Plant morphological complexity impacts foraging efficiency of adult Coccinella septempunctata L. (Coleoptera: Coccinellidae)

Plant morphological complexity could provide a physical refuge to prey and/or could interfere with foraging activities of a natural enemy. Few studies have rigorously tested the hypothesis that plant structural complexity influences the behavior of natural enemies and thus predator-prey interactions. Thus, we tested the hypotheses that increased plant morphological complexity reduces the predation efficacy and new area search efficiency of Coccinella septempunctata L. as a predator of the pea aphid Acyrthosiphon pisum Harris. Essential to testing these hypotheses is the use of near-isogenic lines of the pea plant. The Normal, tl, and aftl near-isogenic lines used in experiments manifest distinct levels of morphological complexity ranging from low to high complexity. Further, the use of these genetic isolines allowed us to control, as much as possible, for non-morphological plant characters such as phytochemicals and surface waxes. Increased plant morphological complexity decreased the predator's efficacy with most aphids surviving on the aftl plant. Observations on the predator foraging activity suggest that complexity in the form of increased leaf edge to leaf area ratio and increased number of junctions reduced the new area search efficiency of the predator. This study supports the notion that plant complexity can interfere with the foraging success of insect predators.