J. Entomol. Sci. 43(1): 86-94 (January 2008) Abstract Addition of 3 DNA-gyrase inhibitors (i.e., novobiocin, nalidixic acid and oxolinic acid) individually to the NI (New and Improved) oligidic diet for plant bugs was investigated to assess their effect on the biological fitness of Lygus hesperus Knight (Heteroptera: Miridae). Biological fitness was measured by the number, biomass, sex ratio, daily egg count per female, and the egg hatch rate. All measures of biological fitness were not significantly different among the controls and the 3 inhibitors, which demonstrated that the inhibitors can effectively replace present antibiotics for a less expensive diet. Females reared on the NI diet with novobiocin and oxolinic acid showed increased fecundity in comparison with the diet with nalidixic acid, but the types of inhibitors had no effect on egg hatch rate. Furthermore, the egg hatch rate during the first 12 d after oviposition produced the most viable eggs, with the highest hatch rate between the 2nd and g1h days after oviposition commenced, which is comparable to the current eggcollection period used for the L. hesperus colony. These inhibitors could replace the antibiotics currently used in the NI diet and reduce the cost for diet preservation without sacrificing the quality of the insects in the mass-rearing facility.