by the WHO for indoor residual spraying (IRS)-bifenthrin, β-cyfluthrin, etofenprox, α-cypermethrin, and λ-cyhalothrin as well as the neonicotinoid insecticide thiacloprid. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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20 pages, 2990 KiB

Open AccessArticle

Sympatric Populations of the Anopheles gambiae Complex in Southwest Burkina Faso Evolve Multiple Diverse Resistance Mechanisms in Response to Intense Selection Pressure with Pyrethroids

by Jessica Williams, Victoria A. Ingham, Marion Morris, Kobié Hyacinthe Toé, Aristide S. Hien, John C. Morgan, Roch K. Dabiré, Wamdagogo Moussa Guelbéogo, N’Falé Sagnon and Hilary Ranson

Insects 2022, 13(3), 247; https://doi.org/10.3390/insects13030247 - 28 Feb 2022

Cited by 12 | Viewed by 3947

Abstract

Pyrethroid resistance in the Anopheles vectors of malaria is driving an urgent search for new insecticides that can be used in proven vector control tools such as insecticide treated nets (ITNs). Screening for potential new insecticides requires access to stable colonies of the [...] Read more.

Pyrethroid resistance in the Anopheles vectors of malaria is driving an urgent search for new insecticides that can be used in proven vector control tools such as insecticide treated nets (ITNs). Screening for potential new insecticides requires access to stable colonies of the predominant vector species that contain the major pyrethroid resistance mechanisms circulating in wild populations. Southwest Burkina Faso is an apparent hotspot for the emergence of pyrethroid resistance in species of the Anopheles gambiae complex. We established stable colonies from larval collections across this region and characterised the resistance phenotype and underpinning genetic mechanisms. Three additional colonies were successfully established (1 An. coluzzii, 1 An. gambiae and 1 An. arabiensis) to add to the 2 An. coluzzii colonies already established from this region; all 5 strains are highly resistant to pyrethroids. Synergism assays found that piperonyl butoxide (PBO) exposure was unable to fully restore susceptibility although exposure to a commercial ITN containing PBO resulted in 100% mortality. All colonies contained resistant alleles of the voltage gated sodium channel but with differing proportions of alternative resistant haplotypes. RNAseq data confirmed the role of P450s, with CYP6P3 and CYP6Z2 elevated in all 5 strains, and identified many other resistance mechanisms, some found across strains, others unique to a particular species. These strains represent an important resource for insecticide discovery and provide further insights into the complex genetic changes driving pyrethroid resistance. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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27 pages, 936 KiB

Open AccessArticle

Developing Consensus Standard Operating Procedures (SOPs) to Evaluate New Types of Insecticide-Treated Nets

by Natalie Lissenden, Jennifer S. Armistead, Katherine Gleave, Seth R. Irish, Jackline L. Martin, Louisa A. Messenger, Sarah J. Moore, Corine Ngufor, Natacha Protopopoff, Richard Oxborough, Angus Spiers and Rosemary S. Lees

Insects 2022, 13(1), 7; https://doi.org/10.3390/insects13010007 - 21 Dec 2021

Cited by 17 | Viewed by 4915

Abstract

In response to growing concerns over the sustained effectiveness of pyrethroid-only based control tools, new products are being developed and evaluated. Some examples of these are dual-active ingredient (AI) insecticide-treated nets (ITNs) which contain secondary insecticides, or synergist ITNs which contain insecticide synergist, [...] Read more.

In response to growing concerns over the sustained effectiveness of pyrethroid-only based control tools, new products are being developed and evaluated. Some examples of these are dual-active ingredient (AI) insecticide-treated nets (ITNs) which contain secondary insecticides, or synergist ITNs which contain insecticide synergist, both in combination with a pyrethroid. These net types are often termed ‘next-generation’ insecticide-treated nets. Several of these new types of ITNs are being evaluated in large-scale randomized control trials (RCTs) and pilot deployment schemes at a country level. However, no methods for measuring the biological durability of the AIs or synergists on these products are currently recommended. In this publication, we describe a pipeline used to collate and interrogate several different methods to produce a singular ‘consensus standard operating procedure (SOP)’, for monitoring the biological durability of three new types of ITNs: pyrethroid + piperonyl butoxide (PBO), pyrethroid + pyriproxyfen (PPF), and pyrethroid + chlorfenapyr (CFP). This process, convened under the auspices of the Innovation to Impact programme, sought to align methodologies used for conducting durability monitoring activities of next-generation ITNs. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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11 pages, 959 KiB

Open AccessArticle

The Automatic Classification of Pyriproxyfen-Affected Mosquito Ovaries

by Mark T. Fowler, Rosemary S. Lees, Josias Fagbohoun, Nancy S. Matowo, Corine Ngufor, Natacha Protopopoff and Angus Spiers

Insects 2021, 12(12), 1134; https://doi.org/10.3390/insects12121134 - 17 Dec 2021

Cited by 5 | Viewed by 3631

Abstract

Pyriproxyfen (PPF) may become an alternative insecticide for areas where pyrethroid-resistant vectors are prevalent. The efficacy of PPF can be assessed through the dissection and assessment of vector ovaries. However, this reliance on expertise is subject to limitations. We show here that these [...] Read more.

