The efficacy of some local isolates of the fungus Beauveria bassiana (Ascomycota: Hypocreales) on the red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionida)

The efficacy of four local isolates of the entomopathogenic fungus Beauveria bassiana (Ascomycota: Hypocreales) was tested. There were b58 isolated from moor soil (Al Heffah region), K isolated from citrus orchards soil (Al Bassah region), Bb isolated from Zeuzera pyrina larva (Oramo region) and Br isolated from red palm weevil adult in Lattakia governorate. Experiments were carried out on adults and fifth L5 larvae stage of the red palm weevil Rhynchophorus ferrugineus (Olivier) at a concentration of 10⁷ spores mL^‑1 of each isolate. Results showed that Br isolate is the most effective on adults and L5 larvae stage. Mortality rate of insects was 100% on the last day of experiment, while the Bb isolate was the least effective. The LC₅₀ values ranged between 2.4 and 6.8 days for L5 larvae and between 4.3 and 13.2 days for adults at the end of the experiment. The efficacy of different concentrations (10⁴, 10⁶, 10⁸ spores mL^‑1) of Br isolate was tested on adults and L3, L7 larvae stage of red palm weevil then. Morality and LC₅₀ were taken for each of them. Results showed that the third larvae stage is the most sensitive to the fungus. Mortality rates were 85, 100 and 100% for the three suspension concentrations of the Br isolate (10⁸, 10⁶, 10⁴ spores mL^‑1), respectively, whereas they were 58, 87 and 90% for the seventh larvae stage within 7 days of the experiment. The LC₅₀ for third instar larvae was 0.15×10² and 1×10³ spores mL^‑1 for seventh instar larvae. While the adult mortality rates during the 14 days of the experiment were 54, 83 and 100% for each concentration (10⁸, 10⁶, 10⁴ spores mL^‑1), respectively, and the LC₅₀ was 7×10³ spores mL^‑1. However, mortality rates in the control for L3, L7, and adult weevils were always 0%.