In vitro and in vivo acaricide action of juvenoid analogs produced from the chemical modification of Cymbopogon spp. and Corymbia citriodora essential oil on the cattle tick Rhipicephalus (Boophilus) microplus

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.

Acaricides containing zein nanoparticles: a tool for a lower impact control of the cattle tick Rhipicephalus microplus

Nanoformulations containing zein nanoparticles (ZN) can promote the stability and protection of molecules with acaricidal activity. The present study sought to develop nanoformulations with ZN associated with cypermethrin (CYPE) + chlorpyrifos (CHLO) + a plant compound (citral, menthol or limonene), characterize them, and verify their efficacy against Rhipicephalus microplus ticks. Additionally, we aimed to assess its safety in nontarget nematodes found in soil at a site subjected to contamination by acaricides. The nanoformulations were characterized by dynamic light scattering and nanoparticle tracking analysis. Nanoformulations 1 (ZN+CYPE+CHLO+citral), 2 (ZN+CYPE+CHLO+menthol), and 3 (ZN+CYPE+CHLO+limonene) were measured for diameter, polydispersion, zeta potential, concentration, and encapsulation efficiency. Nanoformulations 1, 2, and 3 were evaluated in a range from 0.004 to 0.466 mg/mL on R. microplus larvae and caused mortality > 80% at concentrations above 0.029 mg/mL. The commercial acaricide Colosso® (CYPE 15 g + CHLO 25 g + citronellal 1 g) was evaluated also from 0.004 to 0.512 mg/mL and resulted in 71.9% larval mortality at 0.064 mg/mL. Formulations 1, 2, and 3 at 0.466 mg/mL showed acaricidal efficacy of 50.2%, 40.5%, and 60.1% on engorged females, respectively, while Colosso® at 0.512 mg/mL obtained only 39.4%. The nanoformulations exhibited long residual period of activity and lower toxicity to nontarget nematodes. ZN was able to protect the active compounds against degradation during the storage period. Thus, ZN can be an alternative for the development of new acaricidal formulations using lower concentrations of active compounds.

3-Isobutyl-5,5,7-tris(3-methylbut-2-en-1-yl)-1-phenyl-1,7-dihydro-4H-indazole-4,6(5H)-dione

Here we describe the functionalization of lupulone natural compound in obtaining 3-isobutyl-5,5,7-tris(3-methylbut-2-en-1-yl)-1-phenyl-1,7-dihydro-4H-indazole-4,6(5H)-dione. The lupulone-H-indazole derivative was prepared with 75% yield through the reaction between lupulone and phenyl-hydrazine employing SiO2/ZnCl2 (30% m/m) as a support solid in a solvent-free condition. Based on the possibilities of products, a complete NMR structural characterization of this lupulone-H-indazole was performed by 1H, 13C{1H}, COSY, HSQC and HMBC NMR experiments, showing an important contribution in producing the first results related to lupulone reactivity.

Transcriptome profile of Haemaphysalis longicornis (Acari: Ixodidae) exposed to Cymbopogon citratus essential oil and citronellal suggest a cytotoxic mode of action involving mitochondrial Ca2+ overload and depolarization

Haemaphysalis longicornis is an ixodid tick species of medical and veterinary importance. Investigation into the acaricidal activities of botanicals have increased recently but information about their molecular mechanism of action is scarce. Here, RNA-seq analysis of the ticks exposed to Cymbopogon citratus essential oil and citronellal was performed and the responsive genes were identified. More than 6.39 G clean reads with Q₂₀ ≥ 94.88% were obtained for each H. longicornis sample, with an average GC content of 50.94%. Using the Trinity method, 166,710 unigenes with a mean length of 869 bp and a maximum contig length of 29,156 bp were obtained. The upregulation of genes was concentration-dependent in most of the treated groups. Many genes responsive to C. citratus oil and citronellal were stress-related and they include genes associated with adrenergic signaling/calcium channels, cGMP-PKG signaling, apoptosis, focal adhesion, ECM-receptor interaction, ubiquitin-mediated proteolysis, mTOR signaling pathway, and longevity regulating pathway. The upregulation of genes (CACNAID, ADCY9, TPM1, and MYH6) associated with calcium channels suggests a neurotoxic mode of action, whereas, the upregulation of apoptosis-associated genes (CYC, DRONC, CASP7, CASP9, BCL2L1, bcl-xL, etc.) suggests a cytotoxic mode of action. The metabolism of C. citratus essential oil generates oxidative stress which increases the intra-mitochondrial free Ca²⁺ and triggers the formation of reactive oxygen species (ROS) that culminates to mitochondrial depolarization, ATP depletion, and either necrotic or apoptotic death. The neurotoxic and cytotoxic effects exhibited by the monoterpenes in H. longicornis is vital and could be exploited for the advancement of acaricide development and eco-friendly tick control.

