Plant products and secondary metabolites with acaricide activity against ticks

A systematic literature review of the efficacy of acaricidal plants, plant extracts, and tick assays used against dog-associated ticks

Dogs are an integral part of many households and important companion animals to humans. Their inquisitive and exploratory behaviour leads them to roam natural environments, making them susceptible to tick infestations that can also be transmitted to humans. To control these ticks, various plant extracts have been evaluated for their efficacy as acaricides and/or repellents against various species. This study was aimed at consolidating the data that has been published in terms of the plant species that have shown efficacy against ticks that parasitize dogs, it further evaluated the methods used in preparing these formulations. A keyword-Boolean strategy was created to extract a total of n = 103 articles that were included in the study. The leading countries in terms of the global distribution of acaricidal plant investigation outputs were Brazil at 23 %, India at 17 % and Turkey at 7 %. A total of n = 13 tick species were used in the evaluated studies. The dog tick Rhipicephalus sanguineus was the most widely used for efficacy testing at 43 % frequency. The Lamiaceae plant family had the highest frequency for reported use across the evaluated studies at 18 %, this was followed by the family Asteraceae at 11 %. Adult immersion test, larval packet test and larval immersion test were the most preferred assays for acaricidal efficacy studies. Leaves were the most preferred plant parts utilized for crude plant metabolites extraction (n = 43), while essential oils were the most highly reported extracts (n = 60). Lastly, extracts were primarily subjected to Gas chromatography for analysis of the plant compounds (n = 38). This paper gives the current global status of potential acaricidal plants utilized against ticks parasitizing dogs.

Medicinal plants: bioactive compounds, biological activities, combating multidrug-resistant microorganisms, and human health benefits - a comprehensive review

In recent years, medicinal plants have gained significant attention in modern medicine due to their accessibility, affordability, widespread acceptance, and safety, making herbal remedies highly valued globally. Consequently, ensuring medicinal plants' quality, efficacy, and safety has become a critical concern for developed and developing nations. The emergence of multidrug-resistant microorganisms poses a serious global health threat, particularly in low-income regions, despite significant advancements in antimicrobial drugs and medical research over the past century. The rapid spread of these multidrug-resistant infections is primarily attributed to improper prescriptions, overuse, and unregulated access to antibiotics. Addressing these challenges, the standardization of plant-derived pharmaceuticals could pave the way for a transformative era in healthcare. Preserving and leveraging the historical knowledge of medicinal plants is essential before such valuable information is lost. Recently, there has been growing interest among natural and pharmaceutical scientists in exploring medicinal plants as potential sources of antimicrobial agents. This current review aims to identify the most common pathogens threatening human health, analyze the factors contributing to the rise of drug-resistant microorganisms, and evaluate the widespread use of medicinal plants across various countries as alternative antibiotics, highlighting their unique mechanisms of antimicrobial resistance.

Survival analysis of Rhipicephalus microplus larvae treated with coumarinic derivatives

Rhipicephalus (Boophilus) microplus represents one of the greatest challenges for livestock production in tropical and subtropical regions. Its control has been based on the use of synthetic chemical acaricides, which has led to the development of resistance to active ingredients belonging to the pyrethroid and organophosphate groups. Therefore, the search for new compounds with acaricidal potential is a priority in the control of ticks in cattle. This study evaluated the effect of different concentrations of coumarin derivatives (CD) on the survival of R. (B.) microplus larvae by larval bundle testing. The data obtained were analyzed using the Cox proportional hazard model. A reduction in larval survival was observed with coumarins that had methyl substituents in the R4 or R7 positions, especially C12, while an opposite effect was detected with chloromethyl substituents in R4 or isobutyl in R3. These findings highlight the potential of coumarin derivatives in the development of new strategies for tick control and the management of resistance to conventional acaricides.

Evaluation of phytochemicals and essential oils of Cupressus semprevirens in controlling cattle tick Rhipicephalus annulatus (Acari: Ixodidae)

BACKGROUND

Cupressus sempervirens is one of the conifer plants, that is used as an antimicrobial, antioxidant, anthelminthic, and many other health purposes. Rhipicephalus annulatus is one of the hard tick genera affecting the production and health of domestic animals in Egypt. Extensive use of chemical acaricides in the management of ticks caused acaricide resistance, environmental contamination, residues in meat and milk, and harmful effects on non-target species. For these reasons, there is an urgent need to create efficient, environmentally friendly acaricides. This work aimed to assay the essential oils and establish the phytochemical analysis of C. sempervirens extract, its effects against the semi-engorged females of R. annulatus, and discuss their possible control effects.

RESULTS

Using the spray-dip method by C. sempervirens ethanol, methanol, distal water, and chloroform extracts at different concentrations (10-50%), revealed a decrease in the percentage of mobile female R. annulatius ticks, and increased mortality proportionally with days after treatments (14 days) and/or extract concentrations (10-50%). The ethanol extracts showed their strongest acaricidal effect, where the female mortality percentage reached 100% using all concentrations at the end of the examined period. In addition, the estimated LC50 and LC95 of C. sempervirens ethanolic extract were recorded as the lowest values (12.2% and 17%, respectively) after 14 days of treatment compared with other extract types. The 50% ethanolic extract of C. sempervirens (the most effective one) revealed the presence of bioactive metabolites i.e. flavonoids, tannins, and carbohydrates (TSS). Also, its total antioxidant capacity and potential free-radical activity (DPPH) were estimated. Using GC-MS, the extracted oil revealed the presence of four major compounds i.e., Eicosapentaenoic acid (50.85%), 10,12-Docosadiynedioic acid (27.58%),10-Undecynoic acid (14.28%) and Palmitic acid (5.42%). The efficiency of all phytochemicals and essential oils was discussed in the current study.

CONCLUSION

The phytochemicals and essential oils found in C. sempervirens could enhance our understanding and help in developing potential strategies for controlling ticks in general and for R. annulatus, in particular, using environmentally friendly agents.

Evaluation of acaricidal effect of terpinolene and γ-terpinene on Hyalomma anatolicum and in silico screening of herbs

IMPORTANCE

Terpenoids of a plant origin are a class of alternatives to chemical acaricides for tick control. Despite this, few studies have evaluated the efficacy of terpenoid-containing herbal extracts or individual terpenoids in Hyalomma anatolicum.

OBJECTIVE

This study evaluated the killing efficacy of terpinolene and γ-terpinene against H. anatolicum to identify herbs rich in these compounds as potential candidates for future materials in the control of H. anatolicum.

METHODS

Terpinolene and γ-terpinene were subjected to adult tick immersion experiments to evaluate their killing effect on H. anatolicum, following their identification post-collection. The herbs were screened for the two terpenoids using the HERB database, and the resulting data were categorized and analyzed.

RESULTS

The acaricidal effect of terpinolene and γ-terpinene against H. anatolicum showed a clear dose-response relationship, with effective doses LC₅₀ of 6.60 mg/mL and 4.86 mg/mL, respectively. In silico analysis revealed the presence of terpinolene and γ-terpinene in 52 and 36 herbs, respectively, with 16 herbs containing both compounds. These herbs could be grouped into 35 plant families. In particular, Lamiaceae and Apiaceae emerged as the most represented families, each accounting for 9.23% of the total herbs identified, followed by Zingiberaceae (7.69%) and Asteraceae and Rutaceae (6.15% each).

CONCLUSIONS AND RELEVANCE

Terpinolene and γ-terpinolene have good killing effects against H. anatolicum. Herbs rich in the two terpenoids are promising candidates as plant-derived materials for managing H. anatolicum.

Sustainable management of tick infestations in cattle: a tropical perspective

The increasing challenge of tick infestations in cattle production systems calls for innovative and sustainable solutions. This article explores the diverse ethnoveterinary practices and livestock farming systems prevalent in tropical regions, capitalizing on the characteristic biodiversity, to provide valuable insights and lessons for tick management at a global scale. Additionally, leveraging the genetic diversity of indigenous cattle breeds presents a promising approach for reducing reliance on chemical acaricides and fostering eco-friendly practices. While genomic selection is the cornerstone for addressing the polygenic nature of tick resistance, complementary genomic tools such as marker-assisted selection (MAS) can still play a valuable role. Integrating MAS and genomic tools could facilitate the development of tick-resistant cattle breeds, benefiting both tropical and temperate regions. Addressing challenges such as limited genomic resources, region-specific phenotyping methods, and the need for robust data infrastructure is essential for achieving tick management through genetic selection. Thus, tropical countries can contribute not only to their own livestock agriculture but also to global efforts in sustainable tick management. While some integrated approaches exist, further research is needed to objectively evaluate and optimize the combination of these different management strategies to effectively address tick challenges.

Endemic Yucatan Peninsula Plants with Pesticidal Potential: Herbarium-Based Literature Review

Agricultural pests present a significant challenge to humanity, often managed through synthetic chemicals that, when misused, can cause irreversible harm to both the environment and human health. This study focuses on endemic plants from the Yucatán Peninsula in Mexico, particularly from the state of Campeche, to identify their historical uses and propose an updated list of species with pesticide potential in the region. We systematically reviewed specimens from the Center for Sustainable Development and Wildlife Management (CEDESU) herbarium and local databases. Of the 3084 specimens collected, 2524 (81.84%) were from Campeche. The collection encompasses 106 botanical families, 459 genera, and 747 species. The study identified 201 plant species from 48 taxonomic families that are endemic to the Yucatán Peninsula Biotic Province (YPBP), of which 123 species are exclusive to the Mexican Yucatán Peninsula (MYP), representing 61.19% of the endemic species. Campeche contains 134 species (66.66%), distributed across 96 genera and 43 families. Notably, 46.26% of the species (62 species) belong to the Mexican region, with 8 species (12.90%) exclusive to Campeche. The research revealed that 27.90% of the families and 19.79% of the genera present in the state have been the subject of previous scientific studies regarding their use as pesticides. The most extensively studied families were Euphorbiaceae and Fabaceae. However, there is a notable lack of research on endemic plants from the Yucatán Peninsula, underscoring the need for increased attention to these species. The identified genera and families contain chemical compounds with activity against significant pests, demonstrating substantial potential for the development of natural pesticides.

