Levels of plant resistance to herbivores often vary between when herbivores choose multiple plant types and when they feed on a single plant, indicating a potential impact of the presence of substitute hosts on the strength of the plant-herbivore interactions. Little is known, however, about factors responsible for the differential levels of plant resistance. Here we conducted a meta-analysis on 144 measures from 47 publications that compared herbivore responses under the choice and no-choice conditions. We compiled levels of damage of resistant phenotypes relative to damage of susceptible phenotypes (relative susceptibility of resistant phenotype: RSR) and compared RSR between the two conditions. We found that RSR decreased and increased under the choice conditions when herbivores were oligophagous and polyphagous, respectively. The difference between oligophages and polyphages became prominent when resistance traits were chemical ones. We also observed a decrease of RSR under the choice conditions in woody plants, irrespective of the herbivore type. This study characterizes potential factors altering the strength of plant-herbivore interactions during the host choice process of herbivores.