Evaluation of Clove Oil, Icaridin, and Transfluthrin for Spatial Repellent Effects in Three Tests Systems Against the Aedes aegypti (Diptera: Culicidae)

Fatally impaired glucose digestion by propylene glycol in Aedes aegypti (Diptera: Culicidae) and co-formulation with terpenoids for enhancing attractive toxic sugar baits

Propylene glycol (PG) demonstrates greater efficacy than other sugar polyols. However, the attributes it confers for toxicity and possible co-formulation with other ingredients are unknown. To evaluate this, α-glucosidase and glucose oxidase reactions were performed in Aedes aegypti (L.) (Diptera: Culicidae) to categorize if PG behaves similarly to prior studied sugar alcohols. A combination of no-choice and choice assays was used to determine effective ratios of PG and sucrose, competitiveness against a control of 10% sucrose, and whether mosquitoes recovered from PG consumption. The final trials included β-cyclodextrin encapsulated cinnamon leaf oil, clove stem oil, patchouli oil, garlic oil, cedarwood oil, and papaya seed oil formulated with 5% sucrose + 5% PG. PG functioned as a linear competitive inhibitor of α-glucosidase. The efficacy of PG was synergized by co-ingestion with equivalent ratios of sucrose. Unlike the high diuretic response to other sugar alcohols, PG resulted in diminished excretion regardless of being co-formulated with sucrose or terpenoids. PG is not especially competitive against unadulterated sugar meals but is likewise not clearly repellent. Although mosquitoes did not recover from ingestion of the glycol meals, there was no indication that mortality would continue to accumulate once the treatments were removed. Of the terpenoids tested, cinnamon and patchouli caused ~50% or less mortality; garlic, cedarwood, and clove caused 80-90% mortality; and papaya seed caused 100% mortality, exceeding all other test groups and the formulation blank. PG is a useful supporting ingredient in attractive toxic sugar bait formulations with flexibility in formulation.

Hydrophobic solution functions as a multifaceted mosquito repellent by enhancing chemical transfer, altering object tracking, and forming aversive memory

Developing a safe and potent repellent of mosquitoes applicable to human skins is an effective measure against the spread of mosquito-borne diseases. Recently, we have identified that hydrophobic solutions such as low viscosity polydimethylsiloxane (L-PDMS) spread on a human skin prevent mosquitoes from staying on and biting it. This is likely due to the ability of L-PDMS in wetting mosquito legs and exerting a capillary force from which the mosquitoes attempt to escape. Here we show three additional functions of L-PDMS that can contribute to repel Aedes albopictus, by combining physicochemical analysis and behavioral assays in both an arm cage and a virtual flight arena. First, L-PDMS, when mixed with topical repellents and applied on a human skin, enhances the effect of topical repellents in reducing mosquito bites by efficiently transferring them to mosquito legs upon contact. Second, L-PDMS applied to mosquito tarsi compromises visual object tracking during flight, exerting an influence outlasting the contact. Finally, L-PDMS applied to mosquito tarsi acts as an aversive reinforcer in associative learning, making mosquitoes avoid the conditioned odor. These results uncover a multifaceted potential of L-PDMS in altering a sequence of mosquito behaviors from biting a human skin, visual object tracking following takeoff, to the response to an odor linked with L-PDMS.

Behavioral responses of field-collected German cockroaches to pyrethroids and pyrethroid-formulated insecticides

BACKGROUND

Pyrethroids are synthetic insecticides with low mammalian toxicity and broad-spectrum activity across insects. One major challenge with pyrethroids is their perceived repellency. This perception can influence decisions made by pest control operators, especially when insecticides are used to reduce insect entry into or movement within structures. One major indoor pest that has been repeatedly shown to be repelled by some pyrethroids is the German cockroach, Blattella germanica. However, most experiments evaluating pyrethroid repellency in the German cockroach have used end-point assays, which do not provide information on the movement that led to the final position. Therefore, we evaluated the kinetic behavioral response of field-collected German cockroaches to five pyrethroid-based products and their active ingredients (A.I.) in open behavioral arenas using advanced video tracking software. In addition, in an effort to compare our free-moving experiments with end-point assays, we evaluated sheltering behavior using two-choice harborage arrestment assays where German cockroaches were provided a choice between pyrethroid-treated and untreated shelters.

