Seasonal and Circadian Evaluation of the Pectis brevipedunculata Essential Oil and Its Acaricidal Activity against Rhipicephalus microplus (Acari: Ixodidae)

Pectis brevipedunculata is native species and widely available in dry and semi-arid ecosystems showing high biotechnological potential. The objective of this study was to evaluate the circadian and seasonal chemical variation of the essential oil (EO) of P. brevipedunculata, as well as its acaricide effect on Rhipicephalus microplus larvae. Aerial parts were collected and submitted to the hydrodistillation process, and the chemical composition was determined by gas chromatography mass spectrometry (GC-MS). For the assays with R. microplus, the larval immersion test was performed. The main constituents were citral (75% of the EO), followed by α-pinene and limonene. In the seasonality analysis, the highest yields were in the months of April (2.08%) and August (2.05%), while in the study of circadian rhythm, the percentage was 2.0% at 6 p.m. in the rainy season, and 1.2%, dry season at 6 p.m. Concerning acaricidal activity (50% lethal concentration (LC50)), the April (1.17 mg mL-1), March (1.28 mg mL-1), June (1.37 mg mL-1), and October (1.27 mg mL-1) oils obtained were the most active and assays performed with circadian rhythm revealed in the rain season (April) at 6 p.m. and dry season (September) at 12 a.m. LC50 values of 1.75 and 1.75 mg mL-1, respectively. Additionally, this EO is selective to non-target organisms, i.e., ladybeetles and lacewing.

短柄臭春黄菊（Pectis brevipedunculata）为本土物种，广泛分布于干旱与半干旱生态系统中，具备极高的生物技术应用潜力。本研究旨在探究该植物精油（essential oil, EO）的昼夜与季节化学组分变化，及其对微小牛蜱（Rhipicephalus microplus）幼虫的杀蜱活性。研究人员采集该植物的地上部分，采用水蒸馏法提取精油，并通过气相色谱-质谱联用法（gas chromatography mass spectrometry, GC-MS）分析其化学组成。针对微小牛蜱的生物活性测定，本研究采用幼虫浸渍法开展实验。该精油的主要组分为柠檬醛（占精油总量的75%），其次为α-蒎烯与柠檬烯。季节变化分析结果显示，精油提取率最高的月份为4月（2.08%）与8月（2.05%）；而昼夜节律研究结果表明，雨季当日18:00时精油提取率可达2.0%，旱季当日18:00时提取率为1.2%。在杀蜱活性方面，以半数致死浓度（50% lethal concentration, LC50）为评价指标，4月、3月、6月及10月采集的精油活性最强，其LC50值分别为1.17 mg·mL⁻¹、1.28 mg·mL⁻¹、1.37 mg·mL⁻¹与1.27 mg·mL⁻¹；昼夜节律相关实验结果显示，雨季（4月）当日18:00时与旱季（9月）当日00:00时采集的精油，LC50值均为1.75 mg·mL⁻¹。此外，该精油对非靶标生物具有选择性，如瓢虫（ladybeetles）与草蛉（lacewing）。