Plant Colors Influence Predator Location In Corn
Previous studies have shown that some parasitoids use plant smells to help locate their prey. Can predators also use plant characteristics, such as smell or color, in order to find prey? A field study was conducted to determine if differences in plant color influence where lady beetles and lacewings forage. In this case light-colored, nutrient-stressed corn plants were compared with normal-colored, well-fertilized plants.
Aphid-free plants were grown in the greenhouse at two densities (1 or 3 plants per pot), and then transplanted to the field. Six different corn lines were evaluated which differed in resistance to corn leaf aphids. Plants were rated visually on a 1 (=yellow) to 5 (=green) scale by individuals who did not know the purpose of the experiment. For all corn lines, plants grown at higher densities were lighter in color (yellow) than plants grown at the lower density (green). Plants in the field were examined for predators daily for 4 consecutive days starting 5 days after plants were put out in the field.
The only aphid-feeding predators recorded were lady beetles and green lacewings. Lady beetles observed included seven species of Cocinella, Hippodamia, Adalia and Propylea. Significantly more lady beetle adults occured on the stressed than on the control plants, and this trend did not significantly vary with the corn line. The relative difference within a corn line varied from ~10% increase to 3 times as many lady beetles on the stressed plants.
The opposite relationship occurred with green lacewings. No adult lacewings were observed, but eggs and young larvae were counted. In three out of 5 lines, lacewings were significantly more abundant (~3-5 times) on the non-stressed, green plants; in the other two lines there was no significant difference.
The authors suggest that these behaviors may have evolved as a way for lady beetles and green lacewings, which both feed on aphids, to avoid competition with each other.
F. Lorenzetti, J. T. Arnason, B. J. R. Philogene & R. I. Hamilton. 1997. Evidence for spatial niche partitioning in predaceous aphidophaga: Use of plant colour as a cue. Entomophaga 42:49-56.
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