Assessment of synergistic and antagonistic interactions between volatile compounds thymol, carvacrol, and eugenol diluted in solvents against Rhipicephalus microplus in in vitro tests

The cattle tick Rhipicephalus microplus is prevalent in tropical and subtropical regions, causing substantial economic losses due to its resistance to conventional acaricides. There is an urgent need to identify safe and effective new acaricidal agents. Essential oils and their volatile compounds are promising alternatives. Ensuring the use of optimal solvents or surfactants that do not compromise the acaricidal activity of these compounds during testing is crucial. This study aims to evaluate how compounds thymol, carvacrol and eugenol interact with xylol, methanol, ethanol, acetone, isopropyl alcohol, glycerol, dimethyl sulfoxide, castor oil, propylene glycol, vaseline, and Tween 80® to enhance (or to worse) their acaricidal efficacy against R. microplus. Larval mortality time were compared against one negative control (soybean oil) and two positive controls (commercial pour-on products). The experiments were conducted in 48-well polyethylene plates, with around 100 larvae immersed in 200 μl of each solvent at 100, 50, 25, 12.5, 6.25, 3.125 and 1.56% and diluted in soybean oil or water, according to solubility. Each volatile compound (Thymol, carvacrol and eugenol) was diluted in the tested solvents to assess larval mortality time. Xylol demonstrated the shortest larval mortality time, even at a minimum concentration (p < 0.05). In contrast, liquid vaseline exhibited the longest larval mortality time. When thymol, carvacrol, and eugenol were combined with xylol, they achieved the shortest larval mortality time. Conversely, when diluted in liquid vaseline they exhibited synergistic effects decreasing the mortality time. Tween 80® worsen the efficacy of thymol, carvacrol, and eugenol, resulting in prolonged larval mortality times. These findings emphasize the critical role of solvent selection, indicating the choice of solvent profoundly affects the formulation's effectiveness, directly influencing the activity of the active compounds.

Comparative toxicity of three variant oils and their nanoemulsions on the brown dog tick Rhipicephalus sanguineus

Tick control mainly depends on using chemical acaricides that have led to the emergence of resistant tick populations along with environmental hazards. Natural alternatives including essential oils are now widely used to avoid the undesirable effects of chemicals on human, animals and environment. In this study, three commercial oils (myrrh, patchouli, and cypress) and their nanoemulsions (NEs) were tested against Rhipicephalus sanguineus sensu lato unfed adults. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the nanoemulsions. Four concentrations with three replicates were used in the bioassay of oils and NEs against ticks using an adult immersion test. Furthermore, a toxicity study of the three oils and their NEs using normal fibroblast cells (BJ-1) was performed. TEM revealed particle size ranges from 29 to 211 nm with spherical droplets. The droplet size and polydispersity index were (29.30 nm & 0.367), (211.6 nm & 0.221) and (164.2 nm & 0.237) for myrrh NE, patchouli NE, and cypress NE, respectively. Myrrh and patchouli oils recorded high acaricidal activity followed by cypress oil with LC50 value 5 days after treatment of 9.01, 12.40, and 15.21%, respectively. The acaricidal efficacy of oil was potentiated in the NEs form which was proved by the reduction in LC50 values that were recorded 7 days after treatment 4.17, 8.57, and 5.04%, for myrrh, patchouli, and cypress NE, respectively. As an alternative for lab animals, we applied the cytotoxicity of myrrh, patchouli, and cypress on normal fibroblast cells. The oils showed low cytotoxic activity of 10.6, 21.5, and 23.6% for Myrrh, Patchouli, and Cypress, respectively. The nanoemulsion was revealed to be safe for normal cells up to a concentration of 0.62% (cytotoxicity%= 24.4, 34.4, and 16.3%, respectively), and the moderate cytotoxic effect appeared at around a concentration of 1.25% (cytotoxicity%= 42.2%, 57.0%, and 36.8% respectively). In conclusion, the three oils and their NEs have good acaricidal activity against Rhipicephalus sanguineus unfed adults. Further toxicity studies on mammals are needed to ensure the safe use of these formulations for the control of ticks on infested animals.

Acaricide effect of plants from the Brazilian savanna on a population of Rhipicephalus microplus with phenotypic resistance to cypermethrin and trichlorfon

Rhipicephalus microplus is among the most important ectoparasites for livestock. The use of synthetic acaricides has raised some concerns due to the selection of tick populations that are resistant to acaricides and environmental contamination. Therefore, plant extracts have been used as alternatives for the treatment of animals infested with ticks. In this study, R. microplus populations from seven different dairy farms were collected and assessed for their resistance to the acaricides cypermethrin or trichlorfon. Larvae of the most resistant population were used in assays to evaluate the acaricide effect of leaf extracts from plants of the Brazilian savanna. The most active extracts were also tested against fully engorged females. Among seven tick populations, five and three showed resistance level ≥ III for cypermethrin or trichlorfon, respectively. The most resistant tick population was evaluated in mortality assays with the plants Piptadenia viridiflora, Annona crassiflora, Caryocar brasiliense, Ximenia americana, and Schinopsis brasilienses. The ethanolic extracts of C. brasiliense, X. americana and S. brasilienses showed higher larvicidal effects in comparison to the other extracts and cypermethrin. The ethanolic extract of X. americana showed 60.79 % efficacy against fully engorged females of the acaricide resistant tick strain. The ethanolic extracts of C. brasiliense, X. americana, and S. brasilienses showed peaks in HPLC-DAD, indicating the presence of tannins and flavonoids. Three of the plants showed promising results and should be explored in further studies to develop novel tools to control R. microplus in cattle.

Acaricidal activity of Erigeron acer L. root against Haemaphysalis longicornis and phytochemical profiling by liquid chromatography-tandem mass spectrometry

The present study is focused on evaluating acaricidal activity and chemical compositions of Erigeron acer root, which was identified as a promising candidate among fifteen Mongolian plant extracts tested for acaricidal activity. The acaricidal effect was evaluated against Haemaphysalis longicornis, assessed for toxicity to normal human skin fibroblast, and analyzed for its chemical constituents. The acetone extract of E. acer root showed significant activity against H. longicornis, with a lethal concentration (LC50) of 5.31 mg/mL and low toxicity, evidenced by a cytotoxic concentration (CC50) of 267.00 µg/mL. Using liquid chromatography-tandem mass spectrometry and molecular networking, thirteen natural compounds were identified, including pyrrolidines, alkaloids, fatty acids, and flavonoids, highlighting the efficacy of E. acer root extract as an effective acaricide against H. longicornis and offering insights for developing new tick control solutions.

Acaricidal activity of Egyptian crude plant extracts against Haemaphysalis longicornis ticks

Haemaphysalis longicornis is a common Ixodida tick species found in temperate areas of Asian countries. An anti-tick assay was conducted on adult female H. longicornis ticks. Plant extract solutions were prepared at concentrations of 50, 25, and 10 mg/mL. Tick survival and mortality were assessed by counting the number of dead and live ticks at 24 h, 48 h, 72 h, and 96 h posttreatment. Out of 11 plant extracts screened, Artemisia judaica extract exhibited the highest potency with 100% mortality (5/5) at 48 h when applied at high and moderate concentrations (50 and 25 mg/mL). Similar results were observed at 96 h for the 10 mg/mL group compared to the untreated ticks. Cleome droserifolia extract demonstrated partial activity with 60% (3/5) and 20% (1/5) mortality at 96 h posttreatment at concentrations of 50 and 25 mg/mL, respectively. Forsskaolea tenacissima extract showed a weak effect with 100% tick mortality (5/5) only at the highest treatment concentration after 96 h. To confirm the activity of A. judaica, trial 2 was conducted. A. judaica demonstrated potency within 48 h in high dose and 72 h in moderate dose, with 100% mortality (15/15) at 96 h posttreatment compared to untreated ticks. The median lethal time 50 (LT50) values were 30.37 h for the high and 55.08 h for the moderate doses. Liquid chromatography‒mass spectrometry was performed on the most potent candidate (A. judaica) to identify its phytochemical components. The results revealed the presence of 9 compounds identified through manual annotation and 74 compounds from the Global Natural Products Social library. These compounds included terpenoids, steroids, phenylpropanoids, flavonoid glycosides, flavonoids, and benzenoids. Camphor was identified as the major component via both approaches. These findings suggest the potential use of A. judaica extract in the future development of acaricidal therapeutics.

