OFF! Clip-on Repellent Device With Metofluthrin Tested on Aedes aegypti (Diptera: Culicidae) for Mortality at Different Time Intervals and Distances

Experimental hut and field evaluation of a metofluthrin-based spatial repellent against pyrethroid-resistant Anopheles funestus in Siaya County, western Kenya

BACKGROUND

Spatial repellents (SR) may complement current vector control tools and provide additional coverage when people are not under their bednets or are outdoors. Here we assessed the efficacy of a metofluthrin-based SR in reducing exposure to pyrethroid-resistant Anopheles funestus in Siaya County, western Kenya.

METHODS

Metofluthrin was vaporized using an emanator configured to a liquid petroleum gas (LPG) canister, placed inside experimental huts (phase 1) or outdoors (phase 2), and evaluated for reductions in human landing rate, density, knockdown and mortality rates of An. funestus, which are present in high density in the area. To demonstrate the mosquito recruiting effect of LPG, a hut with only an LPG cooker but no metofluthrin was added as a comparator and compared with an LPG cooker burning alongside the emanator and a third hut with no LPG cooker as control. Phase 2 evaluated the protective range of the SR product while emanating from the centre of a team of mosquito collectors sitting outdoors in north, south, east and west directions at 5, 10 and 20 feet from the emanating device.

RESULTS

Combustion of LPG with a cook stove increased the density of An. funestus indoors by 51% over controls with no cook stove. In contrast, huts with metofluthrin vaporized with LPG combustion had lower indoor density of An. funestus (99.3% less than controls), with knockdown and mortality rates of 95.5 and 87.7%, respectively, in the mosquitoes collected in the treated huts. In the outdoor study (phase 2), the outdoor landing rate was significantly lower at 5 and 10 feet than at 20 feet from the emanator.

CONCLUSIONS

Vaporized metofluthrin almost completely prevented An. funestus landing indoors and led to 10 times lower landing rates within 10 feet of the emanator outdoors, the first product to demonstrate such potential. Cooking with LPG inside the house could increase exposure to Anopheles mosquito bites, but the use of the metofluthrin canister eliminates this risk.

Graded Atmospheres of Volatile Pyrethroid Overlaid on Host Cues Can Be Established and Quantified Within a Novel Flight Chamber for Mosquito Behavior Studies

Spatial repellents are emerging as a promising approach to reduce vector-disease burden; however, the evolution of genetically resistant mosquitoes decreases repellent efficacy. The development of flight chambers to investigate spatial repellent application techniques is vital for sustainable mosquito control. We present an air-dilution chamber as a novel bioassay to study mosquito flight behavior responses to chemical gradients of the volatile, pyrethroid transfluthrin (TF). Air dilution was used to simulate a larger environment of stable concentration gradients verified with carbon dioxide (CO2) which was homogenously delivered and measured across the chamber to achieve a 5× inlet/outlet [CO2] ratio with 0.17 m/s outlet velocity. Female Aedes (Ae.) aegypti (Diptera: Culicidae, Linnaeus, 1762) were exposed to volatilized TF paired with heat, CO2, and Biogents-Sweetscent host-cues. Tandem solvent extraction-gas chromatography-mass spectrometry (SE-GC-MS) was used to quantify air samples taken during TF emanations with a limit of detection (LOD) and quantification (LOQ) of 2 ± 1 and 5 ± 2 parts-per-trillion (ppt) TF, respectively. Homogenous air diluted emanation of the spatial repellent TF was at least twice that of the 5× CO2 gradient with the same air flow in the chamber. The airborne TF concentrations the mosquitoes were exposed to range from 1 to 170 ppt. Video recordings of mosquito behavior during host-cues exposure revealed increased inlet activity, while exposure to TF protected host resulted in decreased inlet activity over time with inlet-outlet mosquito positional variation. This novel flight chamber design can simulate 'long'-range exposure with simultaneous quantitation of airborne spatial repellent to understand dose-dependent effects on mosquito behavior.

