Virtual plant models of predatory mite movement in complex plant canopies

Abstract

The movement of predators between patches of pests is crucial to the success of any biological control programme. In ornamental crops, predators are required to locate sparsely distributed pest patches very rapidly, and the success of predators in doing this depends greatly on the structure of the plant canopy. However, due to the extremely wide diversity of ornamental crop plants, experimentally determining the effect of canopy structure on predator movement is difficult. This paper presents a novel modelling approach that can be used to examine the impact of plant architecture and canopy connectedness on the movement of predators within a complex canopy, using the technique of virtual plants. This technique allows the three-dimensional structure of the plant canopy to be explicitly incorporated into models, and hence to determine the impact of the number of connections both between and within plants on the movement of predators within the canopy. This model is a major step forward from previous simulation models of predator–prey spatial dynamics, where insect movement is considered in a simplistic way, and is the first model to explicitly consider the three-dimensional structure of the crop when modelling the movement of predator arthropods. Simulation experiments on a simplified plant canopy, using randomly searching predators, have shown that increased plant connectedness allows predators to search a greater proportion of the plant canopy. However, the proportion of plant canopy searched is mediated by the complexity of the plant structure, with a lower proportion of the canopy visited on more complex plant architectures. The simulations accurately predict the distribution of visits of predators to corner, edge and central plants within a range of differently sized grids of plants, in line with theoretical predictions. The simulations provide a foundation for investigation of the impact of canopy structure and predator searching behaviour on the movement of predators through complex plant canopies, when searching for sparsely distributed prey patches.