Efficacy and safety of geranium-oregano-thymol formulations to control of dog tick Rhipicephalus sanguineus sensu lato under laboratory and field conditions

The present study evaluated, in laboratory and field, the efficacy and safety of formulations of Pelargonium graveolens (geranium - G), Origanum majorana (oregano - O) commercial essential oils (EO) and thymol (T) to control of Rhipicephalus sanguineus sensu lato. In the laboratory, three formulas (A: 2% tween 80%, B: powder and C: nanoemulsion) by a mixture of these components (GOT) were prepared and evaluated, and the best one was used to assess its safety and field application against R. sanguineus s. l. on naturally infested dogs. Besides the major compounds of the EO used were identified. The results of the lab study showed that formula A (2.5 g of each G + O + T + 2% tween 80 to complete 100 mL) was significantly more effective than the other two formulas tested and exhibited highly effective adulticidal, larvicidal, and ovicidal activity against R. sanguineus s.l. Significant LC50 and LC90 values of GOT were evaluated (13.4 and 21.5 mg/mL, respectively) for the adulticidal activity, (2.81 and 4.46 mg/mL, respectively) for ovicidal activity and (2.44 and 4.45 mg/mL, respectively) for larvicidal activity. The safety of formula A has been proven by the absence of its cytotoxicity on a cell line of human epidermoid carcinoma. Citronella and carvacrol were the major compounds identified in the commercial essential oils of P. graveolens and O. majorana, respectively. Formula A was used in a field control trial for almost 8 months, during the tick infestation season (April to November, 2022). Fourteen naturally infested dogs were divided into two groups, each with seven dogs. One group received formula A spraying five times during an experiment that continued for 8 months, while the other group received treatment with commercially available malathion acaricide. The animals were sprayed on five occasions throughout the experiment (April, June, July, August, and September). The results showed a substantial percentage of effectiveness after the first application of formula A with a 99.3% reduction in tick count at day 28 post-application (PA). In the case of severe infestation 60 days after the first application of formula A (more than 180 ticks per dog), the second application was done, achieving an efficacy of 54.9% at day 3 PA, so an emergency spray was done at day 5 PA to combat the rest of the tick infestation, achieving efficacy of 99% after 3 days. Consequently, a regular spray (third, fourth, and fifth application) was done every 35 days. This regular spray revealed 100% effectiveness at 14 days PA. Biochemical parameters of treated dogs were evaluated to confirm the safety of formula A. Creatinine, ALT, and albumin of the dogs treated with formula A were within the normal range of dogs, while urea and AST were higher than the normal range. In conclusion, formula A can safely treat R. sanguineus s.l. infestations in dogs with regular application every 5 weeks.

First report of acaricidal efficacy from plumbagin on larvae of Rhipicephalus microplus and Rhipicephalus sanguineus resistant to conventional acaricides

The problem of resistance to acaricides in ticks such as Rhipicephalus microplus and R. sanguineus has motivated the search for control alternatives, such as the use of extracts and secondary metabolites from plants. Plumbagin is a natural product present in plants such as Plumbago zeylanica L., Diospyros kaki, and D. anisandra, of which acaricidal activity has been reported. Therefore, the objective of this study was to evaluate in vitro the acaricidal efficacy of plumbagin on larvae of R. microplus and R. sanguineus resistant to conventional acaricides. Larvae from engorged female ticks, collected from naturally infested dairy cattle and domiciled dogs, in Yucatan, Mexico, were used. The larval packet test and the larval immersion test were performed to detect acaricide susceptibility. Both tick populations were detected as resistant to cypermethrin and amitraz. Then, the modified larval immersion test was used and plumbagin was evaluated at concentrations of 1%, 0.5%, 0.25%, and 0.125% (%w/v), obtaining a mortality of 100% in the four concentrations for both tick species. Subsequently, lower doses of plumbagin were evaluated at concentrations of 0.0625%, 0.03125%, 0.015625% and 0.0078125%, obtaining mortalities of 100 to 36.26% for R. microplus and 100%-5.33% for R. sanguineus. Using Probit analysis, lethal concentrations at 50% (LC50), 99% (LC99) and confidence intervals at 95% (CI95%) were calculated. R. microplus showed a LC50 of 0.011% (CI95%: 0.010-0.011) and LC99 of 0.019% (CI95%: 0.018-0.022). R. sanguineus presented a LC50 of 0.017% (CI95%: 0.015-0.018) and CL99 of 0.031% (CI95%: 0.027-0.036). It was concluded that plumbagin has high acaricidal efficacy against larvae of R. microplus and R. sanguineus resistant to amitraz and cypermethrin. R. microplus larvae were significantly more susceptible to LC50 and LC99 compared to R. sanguineus. This is the first report on the acaricidal efficacy of plumbagin on larvae of R. microplus and R. sanguineus resistant to conventional acaricides.

Essential oils and isolated compounds for tick control: advances beyond the laboratory

BACKGROUND

Tick control is a worldwide challenge due to its resistance to acaricides. Essential oils (EOs) and isolated compounds (EOCs) are potential alternatives for tick control technologies.

METHODS

A review with EOs and EOCs, under field and semi-field conditions, was performed based on Scopus, Web of Science and PubMed databases. Thirty-one studies published between 1991 and 2022 were selected. The search was performed using the following keywords: "essential oil" combined with "tick," "Ixodes," "Argas," "Rhipicephalus," "Amblyomma," "Hyalomma," "Dermacentor," "Haemaphysalis" and "Ornithodoros." The words "essential oil" and "tick" were searched in the singular and plural.

RESULTS

The number of studies increased over the years. Brazil stands out with the largest number (51.6%) of publications. The most studied tick species were Rhipicephalus microplus (48.4%), Ixodes scapularis (19.4%), Amblyomma americanum and R. sanguineus sensu lato (9.7% each). Cattle (70%) and dogs (13%) were the main target animal species. Regarding the application of EOs/EOCs formulations, 74% of the studies were conducted with topical application (spray, pour-on, foam, drop) and 26% with environmental treatment (spray). Efficacy results are difficult to evaluate because of the lack of information on the methodology and standardization. The nanotechnology and combination with synthetic acaricides were reported as an alternative to enhance the efficacy of EOs/EOCs. No adverse reactions were observed in 86.6% of the studies evaluating EOs/EOCs clinical safety. Studies regarding toxicity in non-target species and residues are scarce.

CONCLUSIONS

This article provides a comprehensive review on the use of EOs and EOCs to reduce tick infestations, in both the hosts and the environment. As future directions, we recommend the chemical characterization of EOs, methodology standardization, combination of EOs/EOCs with potential synergists, nanotechnology for new formulations and safety studies for target and non-target organisms, also considering the environmental friendliness.

Acaricidal activity of a 2-methoxy-clovan-9-ol rich fraction from Eugenia copacabanensis (Myrtaceae) extract on Rhipicephalus microplus (Acari: Ixodidae)

Rhipicephalus microplus (Ixodidae, canestrini, 1888) is an invasive ectoparasite of cattle which causes high economic losses in emerging countries such as Brazil. Phytochemical compounds have been tested as an alternative to synthetic acaricides due to potentially lower mammalian toxicity. This study evaluated the acaricidal activity against R. microplus of the 2-methoxy-clovan-9-ol rich fraction obtained from Eugenia copacabanensis Kiaersk.leaves, a little known Myrtaceae species from the Brazilian Atlantic Forest. This fraction was obtained by maceration with methanol, partition with n-hexane and purification by normal-phase column chromatography. GC-MS, 1H and 13C NMR and IR analysis contributed to the identification of a major compound as the sesquiterpene 2-methoxy-clovan-9-ol, reported for the first time for the Myrtaceae family. The fraction was tested against R. microplus unfed larvae and engorged females and a 93% larval mortality was observed at the concentration of 50 mg mL-1. Lower concentrations of the solution tested demonstrated a significant difference in egg mass weight, hatching and control percentage. Experiments with 50.0 mg mL-1 showed significative results, with lower concentration and maximum efficacy for both assays. The IC50 values for unfed larvae and engorged females were 21.76 and 11.13 mg mL-1, respectively. These results were similar to those obtained in other studies with isolated botanical compounds and essential oils. The lower IC50 for engorged females than for unfed R. microplus larvae had also been described for other plant materials, including plants from the same Myrtaceae family. The present result suggested different mechanisms of action of the compound on the reproductive biology of engorged females, improving its effect against egg viability. These results are important for tick control, suggesting that 2-methoxy-clovan-9-ol could be a potential natural acaricidal product against both R. microplus unfed larvae and engorged females.

Efficacy of hydroethanolic extract of Randia aculeata seed against the southern cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) on naturally infested cattle under field conditions

The cattle tick Rhipicephalus (Boophilus) microplus is a major problem of concern for cattle industry in tropical and subtropical areas. Control of cattle tick is based mainly on the use of chemical acaricides, which has contributed to the emerging problem of selection of resistant tick lineages. Plants have been used as an alternative to conventional acaricidal drugs. On the other hand, the acaricidal activity of hydroethanolic extract of Randia aculeata seed (EHRA) has been demonstrated against R. microplus under laboratory conditions. However, the utility of EHRA seed as a potential acaricidal needs to be determined under field conditions. For this reason, the aim of this study was to evaluate the efficacy of the EHRA against R. microplus sprayed on naturally infested calves, determine the effect of the EHRA seed on acetylcholinesterase activity in R. microplus larval and identify the chemical composition of EHRA. Forty-five male calves were divided in three groups and treated with: G1 water; G2 EHRA 20% w/v and G3 coumaphos 0.2% v/v. Acetylcholinesterase (AChE) activity in R. microplus larvae was determined by a colorimetric assay. The chemical composition of EHRA was accessed through HPLC/MS. Significantly fewer ticks were observed after 24 h on the treated group compared to control group. EHRA significantly inhibited in vitro AChE activity in R. microplus at all tested concentrations. Chlorogenic acid, vanillinic acid, p-coumaric acid, caffeic acid. rutin, quercetin, (-)-epicatechin, 4-hydroxybenzoic acid, quercetin, vanillin, 2,4-dimethoxy-6-methylbenzoic acid, scopoletin and ferulic acid were identified in the extract. The results provided new data for the elucidation of the mechanisms of EHRA acaricide action and to further evaluate the use as a new alternative control agent against R. microplus under in vivo conditions.

