Fumigant toxicity of three Satureja species on tomato leafminers, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is one of the major insect pests of solanaceous crops especially tomatoes. As plants contain secondary metabolites with protective properties against unwanted agents, they can be used as insecticides after extraction from plants as essential oils (EOs). In this study, essential oils of three savory species, including Satureja khuzestanica, S. bachtiarica, and S. rechingeri were extracted. Analyzing the chemical compositions via gas chromatography-mass spectrometry (GC/MS) revealed that geraniol was the main component of all essential oils. The volatile activity of these three savory species on the fourth instar larvae of T. absoluta during 24 h, indicated that LC50 values of S. khuzestanica, S. bachtiarica, and S. rechingeri oils were 17.51, 25.03, and 34.33 mu gL(-1)(air), respectively. Enzyme assays in vivo using alpha-naphthyl acetate (alpha-NA) as a substrate, showed that in the fourth instar larvae treated with 10 percent lethal concentration (LC10), general esterases of these larvae increased significantly in all treatments (p < .05). Polyacrylamide gel electrophoresis with a solution mixture of both substrates (alpha-and ss-NA) clarified three bands of esterases. However, this method failed to show any sublethal effects of the oils (LC10 value) on the larvae esterase bands. Considering the potential toxicity of these three species of Satureja essential oils to the tomato leafminers due to existence of several secondary metabolites, we can expect that new bio-pesticides can be developed from these promising plants in near future.

Automated summary

Essential oils extracted from three savory species showed significant insecticidal activity against Tuta absoluta larvae and increased general esterases in treated larvae. However, sublethal effects of the oils on larval esterase bands were not demonstrated. This suggests the potential development of new bio-pesticides from these promising plants in the future.