Scared sick?: Predator-pathogen facilitation strengthens biological control

Herbivore suppression often strengthens with increasing predator biodiversity, but little is known about the role of pathogens in these relationships. We manipulated species richness among a community of predators and pathogens attacking the Colorado potato beetle, and found that herbivore mortality increased, and plant damage decreased, with greater natural enemy biodiversity. However, closer examination revealed that it was the pairing of predator with pathogen species, rather than greater enemy biodiversity per se, that strengthened herbivore suppression. Subsequent experiments revealed that beetles exposed to predation earlier in development were more susceptible to later infection by pathogens, perhaps due to conflicting energetic demands for anti-predator versus immune defenses. Thus, synergism between the two natural enemy classes resulted from predators facilitating resource capture by pathogens.