Natural Products as Mite Control Agents in Animals: A Review

Mites have been a persistent infectious disease affecting both humans and animals since ancient times. In veterinary clinics, the primary approach for treating and managing mite infestations has long been the use of chemical acaricides. However, the widespread use of these chemicals has resulted in significant problems, including drug resistance, drug residues, and environmental pollution, limiting their effectiveness. To address these challenges, researchers have shifted their focus towards natural products that have shown promise both in the laboratory and real-world settings against mite infestations. Natural products have a wide variety of chemical structures and biological activities, including acaricidal properties. This article offers a comprehensive review of the acaricidal capabilities and mechanisms of action of natural products like plant extracts, natural compounds, algae, and microbial metabolites against common animal mites.

Combinations of amitraz with essential oils from Lippia sidoides and Thymus vulgaris, thymol and thymol acetate for Rhipicephalus microplus control: studies under laboratory and field conditions

This study aimed to assess the effect of combining amitraz with essential oils (EOs) from Thymus vulgaris and Lippia sidoides, as well as the monoterpenes thymol and thymol acetate, on Rhipicephalus microplus in laboratory conditions, and to select the most effective combination for testing in field conditions. The chemical analysis showed that EOs were mainly composed of monoterpenes, with thymol and p-cymene as the major compounds. In larval (LIT) and adult (AIT) immersion tests using different concentrations of the oils and terpenes mixed with amitraz, the results showed that both EOs and thymol improved the efficacy of amitraz against larvae and engorged females of R. microplus, whereas thymol acetate only enhanced activity against larvae. The most favorable outcome was obtained with the EO of L. sidoides combined with amitraz, resulting in 99 % and 100 % efficacy against larvae and engorged females, respectively. Furthermore, the combination of amitraz with thymol showed presented an efficacy of 94 % and 91 % against larvae and engorged females, respectively. Thus, for the other tests, the combination of thymol + amitraz was chosen due to the ease of working with pure thymol in bioassays, and easier standardization. The immersion test (thymol + amitraz) with semi-engorged females showed 100 % efficacy for the combination of thymol + amitraz, while in tests with different solvents (thymol + amitraz), ethanol being the most effective solvent among those tested (ethanol, Triton, and Tween), resulting in 95 % efficacy on engorged females. In the field test, in treatments with amitraz and thymol + amitraz, efficacy of 54 % and 74 % was observed on day + 3 and 33 % and 43 % on day + 7, respectively. Assessing the reproductive biology of females recovered from animals treated with amitraz or amitraz + thymol, in day + 7, efficacies of 33 % and 52 %, respectively, were observed. EOs from T. vulgaris and L. sidoides and thymol improved the acaricidal activity of amitraz on larvae and engorged females of R. microplus under laboratory conditions, while thymol acetate only enhanced activity against larvae. Thymol increased the efficacy of amitraz under field conditions, however for the development of a commercially available acaricide to R. microplus control, additional studies are needed to increase the efficacy. Further research is needed (by changing concentrations, adding other compounds and/or developing formulations) to increase acaricidal efficacy and develop new effective products to combat R. microplus infestations in cattle.

Thymol and eugenol against Rhipicephalus sanguineus sensu lato engorged females: Biological, histopathological and bioinformatic analysis

The aim of this study was to evaluate the reproductive biology and histopathology of the ovaries of engorged females of Rhipicephalus sanguineus sensu lato exposed to combinations of thymol and eugenol, as well as to evaluate in silico the possible interactions of thymol and eugenol in tick cell membranes. To evaluate the tick reproductive biology, the adult immersion test (AIT) was performed, in which the engorged females were immersed in solutions of thymol and eugenol, combined or alone, at concentrations of 2.5 and 5.0 mg/mL. Two control groups (water and 3% DMSO) were also performed. The ticks were kept in a controlled chamber (B.O.D - 27 ± 1 °C and 80% ± 5% RH) to evaluate egg production and viability. To perform the ovaries histopathological evaluation, females were immersed in combination of thymol and eugenol (each at 2.5 and 5.0 mg/mL) and control (water and 3% DMSO) solutions. After immersion, the females were kept in B.O.D (27 ± 1 °C and RH of 80% ± 5%) for four days, they were dissected and the ovaries processed for histological analysis. In addition, an in silico analysis was performed using PASS online® software to predict probability activity (PA) of thymol and eugenol in cell membranes. The treatment with the combination of thymol and eugenol (each at 5.0 mg/mL) caused a reduction (p < 0.01) in oviposition, while the treatments with thymol (5.0 mg/mL) and combination of thymol and eugenol (5.0 mg/mL) reduced (p < 0.05) the egg viability. The treatment with combination of thymol and eugenol (5.0 mg/mL) resulted in a control percentage of 99.9%, while in the other treatments, control percentages below 56% were observed. Oocytes from the females exposed to the combinations of thymol and eugenol (each compound at 2.5 mg/mL) showed histopathological changes, except on oocyte V, while those treated with these compounds alone at 2.5 mg/mL, did not reveal any change. Changes in the shape of the oocyte, presence of vacuoles in the cytoplasm and germinal vesicle, reduction and fusion of yolk granules and rupture of some oocytes were observed. In silico analysis, showed that these compounds can act as membrane permeability inhibitors, membrane permeability agonists, membrane integrity antagonists and apoptosis agonists. We conclude that the combination of thymol and eugenol causes changes in the reproductive biology and morphophysiology of engorged females oocytes. The in silico analysis using thymol and eugenol revealed the possibility of disorganization in the cell membranes, a fact that may explain the histopathological alterations observed.

Parasiticides: Weapons for Controlling Microbial Vector-Borne Diseases in Veterinary Medicine; The Potential of Ethnobotanic/Phytoparasiticides: An Asset to One Health

Some ectoparasites are vectors of illness-causing bacteria and viruses, and these are treated with antibiotic and antiviral drugs, which eventually contribute to the excessive use of antimicrobials. Therefore, the control of ectoparasites is crucial, and the challenge will be to manage them in a sustainable way. Data from a preliminary ethnobotanical survey was reanalyzed to obtain information on the use of various plant species in companion animals and livestock as ectoparasiticides. The survey responses were reviewed for traditional use of plants as ectoparasiticides, and cross-sectional bibliographic research was undertaken. The following plants were selected among the nine mentioned plants: Juglans regia, Daphne gnidium and Ruta graveolens, which have the most potential to be developed as veterinary ectoparasiticides. Moreover, the absence of published data for Plantago lanceolata and Cistus populifolius suggests that their traditional use as ectoparasiticides is noted here for the first time. In summary, these plants could give promising plant-derived veterinary ectoparasiticides that, ultimately, will help reduce and even avoid the excessive use of antimicrobials.

Ethanolic Extracts of Datura innoxia Have Promising Acaricidal Activity against Rhipicephalus microplus as It Blocks the Glutathione S-Transferase Activity of the Target Tick

Rhipicephalus microplus is a major bovine ectoparasite that negatively impacts the cattle industry. The acaricidal activity of Datura innoxia ethanolic plant extract against R. microplus, compared with trichlorfon, was examined using the adult immersion test (AIT), and larval packet test (LPT). In vitro acaricidal activity of the selected plant extract against R. microplus engorged females was evaluated at different concentrations (2.5, 5, 10, 20, and 40 mg/mL), and was the same for AIT and LPT. It was further supported by in silico molecular docking of D. innoxia's 21 phytochemicals against the R. microplus Glutathione S-transferases (RmGST) protein's three-dimensional (3D) structure predicted by the trRosetta server. The modeled 3D structure was then evaluated and confirmed with PROCHECK, ERRAT, and Verify3D online servers. To predict the binding mechanisms of these compounds, molecular docking was performed using Auto dock Vina software, and molecular dynamic (MD) simulations were used to investigate the protein atom's dynamic motion. D. innoxia has a relatively higher inhibitory effect on oviposition (from 9.81% to 45.37%) and total larval mortality (42.33% at 24 h and 93.67% at 48 h) at 40 mg/mL. Moreover, the docking results showed that the chemicals norapoatropine and 7-Hydroxyhyoscyamine have strong interactions with active site residues of the target protein, with a docking score of -7.3 and -7.0 Kcal/mol, respectively. The current work also provided a computational basis for the inhibitors of Glutathione S-transferases that were studied in this research work, and this new knowledge should aid in creating new and effective acaricidal chemicals. Furthermore, this plant extract's acaricide activity and its effect on oviposition and larval mortality were established in this work for the first time, indicating the possible use of this extract in the management of ticks.

Combination of synthetic acaricides with (E)-cinnamaldehyde to control Rhipicephalus microplus

This work had the objectives to (1) evaluate the susceptibility of various Rhipicephalus microplus populations to commercial acaricides, and (2) select commercial acaricides (50-80% effective) and evaluate the effects of binary combinations of the phenylpropanoid (E)-cinnamaldehyde with selected commercial acaricides to control R. microplus under laboratory and field conditions. Using adult immersion tests with 116 populations and 14 commercial acaricides, products showing 50-80% effectiveness (percent control) with the lowest number of active ingredients were selected. Acaricides containing amitraz or chlorfenvinphos were tested in combination with (E)-cinnamaldehyde on a field population (strain CM). We found that (E)-cinnamaldehyde enhanced the activity of both commercial acaricides against R. microplus larvae; however, the enhancement was more accentuated when using amitraz. Experiments combining (E)-cinnamaldehyde + amitraz on unfed larvae and engorged females from another population (strain Gyn) were performed, verifying (E)-cinnamaldehyde enhanced the activity of amitraz. In the field experiment, the application of (E)-cinnamaldehyde appeared toxic to the tick hosts (cattle). We concluded that (E)-cinnamaldehyde enhanced the activity of amitraz against unfed larvae and engorged females of R. microplus; however, in the field test this phenylpropanoid caused intoxication in the cattle. Studies searching for new combinations of compounds from essential oils with amitraz deserve attention, as well as studies to develop formulations using amitraz + (E)-cinnamaldehyde that will be efficient and will not have toxic effects in cattle.

