Repellent effect of sweet basil compounds on Ixodes ricinus ticks

Challenges encountered by natural repellents: Since obtaining until the final product

Vector-borne diseases, particularly the arboviruses dengue, Zika, chikungunya, and yellow fever caused by the Aedes aegypti mosquito, have been driving the use of repellents worldwide. The most representative synthetic repellent, DEET stands out as the market's oldest and most efficient repellent. It is considered a reference standard but presents considerable toxicity, not recommended for children up to 6 months old and pregnant women. For this reason, alternatives have been sought, and natural repellents derived mainly from essential oils have been studied, highlighting the essential oils of lemon (Corymbia citriodora), citronella (Cympobogon sp.), Andiroba (Carapa guianensis). However, the development and commercialization of products containing natural repellents are significantly lower when compared to DEET and other synthetic repellents. In order to understand the reasons, aspects related to safety, mechanism of action, efficacy as well development and complexity of the products were evaluated. It is concluded that, as for safety, there is lacking information in the literature regarding the effects on non-target organisms and robust toxicity data. The mechanism of action is based on theories, with less information on the exact mode of action, molecular targets, and interaction with the olfactory and taste receptors of insects. Despite being a current trend to search for actives from natural sources highly present in essential oils, however they reduced action time because due to rapid evaporation after application to the skin, thus requiring repellent vehicles. The development and complexity related to these products bring challenging aspects, beginning on the plant cultivation and extraction processes to produce essential oils with a more homogeneous chemical composition towards the formulation stabilization processes due to fast evaporation and short action time, with the use of pharmaceutical technology such as encapsulation techniques.

Effectiveness of Herbal Essential Oils as Single and Combined Repellents against Aedes aegypti, Anopheles dirus and Culex quinquefasciatus (Diptera: Culicidae)

Mosquito repellents reduce human-vector contact of vector-borne diseases. We compared the repellent activity of 10 undiluted essential oils (anise, basil, bergamot, coriander, patchouli, peppermint, petitgrain, rosemary, sage and vetiver) against A. aegypti, A. dirus and C. quinquefasciatus using the arm-in-cage method. Petitgrain oil was the most effective against A. aegypti (270 min). Peppermint oil was the most effective against A. dirus (180 min). Interestingly, all single oils had attributes of repellency against C. quinquefasciatus (ranged, 120−360 min). Moreover, we integrated their binary combinations of highly effective essential oils against A. aegypti and A. dirus to potentially increase the protection time. A 1:1 combination of petitgrain/basil, petitgrain/coriander, basil/coriander and basil/sage reduced the median complete-protection time of 150 min for A. aegypti; a combination of sage and patchouli oils prolonged the median complete-protection time of 270 min for A. dirus. Combining essential oils effect protection time from these two mosquito species.

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.

Electrophysiological and behavioral responses of red imported fire ants (Hymenoptera: Formicidae) to an essential balm and its components

BACKGROUND

An over-the-counter medicine product of China known as essential balm effectively repelled red imported fire ants, Solenopsis invicta Buren. However, it was not clear which chemical component(s) accounted for the repellency, and whether they would effectively repel S. invicta in the field.

RESULTS

Five components, eucalyptol, camphor, menthol, methyl salicylate, and eugenol, were identified in essential balm using gas chromatography-mass spectrometry (GC-MS). Each component elicited concentration-dependent electroantennography (EAG) response. Under field conditions, all components showed repellency against foraging ants. Interestingly, foraging ants managed to access the food items placed on a surface smeared with eucalyptol, camphor, menthol, or methyl salicylate by depositing soil particles on the surface and then walking on soil particles. However, they failed to do so when the surface was smeared with eugenol. Repellency of eugenol lasted for > 24 h, which was much longer than that of the other four components of essential balm and is comparable to that of N,N-diethyl-m-toluamide (DEET), the standard for insect repellants.

CONCLUSION

Olfactory response of S. invicta to all five components of the essential balm was confirmed. Each component showed repellency against S. invicta workers in the field. However, only eugenol significantly suppressed both foraging and particle-covering behavior within 24 h. The repellent effect of eugenol lasted much longer than the other four components. Particle-covering behavior has been largely ignored in studying fire ant repellants. Our study demonstrated that it is necessary to consider such behaviors in ant repellent bioassays in the future. © 2020 Society of Chemical Industry.

