The effect on plant fitness of the interaction between various types of plant resistance to herbivores and natural enemies of those herbivores was studied in caged field experiments in North Carolina from May 2002 to November 2004. In a comparison of Mexican bean beetles (Epilachna varivestis Mulsant) feeding on soybean plants (Glycine Max (L.)) with differing levels of herbivore resistance, it was found that the generalist predator Podisus maculiventris (Say) was more effective in decreasing herbivore damage and increasing plant fitness on non-resistant plants than plants with strong constitutive resistance to herbivores. Further studies showed that Podisus maculiventris were more effective in reducing Mexican bean beetle damage and increasing plant fitness on soybean plants with late induced resistance to herbivore damage than plants with strong constitutive resistance. These experiments could help determine why certain characteristics, such as induced plant resistance, are present in certain systems and not others. This should improve understanding of when defensive traits will enhance or detract from the fitness benefits plants receive from natural enemies and potentially allow for more accurate predictions of the speed and direction of evolution of defensive traits in plants.