Influence of temperature on pathogenicity of some entomopathogenic nematode isolates (Steinernema spp.) from Japan screened for ability to control some noctuid moth larvae

Pathogenicity of indigenous steinernematids against some noctuid larvae was examined to screen candidates in a biological control program. First, 17 isolates from ten species (Steinernema feltiae, S. kraussei, S. kushidai, S. litorale, S. monticolum and five RFLP types) were screened for pathogenicity against the middle instar larvae of Peridoroma saucia, and S. feltiae and S. litorale were selected. Secondly, three isolates of S. feltiae and eight isolates of S. litorale were screened for pathogenicity against the middle instar larvae of Agrotis segetum, and S. feltiae HkEr36 and S. litorale IbKt142 were selected. Both isolates showed high pathogenicity at 25°C and below, but reduced pathogenicity at 30°C. Therefore, with the addition of a subtropical species S. abbasi collected after the second screening, the screened isolates were compared with an introduced nematode, S. carpocapsae All, for their pathogenicity against the late instar larvae of A. segetum and Spodoptera litura. The isolate S. litorale IbKt142 showed high pathogenicity between 7 and 25°C, and caused significantly higher mortality of A. segetum at 7, 10 and 15°C and S. litura at 7 and 10°C than S. carpocapsae All did. Moreover, S. abbasi OnIr181 caused significantly higher mortality of A. segetum at 30 and 35°C and S. litura at 35°C than S. carpocapsae All did.