Acaricidal efficacies of Lippia gracilis essential oil and its phytochemicals against organophosphate-resistant and susceptible strains of Rhipicephalus (Boophilus) microplus

Abstract

Plant-derived natural products can serve as an alternative to synthetic compounds for control of ticks of veterinary and medical importance. Lippia gracilis is an aromatic plant that produces essential oil with high content of carvacrol and thymol monoterpenes. These monoterpenes have high acaricidal activity against Rhipicephalus (Boophilus) microplus. However, there are no studies that show efficacy differences of essential oils between susceptible and organophosphate resistant strains of R. (B.) microplus. The aim of the present study was to compare acaricidal effects of essential oils extracted from two different genotypes of L. gracilis and the main monoterpenes on larvae of both susceptible and organophosphate resistant R. (B.) microplus larvae. The efficacy of the essential oil of two genotypes of L. gracilis (106 and 201) and their monoterpenes carvacrol and thymol was measured using the larval immersion test on coumaphos-resistant and susceptible strains of R. (B.) microplus. Lethal concentrations were calculated using GraphPad Prism 6.0. Chemical analysis was performed by GC-MS and FID. Thymol and carvacrol were observed to be major constituents in 106 and 201L. gracilis genotype essential oils, respectively. Essential oils of both genotypes were more effective against organophosphate-resistant tick strain than susceptible tick strain. Carvacrol was 3.2 times more toxic to organophosphate resistant strain than to susceptible strain. Thymol was equally toxic to resistant and susceptible tick strains. The significantly higher efficacy monoterpene carvacrol against resistant ticks may lead to development of new natural product acaricide formulations for use to control organophosphate resistant R. (B.) microplus populations.

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

“…The acaricidal effect against Rhipicephalus (Boophilus) microplus (a thick that parasites multiple livestock species) of EOs obtained from different Ocimum species was studied by Hüe et al [103], the best results being obtained for Ocimum urticaefolium and O. gratissimum originating from Cameroon. The same tick was used by Costa-Júnior et al [104], Monteiro et al [105], and Vinturelle et al [106] to test the acaricidal effect of EOs isolated from Lippia gracilis, Cinnamomum verum Presl, respectively, Piper nigrum, and Citrus limonum (further details presented in Table 3). While Costa-Júnior et al [104] assigned the acaricidal effect of EOs to the monoterpenes present, especially carvacrol and thymol, Vinturelle et al [106] compared the efficiency of two different composition EOs (C. limonum dominated by monoterpenes, respectively, P. nigrum dominated by sesquiterpenes), obtaining superior results for the C. limonum EO, thus suggesting a more potent acaricidal effect related to the presence of monoterpenes.…”

“…Similar with the insecticidal potential, the acaricidal potential of EOs is usually assigned by the authors to their monoterpenes content [104], and more than that, those monoterpenes components (such as carvacrol or thymol) were proposed as efficient agents against the metabolic resistance mechanisms or insensitive acetylcholinesterases (AChE) in the case of organophosphate resistant Acari [104].…”

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

“…Essential oils, extracts, or pure allelochemicals are the primary forms of plant-based products with biocidal features in tick assays. Methods including steam distillation [ 117 ], hydrodistillation [ 118 ], ethanolic and aqueous extraction [ 119 ], methanolic extraction and spilanthol [ 120 ], and hexane, ethyl, and acetate extractions [ 120 , 121 ] have been used to obtain these substances.…”

Acaricidal activity of cashew nut shell liquid associated with essential oils from Cordia verbenacea and Psidium guajava on Rhipicephalus microplus

“…An alternative is the development of formulations based on natural products, which reduce the risk of food and environment contamination. Natural products can be effective and to control resistant strains of ticks (4). One advantage of the use of plant oils is that the development of resistance can be slower than normally occurs when single compounds are used.…”