The two cynipid wasps,Diplolepis fusiformans(Ashmead) andD. spinosa(Ashmead), which induce galls on shoots ofRosa arizonicaRydberg, attack longer, more vigorous shoots with a higher probability than less vigorous shoots. Also, more adult insects emerge per gall on more vigorous shoots includingDiplolepis, the cynipid inquilinePericlistus, and parasitoids. This indicates that establishment in galls on vigorous shoots in relation to plant resistance is higher than on less vigorous shoots. However, the presence ofPericlistus, which makes multiple chambers perDiplolepishost, complicates an exact interpretation of the relative roles of plant resistance and natural enemies in the survivorship ofDiplolepisgallers. As ramets ofR. arizonicaage, mean shoot length declines, and attacks byDiplolepisare concentrated on young vigorous plants. The patterns of attack and establishment ofDiplolepisspecies are similar to those described for three species of tenthredinid sawfly gallers in the genusEuura. This study therefore contributes to an understanding that some herbivores require vigorous plants for successful use of resources, in contrast to arguments that herbivores survive best on stressed plants.