Efficacy of 11 Brazilian essential oils on lethality of the cattle tick Rhipicephalus (Boophilus) microplus

Biological effects of Lippia alba essential oil against Anopheles gambiae and Aedes aegypti

The management of mosquito resistance to chemical insecticides and the biting behaviour of some species are motivating the search for complementary and/or alternative control methods. The use of plants is increasingly considered as a sustainable biological solution for vector control. The aim of this study was to evaluate the biological effects of the essential oil (EO) of Lippia alba harvested in Abidjan (Côte d'Ivoire) against Anopheles gambiae and Aedes aegypti mosquitoes. Phytochemical compounds were identified by GC-MS. Knockdown and mortality were determined according to the WHO test tube protocol. Contact irritancy was assessed by observing the movement of mosquitoes from a treated WHO tube to a second untreated tube. Non-contact repellency was assessed using a standardised high-throughput screening system (HITSS). Blood meal inhibition was assessed using a membrane feeding assay treated with EO. The EO was identified as the citral chemotype. The EO gave 100% KD60 in both species at a concentration of 1%. Mortalities of 100% were recorded with An. gambiae and Ae. aegypti at concentrations of 1% and 5% respectively. The highest proportions of females escaping during the contact irritancy test were 100% for An. gambiae at 1% concentration and 94% for Ae. aegypti at 2.5% concentration. The 1% concentration produced the highest proportions of repelled mosquitoes in the non-contact repellency tests: 76.8% (An. gambiae) and 68.5% (Ae. aegypti). The blood meal inhibition rate at a dose of 10% was 98.4% in Ae. aegypti but only 15.5% in An. gambiae. The citral chemotype of L. alba EO has promising biological effects in both species that make it a potentially good candidate for its use in mosquito control. The results obtained in this study encourage the further evaluation of L. alba EOs from other localities and of different chemotypes, under laboratory and field conditions.

Acaricidal action of ozone on larvae and engorged females of Rhipicephalus microplus: a dose-dependent relationship

The tick Rhipicephalus microplus is a vector of infectious agents that causes great economic loss in the productivity of cattle herds. Several studies have sought natural compounds with acaricidal activity to control ticks, without allowing the development of resistance, without causing environmental damage, and without presenting toxicity to the hosts. The activity of ozone on the natural biomolecules of living beings has been studied as an alternative to control arthropods and acaricidal effects were shown on ticks. The aim of the present study was to assess the acaricidal effect on larvae and engorged females of R. microplus according to ozone dose. Larvae (n = 377) were distributed in 10 groups and engorged females (n = 284) were distributed in 14 groups. One group was used as control (not exposed to ozone) and the other groups were exposed to ozone gas for 5-105 min. Ozone had a dose-dependent acaricidal effect on both larvae and engorged females. Dosages between 355 and 2130 mg/L min had a delayed acaricidal effect (12-180 h), leading to the death of all engorged females before laying eggs, whereas doses between 3195 and 7455 mg/L min showed immediate acaricidal effect (5 min to 4 h). Doses between 1775 and 6390 mg/L min had an immediate (up to 5 min) acaricidal effect on the larvae of this species. Further studies should consider longer follow-up times during the assessment of the acaricidal activity against ticks.

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.

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.

Nanoformulations with synthetic and plant-derived compounds for cattle tick control