Efficacy of the transfluthrin-based personal insect repellent kit (PIRK) against the ixodid ticks Ixode s scapularis, Amblyomma americanum and Dermacentor variabilis

An assay series was performed to assess the contact and spatial efficacy of the Personal Insect Repellent Kit (PIRK) against three species of ixodid ticks. The PIRK, a portable, passive device comprised of an inert physical substrate incorporated with the active ingredient (AI) transfluthrin (TF), has demonstrated spatial efficacy against flying insects, including three species of mosquitoes, sand flies and stable flies. The device is the only TF end-use product registered with the EPA. Here we report the first studies to explore potential of the PIRK to control Ixodes scapularis, Amblyomma americanum and Dermacentor variabilis. Dose-response assays confirmed toxicity of TF to larvae of all species in the μg/ml range following a 30-min exposure period. Nymphs and adults exhibited irritancy and avoidance behaviors on contact with the PIRK. Greater than 90% knockdown (KD) of I. scapularis nymphs and adults was observed after a 10-s exposure, and of A. americanum nymphs and adults after 10-s and 120-s exposure, respectively. Additionally, greater than 90% mortality was observed in I. scapularis nymphs and adults after 10-s and 40-s exposure, respectively. In spatial assays, the PIRK caused KD and post-exposure mortality of adult female I. scapularis exposed at a range of 5-28 cm. These results suggest both contact and spatial capacity of the PIRK, with greatest potency to nymphs versus adults and the prostriate tick I. scapularis versus the metastriate species A. americanum and D. variabilis. Future studies will explore spatial activity at a range of distances and exposure times, in the presence and absence of host cues and under semi-field conditions.

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

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.

The entomological impact of passive metofluthrin emanators against indoor Aedes aegypti: A randomized field trial

Background

In the absence of vaccines or drugs, insecticides are the mainstay of Aedes-borne disease control. Their utility is challenged by the slow deployment of resources, poor community compliance and inadequate household coverage. Novel application methods are required.

Methodology and principal findings

A 10% w/w metofluthrin “emanator” that passively disseminates insecticide from an impregnated net was evaluated in a randomized trial of 200 houses in Mexico. The devices were introduced at a rate of 1 per room and replaced at 3-week intervals. During each of 7 consecutive deployment cycles, indoor resting mosquitoes were sampled using aspirator collections. Assessments of mosquito landing behaviours were made in a subset of houses. Pre-treatment, there were no differences in Aedes aegypti indices between houses recruited to the control and treatment arms. Immediately after metofluthrin deployment, the entomological indices between the trial arms diverged. Averaged across the trial, there were significant reductions in Abundance Rate Ratios for total Ae. aegypti, female abundance and females that contained blood meals (2.5, 2.4 and 2.3-times fewer mosquitoes respectively; P<0.001). Average efficacy was 60.2% for total adults, 58.3% for females, and 57.2% for blood-fed females. The emanators also reduced mosquito landings by 90% from 12.5 to 1.2 per 10-minute sampling period (P<0.05). Homozygous forms of the pyrethroid resistant kdr alleles V410L, V1016L and F1534C were common in the target mosquito population; found in 39%, 24% and 95% of mosquitoes collected during the trial.

Conclusions/Significance

This is the first randomized control trial to evaluate the entomological impact of any volatile pyrethroid on urban Ae. aegypti. It demonstrates that volatile pyrethroids can have a sustained impact on Ae. aegypti population densities and human-vector contact indoors. These effects occur despite the presence of pyrethroid-resistant alleles in the target population. Formulations like these may have considerable utility for public health vector control responses.

Insecticidal control tools are heavily relied on for the control of mosquito-borne viruses such as dengue, chikungunya and Zika, but the logistics associated with conventional insecticide use (e.g. space sprays and residual formulations) are challenging. Considerable time and resources are required to treat household interiors; an impediment exacerbated by the difficulty in gaining entrance to households, and sometimes by limited compliance in the community. Another constraint to effective insecticide use is that many mosquito populations are resistant to the chemicals used. Volatile pyrethroids, exhibiting both lethal and behavioural effects on mosquitoes are available in formulations that release insecticides passively to the air, at room temperature. These may be suitable for deployment in houses with the aim of creating “bite-free” spaces. By removing the need for conventional application methods, these devices might be rapidly deployed with minimum disruption to households. This is the first large-scale, randomized control trial to evaluate the entomological impacts of volatile pyrethroids in an urban environment. Using metofluthrin as an example, we confirm that some formulations have a significant impact on Aedes aegypti densities and landing behaviour indoors. These effects occur despite the presence of pyrethroid-resistance alleles associated with conventional insecticide resistance.

