The Efficacy of Beauveria bassiana against Two-Spotted Spider Mites, Tetranychus urticae, (Acari: Tetranychidae) in Jimma, Ethiopia

Two-spotted spider mites ( Tetranychus urticae ) are significant agricultural pests that affect fruits, vegetables, forage crops, ornamentals, and greenhouse plants, rapidly developing resistance to many classes of acaricides. In Ethiopia, these mites severely impact horticultural products and field crops. This study aimed to assess the efficacy of Beauveria bassiana on T. urticae under laboratory and greenhouse conditions in Jimma town, Southwest Ethiopia. Mites were collected in sterilized polyethylene bags and transported to the Biotechnology Laboratory at Jimma University, where they were inoculated onto healthy bean leaves. Wax moth larvae were used to isolate B. bassiana , followed by standard isolation and characterization procedures. Screening bioassays identified a strain of B. bassiana that caused an average mortality rate of over 75% in adult mites at 7 days post-inoculation with a concentration of 2 × 10 ⁸ conidia ml ^− 1 . Results indicated that B. bassiana effectively controlled T. urticae adults, with significant mortality observed starting from 2 days after treatment. The fungus also affected mite eggs, with hatchability rates of 72.9%, 74.1%, and 85.2% at conidia concentrations of 2 × 10 ⁶ , 2 × 10 ⁷ , and 2 × 10 ⁸ ml ^− 1 , respectively. As the dose increased, egg hatchability decreased. The selected concentration of 2 × 10 ⁸ ml ^− 1 , was further tested under greenhouse conditions, where adult mortality reached 90%. This study demonstrates that B. bassiana can effectively kill both eggs and adults of T. urticae , providing a viable alternative to synthetic chemicals.