Natural insensitivity and the effects of concentration on the repellency and survival of American dog ticks (Dermacentor variabilis) by DEET

Repellent Activity of DEET and Biont-Based Mosquito Repellents in the Chinese Market Against the Asian Long-Horned Tick, Haemaphysalis longicornis

To investigate the repellent efficacy of commercially available mosquito repellents in China against Haemaphysalis longicornis, four representative DEET-based repellents and biont-derived repellents were selected. This study utilized a modified circular filter paper method repellent testing device to establish an evaluation system for assessing the repellent effects of each product against three developmental stages of H. longicornis: larvae, nymphs, and adults. In our study, for DEET-based repellents, Johnson demonstrated the highest repellency against larvae within 1 h, with an average repellency rate exceeding 80.14%. Yamei and Johnson exhibited repellency rates more than 91.11% for nymphs within 1 h, surpassing the other two DEET products. Repellency rates of Longliqi and Xiaohuanxiong fluctuated between 80.95% and 100% at different time points. Yamei, Longliqi, and Johnson achieved 100% repellency to adults within 1 h, while Xiaohuanxiong showed slightly lower efficacy. The four biont-derived repellents showed significant variations in efficacy: larval-stage repellency ranged from 14.29% to 88.89%, nymphal-stage repellency from 57.89% to 100%, and adult-stage repellency from 50% to 79.49%. CaliforniaBaby exhibited the highest efficacy, comparable or superior to DEET-based products, whereas Longhu demonstrated the weakest repellency and poor persistence. We further conducted a persistence test for CaliforniaBaby and found that it maintained >75% repellency against H. longicornis for 6 h. This study provides scientific evidence for selecting tick repellents in practice, offers guidance for purchasing commercial biont-derived tick repellents, and serves as a reference for developing safer, more effective tick repellents.

HL-TRP channel is required for various repellents for the parthenogenetic Haemaphysalis longicornis

BACKGROUND

Ticks can transmit a wide range of pathogens that endanger human and animal health. Although repellents are commonly used for tick control, understanding their mechanisms aren't  complete.

METHODS

The repellent effects of N, N-diethyl-meta-toluamide (DEET); sec-butyl 2-(2-hydroxyethyl) piperidine-1-carboxylate (icaridin); N, N-diethyl-3-methylbenzamide (IR3535); and cinnamaldehyde on the parthenogenetic tick Haemaphysalis longicornis at the nymph stage were assessed using Y-tubes. The involvement of transient receptor potential (HL-TRP) channel molecules in the repellent mechanism was investigated through in situ hybridization, subcellular localization, real-time fluorescence quantitative polymerase chain reaction (PCR), RNA interference, and electroantennography. In addition, the binding affinity of HL-TRP molecules to repellents was predicted using AlphaFold3.

RESULTS

DEET, icaridin, IR3535, and cinnamaldehyde have been shown to effectively repel nymphs. HL-TRP channel is shared among various arthropods, particularly several species of ticks. It is localized to the cell membrane and Haller's organ. Moreover, microinjection of double-stranded RNA elicited tick repellency behavior, and the electroantennogram responses to those repellents were significantly decreased. The TYR783 site was proposed as an essential binding site to establish hydrogen bonds with icaridin, DEET, and cinnamaldehyde.

CONCLUSIONS

This exploration of ticks and repellents found that HL-TRP channel functions as a chemosensory receptor for repellents and, thereby, mediates avoidance behavior.

Exploiting a natural instance of vertebrate-posed chemical aposematism for tick bite prevention: Repellency of Ixodes scapularis with (E)-Oct-2-enal

Ticks are medically important, nuisance arthropods found worldwide. Applications of semiochemical-based tick repellents for personal protection and reproductive/reservoir host-targeted tick interventions are understudied. We evaluated the repellency of a semiochemical allomone of donkey sebum, (E)-oct-2-enal, against adult Ixodes scapularis ticks - the most frequent human-biting tick in the United States. Ticks were exposed to 20% solutions of (E)-oct-2-enal or DEET. A filter paper bioassay was applied under laboratory conditions. Behaviour was observed for 10-min and captured with a tracking software. Changes in velocity and peregrination were assessed relative to negative (ethanol) control groups using multivariable robust regression models. Repellent longevity was defined by preventing ticks from crossing the treated surface and was evaluated as time-to-event data with a Cox proportional hazard regression model. Significant reductions in velocity, increases in peregrination, and strong longevity were observed for both repellents. Overall assessment of repellency indexes with a Principal Component Analysis showed that DEET and (E)-oct-2-enal were more effective against male ticks than female ticks. There was no difference in effect on females for each repellent. However, the repellency index for male ticks exposed to (E)-oct-2-enal was significantly greater than DEET. This represents the first report, to our knowledge, of the repellency of a natural, vertebrate-emitted semiochemical against I. scapularis ticks. Work is needed to understand the underlying mechanism of action of semiochemical repellents. The development of (E)-oct-2-enal formulations for practical use in personal protection or reproductive/reservoir host-targeted tick control products warrants further consideration.

