Molecular Characterization and Pathogenicity of two local Isolates of Bacillus thuringiensis against the Larvae of Red Palm Weevil, Rhynchophorus ferrugineus in Syria

Abstract

The pathogenicity of two local isolates, Hzs4 and Hss8, of Bacillus thuringiensis (Bt) bacteria, identified using polymerase chain reaction, was evaluated on the second and fourth larval instars of the red palm weevil, Rhynchophorus ferrugineus, under laboratory conditions in 2025. This was done by treating the larvae with three concentrations (1.5×10⁹, 1.5×10⁸, 1.5×10⁷ CFU/ml). The results obtained showed that the corrected average mortality rates for second-instar larvae, five days after treatment, were 75.69, 78.38 and 100% for the three concentrations, respectively, whereas the mortality rates for the fourth-instar larvae after the same period, reached 79.48, 89.18 and 100% for the three concentrations, respectively, compared to a mortality rate of 7.5% in the control treatment. The median lethal concentration (LC₅₀) was 8.73×10⁶ CFU/ml and 5.39×10⁶ CFU/ml for the second and fourth larval instars, respectively. The results clearly showed that the concentration of 1.5×10⁹ CFU/ml was significantly superior to the concentrations of 1.5×10⁸ and 1.5×10⁷ CFU/ml for both larval instars, and the mortality rate increased proportionally with time after treatment and Bt concentration.

Keywords:

Bacteria, Bacillus thuringiensis, molecular characterization, second instar larvae, fourth instar larvae, red palm weevil, Rhynchophorus ferrugineus, median lethal concentration, Syria.