Abstract Lygus hesperus Knight (Hemiptera: Miridae) is a major pest of California strawberries, where feeding injury from nymphs and adults leads to fruit deformation and economic losses. Management relies heavily on insecticides, with supplemental mechanical removal using bug vacuums. Insecticide resistance and inconsistent vacuum efficacy have prompted interest in non-chemical alternatives. Ultraviolet-C light is currently used for powdery mildew management in California strawberries but has not been evaluated for efficacy against L. hesperus. This study assessed the ovicidal effects of ultraviolet-C on L. hesperus and determined LD50 and LD90 values for 1st, 3rd, and 5th instars. In laboratory assays, ultraviolet-C exposure at 350 J/m2 significantly reduced egg hatch compared to the control, while higher doses (650 and 1,000 J/m2) did not differ statistically. In the field-applied ultraviolet-C treatments, the 2024 results did not show significant hatch reductions, whereas the 2025 results showed a significant reduction in egg hatch at 1,015 J/m2. Dose–response modeling showed high lethal thresholds, with LD50 values ranging from 19,527 to 25,591 J/m2 across instars. Occasional molting disruption and wing deformities were observed after 5th instars molted into adults. These findings suggest that ultraviolet-C is not a viable stand-alone strategy for controlling L. hesperus nymphs but may offer a slight ovicidal effect. Further research is needed to evaluate sublethal effects and to explore integration with mechanical control methods, particularly in organic production systems where effective chemical strategies are limited.
Koubek et al. (Wed,) studied this question.