Pyriproxyfen (PPF) may become an alternative insecticide for areas where pyrethroid-resistant vectors are prevalent. The efficacy of PPF can be assessed through the dissection and assessment of vector ovaries. However, this reliance on expertise is subject to limitations. We show here that these limitations can be overcome using a convolutional neural network (CNN) to automate the classification of egg development and thus fertility status. Using TensorFlow, a resnet-50 CNN was pretrained with the ImageNet dataset. This CNN architecture was then retrained using a novel dataset of 524 dissected ovary images from An. gambiae s.l. An. gambiae Akron, and An. funestus s.l., whose fertility status and PPF exposure were known. Data augmentation increased the training set to 6973 images. A test set of 157 images was used to measure accuracy. This CNN model achieved an accuracy score of 94%, and application took a mean time of 38.5 s. Such a CNN can achieve an acceptable level of precision in a quick, robust format and can be distributed in a practical, accessible, and free manner. Furthermore, this approach is useful for measuring the efficacy and durability of PPF treated bednets, and it is applicable to any PPF-treated tool or similarly acting insecticide. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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15 pages, 1202 KiB

Open AccessArticle

A Yeast RNA-Interference Pesticide Targeting the Irx Gene Functions as a Broad-Based Mosquito Larvicide and Adulticide

by Keshava Mysore, Longhua Sun, Limb K. Hapairai, Chien-Wei Wang, Jessica Igiede, Joseph B. Roethele, Nicholas D. Scheel, Max P. Scheel, Ping Li, Na Wei, David W. Severson and Molly Duman-Scheel

Insects 2021, 12(11), 986; https://doi.org/10.3390/insects12110986 - 2 Nov 2021

Cited by 9 | Viewed by 3219

Abstract

Concerns for widespread insecticide resistance and the unintended impacts of insecticides on nontarget organisms have generated a pressing need for mosquito control innovations. A yeast RNAi-based insecticide that targets a conserved site in mosquito Irx family genes, but which has not yet been [...] Read more.

Concerns for widespread insecticide resistance and the unintended impacts of insecticides on nontarget organisms have generated a pressing need for mosquito control innovations. A yeast RNAi-based insecticide that targets a conserved site in mosquito Irx family genes, but which has not yet been identified in the genomes of nontarget organisms, was developed and characterized. Saccharomyces cerevisiae constructed to express short hairpin RNA (shRNA) matching the target site induced significant Aedes aegypti larval death in both lab trials and outdoor semi-field evaluations. The yeast also induced high levels of mortality in adult females, which readily consumed yeast incorporated into an attractive targeted sugar bait (ATSB) during simulated field trials. A conserved requirement for Irx function as a regulator of proneural gene expression was observed in the mosquito brain, suggesting a possible mode of action. The larvicidal and adulticidal properties of the yeast were also verified in Aedes albopictus, Anopheles gambiae, and Culexquinquefasciatus mosquitoes, but the yeast larvicide was not toxic to other nontarget arthropods. These results indicate that further development and evaluation of this technology as an ecofriendly control intervention is warranted, and that ATSBs, an emerging mosquito control paradigm, could potentially be enriched through the use of yeast-based RNAi technology. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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18 pages, 2144 KiB

Open AccessArticle

Colonization and Authentication of the Pyrethroid-Resistant Anopheles gambiae s.s. Muleba-Kis Strain; an Important Test System for Laboratory Screening of New Insecticides

by Salum Azizi, Janneke Snetselaar, Alexandra Wright, Johnson Matowo, Boniface Shirima, Robert Kaaya, Rashid Athumani, Filemoni Tenu, Natacha Protopopoff and Matthew Kirby

Insects 2021, 12(8), 710; https://doi.org/10.3390/insects12080710 - 8 Aug 2021

Cited by 10 | Viewed by 4022

Abstract

Background: The emergence and spread of insecticide resistance in malaria vectors to major classes of insecticides call for urgent innovation and application of insecticides with novel modes of action. When evaluating new insecticides for public health, potential candidates need to be screened against [...] Read more.

