Summary: What omnivores eat: direct eects of induced plant
resistance on herbivores and indirect consequences for
diet selection by omnivores
ANURAG A. AGRAWAL* and CORINNE N. KLEIN
Department of Entomology and Center for Population Biology, One Shields Avenue, University of California at
Davis, Davis, CA 95616-8584, USA
1. Omnivory, where an animal crosses trophic boundaries, is thought to be com-
mon in natural and managed communities. Foraging theory predicts that omni-
vores will balance their diet as a result of nutritional needs, food quality and
availability of alternate foods. We investigated diet selection of the western Żower
thrips [Frankliniella occidentalis (Pergande)], a herbivore under some circumstances,
and a predator under other circumstances.
2. We demonstrate that induced plant resistance can indirectly aect diet selection
by thrips. The density of herbivorous spider mites is reduced on induced plants
compared to controls and is also positively correlated with the number of mite eggs
that the thrips consume.
3. In choice tests, mite eggs from induced plants were less preferred by thrips than
eggs from control plants. Mite egg size was also smaller on induced plants com-
pared to controls. However, this alone did not explain the diet selection by thrips.