Insecticidal properties of Ocimum basilicum and Mentha piperita essential oils against South American Tomato moth, Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelichiidae)

Abstract

Phthorimaea absoluta (Meyrick) is one of the most destructive pests of tomato, causing 100% yield loss in the absence of control measures. The important method of managing the pest is by using synthetic insecticides. However, intermittent and indiscriminate uses of certain insecticides have negative effect on the environment. Use of herbal insecticides such as secondary metabolites and essential oils is a key for sustainable long term crop protection. Investigation on the insecticidal properties of Ocimum basilicum, Mentha piperita essential oils (EOs) and their constituents was carried out against P. absoluta. The M. piperita EO showed highest mortality (100%) of P. absoluta with LC₅₀ 1.78 μl/ml due to alloaromadendrene (27.99%), levomenthol (18.31%) and santolina triene (9.78%). The O. basilicum EO also had significant mortality (90%) effect with LC₅₀ 3.58 μl/ml due to humulene (32.31%), alpha farnesense (27.22%), estragole (19.24%) and 4-cerene (10.61%). Among binary compounds, levomenthol showed highest mortality (100%) having LC₅₀ 13.18 μl/ml followed by alpha-pinene (100%) with LC₅₀ 16.10 μl/ml, 4-cerene (95%) with LC₅₀ 38.20 μl/ml and alpha-phellandrene (90%) having LC₅₀ 46.83 μl/ml. The observed toxicity in all compounds was due to significant changes in the activity of esterases, glutathione S-transferase and acetylcholine esterases over the time. The present study suggests that O. basilium and M. piperita EOs would provide an additional approach for the management of P. absoluta over synthetic insecticides.

Keywords: Acetylcholine esterase; Bioassay; Botanicals; Esterases; GC–MS; Glutathione S-transferase.