<p>We used meta-analyses to examine the effects of different enemy taxa on insect prey populations as well as tri-trophic effects on their host plants. We also compared the effects of classical biocontrol, the use of biocontrol enemies for conservation biocontrol, and the use of naturally occurring enemies. Overall, there were strong negative effects of most enemy taxa on insect prey, but the effects of biocontrol enemies were significantly stronger than other naturally occurring enemies. There were differences in the strength of effects of enemy taxa with parasitoids, flying insect predators, ground insect predators other than ants, and spiders having stronger effects than ants or vertebrates such as birds, frogs, and bats. There were no significant differences between insect prey targets such as sucking insects, concealed feeders, leaf chewers, insect predators and detritivores. There were also no significant differences in the effects of enemies between insect prey of different origin, native or invasive, or host plant origin, native, invasive or introduced. However, the effects of enemies on their prey differed according to growth form of the prey host plant, with stronger effects of enemies or herbs and shrubs than on trees or grasses. There were no significant tri-trophic effects of enemies on the host plant morphometrics of their prey. There were also no significant difference in tri-trophic effects between biocontrol and non-biocontrol studies, enemy taxa, insect or plant origin, or plant growth form. However, the effects of enemies on prey were significantly negatively correlated with tri-trophic effects on plant morphometrics.</p>