Effects of Ultraviolet on the Insecticidal Activity of the Entomopathogenic Nematode, Steinernema kushidai, Sprayed on Turfgrass

Abstract

Infective juveniles of the entomopathogenic nematode Steinernema hushidai, suspended in Petri dishes were exposed to UV-C. The nematode mortality of 30.3% at 10 sec exposure was not significantly higher than that without exposure. However, 20 sec exposure caused 61.9% nematode mortality and more than 60 sec exposure caused 100%. The third instar larvae ofAnomala cuprewere released in pot cultured turfgrass. The nematode suspension was sprayed on the turfgrass and the turfgrass was exposed to UV-C for 60 sec. The mortality of the third instar larvae did not significantly decrease compared with mortality of those without UVC exposure, whether or not watering treatment was applied after nematodes were sprayed. After the nematode suspension was sprayed on field cultured turfgrass, the turfgrass was immediately exposed to UV-C for 60 sec in a laboratory. The mortality of the released third instar larvae also did not significantly decrease. The nematode suspension was sprayed on field cultured turfgrass and the turfgrass was exposed to sunlight for 60 min. The mortality of the released third instar larvae by the nematodes significantly decreased as compared with that without exposure to sunlight, both with and without watering treatment after nematodes were sprayed. The decrease of insecticidal activity was caused by the high nematode mortality due to the high temperature, above 35°C, with the 60 min exposure to sunlight.