RESULTS

All pyrethroid-formulated products and their respective A.I.'s failed to affect field-collected German cockroach movement behavior in free-moving assays, while positive controls (DEET, corn mint oil) resulted in reduced time spent by German cockroaches in treated areas. However, despite their willingness to move over pyrethroids-treated surfaces, field-collected German cockroaches displayed a reduced propensity to arrest on pyrethroids treated tents.

CONCLUSION

While most pyrethroids/pyrethroid-formulated products affected German cockroach arrestment, pyrethroids and pyrethroid-formulated products failed to change German cockroach movement behavior in free-moving assays. These results indicate the pyrethroids tested act as contact irritants rather than true-spatial repellents on field-collected German cockroaches. This distinction is critical to refining pest management strategies involving pyrethroids. © 2023 Society of Chemical Industry.

Transfluthrin enhances odorant receptor-mediated spatial repellency in Aedes aegypti

Mosquito-borne diseases are an increasing global health challenge and vector-based interventions remain the most important methods for reducing the public health burden of most mosquito-borne diseases. Transfluthrin, a volatile pyrethroid insecticide, is used widely and effectively as an insecticide and as a repellent. In a recent study, we showed that at very low concentrations transfluthrin repels Aedes aegypti mosquitoes in a hand-in-cage assay without detectable stimulation of antennal olfactory responses. Furthermore, activation of sodium channels by transfluthrin enhances repellency by DEET, which has been reported to repel mosquitoes via odorant receptor (Or)-dependent and Or-independent mechanisms. However, whether activation of sodium channels by transfluthrin can serve as a general mechanism for synergizing the activities of other repellents remain unknown. In this study, we found that, in hand-in-cage assay, transfluthrin enhanced repellency by geranyl acetate and (E)-β-farnesene, which activate AaOr31. Such enhancement was not observed in AaOr31-knockout mosquitoes and dampened in a pyrethroid-resistant strain carrying two sodium channel mutations, which reduce the action of transfluthrin on sodium channels. In addition, transfluthrin also enhanced repellency by (-)-borneol, (±)-citronellal, camphor, and eucalyptol, which activate Or-mediated repellency. Our study has uncovered the ability of transfluthrin to enhance the repellency to a variety of mosquito repellents, beyond DEET, and provided experimental support for the emerging paradigm of synergistic interactions between repellency mediated by sodium channel activation and Or activation. These findings have potential implications in the development of more effective mosquito repellent mixtures.

Recent advances in nutritional composition, phytochemistry, bioactive, and potential applications of Syzygium aromaticum L. (Myrtaceae)

Syzygium aromaticum is an aromatic plant native to Indonesia, and introduced to tropical regions worldwide. As an ingredient in perfumes, lotions, and food preservation, it is widely used in the food and cosmetic industries. Also, it is used to treat toothache, ulcers, type 2 diabetes, etc. A variety of nutrients such as amino acids, proteins, fatty acids, and vitamins are found in S. aromaticum. In addition to eugenol, isoeugenol, eugenol acetate, β-caryophyllene and α-humulene are the main chemical constituents. The chemical constituents of S. aromaticum exhibit a wide range of bioactivities, such as antioxidant, antitumor, hypoglycemic, immunomodulatory, analgesic, neuroprotective, anti-obesity, antiulcer, etc. This review aims to comprehend the information on its taxonomy and botany, nutritional composition, chemical composition, bioactivities and their mechanisms, toxicity, and potential applications. This review will be a comprehensive scientific resource for those interested in pursuing further research to explore its value in food.