Acaricidal activity of carvacrol and thymol on acaricide-resistant Rhipicephalus microplus (Acari: Ixodidae) populations and combination with cypermethrin: Is there cross-resistance and synergism?

This study evaluated the acaricidal activity of thymol and carvacrol on Rhipicephalus microplus populations with different resistance profiles and investigated the synergistic effect of combinations of these monoterpenes with cypermethrin. The adult immersion test (AIT) was used to characterize the susceptibility of tick populations (45 field populations) to synthetic acaricides: deltamethrin, amitraz and chlorfenvinphos. The larval packet test (LPT) was used to determine the LC₅₀ values for thymol (25 tick populations) and carvacrol (20 tick populations). The susceptible strain Porto Alegre (POA) was used as a reference for calculating the resistance ratio (RR). Subsequently, larval immersion tests (LIT) were performed with combinations of cypermethrin with thymol or carvacrol to assess a synergistic effect. In the AIT, deltamethrin showed efficacy > 90% in one (2.2%) population tested (mean: 12.1 and 11.1 for populations 1-25 and 26-40, respectively), whereas amitraz and chlorfenvinphos showed efficacy > 90% for two (4.4%) populations (mean: 61.3 and 47.3 for populations 1-25 and 26-40, respectively) and eight (17.7%) populations (mean: 69.7 and 59.7 for populations 1-25 and 26-40, respectively). In the LPT, the LC₅₀ values for thymol and carvacrol varied from 0.67 to 2.12 mg/mL and 0.55-3.21 mg/mL, with an average LC₅₀ for populations of 1.49 and 1.75 mg/mL, respectively. For thymol, no resistance was observed in any of the populations, values of RR₅₀ > 1.5. There was no correlation between the LC₅₀ values for thymol and the efficacy of the chemical acaricides tested. Regarding carvacrol, for only one tick population had the value of RR₅₀ > 1.5, indicating an incipient resistance. No correlation was observed between the LC₅₀ values for carvacrol and the efficacy of tested acaricides. The combination of thymol and carvacrol with cypermethrin showed a synergistic effect in the resistant population (Jaguar - thymol 4.19 and carvacrol 3.67), and no synergistic interaction were showed in the susceptible population. Answering the questions we conclude that: 1 - The comparison between the LC₅₀ values for thymol and carvacrol in field populations and the susceptible strain POA suggests the absence of cross-resistance (ticks and terpenes), and the differences between the LC₅₀ values for thymol and carvacrol in the different R. microplus populations are inherent to the characteristics of each population tested; 2 - the combination of thymol or carvacrol with cypermethrin showed a synergistic effect with different activity according to the population of ticks.

Balsam fir (Abies balsamea) needles and their essential oil kill overwintering ticks (Ixodes scapularis) at cold temperatures

The blacklegged tick, Ixodes scapularis, vectors Borrelia burgdorferi, a bacterium that causes Lyme Disease. Although synthetic pesticides can reduce tick numbers, there are concerns about their potential effects on beneficial insects, such as pollinators. Plant-based pest control agents such as essential oils could provide an alternative because they have low environmental persistency; however, these products struggle to provide effective control. We found a new natural acaricide, balsam fir (Abies balsamea) needles, that kill overwintering I. scapularis ticks. We extracted the essential oil from the needles, analyzed its chemical composition, and tested it for acaricidal activity. We placed ticks in tubes with substrate and positioned the tubes either in the field or in incubators simulating winter temperatures. We added balsam fir essential oil, or one of the main components of balsam fir essential oil (i.e., ß-pinene), to each tube. We found that both the oil and ß-pinene kill overwintering ticks. Whole balsam fir needles require several weeks to kill overwintering ticks, while the essential oil is lethal within days at low temperatures (≤ 4 °C). Further, low temperatures increased the efficacy of this volatile essential oil. Higher temperatures (i.e., 20 °C) reduce the acaricidal effectiveness of the essential oil by 50% at 0.1% v/v. Low temperatures may promote the effectiveness of other natural control products. Winter is an overlooked season for tick control and should be explored as a possible time for the application of low toxicity products for successful tick management.

Acaricidal, Larvacidal, and Repellent Activity of Elettaria cardamomum Essential Oil against Hyalomma anatolicum Ticks Infesting Saudi Arabian Cattle

Background: In this experimental study, we aimed to assess the acaricidal effects of Elettaria cardamomum L. essential oil (ECEO) against Hyalomma anatolicum tick in cattle from Saudi Arabia. Methods: Gas chromatography-mass spectrometry (GC-MS) was performed to identify the chemical composition of ECEO. The acaricidal, larvicidal, and repellent activity of ECEO against H. anatolicum was studied through the adult immersion test (AIT), the larval packet test (LPT), the vertical movement behavior of tick’s larvae technique, anti-acetylcholinesterase (AChE) activity, and oxidative enzyme activity. Results: By GC/MS, the most compounds were 1,8-cineole (34.3%), α-terpinyl acetate (23.3%), and α-pinene (17.7%), respectively. ECEO significantly (p < 0.001) increased the mortality rate as a dose-dependent response. After ECEO Treatment, number of eggs, egg weight, and hatchability significantly declined as a dose-dependent response. ECEO at concentrations of 5 µL/mL and above completely killed the larva. The LC50 and LC90 values for ECEO were 1.46 and 2.68 µL/mL, respectively. ECEO at concentrations of 10, 20, and 40 µL/mL showed 100% repellency activity up to 60, 120, and 360 min incubation, respectively. ECEO, especially at ½ LC50 and LC50, significantly inhibited GST and AChE activities of H. anatolicum larvae compared to the control group. Conclusions: We found promising adulticidal, larvicidal, and repellent effects of ECEO against H. anatolicum as a vector of theileriosis in Saudi Arabia. We also found that ECEO displayed these activities through inhibiting AChE and GST. Nevertheless, additional investigations are required to confirm the accurate mechanisms and the relevance of ECEO in practical application.

The bioactive compound carvacrol as a potential acaricide: An assessment of its effects on the integument of female Rhipicephalus sanguineus sensu lato ticks

Studies seeking control methods for infestation of Riphicephalus sanguineus sensu lato (s.l.) ticks (dog ticks) have been carried out in order to minimize damage to both the tick's hosts and the environment, the latter due to the misuse of acaricide products. In this regard, carvacrol has been used as a natural alternative against ticks as it displays several properties including acaricidal. In this context, the present study aimed to evaluate the ultramorphology and morphohistochemistry of the integument of semi-engorged R. sanguineus s.l. females exposed to different carvacrol concentrations. The findings indicate that the integument surface of females exposed to the highest carvacrol concentration (25 μl/ml) became wrinkled, suggesting dehydration or the result of integument cuticular and epithelial layer disorganization in response to the toxic product. Morphohistochemical integument layer alterations were more significant and intense in females exposed to the highest carvacrol concentration (25 μl/ml), confirming dose-dependent carvacrol action. Among other cell and tissue alterations, changes in epithelial cell shape, size, and arrangement (epidermal layer) were noted, alongside altered and pyknotic-shaped nuclei, suggesting a death process for these cells. This epithelium changed from simple cubic to stratified, also in response to the presence of the evaluated bioactive compound. Thus, the findings reported herein demonstrate that carvacrol may be an alternative for an efficient and more sustainable tick control in the near future.

Combination of cypermethrin and thymol for control of Rhipicephalus microplus: Efficacy evaluation and description of an action mechanism

The cattle tick Rhipicephalus microplus is one of the most important ectoparasites in the tropical and subtropical regions of the world. Synthetic pyrethroids are widely used to control this tick, and the selection of resistant populations is a huge problem worldwide. The activity of thymol, a natural monoterpene, free or in combination with other compounds, has been demonstrated against different species of ticks. However, the mode of action is not fully understood. The present study aimed to evaluate the efficacy and the potential mode of action of the combination of cypermethrin and thymol on ticks from two populations with different levels of susceptibility to cypermethrin (low and high susceptibility). The isolated acaricidal activity of cypermethrin and thymol on larvae was carried out in different concentrations. The combination with different concentrations of cypermethrin and fixed concentrations of thymol (1300 µg/mL for the low susceptibility population; 690 µg/mL for the high susceptibility population) were performed. Adult engorged females were divided into five experimental groups (n = 20): 1) Control group untreated; 2) Control group: 2.0% (v/v) DMSO; 3) Thymol group: 1300 µg/mL thymol; 4) Cypermethrin group: 3700 µg/mL cypermethrin; 5) Association of cypermethrin (3700 µg/mL) + thymol (1300 µg/mL). A subgroup was used to study the efficacy of the reproductive parameters and another subgroup, with ten adults from each treatment, was used to quantify thymol and cypermethrin by HPLC chromatographic analysis. All compounds tested were effective on larvae from both populations, and the combination with thymol decreased the LC₅₀ of cypermethrin (232.4 to 52.7 µg/mL) on the low-susceptibility population. The combination of thymol and cypermethrin was effective in both populations of R. microplus (reproductive performance of engorged females) when compared to the untreated control group, even with higher percent control values (pop. 1: 93.5 ± 5.6% and pop. 2: 92.7 ± 1.1%) than the group treated only with cypermethrin (pop. 1: 87.3 ± 7.3% and pop. 2: 83.5 ± 1.2%). From the HPLC analyzes, a higher concentration of cypermethrin (pop. 1: 30.3 ± 6.9 and pop. 2: 45.4 ± 17.7 ng/mg) was detected in the tissues of engorged females treated with the combination compared to analyte concentrations in groups treated with cypermethrin only (pop. 1: 12.4 ± 4.4 pop. 2: 25.5 ± 9.4 ng/mg). This was the first study to investigate the acaricidal efficacy of the combination of thymol + cypermethrin on R. microplus and demonstrate that the presence of thymol increases the concentration of cypermethrin in the internal tissues of engorged females through a possible mechanism for increasing the penetration of cypermethrin at the cuticular level.

