Beauveria bassiana submerged spores for control of two-spotted spider mite ( Tetranychus urticae Koch (Acari: Tetranychidae)): production, stability, and virulence

In this study, IBCB 66, IBCB 868, and CBMAI 1306 isolates of Beauveria bassiana were grown in liquid culture for 4 days, leading to elevated submerged spores (SS) levels. The influence of the addition of different glycerol concentrations (0, 3, and 6%) (v/v) in the liquid culture was investigated regarding the stability (at 4 and 27 °C) of dried formulations. The virulence of SS was compared with aerial spores (AS) against Tetranychus urticae (Koch) (Acari: Tetranychidae). The results demonstrate the potential of using SS to control T. urticae . CBMAI 1306 and IBCB 868 isolates caused T. urticae mortality rates of 91.11% and 88.89% 5 days after treatment, respectively, when applied at concentrations of 1 × 10 8 SS mL −1 . The median Lethal Time (LT 50 ) values for these strains were 2.64 and 2.61 days, respectively. The dried formulations showed potential acaricidal activity. Higher glycerol concentrations in the liquid culture medium reduced formulation stability at 27 °C.