Spatial Repellents Research Articles

Efficacy Of Transfluthrin Varies By Species And Placement In A Warm Temperate Mediterranean Environment

ABSTRACT Spatial repellents may protect personnel in delimited areas from incursion of vector or nuisance Diptera, such as mosquitoes and sand flies. We investigated the efficacy of resin diffusers impregnated with transfluthrin in protecting 2 simulated military field scenarios (partially opened tents and open bivouacs lacking shelter) from natural populations of Culex species mosquitoes and Phlebotomus species sand flies. Using a benchmark efficacy of 61% expected reduction from a recent literature survey, we found that transfluthrin protected bivouacs from sand flies (74.1% average reduction; P < 0.001, t(38) = 4.234) but not mosquitoes (13.1% mean reduction, not significant). However, treated tents were not sufficiently protected from sand flies (33.3% mean reduction, not significant), and mosquito numbers increased by an average of 89.3% (not significant). Spatial repellents such as transfluthrin can be highly effective, but efficacy may vary by species and placement, and they should be incorporated into integrated vector management with care.

Deterrence and behavioral mode of coconut oil-derived free fatty acids on Zeugodacus cucurbitae oviposition.

Previous studies have shown oviposition deterring properties of 8 coconut free fatty acid (CFFA) compounds on fruit flies with different key deterrent components for different species. Here we evaluated oviposition deterrence of CFFA using laboratory 2-choice bioassays against Zeugodacus cucurbitae, determined key-bioactive deterrent compounds, and evaluated their behavioral mode. Unlike other reported fruit fly species, CFFA mixture increased Z. cucurbitae oviposition when directly applied on an oviposition substrate. When tested individually in subsequent tests, 4 compounds (caprylic, capric, oleic, and linoleic acids) significantly reduced the oviposition ("negative-compounds"), 1 compound (stearic acid) had no effect ("neutral-compound"), and 3 compounds (lauric, myristic, and palmitic acids) stimulated the oviposition ("positive-compounds"). The 4-component negative-compound blend was effective at reducing oviposition. However, adding stearic acid to the 4-component blend (5-component blend, 5c) further reduced oviposition. Adding any of the positive-compounds to the 5c resulted in loss of oviposition deterrence, suggesting the 5c as the key deterrent component blend. The blend was also effective in no-choice assays and when applied on cucumbers, a preferred host of Z. cucurbitae. When given a choice, Z. cucurbitae made 48.5% fewer visits, spent 39% less time, and oviposited 88.2% fewer eggs per min on 5c treated pumpkin agar than on control agar, suggesting that the 5c blend has both spatial repellency and contact deterrence. Given that all compounds are registered food additives and generally regarded as safe, this blend has potential application in behavioral control strategies, such as push-pull, to protect host fruit against Z. cucurbitae.

High-Throughput Screening System Evaluation of Andrographis paniculata (Burm.f.) Extracts and Their Fractions against Mosquito Vectors.

Infectious diseases that cause illness and/or death in humans can be contracted from mosquito bites. A viable and alternate method of personal protection that can lower the danger of human exposure to mosquito-borne diseases is the use of plant-based repellents. Using a high-throughput screening system, the current work examined the toxicity, contact irritancy, and spatial repellency of Andrographis paniculata crude extract and its fractions against Aedes aegypti, Anopheles minimus, and An. dirus. Five fractions (i.e., F1, F2, F3, F4, and F5) were separated from the crude extract by column and thin layer chromatography and analyzed using high-performance liquid chromatography and mass spectrometry. The major active compounds identified from F3 and F5 were 4-deoxy-11,12-didehydroandrographolide and andrographolide. Three concentrations (1.0, 2.5, and 5.0%) for each of the crude extracts and the five fractions were individually impregnated on nylon netting strips and evaluated against the three mosquito species. Results showed that the highest contact irritancy was elicited by the crude extract at 5% concentration against Ae. aegypti (43.70% escaped). Results of the spatial activity index (SAI) showed that fractions F3 and F5 at 2.5% demonstrated the strongest repellency against Ae. aegypti (SAI = 0.84) and An. minimus (SAI = 0.83), respectively. Both the crude extract and its components did not cause any knockdown or mortality. These findings suggest that fractionation of A. paniculata extracts is valuable in assessing their spatial repellent efficacy against mosquitoes. Fractions F3 and F5 hold promise as natural mosquito repellents and could contribute to developing effective mosquito control strategies.

