Acaricidal and Repellent Activities of Rhizobacterial Isolates Against Tetranychus urticae (Acari: Tetranychidae) Under Laboratory and Greenhouse Conditions

The two-spotted spider mite, Tetranychus urticae Koch, is a highly polyphagous and economically important pest affecting a wide range of crops worldwide. This study evaluated the potential of four rhizobacterial isolates—Leucobacter aridicollis (IQR1), Paenochrobactrum sp. (IQR2), uncultured bacterium IQR3, and marine bacterium AK6_052 (IQR5)—as candidate biological control agents against T. urticae. The rhizobacterial isolates were obtained from the tomato rhizosphere at the INRA experimental farm (Agadir, Morocco) and evaluated for their acaricidal and repellent activities against T. urticae. Corrected mortality and repellency index were assessed after 24, 48, and 72 h of exposure. All four isolates exhibited acaricidal activity, with IQR3 and IQR5 showing the greatest efficacy. Corrected mortality reached 69.9% with IQR3 at the highest concentration after 72 h of exposure. The isolates showed no statistically significant repellent activity. Under greenhouse conditions (108 CFU mL−1), IQR3 was associated with the lowest infestation incidence (64%), the lowest infestation severity (13.3%) and the lowest adult density (1.8 adults leaf−1); IQR5 showed a comparable trend. Overall, IQR3 and IQR5 represent promising rhizobacterial candidates for the sustainable management of T. urticae in tomato production. Further studies are needed to optimize their formulation, elucidate their mechanisms of action, and validate their efficacy under field conditions.