Acaricidal and Repellent Effects of Essential Oils against Ticks: A Review

Tick control is a priority in order to prevent the transmission of vector-borne diseases. Industrial chemical acaricides and repellents have been the most efficient tools against hard ticks for a long time. However, the appearance of resistances has meant the declining effectiveness of the chemicals available on the market. The trend today is to develop alternative control methods using natural products to replace nonefficient pesticides and to preserve the efficient ones, hoping to delay resistance development. Traditional in vitro evaluation of acaricidal activity or resistance to synthetic pesticides have been reviewed and they mainly focus on just one species, the one host tick (Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)). Recent reports have called for the standardization of natural product components, extraction techniques, and experimental design to fully discover their acaricidal potential. This study reviews the main variables used in the bibliography about the efficiency of natural products against ticks, and it proposes a unification of variables relating to ticks, practical development of bioassays, and estimation of ixodicidal activity.

Acaricidal activity of the essential oils from Leptospermum scoparium, Origanum vulgare and Litsea cubeba on Rhipicephalus microplus: Influence of the solvents and search for fractions with higher bioactivity

The use of natural products in research on tick control for Rhipicephalus microplus is increasing year by year, with promising results. In this regard, the aim of the present study was to phytochemically characterize the essential oils (EOs) of Leptospermum scoparium, Origanum vulgare and Litsea cubeba, and to evaluate the acaricidal activity of these EOs in solutions prepared using ethanol, dimethylsulfoxide (DMSO) and Tween 80 on larvae and females of R. microplus. In addition, three L. scoparium fractions were also isolated and their acaricidal activity on these larvae and adult females was tested. Gas chromatography and mass spectrometry results showed that cis-calamenene (29.82 %), carvacrol (64.85 %) and geranial (42.44 %) were the majority compounds of L. scoparium, O. vulgare and L. cubeba, respectively. Three fractions were isolated from L. scoparium: A1, rich in sesquiterpene hydrocarbons, and A2 and A3, rich in β-triketones. Bioassays on unfed larvae (immersion test) were performed using all the EOs at concentrations from 2.5 to 10.0 mg/mL; and using the three fractions obtained from L. scoparium EO at concentrations from 0.625 to 10 mg/mL. We observed 100 % mortality of larvae in all treatments with L. scoparium EO at all concentrations (diluted both in DMSO and in ethanol), and in treatments with O. vulgare EO diluted in DMSO. However, L. cubeba EO only gave rise to more than 99 % mortality at a concentration of 10 mg/mL, using the same solvents. For engorged females, the immersion test was performed at concentrations from 2.5 to 10.0 mg/mL. Percentage control greater than 90 % was observed only at the highest concentrations of L. scoparium and O. vulgare EOs diluted in DMSO and ethanol, while L. cubeba EO did not reach 90 % control in any of the treatments. In tests on L. scoparium fractions, larval mortality in the fractions rich in β-triketones (A2 and A3) was above 97 % at a concentration of 2.5 mg/mL, while in the A1 fraction, rich in sesquiterpene hydrocarbons, at the same concentration (2.5 mg/mL), mortality did not reach 22 %. In the adult immersion test, the percentage control was higher than 98 % at the lowest concentration (2.5 mg/mL) of the A1 fraction, while in the treatments with the fractions A2 and A3, the control levels were 16 and 50 %, respectively. Thus, we can conclude that the EOs of L. scoparium, O. vulgare and L. cubeba have acaricidal activity on R. microplus, as also do the fractions derived from L. scoparium EO.

Acaricidal and repellent activity of the essential oils of Backhousia citriodora, Callistemon viminalis and Cinnamodendron dinisii against Rhipicephalus spp

The ticks Rhipicephalus microplus and Rhipicephalus sanguineus sensu lato (s.l) are of great importance to agriculture, veterinary medicine and public health. Due to a number of problems related to the use of synthetic acaricides, natural products emerge as promising substances for alternative tick control. In the present study, essential oils of Backhousia citriodora, Callistemon viminalis and Cinnamodendron dinisii were extracted by hydrodistillation, characterized by GC-MS and GC-FID and biologically evaluated for acaricidal activity against R. microplus and repellent activity against R. sanguineus s.l. Inhibition of acetylcholinesterase (AChe) by the essential oils was also evaluated. The major constituent of B. citriodora is citral (98.9 %), whereas the essential oil from C. viminalis is rich in 1.8-cineole (78.1 %), α-pinene (12.5 %) and limonene (3.36 %), and that from C. dinisii contains α-pinene (30.8 %), β-pinene (12.5 %) and sabinene (11.3 %) as the principal constituents. The median lethal concentrations (LC 50) estimated for the essential oils on engorged R. microplus females were 3.276 μL.mL^-1 for B. citriodora, 8.195 μL.mL^-1 for C. dinisii and 8.936 μL.mL^-1 for C. viminalis. The essential oil of B. citriodora showed the best repellent effect against unfed R. sanguineus s.l. adults, demonstrating repellent action up to 3 h after application. The essential oil of C. viminalis was able to reduce AChe activity, with an average inhibitory concentration (IC 50) of 0.33 μg mL^-1. Thus, these oils can be considered as sources of bioactive compounds for tick control.

Binary combinations of thymol, carvacrol and eugenol for Amblyomma sculptum control: Evaluation of in vitro synergism and effectiveness under semi-field conditions

This study aimed to investigate the in vitro acaricidal effect of thymol, carvacrol and eugenol (binary combinations) and their synergistic effect on unfed larvae and nymphs of Amblyomma sculptum, estimate the cost to prepare a formulation with these compounds, and evaluate the formulations under semi-field conditions against A. sculptum larvae. To evaluate the acaricidal effect of the compounds alone or their binary combinations (1:1 ratio) the larval packet test was performed using six concentrations (0.3125 to 10.0 mg/mL) for larvae and seven concentrations (2.5 to 20.0 mg/mL) for nymphs. The cost to produce 1 L of thymol, carvacrol and eugenol solutions, combined or alone, was estimated. In the semi-field test, formulations were sprayed on Panicum maximum plots experimentally infested with unfed A. sculptum larvae. In the in vitro tests with larvae, a synergistic effect (synergism and moderate synergism) was observed for thymol + eugenol at all concentrations tested, while thymol + carvacrol and eugenol + carvacrol showed a synergistic effect at the concentration of 5.0 mg/mL. In the in vitro tests with nymphs, thymol + eugenol, thymol + carvacrol and carvacrol + eugenol showed a synergistic effect (synergism and moderate synergism) at a concentration of 5.0 mg/mL and higher. Combining the compounds reduced the concentrations required to obtain mortality rate above 95%, resulting in lower costs. Under semi-field conditions, the treatments with thymol + eugenol and carvacrol + eugenol showed efficacies of 63.2% and 42.6%, respectively. We conclude that, depending on the concentrations, the binary combinations of thymol, carvacrol and eugenol have a synergistic acaricidal effect on unfed A. sculptum larvae and nymphs, and under semi-field conditions the associations between thymol + eugenol and carvacrol + eugenol were effective against A. sculptum larvae.

Acaricidal activity of the hexanic and hydroethanolic extracts of three medicinal plants against southern cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The southern cattle tick Rhipicephalus microplus is a major problem for the cattle industry in tropical and subtropical areas worldwide. Chemical products are commonly applied to control it; however, their indiscriminate use has resulted in the appearance of resistant lineages. In the last decades, plants have been used as an alternative to conventional acaricidal drugs, as several plant compounds repel activity, decrease the reproductive potential and reduce the survival rate of ticks. For this reason, the in vitro efficacy of hexanic and hydroalcoholic extracts of Randia aculeata, Moringa oleifera and Carica papaya were evaluated against the larvae and engorged females of R. microplus. Larval packet tests and adult immersion tests were performed with seven concentrations of each of the extracts. The extracts obtained with hydroethanolic solution (polar solvent) exhibited a higher acaricidal activity than extracts prepared with n-hexane (non-polar solvent). Hydroethanolic extracts of R. aculeata seed and shell showed the highest larvicidal activity against R. microplus (100 and 91% mortality, respectively) at a concentration of 100 mg/mL. Randia aculeata (seed and shell), M. oleifera and C. papaya treatments at the same concentration (100 mg/mL) also resulted in adult mortality of 85, 75, 66 and 55%, respectively. The adult immersion test showed that hydroethanolic extracts derived from R. aculeata seed significantly reduced the index of egg laying and increased the percentage inhibition of oviposition of female ticks at a concentration of 100 mg/mL. These results indicate that the tested extracts exhibit acaricidal activity and could be considered as potential agents for the development of alternative natural acaricides against R. microplus.