Background: The emergence and spread of insecticide resistance in malaria vectors to major classes of insecticides call for urgent innovation and application of insecticides with novel modes of action. When evaluating new insecticides for public health, potential candidates need to be screened against both susceptible and resistant mosquitoes to determine efficacy and to identify potential cross-resistance to insecticides currently used for mosquito control. The challenges and lessons learned from establishing, maintaining, and authenticating the pyrethroid-resistant An. gambiae s.s. Muleba-Kis strain at the KCMUCo-PAMVERC Test Facility are described in this paper. Methods: Male mosquitoes from the F₁ generation of wild-pyrethroid resistant mosquitoes were cross-bred with susceptible female An. gambiae s.s. Kisumu laboratory strain followed by larval selection using a pyrethroid insecticide solution. Periodic screening for phenotypic and genotypic resistance was done. WHO susceptibility tests and bottle bioassays were used to assess the phenotypic resistance, while Taqman™ assays were used to screen for known target-site resistance alleles (kdr and ace-1). Additionally, the strains were periodically assessed for quality control by monitoring adult weight and wing length. Results: By out-crossing the wild mosquitoes with an established lab strain, a successful resistant insectary colony was established. Intermittent selection pressure using alphacypermethrin has maintained high kdr mutation (leucine-serine) frequencies in the selected colony. There was consistency in the wing length and weight measurements from the year 2016 to 2020, with the exception that one out of four years was significantly different. Mean annual wing length varied between 0.0142–0.0028 mm compared to values obtained in 2016, except in 2019 where it varied by 0.0901 mm. Weight only varied by approximately 0.001 g across four years, except in 2017 where it differed by 0.005 g. Routine phenotypic characterization on Muleba-Kis against pyrethroids using the WHO susceptibility test indicated high susceptibility when type I pyrethroids were used compared to type II pyrethroids. Dynamics on susceptibility status also depended on the lapse time when the selection was last done. Conclusions: This study described the procedure for introducing, colonizing, and maintaining a resistant An. gambiae s.s. strain in the laboratory with leucine to serine substitution kdr allele which reflects the features of the wild-resistant population in East Africa. Challenges in colonizing a wild-resistant mosquito strain were overcome by out-crossing between mosquito strains of desired traits followed by intermittent insecticide selection at the larval stage to select for the resistant phenotype. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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24 pages, 3058 KiB

Open AccessEditor’s ChoiceArticle

Mosquito-Textile Physics: A Mathematical Roadmap to Insecticide-Free, Bite-Proof Clothing for Everyday Life

by Kun Luan, Andre J. West, Marian G. McCord, Emiel A. DenHartog, Quan Shi, Isa Bettermann, Jiayin Li, Nicholas V. Travanty, Robert D. Mitchell III, Grayson L. Cave, John B. Strider, Yongxin Wang, Florian Neumann, Tobias Beck, Charles S. Apperson and R. Michael Roe

Insects 2021, 12(7), 636; https://doi.org/10.3390/insects12070636 - 13 Jul 2021

Cited by 12 | Viewed by 38622

Abstract

Garments treated with chemical insecticides are commonly used to prevent mosquito bites. Resistance to insecticides, however, is threatening the efficacy of this technology, and people are increasingly concerned about the potential health impacts of wearing insecticide-treated clothing. Here, we report a mathematical model [...] Read more.

Garments treated with chemical insecticides are commonly used to prevent mosquito bites. Resistance to insecticides, however, is threatening the efficacy of this technology, and people are increasingly concerned about the potential health impacts of wearing insecticide-treated clothing. Here, we report a mathematical model for fabric barriers that resist bites from Aedes aegypti mosquitoes based on textile physical structure and no insecticides. The model was derived from mosquito morphometrics and analysis of mosquito biting behavior. Woven filter fabrics, precision polypropylene plates, and knitted fabrics were used for model validation. Then, based on the model predictions, prototype knitted textiles and garments were developed that prevented mosquito biting, and comfort testing showed the garments to possess superior thermophysiological properties. Our fabrics provided a three-times greater bite resistance than the insecticide-treated cloth. Our predictive model can be used to develop additional textiles in the future for garments that are highly bite resistant to mosquitoes. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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22 pages, 2450 KiB

Open AccessArticle

A Three-Pronged Approach to Studying Sublethal Insecticide Doses: Characterising Mosquito Fitness, Mosquito Biting Behaviour, and Human/Environmental Health Risks

by Mara Moreno-Gómez, Rubén Bueno-Marí and Miguel. A. Miranda

Insects 2021, 12(6), 546; https://doi.org/10.3390/insects12060546 - 11 Jun 2021

Cited by 5 | Viewed by 3916

Abstract

Worldwide, pyrethroids are one of the most widely used insecticide classes. In addition to serving as personal protection products, they are also a key line of defence in integrated vector management programmes. Many studies have assessed the effects of sublethal pyrethroid doses on [...] Read more.