Characterization in Effective Stimulation on the Magnitude, Gating, Frequency Dependence, and Hysteresis of INa Exerted by Picaridin (or Icaridin), a Known Insect Repellent

Picaridin (icaridin), a member of the piperidine chemical family, is a broad-spectrum arthropod repellent. Its actions have been largely thought to be due to its interaction with odorant receptor proteins. However, to our knowledge, to what extent the presence of picaridin can modify the magnitude, gating, and/or the strength of voltage-dependent hysteresis (Hys_(V)) of plasmalemmal ionic currents, such as, voltage-gated Na⁺ current [I_Na], has not been entirely explored. In GH₃ pituitary tumor cells, we demonstrated that with exposure to picaridin the transient (I_Na(T)) and late (I_Na(L)) components of voltage-gated Na⁺ current (I_Na) were differentially stimulated with effective EC₅₀’s of 32.7 and 2.8 μM, respectively. Upon cell exposure to it, the steady-state current versus voltage relationship I_Na(T) was shifted to more hyperpolarized potentials. Moreover, its presence caused a rightward shift in the midpoint for the steady-state inactivate curve of the current. The cumulative inhibition of I_Na(T) induced during repetitive stimuli became retarded during its exposure. The recovery time course from the I_Na block elicited, following the conditioning pulse stimulation, was satisfactorily fitted by two exponential processes. Moreover, the fast and slow time constants of recovery from the I_Na block by the same conditioning protocol were noticeably increased in the presence of picaridin. However, the fraction in fast or slow component of recovery time course was, respectively, increased or decreased with an increase in picaridin concentrations. The Hys_(V)’s strength of persistent I_Na (I_Na(P)), responding to triangular ramp voltage, was also enhanced during cell exposure to picaridin. The magnitude of resurgent I_Na (I_Na(R)) was raised in its presence. Picaritin-induced increases of I_Na(P) or I_Na(R) intrinsically in GH₃ cells could be attenuated by further addition of ranolazine. The predictions of molecular docking also disclosed that there are possible interactions of the picaridin molecule with the hNa_V1.7 channel. Taken literally, the stimulation of I_Na exerted by the exposure to picaridin is expected to exert impacts on the functional activities residing in electrically excitable cells.

Sodium channel activation underlies transfluthrin repellency in Aedes aegypti

Background

Volatile pyrethroid insecticides, such as transfluthrin, have received increasing attention for their potent repellent activities in recent years for controlling human disease vectors. It has been long understood that pyrethroids kill insects by promoting activation and inhibiting inactivation of voltage-gated sodium channels. However, the mechanism of pyrethroid repellency remains poorly understood and controversial.

Methodology/Principal findings

Here, we show that transfluthrin repels Aedes aegypti in a hand-in-cage assay at nonlethal concentrations as low as 1 ppm. Contrary to a previous report, transfluthrin does not elicit any electroantennogram (EAG) responses, indicating that it does not activate olfactory receptor neurons (ORNs). The 1S-cis isomer of transfluthrin, which does not activate sodium channels, does not elicit repellency. Mutations in the sodium channel gene that reduce the potency of transfluthrin on sodium channels decrease transfluthrin repellency but do not affect repellency by DEET. Furthermore, transfluthrin enhances DEET repellency.

Conclusions/Significance

These results provide a surprising example that sodium channel activation alone is sufficient to potently repel mosquitoes. Our findings of sodium channel activation as the principal mechanism of transfluthrin repellency and potentiation of DEET repellency have broad implications in future development of a new generation of dual-target repellent formulations to more effectively repel a variety of human disease vectors.

Vector-transmitted human diseases, such as dengue fever, represent serious global health burdens. Pyrethroids, including transfluthrin, are widely used as insecticides and repellents due to their low mammalian toxicity and relatively benign environmental impact. Pyrethroids target voltage-gated sodium channels for their insecticidal action. However, the mechanism of pyrethroid repellency remains unclear and controversial. Insect repellency is traditionally thought to be mediated by olfactory receptors. We made two important discoveries in this study, showing that transfluthrin repellency is via activation of sodium channels and transfluthrin enhances DEET repellency. Discovery of sodium channel activation as a major mechanism of pyrethroid repellency has broad significance in insect olfaction study, repellents development, and control of human disease vectors.

