They can be attached close to one another, or far apart. Branches can be arranged horizontally, vertically, or at right angles to one another. If you also consider that leaves vary widely in size and shape you can begin to see how much the searching environment of a natural enemy can vary on a plant. The size of a plant directly affects the total area that must be searched for pests. In the absence of specialized adaptations that help them find a pest, natural enemies tend to be less efficient on large plants because they have a greater amount of surface area to cover than those on smaller plants.
Structural complexity refers to how the surface area on a plant is put together.
A plant with few small leaves is less structurally complex than a plant with many small leaves. For example, Trichogramma nubilale can more easily find and parasitize European corn borer eggs on artificial leaves with a simple shape than on those whose area is distributed among smaller leaflets. This suggests that biological control of pests on plants with more structurally complex leaves may require greater numbers or more frequent releases of natural enemies. We have found plant structural complexity to be a handy mechanism to explain observed rates of parasitism in studies of two ornamental pests. Aspidiotophagus citrina is a wasp that parasitizes euonymus scale .