Thymol and eugenol microemulsion for Rhiphicephalus sanguineus sensu lato control: Formulation development, field efficacy, and safety on dogs

The present study aimed to develop a microemulsion formulation containing thymol and eugenol for field control of Rhipicephalus sanguineus sensu lato on dogs, as well to evaluate its safety and the physical characteristics of the formulation. The microemulsion using thymol and eugenol (5.0 + 5.0 mg/mL) had as vehicles water, propylene glycol, polysorbate 80 and canola oil. On the next day the preparation (formulation freshly prepared) and after 24 months, the size of the microemulsion droplets, polydispersion index (PdI), organoleptic properties (color, viscosity), and presence of precipitate in the microemulsion were evaluated. For the field assay, on day -1, 10 English Cocker Spaniel dogs were experimentally infested with 200 larvae, 100 nymphs and 30 adults of R. sanguineus s.l. On day 0, after tick counts, the animals were divided into two groups: treated with the freshly prepared microemulsion (10 mL/kg), and control, which received the vehicle (10 mL/kg). Tick counts on dogs were performed daily for three more days. Engorged females were recovered from the dogs and their biological and reproductive parameters were monitored. The dogs' clinical parameters (temperature, mucosa color, and general physical condition) were evaluated daily. In addition, blood samples were collected before infestation to verify hematological (packed cell volume) and biochemical parameters (total serum protein, albumin, globulins, creatinine, urea, alanine transaminase, aspartate aminotransferase, and alkaline phosphatase). Freshly prepared and 24-month aged microemulsions had droplets with mean sizes of 30.94 nm and 27.93 nm, and PdI values of 0.214 and 0.161, respectively. In addition, no difference in the organoleptic properties and no precipitation formation were observed, indicating physical stability. Treatment with the microemulsion resulted in reduction of larvae (p < 0.05) parasitizing the dogs on day 1 while the number of nymphs and adults was not reduced (P> 0.05). In the evaluation of the reproductive biology of engorged females, the larval hatchability (%) was compromised (p < 0.05), and the microemulsion had control rate of 85.5 %. The microemulsion and its vehicles did not change the clinical, hematological and biochemical parameters of the dogs. We concluded that the microemulsion was efficient against R. sanguineus s.l. by reducing the number of larvae and affecting the reproductive parameters of engorged females, safe for dogs, and stable (physical stability) during a two-year interval.

Repellent activity of acetylcarvacrol and its effects on salivary gland morphology in unfed Rhipicephalus sanguineus sensu lato ticks (Acari: Ixodidae)

Rhipicephalus sanguineus sensu lato (s.l.), commonly known as brown dog tick, is a widely distributed tick species that is substantially important for human and veterinary medicine. Therefore, it is the target of different control methods. Carvacrol and its semisynthetic derivative, acetylcarvacrol, are promising chemical compounds for alternative tick control. Thus, this study aimed to compare the repellent activities of carvacrol and acetylcarvacrol at different concentrations and drying times. Additionally, morphological alterations found in salivary glands were evaluated through histological techniques after exposure to acetylcarvacrol. The impact of the morphological changes on the development and survival of acini/cells in salivary glands was measured by a semiquantitative analysis. The repellent action of both compounds did not differ when evaluated at different concentrations, although acetylcarvacrol increased its effects as the concentration raised. Regarding the different drying times, acetylcarvacrol maintained its effects after 3 hours of exposure, while the efficacy of carvacrol decreased during this time period. Salivary glands of unfed R. sanguineus s.l. females showed dose-dependent alterations in the size and shape of acini as well as cytoplasmic vacuolization. Loss of the acinar cell limit, rupture of secretory granules and nuclear changes in the cells were also observed in the treated groups. Thus, our results demonstrated the potential of acetylcarvacrol to act as repellent against R. sanguineus s.l. Additionally, the morphological alterations found in salivary glands may interfere with the feeding process of ticks, which contributes to mitigate infestation by this species.

The application of essential oils as a next-generation of pesticides: recent developments and future perspectives

The overuse of synthetic pesticide, a consequence of the rush to increase crop production, led to tremendous adverse effects, as they constitute a major pollutant for both soils and water, with a high toxicity towards humans and animals and, at the same time, led to development of pest resistance. In the last period, the researches were directed towards finding new solutions with a lower toxicity, less damaging behaviour towards the environment, and a better specificity of action. In this context, the use of essential oils, a complex and unique mixture of compounds, can be considered for the next-generation pesticides. This review aims to present the main applications of the essential oils as insecticides, herbicides, acaricides, and nematicides, as they emerged from the scientific literature published in the last 5 years (2015 to present). From the identified articles within the time period, only those dealing with essential oils obtained by the authors (not commercially available) were selected to be inserted in the review, characterized using established analytical techniques and employed for the envisaged applications. The review is concluded with a chapter containing the main conclusions of the literature study and the future perspectives, regarding the application of essential oils as next-generation pesticides.

Supercritical carbon dioxide extraction of plant phytochemicals for biological and environmental applications - A review

Recently, supercritical fluid CO₂ extraction (SFE) has emerged as a promising and pervasive technology over conventional extraction techniques for various applications, especially for bioactive compounds extraction and environmental pollutants removal. In this context, temperature and pressure regulate the solvent density and thereby effects the yield, selectivity, and biological/therapeutic properties of the extracted components. However, the nature of plant matrices primarily determines the extraction mechanism based on either density or vapor pressure. The present review aims to cover the recent research and developments of SFE technique in the extraction of bioactive plant phytochemicals with high antioxidant, antibacterial, antimalarial, and anti-inflammatory activities, influencing parameters, process conditions, the investigations for improving the yield and selectivity. In another portion of this review focuses on the ecotoxicology and toxic metal recovery applications. Nonpolar properties of Sc-CO₂ create strong solvent strength via distinct intermolecular interaction forces with micro-pollutants and toxic metal complexes. This results in efficient removal of these contaminants and makes SFE technology as a superior alternative for conventional solvent-based treatment methods. Moreover, a compelling assessment on the therapeutic, functional, and solvent properties of SFE is rarely focused, and hence this review would add significant value to the SFE based research studies. Furthermore, we mention the limitations and potential of future perspectives related to SFE applications.

A retrospective review on ixodid tick resistance against synthetic acaricides: implications and perspectives for future resistance prevention and mitigation

The ending of the nineteenth-century was characterized by an escalation of ticks and tick-borne diseases that resulted in the death of many cattle. This necessitated the search for an effective means of tick control. Arsenicals were introduced in Australia in 1895, and arsenic-based dipping vats went on to be used for about 40 years until resistance was found in ticks and more effective alternatives - chemical acaricides - were developed after World War II. However, the development of resistance by ticks, environmental persistence, and mammalian toxicity militated against the sustained use of subsequent chemical acaricides. Furthermore, the development of resistance is a phenomenon that would always evolve, and the multiple mechanisms underlying the synthetic acaricides resistance are of great importance for future integrated control of ticks and tick-borne diseases. Hence, this study retrospectively reviewed the development of synthetic acaricides and the underlying mechanisms of tick resistance against synthetic acaricides in the hope of providing the implications and perspectives for resistance prevention and mitigation for future tick control.

In vitro and in silico studies of the larvicidal and anticholinesterase activities of berberine and piperine alkaloids on Rhipicephalus microplus

Rhipicephalus microplus is responsible for high economic losses in livestock and its control has become difficult due to the establishment of tick populations resistant to commercial acaricides. This study aimed to evaluate the in vitro larvicidal effect of the alkaloids berberine and piperine, and also to investigate their inhibitory mechanisms against the acetylcholinesterase enzyme. The effects of the alkaloids on larvae were observed through the immersion test at the following concentrations: 1.5; 3; 6; 12; 16 and 24 mM. Berberine and piperine presented larvicidal activity greater than 95 %, not differing from 100 % for the positive fipronil control (p > 0.05). Of the two alkaloids, piperine had a lower effective concentration (EC), with an EC₅₀ of 6.04 mM. The acetylcholinesterase enzyme used in the study was obtained from R. microplus larvae (RmAChE) and the anticholinesterase activity was determined spectrophotometrically. The highest anticholinesterase activity, measured as inhibition concentration (IC), was observed for berberine (IC50 = 88.13 μM), while piperine showed lower activity (IC50 > 200 μM). Docking studies in RmAChE, followed by 10 ns molecular dynamics simulation, suggest that berberine stabilizes the RmAChE at lower Root-Mean-Square Deviation (RMSD) than Apo protein. Few hydrogen-bond interactions between berberine and RmAChE residues were balanced by hydrophobic and π-type interactions. Berberine fills preferentially the peripheral anionic site (PAS), which correlates with its non-competitive mechanism. These results suggest that berberine and piperine alkaloids have an in vitro acaricidal action on R. microplus larvae, and the likely mechanism of action of berberine is related to RmAChE inhibition when accessing the PAS residues. These findings could help the study of new natural products that could inhibit RmAChE and aid in the development of new acaricides.

Ethnoveterinary for food-producing animals and related food safety issues: A comprehensive overview about terpenes

Alternatives to the use of conventional veterinary drugs in food-producing animals have gained attention, such as the use of natural products (NPs), mainly to soften the risks to the animal, the environment, and consumer's health. Although NPs have consistent advantages over conventional drugs, they cannot be considered risk free under food safety matters. In this way, this document presents a comprehensive overview of the importance of considering both the pharmacological and toxicological properties of the constituents of a NP from plants intending the standardization and regulation of its use in food-producing animals. Terpenes are the most diverse class of natural substances present in NP of vegetal origin with a broad range of biological activities that can be explored in veterinary science; however, certain plants and terpenes also have significant toxic effects, a fact that can harm the health of animals and consequently generate economic losses and risks for humans. In this context, this review gathered scientific data of vegetal species of importance to ethnoveterinary for food-producing animals, which produce terpenes, its biological effects, and their implications on food safety issues for consumers. For this, more than 300 documents were selected from different online scientific databases. The present data and discussion may contribute to the rational commercial exploration of this class of NPs in veterinary medicine.