Repelling Aedes aegypti mosquitoes with electric fields using insulated conductor wires.

The control and prevention of mosquito-borne diseases is mostly achieved with insecticides. However, their use has led to the rapid development and spread of insecticide resistance worldwide. Health experts have called for intensified efforts to find new approaches to reduce mosquito populations and human-mosquito contact. A promising new tool is the use of electrical fields (EFs), whereby mosquitoes are repelled by charged particles in their flight path. Such particles move between two or more conductors, and the use of uninsulated copper or aluminum plates as conductors has been proven to be effective at repelling mosquitoes. Here, for the first time, we assess if EFs generated using a single row of insulated conductor wires (ICWs) can also successfully repel mosquitoes, and whether mosquitoes are equally repelled at the same EF strength when the electrodes are a) orientated differently (horizontal vs. vertical placement), and b) spaced more apart. Over a period of 23 hours, the number of host-seeking female Aedes aegypti mosquitoes that were successfully repelled by EFs, using ICWs, at EF strengths ranging from 0 kV/cm (control) to 9.15 kV/cm were quantified. Mosquitoes were released inside a 220×220×180 cm room and lured into a BG-Pro trap that was equipped with a BG-counter and baited with CO2 using dry ice. Mosquitoes had to pass through an EF window, that contained a single row of ICWs with alternating polarity, to reach the bait. The baseline interaction between EF strength and repellency was assessed first, after which the impact of different ICW orientations and ICW distances on repellency were determined. Over 50% of mosquitoes were repelled at EF strengths of ≥ 3.66 kV/cm. A linear regression model showed that a vertical ICW orientation (vertical vs. horizontal) had a small but insignificant increased impact on mosquito repellency (p = 0.059), and increasing ICW distance (while maintaining the same EF strength) significantly reduced repellency (p = 0.01). ICWs can be used to generate EFs that partially repel host-seeking mosquitoes, which will reduce human-mosquito contact. While future studies need to assess if (i) increased repellency can be achieved, and (ii) a repellency of 50-60% is sufficient to impact disease transmission, it is encouraging that EF repellency using ICWs is higher compared to that of some spatial repellent technologies currently in development. This technology can be used in the housing improvement toolkit (i.e. preventing mosquito entry through eaves, windows, and doors). Moreover, the use of cheap, over-the-counter ICWs will mean that the technology is more accessible worldwide, and easier to manufacture and implement locally.

Airborne metofluthrin, a pyrethroid repellent, does not impact foraging honey bees.

Outdoor spatial mosquito repellents, such as mosquito coils or heating devices, release pyrethroid insecticides into the air to provide protection from mosquitoes within a defined area. This broadcast discharge of pyrethroids into the environment raises concern about the effect on non-target organisms. A previous study found that prallethrin discharged from a heating device did not affect honey bee (Apis mellifera L.) [Hymenoptera: Apidae] foraging or recruitment. In this second study, there was no significant difference in foraging frequency (our primary outcome), waggle dance propensity, or persistency in honey bees collecting sucrose solution between those exposed to metofluthrin from a different heating device and bees exposed to a non-metofluthrin control. One measure, waggle dance frequency, was higher in the metofluthrin treatment than the control but this outcome was likely a spurious result due to the small sample size. The small particle size of the emissions, averaging 4.43 µm, from the heated spatial repellent products, which remain airborne with little settling, may play an important role in the lack of effect found on honey bee foraging.

