Toxicity and biochemical effects of emamectin benzoate against Tuta absoluta (Meyrick) alone and in combination with some conventional insecticides

Abstract

The tomato leaf miner, Tuta absoluta (Meyrick), is one of the serious insect pests in tomato and potato farms. Along with acute toxicity, effects of emamectin benzoate alone and mixed with some conventional insecticides on esterase enzymes and the protein content of T. absoluta second-instar larvae were assessed in the current study. After 72 h exposure time, emamectin benzoate had the most toxicity (LC₅₀ = 0.52 mg a.i. L⁻¹), followed by azadirachtin (LC₅₀ = 5.19 mg a.i. L⁻¹), indoxacarb (LC₅₀ = 7.13 mg a.i. L⁻¹), imidocloprid (LC₅₀ = 44.63 mg a.i. L⁻¹), thiacloprid (LC₅₀ = 293.92 mg a.i. L⁻¹) and lambda-cyhalothrin (LC₅₀ = 610.08 mg a.i. L⁻¹). Although emamectin benzoate mixed with either azadirachtin or indoxacarb at LC₁₅: LC₁₅ (Lethal Concentration to kill 15% tested insects) ratio had synergistic effects, its combination with imidacloprid or thiacloprid showed additive interactions. However, emamectin benzoate mixed with imidacloprid at both LC₂₅: LC₂₅ and LC₅₀: LC₅₀ ratios showed synergistic effects. Lambda-cyhalothrin mixed with emamectin benzoate showed an antagonistic interaction in all tested ratios. α-esterase activity of larvae increased when emamectin benzoate was mixed with thiacloprid in comparison with emamectin benzoate alone and the control. Combinations of emamectin benzoate with either azadirachtin or indoxacarb significantly reduced the total protein content of larvae. Generally, it can be concluded that the combination of emamectin benzoate with either azadirachtin, indoxacarb, or imidacloprid resulted in more negative impacts against T. absoluta larvae.