Nanocarriers of acaricidal compounds improve the bioavailability, absorption, and tissue distribution of active ingredients, releasing them in a slow, targeted way and protecting them against premature degradation. Thus, this study aimed to develop formulations from solid lipid nanoparticles (SLN), or nanostructured lipid carriers (NLC) associated with cypermethrin (cip) + chlorpyrifos (chlo) and vegetable compounds (citral, menthol, or limonene). Particles were then characterised, and their efficacy was verified on R. microplus in comparison to nanoformulations without the plant-based compounds. Six different formulations were developed and characterised by dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). Formulations 1 (SLN+cyp+chlo+citral), 2 (SLN+cyp+chlo+menthol), 3 (SLN+cyp+chlo+limonene), 4 (NLC+cyp+chlo+citral), 5 (NLC+cyp+chlo+menthol) and 6 (NLC+cyp+chlo+limonene) had mean diameters from 286 to 304 nm; polydispersion from 0.16 to 0.18; zeta potential from -15.8 to -20 mV, concentration from 3.37 ± 0.24 × 10¹³ to 5.44 ± 0.18 × 10¹³ particles/mL and encapsulation efficiency (EE) > 98.01 % for all active ingredients. All formulations were evaluated for their acaricidal potential by the larval packet test (LPT) and compared with nanoformulations without the plant-based compounds. Formulations were also compared with positive (Colosso® at 512 µg/mL) and negative controls (distilled water and nanoparticles without active ingredients). The SLN (1, 2 and 3) and NLC (4, 5 and 6) formulations, at 7 µg/mL, resulted in 90.4 % , 75.9 % , 93.8 % , 100 % , 95.1 % and 72.7 % mortality. The data demonstrated that the addition of citral, menthol or limonene in the formulations improved their acaricide action against tick larvae. Except for formulation 4, for which it was not possible to determine lethal concentrations (LC). Formulations, 1, 2, 3, 5 and 6 reached LC₅₀ and LC₉₀ values of 3.3 and 7.2, 5.4 and 9.2, 4.0 and 8.1, 2.3 and 5.4 as well as 5.5 and 9.4 µg/mL, respectively. It was possible to encapsulate the active ingredients and characterise the lipid carrier systems. SLN and NLC protected the active ingredients against degradation in solution and increased the overall stability. A stabile solution is necessary for synthesizing commercial acaricidal products. It is hoped that these findings may contribute to new studies focused on the use of nanocarriers in tick formulations. By reducing the amount or concentration of active ingredients within commercial products, the risk of residues presents in food of animal origin or remaining in the environment is reduced. Nanocarriers help prevent these challenges, while still maintaining effective parasitic control. Utilizing a combination of natural and synthetic products can be part of integrated management solutions and can help overcome widespread acaricide resistance in populations of cattle ticks.

Integrative Alternative Tactics for Ixodid Control

Simple Summary

Hard ticks are important for economic and health reasons, and control has mainly relied upon use of synthetic acaricides. Contemporary development of resistance and concerns relating to health and environmental safety have elicited exploration into alternative tactics for hard tick management. Some examples of alternative tactics involve biological control, desiccant dusts, growth regulators, vaccines, cultural methods, and ingested medications.

Abstract

Ixodids (hard ticks), ectoparasitic arthropods that vector the causal agents of many serious diseases of humans, domestic animals, and wildlife, have become increasingly difficult to control because of the development of resistance against commonly applied synthetic chemical-based acaricides. Resistance has prompted searches for alternative, nonconventional control tactics that can be used as part of integrated ixodid management strategies and for mitigating resistance to conventional acaricides. The quest for alternative control tactics has involved research on various techniques, each influenced by many factors, that have achieved different degrees of success. Alternative approaches include cultural practices, ingested and injected medications, biological control, animal- and plant-based substances, growth regulators, and inert desiccant dusts. Research on biological control of ixodids has mainly focused on predators, parasitoid wasps, infective nematodes, and pathogenic bacteria and fungi. Studies on animal-based substances have been relatively limited, but research on botanicals has been extensive, including whole plant, extract, and essential oil effects on ixodid mortality, behavior, and reproduction. The inert dusts kaolin, silica gel, perlite, and diatomaceous earth are lethal to ixodids, and they are impervious to environmental degradation, unlike chemical-based toxins, remaining effective until physically removed.

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.

Effects of essential oils on native and recombinant acetylcholinesterases of Rhipicephalus microplus

This study reports the action of essential oils (EO) from five plants on the activity of native and recombinant acetylcholinesterases (AChE) from Rhipicephalus microplus. Enzyme activity of native susceptible AChE extract (S.AChE), native resistant AChE extract (R.AChE), and recombinant enzyme (rBmAChE1) was determined. An acetylcholinesterase inhibition test was used to verify the effect of the EO on enzyme activity. EO from Eucalyptus globulus, Citrus aurantifolia, Citrus aurantium var.dulcis inhibited the activity of S.AChE and R.AChE. Oils from the two Citrus species inhibited S.AChE and R.AChE in a similar way while showing greater inhibition on R.AChE. The oil from E. globulus inhibited native AChE, but no difference was observed between the S.AChE and R.AChE; however, 71% inhibition for the rBmAChE1 was recorded. Mentha piperita oil also inhibited S.AChE and R.AChE, but there was significant inhibition at the highest concentration tested. Cymbopogon winterianus oil did not inhibit AChE. Further studies are warranted with the oils from the two Citrus species that inhibited R.AChE because of the problem with R. microplus resistant to organophosphates, which target AChE. C. winterianus oil can be used against R. microplus populations that are resistant to organophosphates because its acaricidal properties act by mechanism(s) other than AChE inhibition.

