To estimate the toxicity of novaluron to eggs from two populations of Oriental fruit moth, Grapholita molesta (Busck), we dipped eggs on waxed paper into a range of concentrations. Treated eggs were held on wheat germ diet, and mortality was assessed after 10 days. We compared the concentration-mortality relationships for eggs from parents reared on ‘Gala’ apples with those of eggs from parents reared on lima bean diet. We also compared the responses of a long-term laboratory colony of G. molesta from Rutgers University and a colony established from Calhoun County in southwestern Illinois. LC₅₀'s of novaluron ranged from 0.10 to 0.83 ppm and did not differ significantly based on parental diet. LC₅₀'s differed significantly between colonies; LC₅₀'s for the Calhoun colony were approximately 2.5 and 8 times greater than those for the Rutgers colony in bioassays that used eggs from parents reared on diet and apples, respectively. LC₉₀'s ranged from approximately 38 to 1000 ppm. For the Calhoun colony, the LC₉₀ for novaluron applied to eggs from parents reared on apples was approximately 10 times greater than the LC₉₀ for novaluron applied to eggs from parents reared on lima bean diet. For eggs from parents reared on apples, the LC₉₀ for the Calhoun colony was approximately 9 times greater than the LC₉₀ for the Rutgers colony. Differences in the colonies' responses may represent natural variation among populations or may be the result of selection by novaluron or other insecticides used in Calhoun County orchards before we collected larvae for our colony.