Acaricidal activity of (E)-cinnamaldehyde and α-bisabolol on populations of Rhipicephalus microplus (Acari: Ixodidae) with different resistance profiles

This study aimed to investigate the acaricidal activity of (E)-cinnamaldehyde and α-bisabolol on populations of Rhipicephalus microplus with different resistance profiles. The adult immersion test (AIT) was used to characterize the susceptibility of tick populations (50 field populations) to synthetic acaricides: deltamethrin, amitraz, and chlorfenvinphos. The larval packet test (LPT) was used to determine the LC₅₀ values for (E)-cinnamaldehyde (populations 1-25) and α-bisabolol (populations 26-50) at the concentrations of 0.31, 0.62, 1.25, 2.0, 2.5, 5.0 and 10.0 mg/mL. The susceptible strain Porto Alegre (POA) was used as a reference for calculating the resistance ratio (RR). In the AIT, deltamethrin did not show efficacy >95 % for any of the populations, whereas amitraz and chlorfenvinphos have presented efficacy >95 % for three (6 %) and 15 (30 %) populations, respectively. In the LPT, the LC₅₀ values of (E)-cinnamaldehyde and α-bisabolol varied from 0.23 to 2.36 mg/mL and 1.57-3.01 mg/mL, respectively. The RR₅₀ for (E)-cinnamaldehyde showed 20 (80 %) populations with values <1.0 and no population with values>1.5. As for α-bisabolol, only two (8%) populations have presented RR₅₀ <1.0, whereas three (12 %) populations showed incipient resistance to this sesquiterpene (RR₅₀ between 1.5 and 2.0). The results indicate that all studied tick populations showed low susceptibility to at least one of the commercial acaricides tested. In addition, comparison between the LC₅₀ values of (E)-cinnamaldehyde and α-bisabolol for the field populations and the susceptible strain POA suggests that there is no cross-resistance of (E)-cinnamaldehyde and α-bisabolol for the tick populations evaluated, and that the differences in the LC₅₀ values are due to population variations.

Plant-Derived Natural Compounds for Tick Pest Control in Livestock and Wildlife: Pragmatism or Utopia?

Ticks and tick-borne diseases are a significant economic hindrance for livestock production and a menace to public health. The expansion of tick populations into new areas, the occurrence of acaricide resistance to synthetic chemical treatments, the potentially toxic contamination of food supplies, and the difficulty of applying chemical control in wild-animal populations have created greater interest in developing new tick control alternatives. Plant compounds represent a promising avenue for the discovery of such alternatives. Several plant extracts and secondary metabolites have repellent and acaricidal effects. However, very little is known about their mode of action, and their commercialization is faced with multiple hurdles, from the determination of an adequate formulation to field validation and public availability. Further, the applicability of these compounds to control ticks in wild-animal populations is restrained by inadequate delivery systems that cannot guarantee accurate dosage delivery at the right time to the target animal populations. More work, financial support, and collaboration with regulatory authorities, research groups, and private companies are needed to overcome these obstacles. Here, we review the advancements on known plant-derived natural compounds with acaricidal potential and discuss the road ahead toward the implementation of organic control in managing ticks and tick-borne diseases.

Analysis of the Physicochemical Properties of Acaricides Based on Lipinski's Rule of Five

This study aimed to explore the similarity between the physical and chemical properties of different acaricides, determine whether Lipinski's Rule of Five (RO5) used in the design of drug molecules is suitable for screening acaricides, and provide methods for selection of new acaricides. We evaluated and predicted the molecular properties of >180 acaricides using Molinspiration. We calculated physicochemical property parameters, such as log p, molecular weight (MW), and number of hydrogen bond donors (HBDs), hydrogen bond acceptors (HBAs), and rotatable bonds (Rot B). We then conducted qualitative and quantitative analyses of the physicochemical properties of acaricides. The MW of all acaricides ranged from 141 to 663, with an average value of 337.8. The number of HBDs ranged from 0 to 5, with an average value of 0.46. The number of HBAs ranged from 0 to 9, with an average value of 4.07. The log p ranged from -0.79 to 8.74, with an average value of 4.61. The number of Rot B ranged from 0 to 14, with an average value of 5.62. Except for the microbial and plant-derived acaricides, the molecular properties of the remaining acaricides are in accordance with the Lipinski's RO5. Therefore, the Lipinski's RO5 can provide a basis for screening new acaricide drugs.

Anti-tick effect and cholinesterase inhibition caused by Prosopis juliflora alkaloids: in vitro and in silico studies

Abstract We investigated the in vitro acaricide activity of the methanolic extract (ME) and alkaloid-rich fraction (AF) of Prosopis juliflora on Rhipicephalus microplus and correlated this effect with acetylcholinesterase (AChE) inhibition. The acaricide activity was evaluated using adult and larval immersion tests. Also, we studied the possible interaction mechanism of the major alkaloids present in this fraction via molecular docking at the active site of R. microplus AChE1 (RmAChE1). Higher reproductive inhibitory activity of the AF was recorded, with effective concentration (EC50) four times lower than that of the ME (31.6 versus 121 mg/mL). The AF caused mortality of tick larvae, with lethal concentration 50% (LC50) of 13.8 mg/mL. Both ME and AF were seen to have anticholinesterase activity on AChE of R. microplus larvae, while AF was more active with half-maximal inhibitory concentration (IC50) of 0.041 mg/mL. The LC-MS/MS analyses on the AF led to identification of three alkaloids: prosopine (1), juliprosinine (2) and juliprosopine (3). The molecular docking studies revealed that these alkaloids had interactions at the active site of the RmAChE1, mainly relating to hydrogen bonds and cation-pi interactions. We concluded that the alkaloids of P. juliflora showed acaricide activity on R. microplus and acted through an anticholinesterase mechanism.

Abnormal Development of Hyalomma Marginatum Ticks (Acari: Ixodidae) Induced by Plant Cytotoxic Substances

The increasing application of toxic plant substances to deter and fight ticks proves the need for investigations focused on the elucidation of their impact on the developmental stages and populations of these arthropods. We examined the course of embryogenesis and egg hatch in Hyalomma marginatum ticks under the effect of cytotoxic plant substances. The investigations demonstrated that the length of embryonic development of egg batches treated with 20 μL of a 0.1875% colchicine solution did not differ significantly from that in the control group. Colchicine caused the high mortality of eggs (16.3%) and embryos (9.7%), disturbances in larval hatch (8.1%), and lower numbers of normal larval hatches (65.6%). In 0.2% of the larvae, colchicine induced anomalies in the idiosoma (67.6%) and gnathosoma (22.5%) as well as composite anomalies (8.5%). The study demonstrates that cytotoxic compounds with an effect similar to that of colchicine can reduce tick populations and cause teratological changes, which were observed in the specimens found during field studies. Since there are no data on the toxic effects of active plant substances on other organisms and the risk of development of tick resistance, a strategy for the use of such compounds in tick control and the management of plant products should be developed.

Insecticidal and Nematicidal Contributions of Mexican Flora in the Search for Safer Biopesticides

Plant metabolites have been used for many years to control pests in animals and to protect crops. Here, we reviewed the available literature, looking for the species of Mexican flora for which extracts and metabolites have shown activity against pest insects and parasitic nematodes of agricultural importance, as well as against nematodes that parasitize domestic cattle. From 1996 to 2018, the search for novel and eco-friendly biopesticides has resulted in the identification of 114 species belonging to 36 botanical families of Mexican plants with reported biological effects on 20 insect species and seven nematode species. Most plant species with detected pesticide properties belong to the families Asteraceae, Fabaceae, and Lamiaceae. Eighty-six metabolites have been identified as pesticidal active principles, and most have been terpenoids. Therefore, the continuation and intensification of this area of research is very important to contribute to the generation of new products that will provide alternatives to conventional pesticide agents. In addition, future studies will contribute to the recognition and dissemination of the importance of propagating plant species for their conservation and sustainable use.

Acaricidal activity and enzyme inhibitory activity of active compounds of essential oils against Psoroptes cuniculi

Plant essential oils and its chemical compositions are commonly applied in medicinal and other industries due to their broad advanced pharmacological activities. In the present study, we systematically evaluated the acaricidal activities of twelve compounds of essential oils against Psoroptes cuniculi in vitro and in vivo. In addition, to support the clinic uses, their toxicities against immortalized human keratinocytes (HaCaT) and human liver cells (HL-7702) and skin irritation were studied for evaluating the liver and skin safety. The possible mechanism of action of certain chemical were investigated by determining the inhibitory activities against cytochrome P450 (P450) acetylcholinesterase (AChE) and glutathione-S-transferase (GST). Among all tested compounds, eugenol exhibited the best acaricidal activity with LC₅₀ value of 56.61 μg/ml in vitro. Meanwhile, after the treatment of eugenol for five times within 10 days, the P. cuniculi were eliminated in the naturally infested rabbits, no skin irritation was found in rabbits treated by eugenol. Moreover, eugenol presented no or weak cytotoxicity against HaCaT cells and HL-7702 cells with IC₅₀ values of greater than 100 μg/ml. Furthermore, the moderate inhibitory activities of eugenol against mites P450 and AChE were demonstrated. Above results indicated that eugenol presented the promising acaricidal activity against P. cuniculi in vitro and in vivo, is safe for both humans and animals at the given doses. This work lays the foundation for the development of eugenol as an environmentally friendly acaricide agent.