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Abstract
Tetradenia riparia (Hochst.) Codd (Lamiaceae) species is native of South Africa, and in Brazil it was introduced as an exotic ornamental plant and is already well-adapted to the climatic conditions. Its oil presents a complex structure of monoterpenes, sesquiterpepnes and deterpepnes with antimicrobial, antimicrobiana, antinociceptive and acaricide activity against Rhipicephalus (Boophilus) microplus. The essential oil from fresh leaves of T. riparia cultivated in the southern region of Brazil, was obtained by hydrodistilation in different seasons of the year (spring, summer, autumn and winter), from september 2011 to august 2012 and was analyzed by GC-MS. The oils were utilized at the concentrations of 2.500, 1.000, 400, 300, 200, 100, 50, 25, 12.5, 6.25, 3.125 µg/mL and tested on larvae of the third development stage of Aedes aegypti L. (Diptera, Culicidae) mosquito, utilizing the larval immersion test (LIT) for 24 h. The chemical composition showed that inside the class oxygenated sesquiterpenes, the major constituents were 14-Hydroxy-9-epi-caryophyllene and cis-Muurolol-5-en-4-α-ol (19.62; 13.33 % spring); (17.96; 12.07 % summer); (17.60;11.80 % autumn) and (11.73; 4.46% winter), respectively. The fenchone (oxygenated monoterpenes) increased in the summer (13.52 %) and autumn season (10.37 %). Calyculone ( oxygenated diterpene) increased in winter (25.42 %), autumn (19.84 %); summer (11.68 %) and spring (11.61 %). The larvicidal activity was mesure by calculating LD50 using the Probit test. The results showed the seasonality influence on the larvicidal action mainly for the DL50 in autumn, spring and summer which had the greatest activity (78.72; 83.29 and 123.02 µg/mL), respectively; and lowest larvicidal action in the winter (2619.79 µg/mL). Thus, this study confirmed that seasonality interfered in the larvicidal action, making important the season of oil extraction for biological purposes.
Acknowledgements
The authors are grateful to CNPq, CAPES and Fundação Araucária for providing a research grant and fellowships.