BACKGROUND: The two-spotted mite, Tetranychus urticae Koch, is one of the most serious mite pests of crops throughout the world.Biocontrol of the mite with fungal agents has long been paid much attention to because of the development of insecticide resistance and severe restriction of the chemical pesticides.In this study, the efficacy of submerged conidia of the entomopathogenic fungus, Isaria cateniannulata strain 08XS-1, against T.urticae eggs, larvae and female adults was evaluated at different temperatures and humidity in laboratory and under field condition.RESULTS: The results showed that a suspension of 2 × 107 submerged conidia/ml caused the highest mortalities of mite eggs, larvae and females (100%, 100% and 70%, respectively) at 100% relative humidity and 25℃ in the laboratory.In the field experiments against the mites, the suspension of 2 × 108 submerged conidia/ml achieved significant efficiency, the relative control effects were 88.6%, 83.8%, and 83%, respectively, in cucumber, eggplant and bean fields after 10 d of treatment.CONCLUSION : The results suggest that the I.cateniannulata strain 08XS-1 is a potential fungal agent, with acceptable cost of the conidia production, against T.urticae in the field in the area, such as southwestern China, with higher air humidity.