Acaricidal activity against Ixodes ricinus nymphs of essential oils from the Libyan plants Artemisia herba alba, Origanum majorana and Juniperus phoenicea.

Ixodes ricinus (L.) (Acari: Ixodidae) is a major vector for the transmission of several important human pathogens. The aim of the present study was to evaluate the in vitro efficacy of different concentrations of essential oils (Eos) on I. ricinus tick nymphs. Oils were obtained from the leaves of three plants native to Libya: white wormwood (Artemisia herba alba Asso), marjoram (Origanum majorana L.) and Arâr (Juniperus phoenicea L., English common name Phoenician juniper). Assays were done using the "open filter paper method". Two concentrations from each oil, 0.5 and 1 µl/cm, were tested. The acaricidal effect was measured in terms of the lethal concentrations (LC50, LC95) and lethal time (LT50, LT95). Mortality rates were obtained by counting the surviving nymphs every 30 min for the first five hours and then at 24, 48 and 72 h. A mortality of 100% was recorded at the higher concentration of oils (1 µl/cm2) from A. herba alba and J. phoenicea at the first 2 h of exposure. Exposure to O. majorana led to 100% mortality on the third day (72 h), and this effect decreased noticeably with 0.5 µl/cm2 oil at the same exposure time. However, 50% of ticks showed a paralysis effect and less movement after 2 h. The LC50 of mortality was reached within the first 24 h of exposure time at 0.5 µl/cm2 of O. majorana, which produced 60% tick's mortality. Chemical composition of the essential oils was elucidated by gas chromatography-mass spectrometry analyses. These results suggest that essential oils deserve further investigation as components of alternative approaches for I. ricinus tick control.

The repellency and toxicity effects of essential oils from the Libyan plants Salvadora persica and Rosmarinus officinalis against nymphs of Ixodes ricinus.

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 ß-pinene, although in markedly different proportions. These results suggest that essential oils have substantial potential as alternative approaches for I. ricinus tick control.

Acaricidal properties of ylang-ylang oil and star anise oil against nymphs of Ixodes ricinus (Acari: Ixodidae).

Ylang-ylang oil (YYO) from Cananga odorata (Lam.) Hook.f. & Thomson and star anise oil (SAO) from Illicium verum Hook.f. were tested at four concentrations 0.05, 0.1, 0.2, 0.4 µl/cm2. Mortality rates were obtained by counting dead nymphs at 30-min intervals during the first 5 h after the start of exposure and then at 24, 48 and 72 h. Mortality increased with increasing oil concentration and time of exposure. The two highest concentrations of YYO (0.2, 0.4 µl/cm2) gave maximum lethal concentrations (LC) of 50 and 95% mortality after 4.5 h exposure. Mortality of 95% was obtained after 24 h with the next highest dose (0.1 µl/cm2), whereas LC95 required 3 days with the lowest YYO (0.05 µl/cm2). The lethal effect time (LT) was correlated with the duration of exposure, with a significant effect at 0.4 µl YYO/cm2 after 3 h' (LT50 = 3.2 h, LT95 = 4.3 h). In contrast, only the highest concentration of SAO, 0.4 µl SAO/cm2, showed increasing mortality with time of exposure. This reached LT50 after 10 h and LT95 after 24 h. However, with the lower concentration (0.2 µl/cm2) 50% mortality was reached after 24 h and 100% at 72 h. At to the lowest concentration of SAO (0.1 µl/cm2), 67% mortality after 48 h. The study indicates that YYO and SAO exhibit strong acaricidal properties against nymphs of I. ricinus and suggest that both YYO and SAO should be evaluated as potentially useful in the control of ticks.

Acaricidal effects of Corymbia citriodora oil containing para-menthane-3,8-diol against nymphs of Ixodes ricinus (Acari: Ixodidae).

The toxicity of para-menthane-3,8-diol (PMD), the main arthropod-repellent compound in the oil of the lemon eucalyptus, Corymbia citriodora, was evaluated against nymphs of Ixodes ricinus using five methods (A-E) of a contact toxicity bioassay. Mortality rates were estimated by recording numbers of dead nymphs at 30 min intervals during the first 5 h after the start of exposure and at longer intervals thereafter. The mortality rate increased with increasing concentration of PMD and duration of exposure with a distinct effect after 3.5 h. From the results obtained by methods A, C and E, the LC(50) range was 0.035-0.037 mg PMD/cm(2) and the LC(95) range was 0.095-0.097 mg PMD/cm(2) at 4 h of exposure; the LT(50) range was 2.1-2.8 h and the LT(95) range was 3.9-4.2 h at 0.1 mg PMD/cm(2). To determine the duration of toxic activity of PMD, different concentrations (0.002, 0.01, 0.1 mg PMD/cm(2)) were tested and mortality was recorded at each concentration after 1 h; thereafter new ticks were tested. This test revealed that the lethal activity of PMD remained for 24 h but appeared absent after 48 h. The overall results show that PMD is toxic to nymphs of I. ricinus and may be useful for tick control.