Advancing spatial repellents for malaria control: effectiveness and cost-effectiveness of a spatial repellent under operational use in Northern Uganda—study protocol for a cluster randomized controlled trial

BackgroundSpatial repellents (SRs) have been widely used for the prevention of mosquito bites, and preliminary findings suggest efficacy against both malaria (1) and Aedes-borne viruses (2) but their effectiveness in reducing mosquito-borne diseases under operational use has never been evaluated. SRs have the potential of being critical tools in the prevention of mosquito-borne diseases in contexts where typical vector control strategies, such as insecticide-treated nets (ITNs) and indoor residual spraying, are inaccessible or underutilized such as among displaced persons or in emergency relief settings.MethodsChildren will be enrolled in 3 separate cohorts to establish the effectiveness of SRs in reducing malaria infection in different distribution channels. One cohort will estimate the direct effect of the SR distributed through a reference channel (study personnel distribution). The two remaining cohorts will estimate the protection of the SR distributed through a voucher channel and the Village Health Team channel. Cohorts will be followed twice a month (approximately every 15 days): during the first scheduled household visit in the month, a blood sample will be taken for malaria rapid diagnostic test (Monthly Visit #1); and, during the second scheduled household visit, a blood sample will only be taken if the participant has a recent history of fever (Monthly Visit #2). The incidence of malaria in each cohort will be estimated and compared to the reference cohort to determine the benefit of using a SR in an area with high, year-round transmission of malaria.DiscussionThis study will address the knowledge gap of whether or not SRs are effective in reducing human malaria disease in humanitarian assistance and emergency response settings in sub-Saharan Africa where underlying transmission rates are historically high and ITNs may or may not be widely deployed. This research will inform policy makers on whether to recommend SRs as a means to further reduce malaria transmission for such operational programs.Trial registrationClinicalTrials.gov NCT06122142. Registered on November 8, 2023.

Role of Non-Residential Larval Habitats in Aedes Spatiotemporal Egg Production.

Aedes mosquitoes play a pivotal role as vectors of several arboviral diseases, presenting significant public health challenges worldwide. Their invasive success in tropical regions has raised substantial medical concerns. In Guatemala, Aedes mosquitoes are widely distributed and are the primary vectors of the dengue virus. Efforts to control and monitor Aedes populations have evolved over time, incorporating strategies such as spatial repellents, larvicides, genetic modifications, and targeted interventions. Previous research has shown the heterogeneous spatial-temporal distribution of these mosquitoes within each season, influenced by temperature variations and favorable environmental conditions for breeding. This study analyzed hot-spot patterns of spatiotemporal egg density in Santa Elena de la Cruz, Petén, Guatemala, from March to September 2022. The aim was to determine whether these patterns were influenced by non-residential larval habitats with plant cover that are not treated by healthcare entities, as well as the proximity between such habitats. Our findings include the collection and registration of over 16,000 Aedes eggs during the study period. Local analyses revealed hot-spot patterns in egg densities associated with non-residential larval habitats and their proximity. These insights highlight critical focal points where targeted interventions could be implemented more effectively, resulting in cost-efficient mosquito vector control.

Air-Drying Time Affects Mortality of Pyrethroid-Susceptible Aedes aegypti Exposed to Transfluthrin-Treated Filter Papers.

Increasing temperature can enhance the geographical spread and behavior of disease vector mosquitoes, exposing vulnerable populations to Aedes-borne viruses and infections. To address this risk, cost-effective and sustained intervention vector control tools are required, such as volatile pyrethroid spatial repellents. This study used a high-throughput screening system toxicity bioassay to determine the discriminating concentrations of transfluthrin-treated filter papers with variable air-drying times exposed to pyrethroid-susceptible Aedes aegypti mosquitoes. At the highest transfluthrin concentration (0.01706%), a significant reduction in mosquito mortality was observed in filter papers air-dried for 24 h compared to those air-dried for 1 h (odds ratio = 0.390, p < 0.001, 95% confidence interval: 0.23-0.66). Conversely, no significant difference in mortality was found between filter papers air-dried for 1 h and those air-dried for 12 h (odds ratio = 0.646, p = 0.107, 95% confidence interval: 0.38-1.10). The discriminating concentration was 2.8-fold higher for transfluthrin-treated filter papers air-dried for 24 h than it was for papers air-dried for 1 h, and it increased 5-fold from 1 h to 336 h of air-drying. These results show that the optimal air-drying period of transfluthrin-treated filter paper is critical, as higher discriminating concentration values may lead to underestimations of insecticide resistance. The instability of transfluthrin-treated papers necessitates the use of the World Health Organization (WHO) bottle bioassay, which is the preferred method for determining mosquito susceptibility to volatile insecticides.

