Plant shape may affect the ability of insect predators to locate prey by altering search paths or by providing partial refugia for prey. As a result, predictions about insect predators drawn from data in simple lab environments without spatial dimension, or on different plant species may be incorrect. The effect of plant morphology on predator foraging success was tested using multicolored Asian lady beetles, Harmonia axyridis, and green lacewings, Chrysoperla carnea, preying on pea aphids, Acyrthosiphon pisum. These predators differed in size and therefore might be expected to have different responses to a given plant morphology. Experiments were conducted using four different pea plant morphologies that differed in fractal dimension, but which were controlled for surface area. The functional response of each predator on each pea morph was determined by measuring the number of aphids consumed in a 24 hour foraging period at 5 prey densities. We also tracked predator search paths using 3D video imaging to determine if the two predators search plants differently.

Results/Conclusions

Data suggest that both predators are more successful at capturing prey on plants with a higher edge to surface area ratio (lower fractal dimension) because they fall off these plants less frequently. The potential mechanism that creates more efficient foraging on plants with lower fractal dimension will be discussed. Preliminary observations indicate that the larger of the two predators, the multicolored Asian lady beetle, is restricted to plant edges where it can maintain a good grip. As a result, aphids are able to evade predation since they congregate on the undersides of leaves where lady beetles cannot walk.