Susceptibilidade de uma população de Euschistus heros (Hemiptera: Pentatomidae) à duas misturas inseticidas (nNonicotinoide + Piretroide)

Abstract

The frequent and repeated use of insecticides with the same mode of action has favored the selection of less susceptible individuals, making resistance monitoring an essential tool to inform management strategies. In this context, the objective was to evaluate the frequency of resistance in a population of Euschistus heros (Fabricius, 1794) (Hemiptera: Pentatomidae) collected from a soybean-growing area at the ‘Fazenda Experimental’ UFGD to two commercial insecticides formulated with mixtures of neonicotinoids and pyrethroids, using a laboratory-maintained population as a susceptibility reference. Concentration-mortality bioassays were conducted with the insecticides Acetamiprid + Bifenthrin and Thiamethoxam + Lambda-cyhalothrin, estimating the lethal concentrations (LC₅₀), the slopes of the curves, and the resistance ratios. The insecticide Acetamiprid + Bifenthrin exhibited greater toxicity for both populations, with an LC₅₀ of 0.009 μg a.i. mL⁻¹ for the laboratory population and 0.076 μg a.i. mL⁻¹ for the field population. For Thiamethoxam + Lambda-cyhalothrin, the LC₅₀ values were 91.890 and 2,717.450 μg a.i. mL⁻¹ for the laboratory and field populations, respectively. The estimated resistance ratios were 8.44 for Acetamiprid + Bifenthrin and 29.57 for Thiamethoxam + Lambda-cyhalothrin, indicating lower susceptibility in the field population, especially to the second insecticide. The steeper slopes of the curves observed in the laboratory population indicated a more homogeneous response to the insecticides, while the field population exhibited greater variability in susceptibility, a characteristic consistent with natural populations. It is concluded that the field population exhibited lower susceptibility to the evaluated insecticides, especially to the thiamethoxam + lambda cyhalothrin formulation, as evidenced by higher LC₅₀ values and resistance ratios compared to the laboratory population, reinforcing the importance of resistance monitoring and the adoption of management strategies to preserve the efficacy of these insecticides in controlling E. heros.