Control of red flour beetle (Tribolium castaneum) in feeds and commercial poultry diets via using a blend of clove and lemongrass extracts

The insects' infestation decreases the nutritive value of the stored grains and causes losses in its weight, quality, or economic values. The aim of the present study was to investigate the efficiency of a natural product of clove and lemongrass extracts in controlling of red flour beetle (Tribolium castaneum) in different feedstuffs and commercial poultry diets. Different concentrations of the tested product (5, 10, 20, 50, 100 mg) were mixed with 10 g of different feedstuffs and poultry diets, and incubated at different time points. The percent repellency (PR), toxicity effect, and antifeedant activity of the plant extracts compound were assessed. The PR was detected depending on the choice method. It was found that the PR was dose and time dependent. The highest doses (50 or 100 mg/10 g feed) achieved the highest repellency effect reaching 70% at 24 h post-application (PA). The minimal PR was reported by the lowest dose of 5 mg/10 g feed reaching 50% at 24 h PA. Moreover, the PR was found to decrease by time. The toxicity effect of this natural product on T. castaneum was cumulative, not acute, in which it was recorded after 1 month of application. Besides, this effect needs high doses of the product (at dose 500 or 1000 mg/50 g feed). The used product achieved a clear antifeedant activity against T. castaneum, as the feeding deterrent index (FDI %) for corn grains was 98.5% at 1.0 and 2.0% concentration, whereas for wheat grains there was a significant difference between both concentration (96.0 vs. 74.4%). In addition, the weight loss of control corn and wheat grains was higher than the treated ones, and it was about 3.15% and 2.0% per month for corn and wheat, respectively. In conclusion, the clove and lemongrass extracts had a repellency effect reaching to 70%. Moreover, it had a lethal effect on T. castaneum. In addition, it can reduce the weight loss of the infested feeds and consequently increasing its FDI %. Therefore, the clove and lemongrass extract blend can be used to protect the feedstuffs from the damage by this insect.

A dual-target molecular mechanism of pyrethrum repellency against mosquitoes

Pyrethrum extracts from flower heads of Chrysanthemum spp. have been used worldwide in insecticides and repellents. While the molecular mechanisms of its insecticidal action are known, the molecular basis of pyrethrum repellency remains a mystery. In this study, we find that the principal components of pyrethrum, pyrethrins, and a minor component, (E)-β-farnesene (EBF), each activate a specific type of olfactory receptor neurons in Aedes aegypti mosquitoes. We identify Ae. aegypti odorant receptor 31 (AaOr31) as a cognate Or for EBF and find that Or31-mediated repellency is significantly synergized by pyrethrin-induced activation of voltage-gated sodium channels. Thus, pyrethrum exerts spatial repellency through a novel, dual-target mechanism. Elucidation of this two-target mechanism may have potential implications in the design and development of a new generation of synthetic repellents against major mosquito vectors of infectious diseases.

Repellency of Novel Catnip Oils Against the Bed Bug (Hemiptera: Cimicidae)

The common bed bug, Cimex lectularius L., resurged as an important urban pest in the last 20 yr. Yet, there are no commercial repellent products labeled for bed bugs available in the United States. We evaluated the repellency of two catnip oils from newly developed cultivars, CR3 and CR9, and compared each to 10 and 25% N,N-diethyl-meta-toluamide (DEET). CR3 contains 63.4% E,Z-nepatalactone and 27.5% Z,E-nepatalactone, and CR9 contains 94.9% Z,E-nepatalactone. Arena studies showed that CR3 and CR9 oils were more effective than DEET within a 24-h period. At 10% concentration, both CR3 and CR9 oils exhibited a repellency of over 94% during the first 8 h. At 25% concentration, the repellency of CR3 and CR9 oils increased to 100%, and repellency of DEET was 92% during the first 24 h. Repellency of 25% CR3 and CR9 oils became lower than 25% DEET after being aged for 3 d. After 28-d aging, repellency of 25% CR3, CR9, and DEET reduced to 25, 64, and 92%, respectively. Soiled socks were placed above repellent treated bands to determine if the repellent can protect soiled socks from being infested. The 20% CR3 oil prevented 100% of bed bugs from infesting soiled socks showing that it was more effective than DEET. These results indicate that catnip oils from CR3 and CR9 cultivars are more repellent than DEET over a 24-h period following application, but their longevity is shorter than DEET after 72 h.

