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 × 108 SS mL−1. The median Lethal Time (LT50) 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.