Mosquito Shield™, a transfluthrin passive emanator, protects against pyrethroid-resistant Anopheles gambiae sensu lato in central Benin

BackgroundSpatial repellents can provide personal and household protection against biting vector mosquitoes by volatizing repellents into the air within a given area. Mosquito Shield™ is a transfluthrin passive emanator undergoing evaluation for malaria control. Studies evaluating its entomological impact against different local malaria vector populations would help guide its deployment in endemic countries.MethodsA two-arm single-blinded small-scale household randomised entomological trial was conducted to assess the impact of Mosquito Shield™ on the human landing rate of wild pyrethroid-resistant Anopheles gambiae sensu lato (s.l.) vector mosquitoes in houses in the Ganhoua village of the Zakpota District of central Benin. From a total of 30 houses, 15 were randomly allocated to receive Mosquito Shield™, while the remainder received a placebo product. The trial lasted through the life of the Mosquito Shield™ product (32 days). Mosquito sampling was performed by human landing catches at baseline and at 6 timepoints post-intervention (days 0–1, 7–8, 14–15, 21–22, 28–29 and 31–32). Collections were performed for 2 nights at each sampling time point. WHO cylinder bioassays were conducted during the trial with F1 An. gambiae s.l. mosquitoes that emerged from larvae from the study area to assess the intensity of resistance to pyrethroids in the wild vector population.ResultsThe vector population in the study area showed a high intensity of resistance to pyrethroids. Baseline An. gambiae s.l. human landing rates were similar in houses in both study arms before product application (11.53/person/night vs 11.67/person/night, p > 0.05). A total of 5736 mosquitoes were collected in the placebo control arm and 3862 in the Mosquito Shield™ arm post-intervention. Overall An. gambiae s.l. post-intervention human landing rates were significantly lower in houses in the Mosquito Shield™ arm (18.13/person/night) compared to the houses in the placebo control arm (26.84/person/night, IRR = 0.658, p < 0.001). Over the lifespan of the product, Mosquito Shield™ provided a significant protective efficacy of 34.2% (22.1–44.4%, p < 0.001) against wild pyrethroid-resistant An. gambiae s.l. vectors compared to the placebo. Human landing rates of other nuisance vector mosquito species (Culex and Mansonia) were also reduced in houses treated with Mosquito Shield™ compared to the placebo.ConclusionMosquito Shield™, a transfluthrin passive emanator, provided significant protection against pyrethroid-resistant malaria vectors to households in Benin. The spatial repellent shows potential to reduce malaria transmission by pyrethroid-resistant An. gambiae s.l. vector mosquitoes and cover gaps in malaria control when deployed to complement existing vector control interventions.

Field evaluation of a volatile pyrethroid spatial repellent and etofenprox treated clothing for outdoor protection against forest malaria vectors in Cambodia

Cambodia’s goal to eliminate malaria by 2025 is challenged by persistent transmission in forest and forest fringe areas, where people are exposed to Anopheles mosquito bites during the day and night. Volatile pyrethroid spatial repellents (VPSRs) and insecticide-treated clothing (ITC) could address these gaps. This study evaluated the outdoor application of one passive transfluthrin-based VPSR, four etofenprox-ITCs paired with a picaridin topical repellent, and a combination of VPSR and ITC against wild Anopheles landing in Cambodia. A 7 × 7 Latin-square study was conducted over 49 collection nights in temporary open structures in Mondulkiri Province. All interventions substantially reduced Anopheles landing, with protective efficacy ranging from 61 to 95%. Mathematical modeling showed significant reductions in vectoral capacity, especially with the combined ITC and VPSR and VPSR alone, albeit with decreased effectiveness over time. These interventions have the potential to reduce outdoor and daytime Anopheles biting, offering valuable contributions to malaria elimination efforts in Cambodia and the Greater Mekong Subregion, contingent upon achieving effective coverage and adherence.