Three molecules found in rosemary or nutmeg essential oils repel ticks (Dermacentor variabilis) more effectively than DEET in a no-human assay

BACKGROUND

Development of new personal repellents to prevent tick bites is progressing to keep up with the increasing threat of tick-borne diseases in humans. However, the market share of natural, plant-based repellents is still quite small. We tested all of the major (>1%) components found in the essential oils of rosemary (Spanish variety) and nutmeg. These were tested with Dermacentor variabilis ticks, a robust tick capable of vectoring human diseases, in a no-human horizontal Petri dish assay. For comparison, we also tested the active ingredients currently recommended by the CDC and EPA as personal repellents for use against ticks.

RESULTS

Of the 16 oil components tested, three performed significantly better than N,N-diethyl-meta-toluamide (DEET) in our assay. These compounds were myristicin and safrole found in the nutmeg oil, and terpinolene found in nutmeg oil and as a minor (<1%) constituent of rosemary oil. The current market natural product, 2-undecanone, also performed strongly in our assay.

CONCLUSIONS

Our assay focused on comparing active ingredients as potential repellents and found that many natural products can elicit a strong response from ticks. Terpinolene is the most promising active ingredient identified, owing to human health concerns regarding myristicin and safrole. Our results from examining individual terpenoids from two essential oils suggest that there remain unexploited natural compounds that could be further developed for new personal tick repellents. © 2020 Society of Chemical Industry.

An online survey of personal mosquito-repellent strategies

Background

Mosquito repellents can be an effective method for personal protection against mosquito bites that are a nuisance and carry the risk of transmission of mosquito-borne pathogens like plasmodia, dengue virus, chikungunya virus, and Zika virus. A multitude of commercially available products are currently on the market, some of them highly effective while others have low or no efficacy. Many home remedies of unknown efficacy are also widely used.

Methods

We conducted a survey study to determine what kind of mosquito repellents and other mosquito control strategies people use. Our online survey was focused on unconventional methods and was answered by 5,209 participants.

Results

The majority of participants resided in the United States, were female (67%), had higher education (81% had a university degree), and were 18 to 37 years old (50%). The most commonly used repellent was DEET spray (48%), followed closely by citronella candles (43%) and ‘natural’ repellent sprays (36%). We collected a plethora of home remedies and other strategies people use that warrant further research into their effectiveness.

Discussion

Our study lays the foundation for future research in alternative, unconventional methods to repel mosquitoes that may be culturally acceptable and accessible for people.

Mosquito repellents: An insight into the chronological perspectives and novel discoveries

Mosquito being the major medically important arthropod vector; requires utmost attention to reduce the sufferings and economic consequences of those living in the endemic regions. This is only possible by minimising the human-mosquito contact by an absolute preventing measure. However, unfortunately, such absolute measures are yet to be developed despite enormous efforts and huge investments worldwide. In the absence of vaccines for number of mosquito-borne diseases, repellents could be an attractive option for both military personal and civilians to minimise the risk of contacting different mosquito-borne diseases. However, to achieve this golden goal, the detailed knowledge of a particular repellent is must, including its mode of repellency and other relevant informations. Here, in the present article, an effort has been made to convey the best and latest information on repellents in order to enhance the knowledge of scientific community. The review offers an overview on mosquito repellents, the novel discoveries, and areas in need of attention such as novel repellent formulations and their future prospective.

From Chemistry to Behavior. Molecular Structure and Bioactivity of Repellents against Ixodes ricinus Ticks

Tick-borne zoonoses are considered as emerging diseases. Tick repellents represent an effective tool for reducing the risk of tick bite and pathogens transmission. Previous work demonstrated the repellent activity of the phenylpropanoid eugenol against Ixodes ricinus; here we investigate the relationship between molecular structure and repellency in a group of substances related to that compound. We report the biological activity of 18 compounds varying for the presence/number of several moieties, including hydroxyl and methoxy groups and carbon side-chain. Each compound was tested at different doses with a bioassay designed to measure repellency against individual tick nymphs. Both vapor pressure and chemical features of the tested compounds appeared to be related to repellency. In particular, the hydroxyl and methoxy groups as well as the side-chain on the benzene ring seem to play a role. These results are discussed in light of available data on chemical perception in ticks. In the course of the study new repellent compounds were identified; the biological activity of some of them (at least as effective as the “gold standard” repellent DEET) appears to be very promising from a practical point of view.