Evaluating putative repellent 'push' and attractive 'pull' components for manipulating the odour orientation of host-seeking malaria vectors in the peri-domestic space

Background

Novel malaria vector control approaches aim to combine tools for maximum protection. This study aimed to evaluate novel and re-evaluate existing putative repellent ‘push’ and attractive ‘pull’ components for manipulating the odour orientation of malaria vectors in the peri-domestic space.

Methods

Anopheles arabiensis outdoor human landing catches and trap comparisons were implemented in large semi-field systems to (i) test the efficacy of Citriodiol^® or transfluthrin-treated fabric strips positioned in house eave gaps as push components for preventing bites; (ii) understand the efficacy of MB5-baited Suna-traps in attracting vectors in the presence of a human being; (iii) assess 2-butanone as a CO₂ replacement for trapping; (iv) determine the protection provided by a full push-pull set up. The air concentrations of the chemical constituents of the push–pull set-up were quantified.

Results

Microencapsulated Citriodiol^® eave strips did not provide outdoor protection against host-seeking An. arabiensis. Transfluthrin-treated strips reduced the odds of a mosquito landing on the human volunteer (OR 0.17; 95% CI 0.12–0.23). This impact was lower (OR 0.59; 95% CI 0.52–0.66) during the push-pull experiment, which was associated with low nighttime temperatures likely affecting the transfluthrin vaporisation. The MB5-baited Suna trap supplemented with CO₂ attracted only a third of the released mosquitoes in the absence of a human being; however, with a human volunteer in the same system, the trap caught < 1% of all released mosquitoes. The volunteer consistently attracted over two-thirds of all mosquitoes released. This was the case in the absence (‘pull’ only) and in the presence of a spatial repellent (‘push-pull’), indicating that in its current configuration the tested ‘pull’ does not provide a valuable addition to a spatial repellent. The chemical 2-butanone was ineffective in replacing CO₂. Transfluthrin was detectable in the air space but with a strong linear reduction in concentrations over 5 m from release. The MB5 constituent chemicals were only irregularly detected, potentially suggesting insufficient release and concentration in the air for attraction.

Conclusion

This step-by-step evaluation of the selected ‘push’ and ‘pull’ components led to a better understanding of their ability to affect host-seeking behaviours of the malaria vector An. arabiensis in the peri-domestic space and helps to gauge the impact such tools would have when used in the field for monitoring or control.

Behavioral responses to transfluthrin by Aedes aegypti, Anopheles minimus, Anopheles harrisoni, and Anopheles dirus (Diptera: Culicidae)

Airborne spatial repellency (SR) is characterized and distinguished from other chemical actions including contact locomotor excitation and toxicity. The use of volatile spatial repellents is a potential new intervention class for combatting mosquito-borne pathogen transmission; therefore, continuing investigations on the actions of these chemicals that modify mosquito host‐seeking behavior (i.e., bite prevention) is needed. The objective of this study is to characterize the key behavioral avoidance actions of transfluthrin (TFT) to advance spatial repellent development into practical products. Behavioral avoidance responses were observed for adult laboratory strains of Aedes aegypti, Anopheles minimus and An. dirus, and two field populations of An. harrisoni and Ae. aegypti, respectively. Established TFT sublethal (LC₅₀ and LC₇₅), lethal concentrations (LC₉₉) and discriminating concentrations (DCs) were selected corresponding to each mosquito test species. Spatial repellency and contact excitation (‘irritancy’) responses on adult mosquitoes to TFT were assessed using an excito-repellency assay system. At LC₅₀, TFT exhibited strong avoidance with An. minimus (60.1% escape) and An. dirus (80% escape) laboratory strains, showing between 12 and 16x greater escape response than Ae. aegypti (5% escape). Repellency responses for field collected Ae. aegypti and An. harrisoni were 54.9 and 47.1% escape, respectively. After adjusting the initial contact escape response (a measure of combined irritancy and repellency) to estimate only escape due to contact, the LC₅₀ and LC₉₉ showed moderate escape irritancy with laboratory Ae. aegypti (41.4% escape) and no contact activity against the field population. Adjustment showed only weak contact activity (16.1% escape) in laboratory An. minimus at LC₅₀. Spatial repellency is the predominant mode of action of TFT among colonized and field mosquitoes used in this study. Established baseline (susceptible) dose-response curves assist in optimizing SR products for mosquito control and pathogen transmission prevention.

