Effects of Beauveria bassiana (Balsamo) Vuillemin infection on feeding and ovipositional behavior of Lygus hesperus Knight were investigated in the laboratory. In the feeding experiment, bugs were inoculated with different concentrations (LC₁₀, LC₅₀, LC₉₀) of B. bassiana conidia and feeding damage was measured on flower buds of Wisconsin fast plants, Brassica rapa L., after 5 d. We detected greater feeding damage by inoculated bugs compared with noninoculated bugs, particularly bugs that died during the experiment. In the oviposition experiment, bugs were inoculated with a high concentration of conidia (LC₉₀ at 25°C) and incubated for 6 d at 25 or 35°C, temperatures that are optimal and suboptimal, respectively, for B. bassiana growth. Most inoculated bugs died at 25°C but survived at 35°C during the 6-d experiment. Incubation temperature did not significantly affect L. hesperus oviposition. B. bassiana inoculation reduced the oviposition rate of lygus bug, particularly in bugs that did not show sporulation at the end of the experiment. If B. bassiana is used for lygus bug control in seed crop fields, the behavioral changes of infected bugs are unlikely to contribute to a reduction in seed damage.