The Efficacy of Egyptian Isolate of Beauveria bassiana Against Red Palm Weevil (Rhynchophorus ferrugineus) Olivier (Coleoptera: Curculionidae): Mortality Rates, Biochemical Responses, and Enzymatic Activity

Abstract Red palm weevil (RPW) larvae, Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae), were evaluated for susceptibility to an Egyptian isolate of the entomopathogenic fungus Beauveria bassiana. The results showed that R. ferrugineus larvae were more susceptible to B. bassiana at the 5th and 10th instars, respectively. A concentration of 10⁸ spores/ml of B. bassiana led to a higher mortality rate, with LT50 and LT90 values of 5.947 and 14.59 days, respectively. However, resistance ratios for concentrations of 10⁷ and 10⁸ spores/ ml were 1.80 and 1.32 times higher in the 10th instar compared to the 5th instar larvae, indicating lower susceptibility. Biochemically, after treatment with B. bassiana, significant changes in total protein and carbohydrate activity were observed in both larval stages. After 96 hours, GST activity increased significantly compared to the control. The effects of B. bassiana on alpha esterase and Glutathione-S-transferase (GST) enzymes varied by concentration and duration. Alpha esterase activity slightly decreased at 10⁸ spores/ ml after 48 hours but was not statistically significant after 96 hours. Conversely, at 10⁷ spores/ ml, alpha esterase decreased after 48 hours but increased after 96 hours. GST activity increased at 10⁸ spores/ ml after 48 and 96 hours and rose significantly at 10⁷ spores/ ml after 48 hours, followed by a decline after 96 hours. These findings suggest that B. bassiana could be used as an effective control agent against R. ferrugineus.