Temporal variation in susceptibility of Euschistus heros ( Hemiptera: Pentatomidae ) to pyrethroids and neonicotinoids, and spatial patterns of control failure likelihood in southern Brazil

BACKGROUND Euschistus heros (Fabricius, 1798) is a major soybean pest in Brazil, managed primarily with chemical insecticides. From 2017 to 2026, we monitored temporal variation in susceptibility and spatial variation in control failure likelihood (CFL) of E. heros populations from Rio Grande do Sul State, southern Brazil, to pyrethroids and neonicotinoids. Mortality was assessed using insecticides alone or in pre‐formulated mixtures at the highest recommended field rates. RESULTS Mortality varied among populations and soybean growing seasons for all insecticides evaluated. Susceptibility to λ‐cyhalothrin and acetamiprid was low but variable across populations until 2024/25 and particularly low in 2025/26, when mortality was <17% for most populations exposed to λ‐cyhalothrin and <37% for all populations exposed to acetamiprid. Bifenthrin and imidacloprid showed more recent declines in susceptibility, with mortality of 33.3–56.7% and 26.2–83.3%, respectively, in 2025/26. Among pre‐formulated mixtures, susceptibility to λ‐cyhalothrin + acetamiprid and bifenthrin + acetamiprid also declined in recent seasons, whereas λ‐cyhalothrin + imidacloprid retained comparatively high activity. CFL was consistently high for λ‐cyhalothrin, reaching 96% in some populations at some locations, and increased recently for acetamiprid and imidacloprid and some acetamiprid‐based mixtures. Overall, susceptibility showed distinct temporal trajectories among insecticides, whereas CFL varied substantially among populations. CONCLUSIONS Persistently low susceptibility of E. heros to λ‐cyhalothrin and acetamiprid, together with recent declines for bifenthrin, imidacloprid and some pyrethroid–neonicotinoid mixtures, indicate reduced insecticide performance under laboratory conditions relative to the selected efficacy threshold. These findings highlight the need for continued susceptibility monitoring and insecticide resistance management strategies based on effective insecticides with distinct modes‐of‐action to preserve field efficacy.