Field Effectiveness of a Metofluthrin Fan-Based Emanator and Deet as Repellents Against Aedes vigilax in Southeast Queensland, Australia1

A field study to compare a formulation containing 40% deet (N,N-diethyl-3-methyl benzamide) in ethanol (Bushman™) and a battery-powered fan emanator with a chemical strip containing 31.2% metofluthrin (OFF!® Clip-On™) was conducted at Redcliffe, Queensland, Australia, in February 2016. The 40% deet provided 100% protection against mosquitoes for 5 h until tests ceased, while the OFF! Clip-On device provided only 42.2-60.8% protection against Aedes vigilax during the same period.

Comparative Evaluation of Metofluthrin as an Outdoor Residual Treatment for Barriers and Harborage Against Aedes albopictus (Diptera: Culicidae)

Spatial repellent studies have demonstrated that volatile pyrethroids reduce human contact with mosquitoes, but field trials targeting the volatile qualities of spatial repellent pyrethroids for integrated pest management are lacking. To investigate the stability and utility of volatile pyrethroids in mosquito management, metofluthrin was formulated into a vegetation spray intended for use on foliage and mosquito harborage. A comparative field evaluation was conducted between Onslaught Fast Cap, the experimental metofluthrin formulation, and a blended treatment of Onslaught Fast Cap and metofluthrin. Environmental fate of the metofluthrin formulation was estimated using aging bioassays to stress the formulated product, while leaf samples were taken from the treated field sites to bioassay against Aedes albopictus (Skuse) and determine a comparative rate of decay. The combined data from the aging bioassays and leaf samples allow inference that the experimental formulation lasts 2-3 wk in most lighting and humidity conditions at ~26.6 ± 1°C. However, regular rainfall jeopardizes continued efficacy. In comparative field efficacy, adult mosquito reductions were comparable between the two products. Onslaught Fast Cap reduced eggs collected in the immediate vicinity by 80-90% but had no effect in adjacent areas. Metofluthrin treatments resulted in a 50-90% reduction of eggs collected for 4 wk up to 60 m away from treated vegetation. However, the blended treatment using metofluthrin as an additive to Onslaught Fast Cap provided ≥80% control of Ae. albopictus adults and eggs, proximal and adjacent to treated areas, for the study duration. Metofluthrin has a great potential as a supporting ingredient to other insecticides.

Olfactometric Comparison of the Volatile Insecticide, Metofluthrin, Through Behavioral Responses of Aedes albopictus (Diptera: Culicidae)

Testing behavioral response to insecticidal volatiles requires modifications to the existing designs of olfactometers. To create a testing apparatus in which there is no chemical memory to confound tests, we detail the technical aspects of a new tool with design influences from other olfactometry tools. In addition, this new tool was used to evaluate a novel formulation of metofluthrin for use as an outdoor residual treatment. After sourcing materials to prioritize glass and metal construction, a modular wind tunnel was developed that hybridizes wind tunnel and olfactometer specifications. Volatile contaminants were removed by strong ultraviolet light within the chamber before and between trials. Repellent trials were conducted with an experimental formulation of metofluthrin and a commercial formulation of esfenvalerate, prallethrin, and piperonyl butoxide (Onslaught Fast Cap) against Aedes albopictus (Skuse). Toxicant vapors were delivered with attractants from a lure with behavioral responses scored 20 min post-exposure. Upwind attraction to the attractant lure and the Onslaught Fast Cap plus lure resulted in 90 and 75% capture, respectively. In contrast, metofluthrin vapors resulted in less than 10% attraction, while also causing repellency, disorientation, knockdown, and mortality effects. Our findings demonstrated that an inert modular wind tunnel was functional for mitigating toxic secondary exposures of spatial repellents amidst complex behavioral analysis in mosquitoes. The resulting observations with formulated metofluthrin positively reinforce the merit of transitioning metofluthrin into expanded roles in mosquito management.

