Assessment of the insecticidal activity of five essential oils used against the subterranean termite Reticulitermes lucifugus (Rossi) (Blattodea, rhinotermitidae) in laboratory

Among Reticulitermes genus the most abundant species living in Italy is Reticulitermes lucifugus Rossi. This termite is very dangerous to wooden structures of artistic heritage and buildings. The traditional control of R. lucifugus is very difficult resulting in negatively impact on the environment, therefore the use of phytochemical, such as essential oils (EOs), could lead to an alternative to synthetic insecticides, with advantages in reducing environmental risks. In this work we investigated the insecticidal activity of EOs of Citrus bergamia Risso, Syzygium aromaticum L., Foeniculum vulgare Mill., Pelargonium odoratissimum L., and Origanum vulgare L. by inhalation against R. lucifugus workers. It is the first study to examine the efficacy of EOs on this termite species. Results showed that after 24 hours of treatment exposure, mortality occurred in all treatments and was dose-dependent, increasing when the treatment dose increased. At the lowest dose (2.5 μl/l), oregano, clove, and geranium EOs resulted in mortality of more than 80%. Oregano EO was the most active already at low doses, while fennel EO was the least effective. 24 hours after the treatment, the lowest DL50, obtained by the dose-response analysis, was detected for oregano EO (1.21 μl/l), followed by those of EOs of clove (1.28 μl/l), geranium (1.73 μl/l), fennel (2.20 μl/l), and bergamot (2.88 μl/l). This study highlighted the possibility of using these EOs in the termite control for the preservation of wooden structures.