Bioactivity-guided investigation of geranium essential oils as natural tick repellents

The evaluation of 10 essential oils of geranium, Pelargonium graveolens (Geraniaceae), were all shown to have repellent activity against nymphs of the medically important lone star tick, Amblyomma americanum (L.). The biological tests were carried out using a vertical filter paper bioassay, where ticks must cross an area of the paper treated with repellent to approach host stimuli. One of the essential oil samples that repelled >90% of the ticks at 0.103 mg/cm(2) was selected for further fractionation studies. The sesquiterpene alcohol, (-)-10-epi-γ-eudesmol, was isolated and identified by spectral methods. (-)-10-epi-γ-Eudesmol at 0.103 and 0.052 mg of compound/cm(2) of filter paper repelled 90 and 73.3% of the ticks, respectively. (-)-10-epi-γ-Eudesmol exhibited similar repellency to the reference standard N,N-diethyl-meta-toluamide (DEET) at concentrations of ≥0.052 mg of compound/cm(2) of filter paper, with (-)-10-epi-γ-eudesmol losing much of its repellency at 0.026 mg of compound/cm(2) and DEET at 0.013 mg of compound/cm(2). Isomenthone and linalool did not repel ticks at the concentrations tested. Most repellents are marketed with much higher concentrations of active ingredient than the concentrations of the natural repellents tested herein; therefore, effective compounds, such as (-)-10-epi-γ-eudesmol, found in geranium oil, have the potential for commercial development.

Chemical composition and repellency of essential oils from four medicinal plants against Ixodes ricinus nymphs (Acari: Ixodidae)

In our search for effective tick repellents from plant origin, we investigated the effect of essential oils of four medicinal and culinary plants belonging to the family Lamiaceae on nymphs of the tick Ixodes ricinus (L.). The essential oils of the dry leaves of Rosmarinus officinalis (Rosemary) (L.), Mentha spicata (Spearmint) (L.), Origanum majorana (Majoram) (L.), and Ocimum basilicum (Basil) (L.) were isolated by steam distillation and 15 microg/cm2 concentration of oils was tested against ticks in a laboratory bioassay. The oils of R. officinalis, M. spicata, and O. majorana showed strong repellency against the ticks 100, 93.2, and 84.3%, respectively, whereas O. basilicum only showed 64.5% repellency. When tested in the field, the oils of R. officinalis and M. spicata showed 68.3 and 59.4% repellency at a concentration of 6.5 microg/cm2 on the test cloths. The oils were analyzed by gas chromatography mass spectrometry and the major compounds from the most repellent oils were 1,8-cineole, camphor, linalool, 4-terpineol, borneol, and carvone.

Anointing chemicals and hematophagous arthropods: responses by ticks and mosquitoes to citrus (Rutaceae) peel exudates and monoterpene components

Some birds and mammals roll on or wipe themselves with the fruits or leaves of Citrus spp. or other Rutaceae. These anointing behaviors, as with anointing in general, are thought to function in the topical acquisition of chemicals that deter consumers, including hematophagous arthropods. We measured avoidance and other responses by nymphal lone star ticks (Amblyomma americanum) and adult female yellow fever mosquitoes (Aedes aegypti) to lemon peel exudate and to 24 volatile monoterpenes (racemates and isomers), including hydrocarbons, alcohols, aldehydes, acetates, ketones, and oxides, present in citrus fruits and leaves in order to examine their potential as arthropod deterrents. Ticks allowed to crawl up vertically suspended paper strips onto a chemically treated zone avoided the peel exudate and geraniol, citronellol, citral, carveol, geranyl acetate, α-terpineol, citronellyl acetate, and carvone. Ticks confined in chemically treated paper packets subsequently were impaired in climbing and other behaviors following exposure to the peel exudate and, of the compounds tested, most impaired to carveol. Mosquitoes confined in chambers with chemically treated feeding membranes landed and fed less, and flew more, when exposed to the peel exudate than to controls, and when exposed to aldehydes, oxides, or alcohols versus most hydrocarbons or controls. However, attraction by mosquitoes in an olfactometer was not inhibited by either lemon peel exudate or most of the compounds we tested. Our results support the notion that anointing by vertebrates with citrus-derived chemicals deters ticks. We suggest that some topically applied compounds are converted into more potent arthropod deterrents when oxidized on the integument of anointed animals.