Worldwide, pyrethroids are one of the most widely used insecticide classes. In addition to serving as personal protection products, they are also a key line of defence in integrated vector management programmes. Many studies have assessed the effects of sublethal pyrethroid doses on mosquito fitness and behaviour. However, much remains unknown about the biological, physiological, demographic, and behavioural effects on individual mosquitoes or mosquito populations when exposure occurs via spatial treatments. Here, females and males of two laboratory-reared mosquito species, Culex pipiens and Aedes albopictus, were exposed to five different treatments: three doses of the pyrethroid prallethrin, as well as an untreated and a negative control. The effects of each treatment on mosquito species, sex, adult mortality, fertility, F1 population size, and biting behaviour were also evaluated. To compare knockdown and mortality among treatments, Mantel–Cox log-rank tests were used. The results showed that sublethal doses reduced mosquito survival, influencing population size in the next generation. They also provided 100% protection to human hosts and presented relatively low risks to human and environmental health. These findings emphasise the need for additional studies that assess the benefits of using sublethal doses as part of mosquito management strategies. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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Review

Jump to: Editorial, Research, Other

24 pages, 629 KiB

Open AccessReview

Plant-Based Bioinsecticides for Mosquito Control: Impact on Insecticide Resistance and Disease Transmission

by Meryem Ş. Şengül Demirak and Emel Canpolat

Insects 2022, 13(2), 162; https://doi.org/10.3390/insects13020162 - 3 Feb 2022

Cited by 98 | Viewed by 23659

Abstract

The use of synthetic insecticides has been a solution to reduce mosquito-borne disease transmission for decades. Currently, no single intervention is sufficient to reduce the global disease burden caused by mosquitoes. Problems associated with extensive usage of synthetic compounds have increased substantially which [...] Read more.

The use of synthetic insecticides has been a solution to reduce mosquito-borne disease transmission for decades. Currently, no single intervention is sufficient to reduce the global disease burden caused by mosquitoes. Problems associated with extensive usage of synthetic compounds have increased substantially which makes mosquito-borne disease elimination and prevention more difficult over the years. Thus, it is crucial that much safer and effective mosquito control strategies are developed. Natural compounds from plants have been efficiently used to fight insect pests for a long time. Plant-based bioinsecticides are now considered a much safer and less toxic alternative to synthetic compounds. Here, we discuss candidate plant-based compounds that show larvicidal, adulticidal, and repellent properties. Our discussion also includes their mode of action and potential impact in mosquito disease transmission and circumvention of resistance. This review improves our knowledge on plant-based bioinsecticides and the potential for the development of state-of-the-art mosquito control strategies. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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18 pages, 1460 KiB

Open AccessReview

Implications of Sublethal Insecticide Exposure and the Development of Resistance on Mosquito Physiology, Behavior, and Pathogen Transmission

by Felipe Andreazza, Eugênio E. Oliveira and Gustavo Ferreira Martins

Insects 2021, 12(10), 917; https://doi.org/10.3390/insects12100917 - 8 Oct 2021

Cited by 20 | Viewed by 4152

Abstract

For many decades, insecticides have been used to control mosquito populations in their larval and adult stages. Although changes in the population genetics, physiology, and behavior of mosquitoes exposed to lethal and sublethal doses of insecticides are expected, the relationships between these changes [...] Read more.

For many decades, insecticides have been used to control mosquito populations in their larval and adult stages. Although changes in the population genetics, physiology, and behavior of mosquitoes exposed to lethal and sublethal doses of insecticides are expected, the relationships between these changes and their abilities to transmit pathogens remain unclear. Thus, we conducted a comprehensive review on the sublethal effects of insecticides and their contributions to insecticide resistance in mosquitoes, with the main focus on pyrethroids. We discuss the direct and acute effects of sublethal concentrations on individuals and populations, the changes in population genetics caused by the selection for resistance after insecticide exposure, and the major mechanisms underlying such resistance. Sublethal exposures negatively impact the individual’s performance by affecting their physiology and behavior and leaving them at a disadvantage when compared to unexposed organisms. How these sublethal effects could change mosquito population sizes and diversity so that pathogen transmission risks can be affected is less clear. Furthermore, despite the beneficial and acute aspects of lethality, exposure to higher insecticide concentrations clearly impacts the population genetics by selecting resistant individuals, which may bring further and complex interactions for mosquitoes, vertebrate hosts, and pathogens. Finally, we raise several hypotheses concerning how the here revised impacts of insecticides on mosquitoes could interplay with vector-mediated pathogens’ transmission. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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23 pages, 23555 KiB

