Microbial biocontrol agents are useful commercially only if they do not harm other natural biocontrol organisms, at recommended use rate in the environment where the microorganism is being used. To test the hypothesis that the predatory warehouse pirate bug, Xylocoris flavipes (Reuter), is not adversely affected by the entomopathogen, Beauveria bassiana (Balsamo) Vuillemin strain GHA, we developed a method using individually confined bugs during a 10-d feeding regime. Three concentrations of a conidial suspension were applied to assay surfaces (filter paper disks) to achieve 2.7 × 10⁷, 2.6 × 10⁶, and 2.6 × 10⁵ conidia per cm², representing 100X, 10X, and a field rate of 2.6 × 10¹³ conidia per ha (±10%), respectively. Fifth instar X. flavipes suffered 0% infection at the field rate when confined to treated filter paper for 10 d (16% and 42% infection, respectively, at 10X and 100X the field rate). Second instar migratory grasshoppers, Melanoplus sanguinipes (F.), exposed to the same doses suffered 97, 92, and 100% mortality at the three respective doses 10 d after exposure. These data indicate that B. bassiana can be used safely at recommended application levels without significant effect on fifth instar populations of X. flavipes.