RESUMO
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.