Intraguild predation decreases predator fitness with potentially varying effects on pathogen transmission in a herbivore host

Predators and pathogens often regulate the population dynamics of their prey or hosts. When species interact with both their predators and their pathogens, understanding each interaction in isolation may not capture the system's dynamics. For instance, predators can influence pathogen transmission via consumptive effects, such as feeding on infected prey, or non-consumptive effects, such as changing the prey's susceptibility to infection. A prey species' infection status can, in turn, influence predator's choice of prey and have negative fitness consequences for the predator. To test how intraguild predation (IGP), when predator and pathogen share the same prey/host, affects pathogen transmission, predator preference, and predator fitness, we conducted a series of experiments using a crop pest (Pseudoplusia includens), a generalist predator (Podisus maculiventris), and a generalist pathogen (Autographa californica multicapsid nuclear polyhedrovirus, AcMNPV). Using a field experiment, we quantified the effects of consumptive and non-consumptive predators on pathogen transmission. We found that a number of models provided similar fits to the data. These models included null models showing no effects of predation and models that included a predation effect. We also found that predators consumed infected prey more often when choosing between live infected or live healthy prey. Infected prey also reduced predator fitness. Developmental times of predators fed infected prey increased by 20% and longevity decreased by 45%, compared with those that consumed an equivalent number of non-infected prey. While this research shows an effect of the pathogen on intraguild predator fitness, we found no support that predators affected pathogen transmission.