Toxic and repellent activity of selected monoterpenoids (thymol, carvacrol and linalool) against the castor bean tick, Ixodes ricinus (Acari: Ixodidae)

Abstract

The castor bean tick, Ixodes ricinus, is a species of medical and veterinary importance. The use of synthetic acaricides for tick control has led to development of resistance, residues in the environment and animal products, and public health concerns. In this regard, plant essential oils and their main constituents represent an appealing alternative strategy to combat ticks. The phenols thymol and carvacrol and the alcohol linalool are monoterpenoids occurring in essential oils of several aromatic and medicinal plants, such as thyme, oregano, savory, lavender and coriander. Recent studies have shown toxicity of these monoterpenoids against selected mosquito vectors and other arthropod pests. However, information on their bioactivity on I. ricinus is not available. On this basis, here we evaluated the ovicidal, larvicidal and repellency effects of these compounds against I. ricinus. Concentrations of 0.25, 0.5, 1, 2 and 5% were sprayed on the egg masses, then hatching rates were noted. Larvicidal assays were conducted on unengorged larvae, following the larval packet technique. The repellency was determined by measuring the vertical migration behavior of ticks in laboratory conditions. Carvacrol and thymol at all concentrations tested led to a significant hatching decrease, showing an efficacy higher than permethrin, whereas linalool did not cause any significant effect. In the larvae treated with carvacrol and thymol (1, 2 and 5%), mortality rates reached 100% after 24h, showing a larvicidal efficacy higher than permethrin, whereas no effect was seen in the larval groups treated with linalool. Carvacrol and thymol at all concentrations tested showed >90% repellency on I. ricinus. Linalool was scarcely effective (50.24% repellency) only at the concentration of 5%. Overall, based on these results, the phenols carvacrol and thymol can be considered as candidate ingredients for the development of novel acaricidal formulations to control the populations of I. ricinus and the spread of related tick-borne diseases.

Larvicidal Activity of Essential Oils of Five Apiaceae Taxa and Some of Their Main Constituents Against Culex quinquefasciatus

“…Moreover, thymol was the major constituent of the essential oil from T. ammi , which is confirmed also by earlier studies . This plant phenol ranks among the most biologically effective compounds when compared with other constituents of essential oils . In addition, it has been demonstrated that thymol is capable of reducing the insect population density even if sublethal doses are applied .…”

“…These compounds possess notable insecticidal activity owing to their lipophilicity which enable them to cross easily the insect cuticle and enter the cells. From a mechanistic perspective, thymol is endowed with notable anti‐acetylcholinesterase activity and is reported as GABA A receptor agonist, whereas myristicin is able to inhibit the cytochrome P450 detoxicative enzymes . Thymol has been reported to possess repellent activity and insecticidal effects against various insects such as house fly, red flour beetle, southern corn rootworm, American cockroach, Formosan subterranean termite and mosquitoes .…”

Chemical composition and antioxidant activity of essential oils in Origanum vulgare subsp. gracile at different phenological stages and plant parts

“…As an aromatic oxygenated monoterpene, carvacrol is known to be attractive to pollinators (Patricelli et al, 2015). Carvacrol has also antifungal and insecticidal properties (Mendes, 2014;Patricelli et al, 2015;Tabari, Youssefi, Maggi, & Benelli, 2017) and, due to the fact that plants are more sensitive to herbivores and disease at an early vegetative stage, high amounts of carvacrol could be functioning as an allomone. Increasing the carvacrol content in flowers and at the flowering stage demonstrates the role of this phenolic monoterpene as a kairomone (Patricelli et al, 2015).…”

In vitro ovicidal activity of current and under‐development scabicides: which treatments kill scabies eggs?

“…Similar observations are reported from other arthropod studies. For example, ivermectin failed to kill the eggs of head lice, and permethrin had limited ovicidal activities against the tick Ixodes ricinus at concentrations that eliminated motile larvae . Only ivermectin has previously been proposed to have limited ovicidal activity on S. scabiei eggs.…”