Rosmarinic acid as a promising biopesticide for red palm weevil (Rhynchophorus ferrugineus) control in date Palm trees

Abstract

The red palm weevil (Rhynchophorus ferrugineus Olivier) is a highly destructive pest that severely limits sustainable date palm (Phoenix dactylifera L.) production worldwide. The intensive use of synthetic insecticides has resulted in environmental contamination, health risks, and the emergence of resistant populations, emphasizing the need for eco-friendly alternatives within integrated pest management (IPM) programs. This study evaluated the insecticidal efficacy of rosmarinic acid (RA), a plant-derived secondary metabolite, against R. ferrugineus under laboratory and field conditions. Standardized bioassays were performed to assess lethal and sublethal effects using artificial diet incorporation across multiple concentrations. Nutritional indices, including efficacy of conversion of ingested food (ECI) and digested food (ECD), were measured to determine physiological disruption. At the molecular level, expression of detoxification enzymes (cytochrome P450, glutathione S-transferase (GST), and general esterases) was analyzed. Field trials were conducted during 2022–2023 in Baltim, Kafr El-Sheikh, Egypt, using trunk injection. RA was applied at 3, 4, and 5 mL L⁻¹, while deltamethrin (0.25 mL L⁻¹) served as a reference insecticide. Tree recovery was monitored for 30 days post-treatment based on new healthy growth and absence of infestation symptoms such as yellowish-brown viscous exudates from trunk tissues. Results showed a clear dose–response relationship, with LC₅₀ values of 2.041, 2.230, and 2.575 mL L⁻¹ for 4th instar larvae, 8th instar larvae, and adults, respectively. RA significantly reduced nutritional efficiency indices, indicating disruption of metabolic and digestive processes, and caused marked downregulation of detoxification-related genes, suggesting a multi-target mode of action. Under field conditions, RA at 5 mL L⁻¹ achieved the highest recovery rate (93.33%), compared with 86.67% for both deltamethrin and RA at 4 mL L⁻¹. These findings support rosmarinic acid as an effective, environmentally safe botanical insecticide for incorporation into IPM strategies for sustainable control of red palm weevil infestations.