Pathogenicity of Newly Detected Steinernema sp. (Nematoda) to Scarabaeid Larvae Injurious to Tree Seedlings

Abstract

Steinernema sp. was isolated from a soil sample collected in Hamakita, Shizuoka Pref. Infectivity to and lethal effect of this nematode on larvae of scarabaeid beetles, soil pests in forest nurseries, were investigated under laboratory conditions. The infective juveniles (JIII) were inoculated onto a moist filter paper, soil and a commercial bark compost in petri dishes. High mortality of the insect larvae placed in these petri dishes containing a single larva of each species was observed 4 or more days after the inoculation. JIII of Steinernema sp. were found to be highly infective on all the tested species of scarabaeid beetles (Anomala cuprea, A. rufocuprea, Heptophylla picea, Maladera japonica, Popillia japonica, Allomyrina dichotoma and Protaetia orientalis). Inoculation with 100 JIII was sufficient to induce a high mortality of the larvae of A. cuprea. Lethal effect of this nematode on H. picea larvae was never observed at temperatures below 15°C. Critical temperature for the lethal effect of the nematode was approximately 17°C. When a water suspension of JIII was kept at 5°C, the survival rate decreased to less than 10% on the 20th day and zero on the 43rd day. At 10°C and 15°C, more than 95% of the JIII survived for 100 days. Lethal effect of JIII kept in soil or bark compost at 25°C was well maintained over 10 months. Preliminary tests for field application suggested that one million/m² JIII was the minimum dose required to achieve effective control of scarabaeid larvae.