Screening of botanical spatial mosquito repellents from 64 essential oils and their interactions with odorant‐binding protein‐3

AbstractPersonal protection from mosquito bites is essential for preventing mosquito‐borne diseases. Mosquito repellents are effective methods for preventing mosquito bites. Due to their ease of use and indirect skin contact, mosquito‐repellent stickers loaded with essential oils (EOs) have recently become favoured as novel spatial repellents. To discover active EOs with high spatial repellency, 64 commercial EOs were screened using a modified arm‐in‐cage assay. Four EOs, including nutmeg, melissa, eucalyptus and cinnamon, displayed longer complete protection times (CPTs) of about 60 min. Ten main constituents from the four active EOs were identified by gas chromatography–mass spectrometry (GC–MS), and their spatial repellent activities were further evaluated. 1,8‐Cineole, cinnamaldehyde and citral showed potent repellent activity, with average CPTs of 67.5, 63.8 and 60 min respectively. The interactions of 1,8‐cineole and citral with odorant‐binding protein‐3 (OBP‐3) were studied via molecular docking. Both compounds are docked well in the high hydrophobic pocket and interacted with AealOBP3 through Van der Waals interactions with Phe105, Phe112, Leu114, Met48 and Val50. These natural products provide promising lead fragments for the further development of botanical spatial repellents.

Repellency of N,N-diethyl-3-methylbenzamide (DEET) during host-seeking behavior of bed bugs (Hemiptera: Cimicidae) in binary choice olfactometer assays.

The bed bug (Cimex lectularius L.) is one of the most prolific and burdensome indoor pests, and suppression of bed bug populations is a global priority. Understanding bed bug behavior is important to the development of new tactics for their control. Major gaps exist in our understanding of how host cues, insecticide resistance, and exposure modality impact the repellency of formulated products to bed bugs. Here, we validate the use of a binary choice olfactometer for assessing bed bug repellency behaviors using N,N-diethyl-3-methylbenzamide (DEET) in a dose-dependent manner, while considering the role of host-associated stimuli (with vs. without CO2), exposure modality (olfactory vs. olfactory and contact), and resistance status (susceptible vs. resistant) on repellency. We observed that host-seeking insecticide-susceptible bed bugs were repelled only when olfactorily exposed to high concentrations of DEET. However, exposure to DEET by contact repelled insecticide-susceptible bed bugs at 100-fold lower dose of DEET. Further, we demonstrate for the first time that insecticide-resistant bed bugs were significantly more responsive to DEET than susceptible bed bugs. We conclude that the 2-choice olfactometer is an effective tool for assessing the behavioral responses of bed bugs to spatial and contact repellents.

Evaluating human landing catches as a measure of mosquito biting and the importance of considering additional modes of action

Entomological evaluations of vector control tools often use human landing catches (HLCs) as a standard measure of a direct human-vector contact. However, some tools have additional characteristics, such as mortality, and HLCS are not sensitive for measuring other effects beyond landing inhibition. Therefore, additional measures may need to be considered when evaluating these tools for public health use. This study has two main aims (1) the evaluate the accuracy of HLCs as a proxy for feeding and (2) to compare the predicted reduction in vectorial capacity when we do and do not consider these additional characteristics. To achieve this, we analyse previously published semi-field data from an experiment which used HLCs and another where mosquitoes were allowed to feed in the presence of different dosages of the volatile pyrethroid spatial repellent, transfluthrin. We compare results for two mathematical models: one which only considers the reduction in feeding effect and one which also considers mortality before and after feeding (using data gathered by the aspiration of mosquitoes after the semi-field feeding/landing period and 24 h survival monitoring). These Bayesian hierarchical models are parameterised using Bayesian inference. We observe that, for susceptible mosquitoes, reduction in landing is underestimated by HLCs. For knockdown resistant mosquitoes the relationship is less clear; with HLCs sometimes appearing to overestimate this characteristic. We find HLCs tend to under-predict the relative reduction in vectorial capacity in susceptible mosquitoes while over-predicting this impact in knockdown-resistant mosquitoes. Models without secondary effects have lower predicted relative reductions in vectorial capacities. Overall, this study highlights the importance of considering additional characteristics to reduction in biting of volatile pyrethroid spatial repellents. We recommend that these are considered when evaluating novel vector control tools.