Evaluation of essential oils as an ecological alternative in the search for control Rhipicephalus microplus (Acari: Ixodidae)

The cattle tick Rhipicephalus microplus is a significant problem for livestock, causing losses of billions of dollars per year. This work aimed to determine the chemical composition of essential oils obtained from Laurus nobilis and Copaifera officinalis and evaluate activity against engorged R. microplus females. Chemical composition analyzed by GC-MS revealed the presence of 39 components accounting for 95.38% of the oil in L. nobilis, the most abundant being 1,8-cineol (25.7%), trans-sabinene-hydrate (20.8%), and α-terpinil acetate (15.0%). Chemical analysis of C. officinalis oil identified 25 components corresponding to 80.5% of the total constituents, where the major compounds were β-caryophyllene (21.1%), caryophyllene oxide (10.7%), and α-trans-bergamotene (9.3%). Adult immersion test (AIT) showed that L. nobilis essential oil at 5% or 10% caused 80.5% mortality of engorged females after 24 h and reached 96.9% and 100% mortality on the third day after treatment, respectively. While the essential oil from C. officinalis caused 84.7% mortality after six days at 10% and at 5%, achieved approximately 100% mortality rate at the end of the experiment (day 15). Both essential oils and the combination significantly inhibited egg-laying; however, the combination treatment showed higher effectiveness than the isolated oils at 2.5%. A possible synergic action of L. nobilis and C. officinalis against the cattle tick R. microplus is therefore suggested. The present work introduces a potential alternative for the development of a formulation environment-friendly (green pesticide) used to control cattle tick infestations.

1,8-cineole and castor oil in sodium lauryl ether sulphate disrupt reproduction and ovarian tissue of Rhipicephalus (Boophilus) microplus

Essential and fixed oils have been researched as alternatives to chemical acaricides. The activity of volatile compounds from essential oils (1,8-cineole, citral and eugenol) at 1.0% (w/v) and fixed oil (castor oil) at 0.3% (w/v) dissolved in 2.0% (v/v) dimethyl sulfoxide (DMSO) + 0.2% (w/v) Tween 80^® was assessed against Rhipicephalus microplus using immersion tests. 1,8-cineole (29.0%) and castor oil (30.2%) had the highest reproductive inhibition rate. A second experiment was performed to verify the effect of the 1,8-cineole (10.0% w/v) and, or castor oil (0.3% w/v) on tick reproduction using different solubilizing agents. The highest reproductive inhibition was observed for the combination of 1,8-cineole/castor oil (94.1%) and 1,8-cineole in 2.0% (w/v) sodium lauryl ether sulphate (SLES) (92.8%). A third experiment showed morphological changes in R. microplus oocytes at different stages of development, as well as in pedicel cells. The most intense effects were observed when ticks were immersed in the formulation containing 1,8-cineole (10.0% w/v) and castor oil (0.3% w/v) dissolved in 2% (w/v) SLES. These findings highlight the potential of this formulation as an alternative for managing cattle ticks as their cytotoxic effects can reduce R. microplus reproductive success.

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.

Repellency effect of Pilocarpus spicatus A. St.-Hil essential oil and nanoemulsion against Rhipicephalus microplus larvae

Rhipicephalus microplus, the cattle tick, is a major cause of economic losses in bovine production. Due to the widespread acaricidal resistance to commercially available products, as well as their toxicity and environmental impact, alternative control methods are required. Nanoformulations produced from plant extracts as bioactive substances are very promising as innovative acaricidal agents. Thus, the aim of this study was to evaluate the in vitro repellent activity of Pilocarpus spicatus essential oil and its nanoemulsion against R. microplus, using larval repellent test (RT). The essential oil was extracted by hydrodistillation, using a Clevenger-type apparatus. The nanoemulsion was prepared with 5% essential oil, 5% tween 80, and 90% water, using the phase inversion method (50 mg/mL). Limonene was the major component (46.8%) of the essential oil, as determined by gas chromatography-mass spectrometry (GC/MS) and confirmed by flame ionization detection (GC/FID). According to the RT results, the essential oil had a repellent activity greater than 69%, from concentrations of 3.12 mg/mL (69.81 ± 10%) to 50 mg/mL (98.10 ± 0.6%), whereas the nanoemulsion at 50 mg/mL presented repellent activities of 97.14 ± 1.37% and 97.89 ± 0.52% 6 and 10 h after treatment, respectively. These values regarding to total repellency were very close to those calculated for mortality corrected by Abbott's formula. The phase inversion method preserved the chemical and physical characteristics of the essential oil since both reached an equal repellent effect at the same concentration. Therefore, P. spicatus essential oil and nanoemulsion had excellent repellent activities against R. microplus larvae, demonstrating its potential for future use as an alternative for tick control.