A scoping review of applied tick control research in North America: funding, implementation, and advancement

Geographic ranges of ticks and tick-borne pathogens within North America are shifting due to environmental changes and human-driven activities, with species of public health concern presenting a multifaceted risk to human health. Innovative strategies and continued collaboration to control tick populations are needed to combat this growing threat. We conducted a scoping review of the literature to describe the nature of applied tick control research conducted in North America (Canada, Mexico, and the United States) to date, with the goal of describing key concepts and identifying gaps in this research area. A total of 244 articles met our inclusion criteria and were reviewed for patterns in applied tick control authorship and funding, study location, target species, and control methodology. Most studies (83.6%) were conducted exclusively in the United States and 75% focused on ticks of public health concern, principally Amblyomma americanum (Linnaeus, Acari: Ixodidae), Dermacentor variabilis (Say, Acari: Ixodidae), Ixodes scapularis Say (Acari: Ixodidae), and Rhipicephalus sanguineus (Latreille, Acari: Ixodidae). The majority of funding was provided through US federal agencies, predominantly the Centers for Disease Control and Prevention and the United States Department of Agriculture. Ixodes scapularis was the target of over 50% of identified articles, with the majority of research conducted within 3 states in the Northeast region of the U.S. Only 8.2% of included studies evaluated integrated tick management interventions. We note gaps in tick control research regarding (i) non-Ixodes medically relevant tick species, (ii) endemic range coverage, and (iii) control methodologies evaluated.

Lemongrass essential oil and DEET inhibit attractant detection in infected and non-infected Ixodes scapularis ticks

Blacklegged tick, Ixodes scapularis Say (Arachnida: Ixodidae), is a growing health concern for humans as vectors the causative agent of Lyme disease, Borrelia burgdorferi, and many other pathogens. Given the potential health threat I. scapularis entails, and the need to find effective strategies to prevent tick bites, it is pivotal to understand the chemosensory system of ticks and their host-seeking behaviour when exposed to repellents. In this study, we investigated whether the exposure to synthetic and plant-derived repellents impairs the ability of I. scapularis to detect attractants and host volatiles (butyric acid), and ultimately how these repellents interfere with host-seeking behaviour in both wild and lab-reared ticks. Furthermore, we screened wild ticks used in electrophysiology and Y-tube behavioural assays for presence of pathogens (Borrelia, Anaplasma, and Babesia) to evaluate if the bacterial infection status would affect the detection of butyric acid under the exposure to repellents. We determined that the exposure to DEET, lemongrass essential oil, citral, and geraniol significantly inhibited the ability of both lab-reared and wild adult female I. scapularis to detect and respond to butyric acid. We found that tick infection status does not significantly impact host-seeking behaviour in adult female I. scapularis. The knowledge gained from our study contributes to advance our understanding of host-seeking behaviour in ticks and the impact that the exposure to repellent has on the tick chemosensory system. These findings will be important for elucidating the mechanism of repellence in ticks and for the development of effective tick repellent management tools.

Repellent and acaricidal activities of basil (Ocimum basilicum) essential oils and rock dust against Ixodes scapularis and Dermacentor variabilis ticks

Repellent and acaricidal activity of essential oils extracted from three varieties of basil (Ocimum basilicum L.) were evaluated on blacklegged ticks (Ixodes scapularis Say) and American dog ticks (Dermacentor variabilis Say) in laboratory conditions. Essential oils were extracted and characterized through gas chromatography-mass spectrometry, and tested at different concentrations for long-term repellent activity using horizontal bioassays. In addition, basil essential oils were combined with an inert material (i.e., granite rock dust) with known insecticidal and miticidal properties to assess acaricidal activities against adult ticks. Among the tested basil varieties, var. Jolina essential oil at 15% vol/vol concentration repelled 96% of tested ticks up to 2 h post-treatment. The EC₅₀ for I. scapularis nymphs was 4.65% vol/vol (95% confidence interval: 4.73-4.57). In acaricidal tests, the combination of essential oil from var. Aroma 2 at 10% wt/wt with rock dust resulted in 100% tick mortality after only 24 h post-exposure, with a LD₅₀ of 3.48% wt/wt (95% CI 4.05-2.91) for freshly prepared treatment tested on I. scapularis adults. The most common compounds detected in basil essential oils by GC-MS were linalool (52.2% in var. Nu Far, 48.2% in Aroma 2, 43.9% in Jolina), sabinene (6.71% in Nu Far, 8.99% in Aroma 2, 8.11% in Jolina), eugenol (11.2% in Jolina, 8.71% in Aroma 2), and estragole (18.2% in Nu Far). The use of essential oils alone and in combination with rock dust provides an innovative and environmentally friendly approach for managing ticks and inhibiting vector-borne disease transmission.

Transcriptional profiling of Dermacentor variabilis (Acari: Ixodidae) provides insights into the role of the Haller's organ in spatial DEET recognition

DEET is the most common active ingredient in commercial repellents, providing effective protection against blood-sucking insects and ticks. However, its mode of action is not fully understood, with several theories put forward to explain its repellency effect. Unique to ticks, the Haller's organ recognizes a variety of external stimuli through non-contact mechanisms, yet the extent to which the organ plays a role in tick chemoreception is not fully known. We previously found that DEET inhibited the expression/activity of cytochrome P450s and cholinesterases in Dermacentor variabilis, however, our experimental design could not distinguish between sexes (males/females), method of exposure (volatile/tactile) or the roles of chemosensory tissues (Haller's organ). In this study, we used RNA sequencing to assess changes in transcript expression induced by volatile DEET in D. variabilis males/females with/without intact Haller's organs. Male ticks showed much greater transcriptional responses to DEET than females, which may be at least partially attributed to the sexual dimorphism of the Haller's organ. Female transcript expression profiles were most influenced by condition (i.e., intact/excised Haller's organs) with minimal changes due to repellent exposure. On the other hand, removal of the Haller's organs caused DEET treated male ticks to exhibit similar expression profiles as control (ethanol) ticks with intact Haller's organs. Consequently, the transcript-level responses to spatial DEET exposure appears largely based on males possessing their Haller's organs. The molecular signature of this response included the suppression of a large number of transcripts involved in detoxification, lipid metabolism and immunity. Taken collectively, this study furthers our understanding of the Haller's organ role in volatile DEET recognition.