Repellent activity of essential oils to the Lone Star tick, Amblyomma americanum

BackgroundThe Lone Star tick, Amblyomma americanum is important to human health because of a variety of pathogenic organisms transmitted to humans during feeding events, which underscores the need to identify novel approaches to prevent tick bites. Thus, the goal of this study was to test natural and synthetic molecules for repellent activity against ticks in spatial, contact and human fingertip bioassays.MethodsThe efficacy of essential oils and naturally derived compounds as repellents to Am. americanum nymphs was compared in three different bioassays: contact, spatial and fingertip repellent bioassays.ResultsConcentration response curves after contact exposure to 1R-trans-chrysanthemic acid (TCA) indicated a 5.6 μg/cm2 concentration required to repel 50% of ticks (RC50), which was five- and sevenfold more active than DEET and nootkatone, respectively. For contact repellency, the rank order of repellency at 50 μg/cm2 for natural oils was clove > geranium > oregano > cedarwood > thyme > amyris > patchouli > citronella > juniper berry > peppermint > cassia. For spatial bioassays, TCA was approximately twofold more active than DEET and nootkatone at 50 μg/cm2 but was not significantly different at 10 μg/cm2. In spatial assays, thyme and cassia were the most active compounds tested with 100% and 80% ticks repelled within 15 min of exposure respectively and was approximately twofold more effective than DEET at the same concentration. To translate these non-host assays to efficacy when used on the human host, we quantified repellency using a finger-climbing assay. TCA, nootkatone and DEET were equally effective in the fingertip assay, and patchouli oil was the only natural oil that significantly repelled ticks.ConclusionsThe differences in repellent potency based on the assay type suggests that the ability to discover active tick repellents suitable for development may be more complicated than with other arthropod species; furthermore, the field delivery mechanism must be considered early in development to ensure translation to field efficacy. TCA, which is naturally derived, is a promising candidate for a tick repellent that has comparable repellency to commercialized tick repellents.Graphical

Development and evaluation of test methods for commercial spatial repellent products using the common fruit flies in laboratory and simulated-use scenarios

Fruit flies and other miniscule flying insects often cause a nuisance in the kitchen areas of our dwellings. To mitigate the invasion of indoor insect pests, behavioral modifications using spatial repellents containing natural products are emerging as alternatives to chemical insecticides especially around the kitchens and food storage areas. However, the absence of standardized testing methods for spatial repellency has undermined the reliability of these products. We introduced three distinct laboratory-scale repellency assays and their relevancy to simulated-use conditions. Out of eleven commercial products tested, five showed effectiveness in laboratory assays, and three of these were further proven effective in simulated-use tests as well. Another issue limiting the utility of commercially available spatial repellents was the lack of clear and comprehensive use instructions on product labels, potentially leading to ineffective applications. We observed that increasing the applied quantity improved the efficacy of one product that was initially determined to be ineffective in a simulated-use test. Based on our findings, we propose three strategies for regulations of spatial repellents: 1) consideration of mixture effects beyond single active ingredients especially using the natural products as their active ingredients, 2) the use of multiple testing systems, while acknowledging the limitations of laboratory assays in predicting real-world efficacy, and 3) ensuring product labels provide detailed and clear instructions for effective use.

Point Protection with Transfluthrin against Musca domestica L. in a Semi-Field Enclosure.

