Abstract
Essential oils extracted from the leaves of Libyan Rosemary (Rosmarinus officinalis L.), and Miswak (Salvadora persica L.) were evaluated for their acaricidal and repellent effects on Ixodes ricinus L. nymphs (Acari: Ixodidae) using a bioassay based on an ‘open filter paper method’. Rosmarinus officinalis leaf essential oil diluted to 0.5 and 1 µl/cm2 in acetone exhibited, respectively, 20 and 100% tick mortality after about 5 h of exposure. A total of 50 and 95% of I. ricinus nymphs were killed by direct contact with the oil when exposed to lethal concentrations (LC) of 0.7 µl/cm2 (LC50) and 0.95 µl/cm2 (LC95), respectively. The LC50 (0.5 µl/cm2) was reached before the end of the first 24 h of exposure time (ET), as tick mortality at 24 h was 60%. Salvadora persica leaf essential oil at 1 µl/cm2 showed a significant repellency effect against I. ricinus nymphs at 1.5 h ET. A 95% repellency was observed at a repellent concentration (RC95) of 1 µl/cm2 of S. persica, but no significant mortality was recorded at this dose of S. persica oil. Gas chromatography–mass spectrometry analyses showed that the main monoterpenes in both oils were 1,8-cineol, α-pinene, and β-pinene, although in markedly different proportions. These results suggest that essential oils have substantial potential as alternative approaches for I. ricinus tick control.
Highlights
Many plant essential oils show a broad spectrum of effects against arthropods pests, including anti-feedant, repellent, and growth regulatory and anti-vector activity
Extracts from both planted were assayed for their possible repellency and acaricidal effects against nymphs of the widespread common tick, I. ricinus
Extracted oils were analysed by gas chromatograph coupled with a mass spectrometer (GC–MS) to determine their chemical composition by retention time and comparison to known standards
Summary
Many plant essential oils show a broad spectrum of effects against arthropods pests, including anti-feedant, repellent, and growth regulatory and anti-vector activity. Previous investigations indicate that some chemical constituents of these oils interfere with the octopaminergic nervous system of the insects (Bischof and Enan 2004; Kostyukovsky et al 2002), which has the advantage of being a target site not shared with mammals. Most essential oils have been shown to be relatively non-toxic to mammals and fish, and meet the criteria for “reduced risk” pesticides (Stroh et al 1998). Examples include azadirachtin, isolated from the neem tree, and other bioactive compounds that have been used successfully for pest control (Isman et al 1990; Park et al 2003; Wang et al 2010). Salvadora persica, commonly known as Miswak, is used for its antibacterial effect on several oral bacteria (Alali and Al-Lafi 2003; Sofrata 2010)
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