Insecticidal activity, chemical characterization, and biochemical responses induced by selected essential oils...

The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a major pest causing severe damage to tomato crops worldwide. The present study evaluated the insecticidal efficacy of Cymbopogon nardus (citronella) and Pelargonium graveolens (geranium) essential oils against T. absoluta larvae and their impact on selected biochemical and oxidative stress parameters under laboratory conditions. GC-MS analysis identified citral and related monoterpenes as the major components of citronella oil, while geranium oil was rich in citronellol. Toxicity assays demonstrated dose-dependent larval mortality for both oils, with citronella oil exhibiting slightly higher potency (LC₅₀ = 3.12%; LC₉₀ = 6.37%) than geranium oil (LC₅₀ = 3.88%; LC₉₀ = 7.65%). Biochemical analyses revealed significant reductions in GABA-transaminase activity, total protein, and total lipid contents in treated larvae, indicating disruption of neurotransmission, metabolism, and energy reserves. Furthermore, oxidative stress markers showed decreased total antioxidant capacity and superoxide dismutase activity, together with increased lipid peroxidation, indicating the induction of oxidative stress in treated larvae. These findings demonstrate that both essential oils possess significant insecticidal activity and induce marked biochemical and oxidative stress responses in T. absoluta larvae. Therefore, citronella and geranium essential oils may represent promising eco-friendly botanical insecticides for incorporation into integrated pest management programs for tomato crops.