Transfluthrin Spatial Repellent on US Military Materials Reduces Culex tarsalis Incursion in a Desert Environment

Standard residual pesticides applied to US military materials such as camouflage netting can reduce mosquito biting pressure in the field but may contribute to the evolution of resistance. However, residual applications of a spatial repellent such as transfluthrin could allow mosquitoes the opportunity to escape, only inducing mortality if insects linger, for example after becoming trapped in a treated tent. In this study we investigated the capability of transfluthrin on 2 types of US military material to reduce natural populations of disease vector mosquitoes in a cool-arid desert field environment in southern California. We found that transfluthrin could reduce Culex tarsalis incursion into protected areas by up to 100% upon initial treatment and up to 45% for at least 16 days posttreatment, showing that this compound could be an effective element in the US Department of Defense integrated vector management system appropriate for further study.

Efficacy of Active Ingredients From the EPA 25(B) List in Reducing Attraction of Aedes aegypti (Diptera: Culicidae) to Humans

Mosquitoes of the Aedes genus are vectors for dengue, chikungunya, Zika, and yellow fever viruses. Mosquito repellents are an effective way to prevent mosquito bites and reduce the spread of mosquito-borne diseases. In the early 90s, the U.S. Environmental Protection Agency (EPA) published a list of active ingredients that pose minimum risk to human health that can be used as pesticides or repellents without passing the EPA registration process. The present study examined the efficacy of 21 of the active ingredients listed by the EPA 25 (B) exempt list and five commercially available sprays that only contained active ingredients from the EPA 25(B) list in repelling female Aedes aegypti (L.) females. We performed choice bioassays in a controlled laboratory environment, using a Y-tube olfactometer to determine attraction rates of humans to female Ae. aegypti in the presence of one of the 21 active ingredients and five commercially available repellent sprays. We found that cinnamon oil, peppermint oil, spearmint oil, lemongrass oil, and garlic oil reduced mosquito attraction to human odor. Of the five commercial repellent sprays, only one reduced mosquito attraction for up to 30 min in our assay. The EPA 25 (B) list contains active ingredients that under the conditions of our assay repel Ae. aegypti.

High-throughput screening method for evaluating spatial repellency and vapour toxicity to mosquitoes

Spatial repellents are an essential tool for personal protection against mosquitoes that bite and transmit disease pathogens to humans. Current repellent screening methods, such as olfactometers and alternative choice tests, are complex systems that require a relatively large quantity of compound (mg). The present study validates a high-throughput spatial repellent screening method using a glass tube that has the ends covered with netting, in addition to treated filters and plastic end caps. The apparatus occupies relatively little space, is easy to decontaminate, and requires small amounts of compound (μg). In a horizontal tube orientation, DEET (N,N-diethyl-meta-toluamide), citronella oil and IR3535 had 1 h half repellent concentration (EC₅₀ ) values of 32, 32 and 298 μg/cm² , respectively, against the Orlando strain of Aedes aegypti (L.) (Diptera: Culicidae). Vertical tube orientation increased EC₅₀ values by approximately two-fold, except IR3535, which remained essentially unchanged. Transfluthrin showed concentration-dependent spatial repellency (1 h EC₅₀  = 0.5 μg/cm² ) without any knockdown, although only in vertical tubes. Transfluthrin showed 50% knockdown in 1 h at 0.5 μg/cm² and 50% mortality at 0.15 μg/cm² in horizontal tubes. In conclusion, this high-throughput screening method is useful for assessing vapour toxicity and the spatial repellency of candidate molecules prior to semi-field and field studies.