Open AccessEditor’s ChoiceReview

Review and Meta-Analysis of the Evidence for Choosing between Specific Pyrethroids for Programmatic Purposes

by Natalie Lissenden, Mara D. Kont, John Essandoh, Hanafy M. Ismail, Thomas S. Churcher, Ben Lambert, Audrey Lenhart, Philip J. McCall, Catherine L. Moyes, Mark J. I. Paine, Giorgio Praulins, David Weetman and Rosemary S. Lees

Insects 2021, 12(9), 826; https://doi.org/10.3390/insects12090826 - 14 Sep 2021

Cited by 25 | Viewed by 4491

Abstract

Pyrethroid resistance is widespread in malaria vectors. However, differential mortality in discriminating dose assays to different pyrethroids is often observed in wild populations. When this occurs, it is unclear if this differential mortality should be interpreted as an indication of differential levels of [...] Read more.

Pyrethroid resistance is widespread in malaria vectors. However, differential mortality in discriminating dose assays to different pyrethroids is often observed in wild populations. When this occurs, it is unclear if this differential mortality should be interpreted as an indication of differential levels of susceptibility within the pyrethroid class, and if so, if countries should consider selecting one specific pyrethroid for programmatic use over another. A review of evidence from molecular studies, resistance testing with laboratory colonies and wild populations, and mosquito behavioural assays were conducted to answer these questions. Evidence suggested that in areas where pyrethroid resistance exists, different results in insecticide susceptibility assays with specific pyrethroids currently in common use (deltamethrin, permethrin, α-cypermethrin, and λ-cyhalothrin) are not necessarily indicative of an operationally relevant difference in potential performance. Consequently, it is not advisable to use rotation between these pyrethroids as an insecticide-resistance management strategy. Less commonly used pyrethroids (bifenthrin and etofenprox) may have sufficiently different modes of action, though further work is needed to examine how this may apply to insecticide resistance management. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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Strain Characterisation for Measuring Bioefficacy of ITNs Treated with Two Active Ingredients (Dual-AI ITNs): Developing a Robust Protocol by Building Consensus

by Rosemary S. Lees, Jennifer S. Armistead, Salum Azizi, Edi Constant, Christen Fornadel, John E. Gimnig, Janet Hemingway, Daniel Impoinvil, Seth R. Irish, William Kisinza, Natalie Lissenden, Henry D. Mawejje, Louisa A. Messenger, Sarah Moore, Corine Ngufor, Richard Oxborough, Natacha Protopopoff, Hilary Ranson, Graham Small, Joseph Wagman, David Weetman, Sarah Zohdy and Angus Spiers Show full author list Hide full author list

Insects 2022, 13(5), 434; https://doi.org/10.3390/insects13050434 - 6 May 2022

Cited by 12 | Viewed by 4104

Abstract

Durability monitoring of insecticide-treated nets (ITNs) containing a pyrethroid in combination with a second active ingredient (AI) must be adapted so that the insecticidal bioefficacy of each AI can be monitored independently. An effective way to do this is to measure rapid knock [...] Read more.

Durability monitoring of insecticide-treated nets (ITNs) containing a pyrethroid in combination with a second active ingredient (AI) must be adapted so that the insecticidal bioefficacy of each AI can be monitored independently. An effective way to do this is to measure rapid knock down of a pyrethroid-susceptible strain of mosquitoes to assess the bioefficacy of the pyrethroid component and to use a pyrethroid-resistant strain to measure the bioefficacy of the second ingredient. To allow robust comparison of results across tests within and between test facilities, and over time, protocols for bioefficacy testing must include either characterisation of the resistant strain, standardisation of the mosquitoes used for bioassays, or a combination of the two. Through a series of virtual meetings, key stakeholders and practitioners explored different approaches to achieving these goals. Via an iterative process we decided on the preferred approach and produced a protocol consisting of characterising mosquitoes used for bioefficacy testing before and after a round of bioassays, for example at each time point in a durability monitoring study. We present the final protocol and justify our approach to establishing a standard methodology for durability monitoring of ITNs containing pyrethroid and a second AI. Full article

(This article belongs to the Special Issue Insecticides for Mosquito Control: Strengthening the Evidence Base)

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