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.

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/cm 2 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/cm 2 (LC 50) and 0.95 µl/cm 2 (LC 95), respectively. The LC 50 (0.5 µl/cm 2) 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/cm 2 showed a significant repellency effect against I. ricinus nymphs at 1.5 h ET. A 95% repellency was observed at a repellent concentration (RC 95) of 1 µl/cm 2 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.

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/cm 2. 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/cm 2) 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/cm 2), whereas LC 95 required 3 days with the lowest YYO (0.05 µl/cm 2). The lethal effect time (LT) was correlated with the duration of exposure, with a significant effect at 0.4 μl YYO/cm 2 after 3 h' (LT 50 = 3.2 h, LT 95 = 4.3 h). In contrast, only the highest concentration of SAO, 0.4 µl SAO/cm 2 , showed increasing mortality with time of exposure. This reached LT 50 after 10 h and LT 95 after 24 h. However, with the lower concentration (0.2 µl/ cm 2) 50% mortality was reached after 24 h and 100% at 72 h. At to the lowest concentration of SAO (0.1 µl/cm 2), 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.

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