Gone in 60 seconds: Sub-lethal Effects of Metofluthrin Vapors on Behavior and Fitness of Resistant and Field Strains of Aedes aegypti (Diptera: Culicidae)

Spatial repellents can reduce fecundity and interrupt oviposition behavior in Aedes aegypti. Yet, it is unclear if short exposure times, resistant phenotypes, and other aspects of spatial repellents can impact these effects on mosquito reproduction. To address these issues, pyrethroid susceptible, pyrethroid resistant, and field strains of Ae. aegypti were used to evaluate the extent to which fecundity and oviposition behavior are affected following metofluthrin exposure. Mosquitoes were exposed for 60 s to a sub-lethal dose (LC30) of metofluthrin before blood feeding and allowed 72 h to become gravid before evaluation in an oviposition bioassay for an additional 72 h. Metofluthrin-exposed susceptible, field, and to a lesser extent resistant strain Ae. aegypti showed oviposition across fewer containers, less egg yield, less egg viability, and reduced larval survivorship in hatched eggs compared to unexposed cohorts. Susceptible mosquitoes retained some eggs at dissection following bioassays, and in one case, melanized eggs retained in the female. Treated resistant and field strain F1 larvae hatched significantly earlier than unexposed cohorts and resulted in increased larval mortality in the first 3 d after oviposition. Upon laying, the treated field strain had incompletely melanized eggs mixed in with viable eggs. The treated field strain also had the lowest survivorship of larvae reared from bioassay eggs. These results indicate that metofluthrin could succeed in reducing mosquito populations via multiple mechanisms besides acute lethality. With the available safety data, pre-existing spatial repellent registration, and possibilities for other outdoor delivery methods, metofluthrin is a strong candidate for transition into broader mosquito abatement operations.

Vapor delivery of plant essential oils alters pyrethroid efficacy and detoxification enzyme activity in mosquitoes

The use of synthetic insecticides to limit the spread of mosquito-borne disease faces a number of significant challenges, including insecticide resistance, concerns related to the environmental impact of widespread insecticide use, as well as slowed development of new insecticide chemistries. One important alternative to broadcast insecticides is the use of personal protection strategies to limit contact with vector species, including the use of spatial repellents that can employ synthetic pyrethroids or botanical products to effect control. A currently underexplored area of research involves the investigation of botanical products for their potential to serve as insecticide synergists when delivered as a vapor. This study describes the development of an assay that facilitates the screening of essential oils delivered as a vapor for enhancement of deltamethrin efficacy in both pyrethroid-susceptible and -resistant strains of the vector mosquito species Aedes aegypti. Deltamethrin efficacy was significantly increased following exposure to cinnamon (Cinnamomum cassia), tagetes (Tagetes bipinnata), and sage (Salvia officinalis) oils, while efficacy was significantly decreased following exposure to amyris (Amyris balsamifera) oil. These effects appeared to be mediated by changes in cytochrome P450 activity. This work demonstrates that some plant-derived essential oils delivered as a vapor are capable of increasing the efficacy of deltamethrin similar to classical synergists such as piperonyl butoxide, supporting the use of a real world delivery method instead of traditional contact exposure studies.

Sublethal effects of a vapour-active pyrethroid, transfluthrin, on Aedes aegypti and Ae. albopictus (Diptera: Culicidae) fecundity and oviposition behaviour

BACKGROUND

It is assumed that mosquitoes surviving exposure to spatial repellents when attempting to bite a host will not have significant adverse impacts on their downstream biology. Therefore, a critical knowledge gap is understanding the extent to which sublethal exposure to volatile pyrethroids may damage the performance of mosquitoes that survive exposure to vapour-active pyrethroids. To address this, laboratory-reared Aedes aegypti (L.) and Ae. albopictus (Skuse) were exposed to one of three sublethal concentrations of transfluthrin before being offered a blood-meal, after which their survival, fecundity, fertility, and egg-laying behaviour was assessed.

RESULTS

Both species expressed reduced skip-oviposition behaviour at all exposures. Both species also suffered a major reduction in viable eggs (50-75% reduction in viable eggs laid). A phenotype where eggs collapsed after laying was observed in Ae. aegypti, and this response increased with exposure concentrations. Dissected females of both species retained 50% or fewer of their eggs, with Ae. albopictus retaining a significant proportion of melanised oocytes following the highest exposure.

