Predation threat modifies Pieris rapae performance and response to host plant quality.

Predators impact prey populations through both consumptive and non-consumptive effects, such as behavioral and physiological changes by prey in response to a predation threat. Additionally, various top-down (e.g. predator characteristics) and bottom-up factors (e.g. plant nutrients) may impact non-consumptive effects, yet little is understood about how these interact. We studied how host-plant choice, leaf consumption, and growth of an herbivore, Pieris rapae, were impacted by different levels of plant nitrogen (N) and two predator species representing varying degrees of threat, Hippodamia convergens (predator of early-instars) and Podisus maculiventris (predator of all-instars). We found that P. rapae adults and larvae made similar choices about bottom-up and top-down factors when threatened by two different predator species. Adults and larvae preferred high N plants when threatened by H. convergens, but plant N did not influence their host plant choice when threatened by P. maculiventris. Additionally, larvae consumed more leaf tissue and grew larger when threatened by H. convergens, but leaf tissue consumption and larval growth did not change under threat by P. maculiventris, suggesting that larvae may change their behavior if they are able to quickly outgrow life stages vulnerable to predation. These results indicate that top-down factors such as predator identity may determine how P. rapae modulate their responses to bottom-up factors such as host plant quality when utilizing anti-predator behaviors.