Is UV-C light compatible with biological control of twospotted spider mite?

Abstract

Biological control agents such as predatory mites, Neoseiulus cucumeris Oudemans, Amblyseius swirskii Athias-Henriot, and Phytoseiulus persimilis Athias-Henriot are effective in the management of a cosmopolitan crop pest, Tetranychus urticae Koch. Studies have shown that physical control by ultraviolet B (UV-B, 280–315 nm) light applications can control T. urticae by reducing egg hatch. However, to have a successful biological control program, the compatibility with other crop management strategies such as use of UV light needs to be determined. Therefore, the objectives of this study were to, 1) assess the impact of UV-C (200–280 nm) application on egg hatchability of biological control agents, A. swirskii, N. cucumeris, P. persimilis, and the pest T. urticae; 2) assess the impact of UV-C application on feeding efficiency of P. persimilis on T. urticae eggs; and 3) determine the LD50 and LD90 of adult female T. urticae to UV-C exposure. Results indicate that more eggs of A. swirskii survived when 200 J/m2 UV-C was used to control T. urticae, which suffered higher egg loss from the same UV-C dose. Also, UV-C treatments of 200 and 350 J/m2 did not have a significant impact on predation by P. persimilis adult females on T. urticae eggs. Therefore, UV-C can be compatibly utilized along with biological control of T. urticae by timing the application before release of predators. After 24 h of application, the UV-C LD50 for T. urticae adults was 8,839.35 J/m2 and the LD90 was 12,352.91 J/m2. After 48 h of application, the LD50 was 7,449.81 J/m2 and the LD90 was 9,621.83 J/m2. These UV-C doses are not feasible for T. urticae adult suppression, but biological control agents can play a crucial role with effective predation on T. urticae adults.