Evaluation of UV-C light for control of Tetranychus urticae and Eotetranychus lewisi (Acari: Tetranychidae) on strawberry

Twospotted spider mite, Tetranychus urticae Koch, is a major arthropod pest of strawberry production in California, while Lewis mite, Eotetranychus lewisi McGregor, has emerged as an occasional but increasingly problematic pest in recent decades. Management of both species relies heavily on miticides and biological control, but resistance to miticides in T. urticae and limited biological control options for E. lewisi highlight the need for alternative management tools. Ultraviolet-C (UV-C) light is currently used in commercial strawberry production to manage powdery mildew, yet its efficacy against mite pests under California field conditions is not clear. This study evaluated the ovicidal and lethal effects of UV-C exposure on T. urticae and E. lewisi through laboratory and open-field evaluations, along with dose–response bioassays. Laboratory ovicide assays demonstrated near complete suppression of egg hatch for both species following UV-C exposure at 600, 1200, and 1800 J/m 2 . Field assays conducted across multiple seasons showed consistent and substantial reductions in egg hatch for T. urticae and E. lewisi , though efficacy varied among trials. Dose–response analyses indicated that larvae were more susceptible than adults, but lethal dose estimates for adults of both species exceeded 9,000 J/m 2 , a UV-C dose currently not advisable under field conditions. Reported LD 50 values confirmed that UV-C is unlikely to provide meaningful direct control of motile life stages at commercially viable exposure levels. To our knowledge, this study is the first to report ovicidal activity and lethal dose estimates for E. lewisi in response to UV-C light. These findings indicate that UV-C applications primarily function as an ovicidal tool for mite pests in strawberry production systems and may complement existing integrated pest management programs by targeting early developmental stages.