MODELLING PLANT CANOPIES FOR BIOCONTROL AND BIODIVERSITY Insect movement, networks and lacunarity

Canopy structure has an important role to play in determining the searching patterns of predators of insect pests in crops. The connections between plants within the canopy are crucial in determining the ability of predators to move around the canopy. Virtual plant models provide an ideal method for providing a realistic background for modelling the movement of insects in plant canopies. Experimental simulations of the movement of the predatory mite Phytoseiulus persimilis have shown that the time taken for the predator to locate the prey decreases as plants become more connected. However, the time to prey location is increased as the internal structure of the individual plants in increased. These two factors therefore have to trade off against each other to determine the optimal canopy structure for the quickest time to location of prey by predators. There is therefore a need to be able to characterize the structure of real canopies to examine how canopy structure influences the searching success of predators. In this paper we discuss potential methods for the characterization of plant canopies, using virtual plants as a tool to model the canopies, and the potential implications of characterizing plant canopies in relation to biological control and biodiversity. THE IMPORTANCE OF CANOPY STRUCTURE The plant is a major component of all ecosystems and provides the battleground for the war between insect pests and their natural enemies. It has been shown that plant structure can have a major influence on the success of many natural enemies (Van Haren et al. 1987; Sütterlin and Van Lenteren 1997; Stavrinides and Skirvin 2003). These studies have focussed mainly on the morphological characteristics of the plant leaves, with a particular emphasis on leaf trichomes, showing that increased density of leaf trichomes reduces the searching ability of parasitoids (Sütterlin and Van Lenteren 1997) and predatory mites (Van Haren et al. 1987; Stavrinides and Skirvin 2003). However, the overall canopy structure, in terms of connections between plants, is also likely to be important, as it will determine the ability of predators to move from