House flies are notoriously difficult to control, owing to their tendency to live in close relationships with humans and their livestock, and their rapid development of resistance to chemical controls. With this in mind, we explored an alternative chemical control, a spatial repellent to deter Musca domestica L. from points we wanted to protect (i.e., a baited trap). Our results demonstrated that the synthetic spatial repellent, transfluthrin, is effective in preventing M. domestica adults from entering protected traps for both a susceptible strain (CAR21) and a field-acquired permethrin-resistant strain (WHF; 24 h LD50 resistance ratio of 150), comprising 22% and 28% of the total number of flies collected, respectively. These results are promising and demonstrate that transfluthrin can be an effective spatial repellent to protect points of interest where needed.

Development and laboratory validation of a plant-derived repellent blend, effective against Aedes aegypti [Diptera: Culicidae], Anopheles gambiae [Diptera: Culicidae] and Culex quinquefasciatus [Diptera: Culicidae

Mosquitoes of the genera Aedes, Anopheles and Culex vector a wide range of pathogens seriously affecting humans and livestock on a global scale. Over-reliance on insecticides and repellents has driven research into alternative, naturally-derived compounds to fulfil the same objectives. Steam distilled extracts of four plants with strong, yet attractive, volatile profiles were initially assessed for repellency in a dual-port olfactometer using Aedes aegypti as the model species. Picea sitchensis was found to be the most repellent, proving comparable to leading products when applied at 100% (p = 1.000). Key components of conifer-derived volatile profiles were then screened via electroantennography before those components eliciting an electrophysiological response were assayed individually in the olfactometer; according to WHO protocol. The most promising 5 were selected for reductive analyses to produce an optimised semiochemical blend. This combination, and a further two variations of the blend, were then progressed to a multi-species analysis using the BG-test whereby bite-attempt frequency on hands was assessed under different repellent treatments; assays were compared between Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus. Efficacy was found against all three species, although it was found that Ae. aegypti was the most susceptible to the repellent, with An. gambiae being the least. Here, a novel, naturally-derived blend is presented with weak spatial repellency, as confirmed in laboratory assays. Further work will be required to assess the full extent of the potential of the products, both in terms of field application and species screening; however, the success of the products developed demonstrate that plant metabolites have great capacity for use in the repellent sector; both to improve upon known compounds and to reduce the usage of toxic products currently on the market.

In Vitro Evaluation of Essential Oils and Saturated Fatty Acids for Repellency against the Old-World Sand Fly, Phlebotomus papatasi (Scopoli) (Diptera: Psychodidae).

The sand fly, Phlebotomus papatasi (Scopoli, 1786), is a major vector for Leishmania major in the Middle East, which has impacted human health and US military operations in the area, demonstrating the need to develop effective sand fly control and repellent options. Here, we report the results of spatial repellency and avoidance experiments in a static air olfactometer using the female P. papatasi testing essential oils of Lippia graveolens (Mexican oregano), Pimenta dioica (allspice), Amyris balsamifera (amyris), Nepeta cataria (catnip), Mentha piperita (peppermint), and Melaleuca alternifolia (tea tree); the 9-12 carbon saturated fatty acids (nonanoic acid, decanoic acid, undecanoic acid, and dodecanoic acid); and the synthetic repellents DEET and IR3535. The materials applied at 1% exhibited varying activity levels but were not significantly different in mean repellency and avoidance from DEET and IR3535, except in regards to nonanoic acid. Some materials, particularly nonanoic and undecanoic acids, produced sand fly mortality. The observed trends in mean repellency over exposure time included the following: (1) P. dioica oil, M. alternifolia oil, decanoic acid, undecanoic acid, DEET, and IR3535 exhibited increasing mean repellency over time; (2) oils of N. cataria, A. balsamifera, M. piperita, and dodecanoic acid exhibited relatively constant mean repellency over time; and (3) L. graveolens oil and nonanoic acid exhibited a general decrease in mean repellent activity over time. These studies identified the essential oils of N. cataria and A. balsamifera as effective spatial repellents at reduced concentrations compared to those of DEET. Additional research is required to elucidate the modes of action and potential synergism of repellents and essential oil components for enhanced repellency activity.