Model-based analysis of experimental data from interconnected, row-configured huts elucidates multifaceted effects of a volatile chemical on Aedes aegypti mosquitoes

BACKGROUND

Insecticides used against Aedes aegypti and other disease vectors can elicit a multitude of dose-dependent effects on behavioral and bionomic traits. Estimating the potential epidemiological impact of a product requires thorough understanding of these effects and their interplay at different dosages. Volatile spatial repellent (SR) products come with an additional layer of complexity due to the potential for altered movement of affected mosquitoes and diffusion of volatile particles of the product beyond the treated house. Here, we propose a paired experimental design and statistical inference framework for estimating these nuanced effects of volatile SRs.

METHOD

We fitted a continuous-time Markov chain model in a Bayesian framework to data on marked mosquitoes released in interconnected experimental huts conducted in Iquitos, Peru. We estimated the effects of two dosages of transfluthrin on Ae. aegypti behaviors associated with human-vector contact: repellency, exiting and knockdown in the treated space and in connected, adjacent huts. We validated the framework using simulated data.

RESULTS

The odds of a female Ae. aegypti being repelled, and thus prevented from entering a treated hut (H_T), increased at both dosages (low dosage: odds = 1.64, 95% highest density interval (HDI) = 1.30-2.09; high dosage: odds = 1.35, HDI = 1.04-1.67). The relative risk of exiting from the treated hut was reduced (low: RR = 0.70, HDI = 0.62-1.09; high: RR = 0.70, HDI = 0.40-1.06), with this effect carrying over to untreated spaces two huts away from the treated hut (H₂) (low: RR = 0.79, HDI = 0.59-1.01; high: RR = 0.66, HDI = 0.50-0.87). Knockdown rates were increased in both treated and downstream huts, particularly under high dosage (H_T: RR = 8.37, HDI = 2.11-17.35; H₁: RR = 1.39, HDI = 0.52-2.69; H₂: RR = 2.22, HDI = 0.96-3.86).

CONCLUSIONS

Our framework is effective at elucidating multiple effects of volatile chemicals used in SR products, as well as their downstream effects. For the examined formulations of transfluthrin, we found notable dose-dependent effects on repellency, movement and knockdown that carry over to adjacent, untreated spaces.

Effect of the Topical Repellent para-Menthane-3,8-diol on Blood Feeding Behavior and Fecundity of the Dengue Virus Vector Aedes aegypti

Dengue fever is an acute disease caused by the dengue virus and transmitted primarily by the mosquito Aedes aegypti. The current strategy for dengue prevention is vector control including the use of topical repellents to reduce mosquito biting. Although N,N-diethyl-m-methylbenzamide (DEET) is the most common active ingredient in topical repellent products, para-menthane-3,8-diol (PMD) is also used commercially. Studies have indicated PMD reduced biting by 90–95% for up to 6–8 h, similar to the efficacy of DEET, depending on the testing environment. The purpose of this study was to evaluate the behavioral effects of PMD on Ae. aegypti blood feeding and fecundity to explore the potential impact of PMD on downstream mosquito life-history traits. Two experiments were performed. In both experiments, cohorts of female Ae. aegypti (Belize strain) were exposed to 20% PMD or ethanol for 10 min in a closed system and introduced to an artificial membrane feeding system. Following a 30min feed time, mosquitoes of Experiment 1 were killed and weighed as a proxy measure of blood meal, whereas mosquitoes of Experiment 2 were monitored for oviposition, a measure of fecundity. Results showed a statistically significant reduction (p < 0.001) in the percentage of Ae. aegypti that blood-fed when exposed to PMD (38%) compared to those non-exposed (49%). No significant difference in fecundity between test populations was indicated. These findings suggest that exposure of Ae. aegypti to 20% PMD may influence the probability of subsequent blood feeding but of those mosquitoes that do blood feed, egg-lay density is not affected. Further studies are warranted to investigate the full range of effects of PMD exposure on other Ae. aegypti life-history traits such as mating, to continue characterizing the potential effects of PMD to impact overall vector population dynamics.