CONCLUSIONS

Our findings suggest that volatile pyrethroids can reduce skip-oviposition, which may improve source reduction outcomes during integrated management. The additional fecundity reduction caused by sublethal exposures to volatile pyrethroids improves our confidence in recommending them for urban vector management. Furthermore, we suggest that volatile pyrethroids should be adapted into delivery methods compatible with mosquito abatement programs.

Relative Insecticidal Efficacy of Three Spatial Repellent Integrated Light Sources Against Aedes aegypti

Three repellent products, OFF! Mosquito Lamp, Insecticandel, and Rescue DecoShield, were comparatively evaluated against Aedes aegypti in 130-m² enclosed areas with a 317-m³ air volume. The results showed that the OFF! Mosquito Lamp with metofluthrin had a greater effect than the Insecticandel with transfluthrin, which had greater effect than the DecoShield with lemongrass oil and several other plant oils against Ae. aegypti. The OFF! Mosquito Lamp was the only product to exceed 50% mortality. An outdoor semi-field evaluation was conducted to determine the effect by distance of the product. Mosquitoes were stationed in cages at 3, 6, 9, 12, and 15 m away from the treatment in a downwind linear array and exposed for 10 min. They were recorded for knockdown after treatment and at 24 h for mortality. The OFF! Mosquito Lamp produced 100% mortality indoors and >80% knockdown and 90% mortality within 6 m while outdoors against Ae. aegypti.

Effects of sublethal exposure to metofluthrin on the fitness of Aedes aegypti in a domestic setting in Cairns, Queensland

Background

Metofluthrin is highly effective at reducing biting activity in Aedes aegypti. Its efficacy lies in the rapid onset of confusion, knockdown, and subsequent kill of a mosquito. In the field, there are a variety of scenarios that might result in sublethal exposure to metofluthrin, including mosquitoes that are active at the margins of the chemical’s lethal range, brief exposure as mosquitoes fly in and out of treated spaces or decreasing efficacy of the emanators with time. Sublethal effects are key elements of insecticide exposure and selection.

Methods

The metofluthrin dose for each treatment group of male and female Ae. aegypti was controlled using exposure time intervals to a 10% active ingredient (AI) metofluthrin emanator. Room size and distance from the emanator for all groups was maintained at 3 m. In bioassay cages, male Ae. aegypti were exposed at 0, 5, 10, 20, 30 and 40-min intervals. Females were exposed in bioassay cages at 0, 10, 20, 30, 40 and 60-min intervals. Mortality rates and fecundity were observed between the exposure time groups for both sexes.

Results

Female Ae. aegypti exposed for 60 min had a significantly higher mortality rate (50%), after a 24-h recovery period, than other exposure times, 10, 20, 30 and 40 min (P < 0.001). An overall difference in fecundity was not observed in females between treatments. A significant effect on male mortality was only observed at 40 min exposure times, three meters from the 10% AI emanator \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left(\overset{-}{X}=98\%,\kern0.5em P<0.001\right) $$\end{document}(X−=98%,P<0.001). Males that survived metofluthrin exposure were as likely to produce viable eggs with an unexposed female as males that had not been exposed (P > 0.05).

Conclusion

Regardless of sex, if a mosquito survived exposure, it would be as biologically successful as its unexposed counterpart. Portability of the metofluthrin emanator and delayed knockdown effects create opportunities for sublethal exposure and potential pyrethroid resistance development in Ae. aegypti, and should be taken into consideration in recommendations for field application of this product, including minimum exposure periods and a prescribed number of emanators per room based on volume.

Reducing biting rates of Aedes aegypti with metofluthrin: investigations in time and space

Background

Indoor residual spraying is key to dengue control in Cairns and other parts of northern Queensland, Australia, where Aedes aegypti is prevalent, but the strategy faces challenges with regards to slow application time and, therefore, community coverage. A faster potential improvement might be the use of polyethylene netting impregnated with the volatile pyrethroid metofluthrin (SumiOne™). This formulation was assessed in rooms in three houses in Cairns, Australia. One emanator was placed in each room and cages of 10 female Aedes aegypti were exposed at distances of 1 and 3 m. Knockdown and landings on a human hand were counted before metofluthrin exposure and at 10, 30, 60, 90 and 120 min during exposure. In addition, two trials continued over 48 h of exposure to assess the long-term sublethal effects of metofluthrin on caged mosquitoes.