AsOBP1 is required for bioallethrin repellency in the malaria vector mosquito Anopheles sinensis.

The use of insecticides, primarily pyrethroids, is a pivotal strategy for mosquito control globally. Bioallethrin, the first commercially available volatile pyrethroid, can elicit spatial (i.e., noncontact) repellency to mosquitoes through the coactivation of olfactory receptor neurons and sodium channels. However, the olfactory mechanism of the repellency elicited by bioallethrin in mosquitoes is still unclear. Here, we demonstrated the involvement of AsOBP1 in the bioallethrin repellency in Anopheles sinensis, one of the main vectors of vivax malaria in China and other Southeast Asian countries. The behavioral and electrophysiological analyses in AsOrco-/- mutant found that the spatial repellency elicited by bioallethrin depended on the odorant receptor (OR)-mediated olfactory pathway. Furthermore, the repellency was reduced in the AsOBP1-/- mutant and a pyrethroid-resistant strain, in which the expression of AsOBP1 was significantly decreased. Moreover, recombinant AsOBP1 protein bound to bioallethrin in an in vitro competition assay. These results indicate that activation of the AsOBP1-mediated olfactory pathway is an important component of bioallethrin repellency. Our research lays the foundation for further elucidation into the olfactory mechanism of bioallethrin repellency and the behavioral modifications of pyrethroid-resistant mosquitoes.

Impact of a spatial repellent intervention on Anopheles kdr insecticide resistance allele in Sumba, Indonesia

BackgroundThe emergence of insecticide resistance and outdoor transmission in malaria-endemic areas underlines the urgent need to develop innovative tools, such as spatial repellents (SR), that may circumvent this residual transmission. With limited options for effective insecticides, regular resistance monitoring is warranted for selecting and using appropriate tools. This study evaluates the pyrethroid knockdown resistance (kdr) allele before and after implementing a transfluthrin-based spatial repellent (SR) intervention in placebo-treated clusters.MethodsThis study looks at the frequency distribution of the kdr allele in Sumba Island from June 2015 to August 2018. Insecticide susceptibility tests were carried out on female Anopheles sp. aged 3–5 days against permethrin 21.5 μg/ml, deltamethrin 12.5 μg/ml, and transfluthrin 10 μg/ml using CDC bottle assay. PCR sequencing of representative samples from adult mosquito collections and insecticide tests revealed the presence of kdr mutations (L1014F and L1014S) in the VGSC gene.ResultsA total of 12 Anopheles species, Anopheles tesselatus, Anopheles. aconitus, Anopheles barbirostris, Anopheles kochi, Anopheles annularis, Anopheles maculatus, Anopheles sundaicus, Anopheles flavirostris, Anopheles balabacensis, Anopheles indefinitus, Anopheles subpictus, and Anopheles vagus were analysed. Anopheles vagus and An. sundaicus predominated in the larval populations. Susceptibility assays for all insecticides identified fully susceptible phenotypes in all species examined. Anopheles increasing frequency of kdr mutant alleles during the 3 year SR deployment was observed in both SR-treated and placebo areas, a statistically significant increase occurred in each arm. However, it is unclear how significant SR is in causing the increase in mutant alleles. The L1014S, knockdown resistance east type (kdr-e) allele was detected for the first time among the mosquito samples in this study. The L1014F, knockdown resistance west type (kdr-w) allele and heteroduplex form (wild-type—mutant) were found in almost all Anopheles species examined, including An. vagus, An. aconitus, An. subpictus, An. tesselatus, An. annularis, An. flavirostris and An. sundaicus.ConclusionThe presence of fully susceptible phenotypes over time, along with an increase in the frequency distribution of the L1014F/S mutations post-intervention, suggest drivers of resistance external to the study, including pyrethroid use in agriculture and long-lasting insecticidal nets (LLINs). However, this does not negate possible SR impacts that support resistance. More studies that enable the comprehension of possible SR-based drivers of resistance in mosquitoes need to be conducted.