Abstract:

The pathogenicity of four entomopathogenic nematodes (EPNs) against the prepupae and pupae of Spodoptera exigua was tested in laboratory to screen the effective strains of EPNs for the control of S. exigua, and the effect of soil moisture on the pathogenicity of EPNs was evaluated. Results showed that four EPNs exhibited different pathogenicity to S. exigua at the prepupa and pupa stages. At the same dose, the lethal effects of All, X-7, and JY-90 strains of Steinernema carpocapsae on the prepupa of S. exigua were better than that of the LN₂ strain of Heterorhabditis indica. When the dose of EPNs was 100 IJs per prepupa, the mortality of the X-7, JY-90, and All strains of S. carpocapsae exceeded 80%, whereas the mortality of the LN₂ strain of H. indica was only about 40%. The pathogenicity of the four EPNs to S. exigua pupae was lower than that to the prepupae. When the dose of EPNs was 1 600 IJs per pupa, the mortality of the X-7, JY-90, and All strains of S. carpocapsae were 67.5%, 40.0%, 18.7%, respectively, and the mortality of the LN₂ strain of H. indica was only 38.6%. The effects of two soil moisture levels, 15% and 20%, on the mortality rate of the X-7 strain were evaluated, with the X-7 strain exhibiting a higher mortality rate for pupae in soil with 20% moisture content, indicating that entomopathogenic nematodes have a good application prospect in the control of S. exigua.

Key words: entomopathogenic nematodes, Spodoptera exigua, prepupa pupa, pathogenicity