Results

Percentage landing rates fell to 0–2.5% in the first 10 min of exposure. Knockdown was most evident between 10 and 30 min (54% at 1 m and 33% at 3 m). Distance from the emanator strongly affected the results: mosquitoes at 3 m exhibited less knockdown and more landings than those at 1 m. As room volume increased, knockdown decreased and the number of landing increased. There is a cumulative mortality and landing inhibition and, for mosquitoes exposed to metofluthrin for > 48 h, mortality was 100% at 1 m and 90% at 3 m. Of those still alive, a small number continued to land and bite. After being removed from metofluthrin-treated rooms, exposed insect cages were found to reducing landing rates for up to 2 h.

Conclusions

Despite only moderate levels of knockdown during the initial hours of exposure, metofluthrin emanators were effective in reducing mosquito landing rates, especially within 1 m, even when exposed on an open veranda. The evaluation methods and results described in this paper will help inform the optimal conditions of deployment of metofluthrin emanators. These devices have the potential to reduce contact between humans and urban disease vectors faster than indoor residual spraying so supplement our current arsenal of dengue control tools.

Collective behavior quantification on human odor effects against female Aedes aegypti mosquitoes-Open source development

Classifying and quantifying mosquito activity includes a plethora of categories, ranging from measuring flight speeds, repellency, feeding rates, and specific behaviors such as home entry, swooping and resting, among others. Entomologists have been progressing more toward using machine vision for efficiency for this endeavor. Digital methods have been used to study the behavior of insects in labs, for instance via three-dimensional tracking with specialized cameras to observe the reaction of mosquitoes towards human odor, heat and CO₂, although virtually none was reported for several important fields, such as repellency studies which have a significant need for a proper response quantification. However, tracking mosquitoes individually is a challenge and only limited number of specimens can be studied. Although tracking large numbers of individual insects is hailed as one of the characteristics of an ideal automated image-based tracking system especially in 3D, it also is a costly method, often requiring specialized hardware and limited access to the algorithms used for mapping the specimens. The method proposed contributes towards (a) unlimited open source use, (b) a low-cost setup, (c) complete guide for any entomologist to adapt in terms of hardware and software, (d) simple to use, and (e) a lightweight data output for collective behavior analysis of mosquitoes. The setup is demonstrated by testing a simple response of mosquitoes in the presence of human odor versus control, one session with continuous human presence as a stimuli and the other with periodic presence. A group of female Aedes aegypti (Linnaeus) mosquitoes are released into a white-background chamber with a transparent acrylic panel on one side. The video feed of the mosquitoes are processed using filtered contours in a threshold-adjustable video. The mosquitoes in the chamber are mapped on the raster where the coordinates of each mosquito are recorded with the corresponding timestamp. The average distance of the blobs within the frames against time forms a spectra where behavioral patterns can be observed directly, whether any collective effect is observed. With this method, 3D tracking will not be required and a more straightforward data output can be obtained.

ThermaCELL and OFF! Clip-On Devices Tested for Repellency and Mortality Against Amblyomma americanum (Acari: Ixodida: Amblyommidae)

The ThermaCELL with allethrin and OFF! Clip-on with metofluthrin were tested in a 939 m² vented enclosure against nymphal lone star ticks, Amblyomma americanum (L.). Repellency assays were conducted at varying distances relative to product specifications for repellency range. Nymphal ticks acclimated for 24 h in chambers attached to 10 repellency tracks per repetition. Devices were turned on, and the tick travel distance and delay until beginning to travel were recorded. Mortality of ticks was recorded after 24 h. Mortality assays were also conducted at the same distances with five ticks per cage, and 12 cages per distance radially distributed around a device. Cages were removed after 5 min, 15 min, 30 min, and 60 min of exposure and checked after 24 h for mortality. Significant travel distance was found when exposed to the ThermaCELL and OFF! Clip-on at their shortest test distances. Significant mortality also resulted at the same distances. Ticks exposed to active devices for longer than 15 min had significant mortality at the shortest distance for OFF! Clip-on and multiple distances for the ThermaCELL. Overall, the spatial repellent devices ThermaCELL with allethrin and OFF! Clip-on with metofluthrin both demonstrated desirable effects when tested against A. americanum nymphs.