Insecticidal activity of essential oils of Cupressus arizonica greene and C. sempervirens L. on Tortrix viridana (Lepidotera, Tortricidae)

Abstract

Tortrix viridana is one of the most important defoliators of oak trees. In 2006 and 2007, this insect caused significant defoliations of oak forests in the Northwestern Tunisia. This work aims at studying the insecticidal activity of essential oils of Cupressus arizonica and C. sempervirens on 3rd, 4th and 5th instars larvae of T. viridana by the contact test. Three different concentrations of essential oils (0.05%, 0.1% and 0.5%) were used to test their contact effectiveness; the Deltamethrin and the ethanol were used as positive and negative controls. Larvicidal activity was determined by measuring the Mean Mortality Time (MMT) to kill 100% of larvae. A total of 28 chemical compounds have been identified from C. arizonica and 20 chemical compounds from C. sempervirens. The difference in MMT of the 3rd instar larva was highly significant between the 3 concentrations of the two tested essential oils, the negative and positive controls. In fact, the concentration (0.5%) was more efficient than the two other concentrations with a MMT=1h31min12s for C. arizonica and 5h11min20s for C. sempervirens. The same results were observed for the 4th (MMT=3h23min24s (Ca) and 4h1min (Cs)) and 5th (MMT= 3h23min24s (Ca) and 4h01min (Cs)) instars. The results revealed that the essential oil of C. arizonica was more effective than C. sempervirens. Therefore, it is recommended to use the essential oil of C. arizonica and not that of C. sempervirens, given its insecticidal efficiency on the 3rd instar larva of T. viridana