A Simulation Model ofPodisus maculiventris(Say) (Heteroptera: Pentatomidae) and Mexican Bean Beetle,Epilachna varivestis(Mulsant) (Coleoptera: Coccinellidae), Population Dynamics in Soybean,Glycine max(L.)

We present a predator–prey model (PREDPREY) that describes the population dynamics of the generalist predatorPodisus maculiventris(Say) (Heteroptera: Pentatomidae) and Mexican bean beetleEpilachna varivestis(Mulsant) (Coleoptera: Coccinellidae) in soybean,Glycine max(L.). PREDPREY is a state-variable model that uses a distributed-delay function to represent temperature-dependent development of both predator and prey species. The predator submodel includes descriptions of immigration, predator search, functional response, survivorship, and reproductive characteristics. The prey submodel includes descriptions of immigration, survivorship, and reproductive characteristics. The plant model describes plant growth as a function of leaf area accumulation over time. The model tracks changes in predator and prey populations over a single growing season using a 1-day time step. The model captures the essence of predator–prey dynamics to provide reasonable predictions of population patterns. Comparison of the no-predator scenario to the standard simulation (1000 predators/ha) indicates that predators bring about a 24% reduction in peak prey (larval) density and a 47% reduction in overwintering prey (adult) numbers. Sensitivity analyses indicate that reproductive and survivorship characteristics of the prey have a relatively large impact on pest density. Among predator characteristics, developmental rate and most reproductive parameters have a greater impact than do search parameters and survivorship. Plant growth rate has a greater impact than the initial size of plants. The model can be used to evaluate the relative effectiveness of natural enemies, investigate augmentative biological control strategies, and evaluate biological control strategies as part of larger IPM programs.