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.

Acaricidal activity and clinical safety of arecoline hydrobromide on calves infested with cattle tick Rhipicephalus microplus (Acari: Ixodidae)

The objective of the present study was to determine the acaricidal activity of arecoline hydrobromide against cattle tick Rhipicephalus microplus infesting calves. in vivo efficacy of arecoline emulsified with polysorbate-80 (2%) was evaluated using ear bag method with the effective dose of 12.5 mg/mL applied on ear pinna of calves infested with ticks. Control group received polysorbate-80 (2%) after larvae infestation, however, reference group received deltamethrin (0.5 %). The experiment was continued for six days (144 h) and treatment of drug was given twice a day. Daily observation of calves was done to count the number of ticks after treatment. Acute dermal toxicity study for test drug was performed on wistar rats. Clinical safety of arecoline was determined by examining hematological profile and skin irritancy assay for calves infested with ticks. Results showed that arecoline significantly (p < 0.01) reduced the number of ticks attached to ear pinna of calves. Fewer number of ticks remained on calves skin at 120 h and 144 h were 8.09 and 6.21, respectively after treatment with arecoline in comparison to control group. Treatment of animals with arecoline hydrobromide significantly (p < 0.01) restored the hematological profile of animals as hemoglobin (Hb) level was 9.01 g/100 mL, PVC was 29.24 %, TEC and TLC were 5.23 and 7.19 106/cumm, respectively as compared to the control group having Hb 9.48 g/100 mL, PVC 31.60 %, TEC 5.64 10⁶/cumm and TLC 7.27 10⁶/cumm. Arecoline showed no toxicity while applied on wistar rats. The drug was mild irritative for an initial 20 min to the calves after that no redness or erythema was seen on the skin of the animals. Thus, arecoline hydrobromide may be an effective alternative to be used as herbal ectoparasiticide for the eradication of R. microplus ticks.

Development of an efficient antitick natural formulation for the control of acaricide-resistant ticks on livestock

Animal production has a key role in global economic development and food security. Ticks, specifically Rhipicephalus microplus cause substantial economic and health impacts on more than eighty percent of the world cattle population. Though synthetic acaricides play a major role in tick management, their injudicious usage has caused environmental pollution and also promote the establishment of multi-acaricide resistant tick populations which is a matter of great concern. To provide an effective tool for controlling these resistant ticks, the present work was aimed to develop safe and inexpensive antitick natural formulations. Our bioprospection studies of Ageratum conyzoides plant established it as a species potentially having strong acaricidal activity due to the presence of potent acaricidal phyto-chemicals. To develop a suitable antitick natural formulation, 41 samples/fractions/formulations were prepared from the dry powder of the whole aerial part of the A. conyzoides plant using different techniques and delivery matrices. The strongest antitick effect was recorded for formulation ACF6, which demonstrated 87 ± 6% mean mortality with 57 % inhibition of oviposition in treated female ticks. Ticks treated with the ACF6 formulation showed a significant (p < 0.001) reduction in cuticular protein (1.238 ± 0.01 mg/mL) as compared to control ticks (2.928 ± 0.01 mg/mL) but no significant difference in chitin content of treated ticks and control ticks was observed. The formulation was found safe in a rat model as no significant differences in biochemical and haematological parameters among treated and control rats were noted. Histopathological studies indicated no sign of hepatocellular necrosis and no significant changes in the weights of liver and spleen was recorded. The overall in vivo efficacy of the formulation was 85 % for experimentally infested cattle with direct mortality of more than 80 % within 96 h post-application. The lethal effect of the formulation was in the form of drying and dead ticks 1-2 d after application. The developed formulation has the potential to be adopted as an alternative tick control measure in an ecofriendly manner.

Repellent and acaricidal activity of essential oils and their components against Rhipicephalus ticks in cattle

Ticks, particularly the Rhipicephalus which are the most prevalent and invasive affect 80 % of the cattle population worldwide. Through transmission of pathogens, tick worry and physical damage to the hides, ticks cause economic loss of billions of dollars each year with 1 billion US dollars loss per annum reported only in Latin-America. These losses can be minimized only by successful management of Rhipicephalus ticks. Various strategies like chemical control, vaccination and biological control are aimed at control of Rhipicephalus ticks. There are some serious limitations associated with them like tick resistance, drug toxicity, antigenic variations etc. In contrast to these issues related with chemical tick control, the botanicals particularly the essential oils obtained from aromatic plants of medicinal importance are eco-friendly and non-toxic to most host. In recent years, essential oils-based control of cattle ticks has gained considerable attraction of scientists all over the world as depicted from this review. A comprehensive effort has been made to critically analyze the role of essential oils in controlling Rhipicephalus ticks with particular emphasis on the mode of action of bioactive compounds both as repellents and acaricides. Furthermore, we have pointed out the most important challenges which need to be addressed for development and commercialization of an essential oil based anti-tick product.

