Development of a stage-structured process-based predator–prey model to analyse biological control of cotton aphid, Aphis gossypii, by the sevenspot ladybeetle, Coccinella septempunctata, in cotton

Agricultural system diversification is well known to affect the population dynamics of crop pests, but predator–prey dynamics in crop systems are difficult to analyse due to interactions between multiple life stages of predator and prey, the modulating effect of temperature, the actions of additional predators, and the open nature of the system, with immigration and emigration of both predators and prey. To better understand and characterize the predator–prey system dynamics under field conditions, we developed a detailed process-based simulation model for the stage structured population interaction between cotton aphid, Aphis gossypii, and its main natural enemy, the sevenspot ladybeetle Coccinella septempunctata. The model includes interactions between all insects stages as affected by temperature and host growth, and was parameterized based on detailed data collection in the laboratory and the field. The model was tested with independent data. Simulations show that the initial predator–prey ratio, as affected by immigration rates of the aphid and the predators into the crop, is the key factor for biological control. The model is a useful tool for scenario assessments on the effects of crop diversification on pest-natural enemy dynamics.