[en] Despite the widespread use of the insecticide imidacloprid (IMI), a neonicotinoid, there is an urgent need for documenting information related to its acute toxicity. Therefore, this study aims to explore the markers of IMI acute toxicity in the testes of the red palm weevil (Rhynchophorus ferrugineus). The LC₅₀ of IMI was determined at 15.7 ppm for male R. ferrugineus. We assessed biochemical alterations in the testes resulting from treatment with four IMI concentrations (10, 15, 20, and 30 ppm). A reduction in glutathione content and acetylcholine esterase activity followed the IMI concentration in a dependent manner. Catalase activity was inhibited only at 20 ppm, while it increased significantly at 30 ppm. Lipid peroxidation increased steadily as the IMI concentrations increased. Based on ultrastructural analyses of spermiogenic stages, acute IMI toxicity produced swelling and degeneration of spermatid mitochondria indicating structural imbalances in their membranes. Further, abnormal chromatin condensation in nuclei and even loss of sperm were also apparent. This study provides biochemical and ultrastructural indicators for acute toxicity resulting from IMI.