The pathogenicity of six strains of the entomopathogenic bacteria Photorhabdus and Xenorhabdus, symbiotically associated with the entomopathogenic nematodes Heterorhabditis and Steinernema, respectively, to the mushroom mite, Luciaphorus perniciosus was studied. Bacterial cultures of the Thai strain Xenorhabdus nematophila (X1) and the imported strain Photorhabdus luminescens (P1), containing 1ϫ10 8 cells/ml, showed the highest virulence to the female mite, resulting in 85 and 83% mortality within 3 days after application, respectively. The fecundity of the surviving L. perniciosus was also significantly reduced by the X. nematophila (X1) strain. These results demonstrate the potential of X. nematophila (X1) to control the mushroom mite.