Effects of ultraviolet light on the entomopathogenic nematode, steinernema kushidai and its symbiotic bacterium, Xenorhabdus japonicus

Effects of ultraviolet (UV) exposure on the survival of Steinernema kushidai infective juveniles (JIII) and its insecticidal activity against the cupreous chafer, Anomala cuprea, Iarvae were examined at 25°C. The UV used was from sunlight and from UV lamps. The peak wavelengths of UV A, UV B and UV C lamps were 350, 310 and 254 nm, respectively. The nematode mortality significantly increased after the exposure to sunlight for 40 min at three intensities (4.3, 3.3 and 3.1 mW/cm2) of UV, and their insecticidal activity decreased. UV A (1.2 mW/cm2) was not harmful to JIII for up to 40 min exposure. Contrarily, all JIII were killed by the exposure to UV B (0.9 mW/cm2) for 5 min and to UV C (0.9 mW/cm2) for 30 s. The insecticidal activity of JIII and the number of A. cuprea cadavers producing nematode progeny after the treatments decreased at 40 min, 5 min and 10 s exposures to sunlight, UV B and UV C, respectively, but did not decrease after the exposure to UV A. Sunlight, UV B and UV C decreased the density of viable symbiotic bacterium. Xenorhabdus japonicus, associated with S. kushidai in the body of JIII.