In vitro acaricidal activity of Cymbopogon citratus, Cymbopogon nardus and Mentha arvensis against Rhipicephalus microplus (Acari: Ixodidae)

The chemical composition and acaricidal activity of plant-derived essential oils was assessed against Rhipicephalus microplus ticks. The essential oils of Mentha arvensis, Cymbopogon citratus and C. nardus were assessed for acaricidal activity against Rhipicephalus microplus. Essential oils (EO) of plants were separated by hydrodistillation (three times) and analyzed using gas chromatography - mass spectrometer (GC-MS). For bioassays, engorged females of R. microplus were exposed to C. citratus and C. nardus EO at 2%, 3%, 4% and 5% concentrations; and to M. arvensis EO at 1%, 3%, and 5% for 5 min. The weight egg mass, nutrient index (N.I), egg production index (E.P.I), hatching and control rate were evaluated. Non-feed larvae of R. microplus were exposed to essential oils with 0.25%, 0.5%; 1%; 1.5% and 2% concentrations; the mortality rate was measured after 48 h. Only engorged females presented reduced biological activities (oviposition, E.P.I) after exposure to M. arvensis at 3%, when in comparison to both positive and negative controls. The hatchability of R. microplus larvae ranged from 66.9% (after exposure to C. nardus EO at 5%) to 99.2% (positive control). The nutrition index was lower (46.6%) for the exposure to M. arvensis EO at 5%. M. arvensis at 3% and 5% concentrations was significantly efficient for engorged females when compared to control (53.7% and 47.5%, respectively). C. citratus EO at 1%, 1.5% and 2% concentrations yielded better results in the larval packet test, causing 100% mortality. Nonetheless, C. nardus and M. arvensis EO at 2% yielded 66% and 39% mortality, respectively. The study showed that M. arvensis presented potential for the control of R. microplus engorged females while C. citratus and C. nardus presented potential as a larvicide.

Effects of the essential oil from Cymbopogon citratus on mortality and morphology of the tick Haemaphysalis longicornis (Acari: Ixodidae)

Haemaphysalis longicornis is one of the most prevalent tick species across eastern Asia, Australia, and New Zealand, and has been implicated as a vector of several pathogenic agents. This study evaluated the in vitro acaricidal efficacy of Cymbopogon citratus (lemongrass) essential oil on unfed H. longicornis using the adult and nymph immersion test, and the larval packet test. Six concentrations with three replications each of 10, 20, 30, 40, 50 and 60 mg/mL (adults and nymphs) were used, and 2.5, 5, 10, 20, 40 and 80 mg/mL (larvae), with control group (50% ethanol). The adult and nymph mortality rates were 98 and 100% at 50 mg/mL, and 95 and 100% at 60 mg/mL, respectively, whereas the larval mortality rate was 94 and 96% at 40 and 80 mg/mL, respectively. Mortality of adult, nymph and larva increased significantly in a dose-dependent manner. The LC₅₀ for adult, nymph, and larva, were 29.21 (95% confidence interval 25.90-32.58), 28.18 (23.78-32.25), and 28.06 (25.57-30.90) mg/mL, respectively. Scanning electron microscopy and light microscopy revealed a disjointed sensilla base from the sockets, cuticular cracks, blocked aeropyles, and shrinking of the midgut. These results showed that C. citratus essential oil could be a good eco-friendly alternative control strategy against ectoparasites like ticks due to its high acaricidal efficacy.

Larvicidal potential of piperovatine in the control of cattle tick

Rhipicephalus (Boophilus) microplus is one of the most important ectoparasites in cattle breeding worldwide, causing direct and indirect losses to animals and producers. Chemical acaricides are utilized in the control of cattle tick and the increase in the development of resistance by ectoparasites makes new alternative necessary. Therefore, research studies have been carried out using bioactive molecules that are quickly degraded and that reduce poisoning to appliers and non-target organisms, environmental contamination and development of resistance. Thus, this study aimed to isolate piperovatine from the roots of Piper corcovadensis, a native species to Brazil, and to evaluate the larvicidal activity against Rhipicephalus (Boophilus) microplus by larval packet test and in ex situ in an open environment. Piperovatine was isolated by classical column chromatography, and identified by ¹H and ¹³C NMR. The lethal concentration (LC) of piperovatine that killed 50% (LC₅₀) and 99% (LC₉₉) of the larvae was determined by Probit analysis. The results indicated LC₅₀ 5.17 and LC₉₉ 25.41 μg/mL. LC₉₉ was tested in ex situ in an open environment, and an efficiency of 96.63% was found, indicating that piperovatine kept the larvicidal action determined in in vitro test and in open environment. Therefore, this study shows new perspectives to develop products that can be applied in natural conditions to control this ectoparasite.