In vitro activity of pineapple extracts (Ananas comosus, Bromeliaceae) on Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Current perspectives and difficulties in the design of acaricides and repellents from plant-derived compounds for tick control

Ticks and tick-borne diseases have gained increasing attention in recent years due to their impact on public health and significant losses in livestock production. The use of synthetic compounds for tick control is becoming problematic, mainly due to the resistance to commercially available products as well as their toxicity. Therefore, new alternative control methods are required. For this purpose, plant-derived extracts may be considered as effective repellents and/or acaricides. The present literature review focuses on studies evaluating the acaricidal and repellent activity of plant-derived extracts and plant secondary metabolites. We also noted recent advances in protein-ligand-docking simulation to examine the possible toxic effect of natural chemical compounds on ticks. In conclusion, plant-derived repellents/acaricides can be effective against ticks, especially in rural areas and livestock farms.

Acaricidal activity of the essential oil from Senecio cannabifolius and its constituents eucalyptol and camphor on engorged females and larvae of Rhipicephalus microplus (Acari: Ixodidae)

The objective of this experiment was to evaluate the acaricidal activity of Senecio cannabifolius essential oil, and two of its constituents, eucalyptol and camphor. Efficacy against females and larvae of Rhipicephalus (Boophilus) microplus was assessed by the adult immersion test (AIT) and the larval immersion test (LIT). The oil was analyzed by gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (MS) and in total 68 components were identified representing 99.2% of the essential oil. AIT revealed that the oil, eucalyptol, and camphor at the highest concentration presented efficacy of 68.9, 57.1, and 71.9%, respectively. LIT revealed that the essential oil and camphor achieved 100% mortality at concentration of 1.6% wt/vol, whereas eucalyptol showed moderate inhibitory activity. Biochemical assays indicated that the essential oil and camphor can reduce significantly overall detoxification enzyme activities in engorged females and larvae at high concentration (≥ 0.4% wt/vol), whereas the inhibitory effect of eucalyptol is weaker than that of the oil and camphor. Taken together our results indicated that the S. cannabifolius essential oil and its isolated constituent had potential for the development of a new and safe acaricide for the control of R. microplus ticks.

In vitro effects of Pilocarpus microphyllus extracts and pilocarpine hydrochloride on Rhipicephalus (Boophilus) microplus

The aim of this study was to assess the activity of aqueous (AE) and ethanolic extracts (EE) and pilocarpine hydrochloride, which were extracted and isolated from Pilocarpus microphyllus (Jaborandi), respectively, on Rhipicephalus (Boophilus) microplus. High performance liquid chromatography (HPLC) was performed to quantify these compounds. Larval packet and adult immersion tests were conducted with different concentrations. Five AE and EE concentrations, ranging from 6.2 to 100.0 mg mL-1, and six concentrations of pilocarpine hydrochloride, ranging from 0.7 to 24.0 mg mL-1, were tested. The lethal concentration (LC50) of each extract for larvae and engorged females was calculated through Probit analysis. The concentration of pilocarpine hydrochloride obtained from the EE and the AE was 1.3 and 0.3% (m/m), respectively. Pilocarpine hydrochloride presented the highest acaricidal activity on larvae (LC50 2.6 mg mL-1) and engorged females (LC50 11.8 mg mL-1) of R.(B.) microplus, followed by the EE which presented LC50 of 56.4 and 15.9 mg mL-1, for larvae and engorged females, respectively. Such results indicate that pilocarpine hydrochloride has acaricidal activity, and may be the primary compound responsible for this activity by P. microphyllus EE.

Tick repellents and acaricides of botanical origin: a green roadmap to control tick-borne diseases?

Arthropods are dangerous vectors of agents of deadly diseases, which may hit as epidemics or pandemics in the increasing world population of humans and animals. Among them, ticks transmit more pathogen species than any other group of blood-feeding arthropods worldwide. Thus, the effective and eco-friendly control of tick vectors in a constantly changing environment is a crucial challenge. A number of novel routes have been attempted to prevent and control tick-borne diseases, including the development of (i) vaccines against viruses vectored by ticks; (ii) pheromone-based control tools, with special reference to the "lure and kill" techniques; (iii) biological control programmes relying on ticks' natural enemies and pathogens; and (iv) the integrated pest management practices aimed at reducing tick interactions with livestock. However, the extensive employment of acaricides and tick repellents still remains the two most effective and ready-to-use strategies. Unfortunately, the first one is limited by the rapid development of resistance in ticks, as well as by serious environmental concerns. On the other hand, the exploitation of plants as sources of effective tick repellents is often promising. Here, we reviewed current knowledge concerning the effectiveness of plant extracts as acaricides or repellents against tick vectors of public health importance, with special reference to Ixodes ricinus, Ixodes persulcatus, Amblyomma cajennense, Haemaphysalis bispinosa, Haemaphysalis longicornis, Hyalomma anatolicum, Hyalomma marginatum rufipes, Rhipicephalus appendiculatus, Rhipicephalus (Boophilus) microplus, Rhipicephalus pulchellus, Rhipicephalus sanguineus and Rhipicephalus turanicus. Eighty-three plant species from 35 botanical families were selected. The most frequent botanical families exploited as sources of acaricides and repellents against ticks were Asteraceae (15 % of the selected studies), Fabaceae (9 %), Lamiaceae (10 %), Meliaceae (5 %), Solanaceae (6 %) and Verbenaceae (5 %). Regression equation analyses showed that the literature grew by approximately 20 % per year (period: 2005-2015). Lastly, in the final section, insights for future research are discussed. We focused on some caveats for future data collection and analysis. Current critical points mainly deal with (a) not uniform methods used, which prevent proper comparison of the results; (b) inaccurate tested concentrations, frequently 100 % concentration corresponded to the gross extract, where the exact amounts of extracted substances are unknown; and (c) not homogeneous size of tested tick instars and species. Overall, the knowledge summarized in this review may be helpful for comparative screening among extensive numbers of plant-borne preparations, in order to develop newer and safer tick control tools.

Assessment and determination of LC50 of carvacrol and salicylic acid analogues with acaricide activity in larvae and adult ticks of Rhipicephalus (Boophilus) microplus

Rhipicephalus (Boophilus) microplus is a tick that causes huge economic losses in cattle. The indiscriminate use of acaricides has generated resistance to most compounds present on the market. Carvacrol and salicylic acid have been widely studied for their biological activities and have been evaluated in different strains of Rhipicephalus. In this research the analogues carvacrol and salicylic acid were evaluated in larvae of R. (B.) microplus with data obtained in larval packet test (LPT) and larval immersion test (LIT). A lethal concentration 50 (LC₅₀) was assessed. The most potent compounds were evaluated in the adult ticks since there are no reports of evaluation in the life state of the parasite. From all the tested compounds, the ethyl 2-methoxybenzoate (91.82 ± 1.66%, 0.91 μmol/mL) and ethyl 2,5-dihydroxybenzoate (89.14 ± 1.61%, 2.04 μmol/mL) showed the highest percentage of mortality and the lowest LC₅₀. They were found to be the best candidates for a study in vivo.