Abstract
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.
