The importance of generalist arthropod predator assemblages in suppressing pests has recently received more attention. However, few studies have investigated the impacts of assemblage structure on pest mortality. This study assessed the influence of relative abundance and taxonomic identity among an assemblage of generalist predators in collards, (Brassica oleracea var. acephala), on the mortality of Pieris rapae. In field surveys and laboratory assays, I determined that Coleomegilla maculata was the numerically dominant while Coccinella septempunctata and Podisus maculiventris were numerically subdominant predators of P. rapae larvae. Experimental mesocosms were used to determine whether numerically dominant predators alone, regardless of taxonomic identity, imposed greater P. rapae larval mortality than when in an assemblage. As numerically dominant species, only C. septempunctata imposed greater P. rapae larval mortality alone than when in an assemblage. This research highlights the importance of considering both relative abundance and identity in studies involving predator assemblages and biocontrol.