Effects of UVC irradiation on predatory mites for biological control efforts in Florida

Tetranychus urticae Koch is a major mite pest in various crops both in the United States and worldwide. Damage caused by T. urticae incurs a significant economic loss to Florida growers, including specialty crops such as strawberries, Fragaria x ananassa Duchesne. Recent studies have shown that ultraviolet radiation has applications in pest management. This study attempts to test the efficacy of the ultraviolet C spectrum (UVC) in suppressing the hatchability of T. urticae eggs using an autonomous robot that has been developed to apply UVC in open-field strawberries. Leaf discs with T. urticae eggs were placed on strawberry plants and exposed to 0 J/m² (control), 200 J/m², or 350 J/m², followed by a minimum of four hours of darkness. An analysis of variance (ANOVA) was conducted to determine statistical differences in egg hatchability. Results showed UVC had a significant impact on the hatchability of T. urticae eggs. Predatory mites such as Neoseiulus cucumeris Oudemans, Phytoseiulus persimilis Athias-Henriot, and Amblyseius swirskii Athias-Henriot are commercially available biological controls known to feed on T. urticae. Eggs of these predator mites were irradiated on leaf discs and the hatchability was recorded after 24, 48, 72, and 96 hours. The number of T. urticae eggs consumed in a 48-hour period by irradiated adult predatory mites was also recorded. Results demonstrate that UVC application can be a potent tool for integrated pest management strategies that target T. urticae egg control, but precautions are needed to conserve biological control agents.