Efficacy and safety of ethanolic Curcuma longa extract as a treatment for sand tampan ticks in a rabbit model

Background and Aim:

The soft tick Ornithodoros savignyi is distributed throughout Africa, including Egypt. It primarily attacks camels, cattle, donkeys, and cows; and rarely affects humans. This study evaluated the acaricidal efficacy of ethanolic Curcuma longa extract (Turmeric) on the second nymphs of O. savignyi and then investigated the safety of this herb in rabbits.

Materials and Methods:

The nymphs were immersed in 10, 5, 2.5, 1.25, and 0.625 mg/ml ethanolic C. longa extract. An additional group was immersed in ethanol as a control. On the 1^st, 7^th, and 15^th-day post-treatment, the mortality percentages, LC₅₀, and LC₉₅ were calculated. The ticks exposed to 10mg/ml ethanol C. longa extract were investigated by scanning electron microscopy (SEM). Three male New Zealand White rabbits were orally administered 2ml (two doses) of 10mg/ml ethanolic C. longa extract, and another three rabbits were orally given two doses of 2ml of absolute ethanol as a negative control. Histopathological examination of the kidney and liver hematology and the kidney and liver function was performed. Chemical analysis of the extract was determined by gas chromatography-mass spectrometry (GC-MS).

Results:

The LC₅₀ and LC₉₅ were 1.31 and 15.07, 1.07 and 8.56, and 0.81 and 6.97mg/ml on the 1^st, 7^th, and 15^thday, respectively. SEM revealed that mamillae and spots on the surfaces of the treated ticks were not discriminating except for some clefts on the surfaces. The histological examination, blood profile, and biochemical analyses revealed no significant differences between the treated and untreated rabbits (p>0.05). GC/MS analysis revealed 50 compounds, and curcumene and tumerone were found to be the major constituents of this ethanolic extract.

Conclusion:

The ethanolic C. longa extract produced a strong acaricidal effect on the second nymph of O. savignyi, and it was safe to use in rabbits.

Efficacy of carvacrol on Rhipicephalus (Boophilus) microplus engorged female ticks (Canestrini, 1887) (Acari: Ixodidae): effects on mortality and reproduction

The activity of carvacrol was evaluated in R. microplus female ticks by estimating the mean lethal concentration (LC₅₀) and the acaricidal efficacy. Ticks were subjected to the Adult Immersion Test (AIT) to calculate LC₅₀. From this value, the AIT was performed again at the concentrations of 20%, 40%, 60%, 80% and 100% of the LC₅₀. Two control groups were established: one treated with distilled water and one with the solvent (ethanol 50%). The following parameters were evaluated: female weight before oviposition, egg mass weight, pre-oviposition and incubation period, hatching percentage, egg production index, fecundity rate, estimated reproduction, reduction in oviposition and hatching, and product efficacy. The obtained LC₅₀ was 20.11 mg/mL. Egg mass weight, egg production index, pre-oviposition and fecundity rates of groups treated with 80% and 100% of LC₅₀ were statistically different when compared to control groups. The product efficacy in groups treated with 100% of LC₅₀ was 61.10%.

Insecticide activity of Curcuma longa (leaves) essential oil and its major compound α-phellandrene against Lucilia cuprina larvae (Diptera: Calliphoridae): Histological and ultrastructural biomarkers assessment

Lucilia cuprina, known as the Australian blowfly, is of high medico-sanitary and veterinary importance due to its ability to induce myiasis. Synthetic products are the most frequent form of fly control, but their indiscriminate use has selected for resistant populations and accounted for high levels of residues in animal products. This study aimed to assess the effect of essential oil from leaves of Curcuma longa (CLLEO), and its major compound α-phellandrene against L. cuprina L3. An additional goal was to determine the morphological alterations in target organs/tissues through ultrastructural assessment (SEM) and light microscopy, as well as macroscopic damage to cuticle induced by CLLEO. Groups of 20 L3 were placed on filter paper impregnated with increasing concentrations of CLLEO (0.15 to 2.86 μL/cm²) and α-phellandrene (0.29 to 1.47 μL/cm²). Efficacy was determined by quantifying L3 mortality 6, 24 and 48 h after contact with CLLEO and by measuring the structural damage to L3. CLLEO and α-phellandrene inhibited adult emergence by 96.22 and 100%, respectively. Macroscopic cuticle damage, appeared as diffuse pigment and darkening of larval body, was caused by both extracts. The SEM revealed dryness on the cuticle surface, distortion of the sensorial structures and general degeneration in treated L3. Furthermore, alterations in target organs (digestive tract, fat body and brain) were noticed and shall be used as biomarkers in future attempts to elucidate the mechanism of action of these compounds. The vacuolar degeneration and pyknotic profiles observed in the brain tissue of treated larvae with both extracts and the decreased motility within <6 h after treatment leads us to suggest a neurotoxic activity of the products. This work demonstrates the potential use of CLLEO and α-phellandrene as bioinsecticides to be used against L. cuprina, representing an ecofriendly alternative for myiasis control in humans and animals.

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.

Comparative study of hatching estimation methods of Rhipicephalus (Boophilus) microplus eggs

Reproductive parameters of Rhipicephalus (Boophilus) microplus are often evaluated. They are good indicators of resistance to commercial acaricides and of plant extracts' efficacy. The objective of this study was to compare the techniques: visual estimation and quantification by sampling used in the Adult Immersion Test (AIT) to calculate the hatching rate of eggs. Engorged females collected from cattle were subjected to the AIT with plant extracts and kept in an incubator for oviposition. The egg hatching was evaluated in 210 syringes by visual estimation (%). Then, eggs and larvae were counted into samples of 100 individuals, in three repetitions by stereo microscope. Significant differences were found between the two tests (p≤ 0.05). The egg hatching average of visual estimation was higher than the quantification by sampling, 56.8-48.0, respectively (correlation = 0.85). We found that the visual assessment leads to a higher estimate of larvae in relation to eggs, because the infertile eggs can be concealed in the center of the syringe. In quantification by sampling, no statistical differences (p = 0.99) were observed in the pairwise counts between the three samples (48.1 ± 26.6%, 47.8 ± 26.9%, 48.1 ± 26.5%) (correlation of repetitions = 0.96). This suggests that counting one sample is sufficient and the result should not differ much, regardless of the evaluator. Regarding the cutoff point of tick resistance status (95%), both methods are reliable. This study contributes to improvement of the AIT and can stimulate researchers to choose more accurate techniques for the assessment of egg hatching.

Efficacy of essential oils from plants cultivated in the Amazonian Biome against gastrointestinal nematodes in sheep

The excessive use of anthelmintics to control nematodes has resulted in anthelminthic resistance. Essential oils (EOs) are a rich source of bioactive molecules that can be assessed for their ability to control resistant parasite populations. The aims of this study were to screen EOs from 10 plant species in vitro for anthelmintic activity against Haemonchus contortus, evaluate the cytotoxicity of those EOs in a human immortalized keratinocyte cell line (HaCaT), and test the most promising EO candidate in vivo in Santa Inês sheep. The efficacy was investigated in vitro using an egg hatch test (EHT) and a larval development test (LDT). EO cytotoxicity was evaluated with the sulforhodamine-B assay. In the in vivo experiment, 28 Santa Inês sheep naturally infected were distributed into groups: G1-Mentha arvensis (EO5), 200 mg kg-1; G2-menthol, 160 mg kg-1; G3-negative control; and G4-positive control (monepantel). EO5, from M. arvensis (86.7% menthol), had the lowest LC50 and LC90 values in the EHT (0.10, 0.27 mg mL-1, respectively), good performance in the LDT (0.015, 0.072 mg mL-1, respectively), and the lowest cytotoxicity (190.9 µg mL-1) in HaCaT cells. In the in vivo test, a single dose of the EO5 (200 mg kg-1 BW) had an efficacy of approximately 50% on days 1, 14, and 21; however, values were not significantly from day 0. Conversely, pure menthol at a dose of 160 mg kg-1 BW showed no in vivo efficacy. This can be attributed to key factors related to bioavailability and pharmacology of terpenes in the host organism, as well as to the fact that menthol is mainly excreted as glucuronides in urine. Thus, further studies should be conducted with formulation systems that deliver bioactives directly to the abomasum, focusing on terpenes, whose excretion route is mainly via faeces.

Biological Activities of Essential Oils: From Plant Chemoecology to Traditional Healing Systems

Essential oils are complex mixtures of hydrocarbons and their oxygenated derivatives arising from two different isoprenoid pathways. Essential oils are produced by glandular trichomes and other secretory structures, specialized secretory tissues mainly diffused onto the surface of plant organs, particularly flowers and leaves, thus exerting a pivotal ecological role in plant. In addition, essential oils have been used, since ancient times, in many different traditional healing systems all over the world, because of their biological activities. Many preclinical studies have documented antimicrobial, antioxidant, anti-inflammatory and anticancer activities of essential oils in a number of cell and animal models, also elucidating their mechanism of action and pharmacological targets, though the paucity of in human studies limits the potential of essential oils as effective and safe phytotherapeutic agents. More well-designed clinical trials are needed in order to ascertain the real efficacy and safety of these plant products.