| Plant foraging by natural enemies of herbivores includes finding, examining and leaving food plants of their victims. These aspects of plant foraging behavior were examined for Diaeretiella rapae M'Intosh (Hymenoptera: Aphidiidae), a solitary endoparasitoid wasp that attacks aphids primarily on cruciferous plants, but sporadically on other plants as well.;Experiments were conducted to test two hypotheses: (1) female wasps should be more likely to find and less likely to leave plants in large patches of crucifers, and (2) plant learning should influence the probability of orienting to plant odors (plant finding) and the duration of searching on a plant after landing on it (plant examining).;Arrival rates of naturally-occurring D. rapae in artificial patches of 5, 10, 20 and 40 potted collard plants were measured in a field experiment. There was no patch size effect (plants in larger patches were not more likely to be found) and plants with aphids were not more likely to be found than aphid-free plants. Leaving rates were measured in a greenhouse experiment using dispersal cages containing 1, 4 or 16 plants and 0, 10 or 100 aphids. Increasing patch size decreased leaving rate, and this occurred independently of aphid density, which also affected leaving rate.;Laboratory experiments using collard as the cruciferous plant and potato as the novel plant demonstrated that plant learning affected plant examining only on the less preferred plant, potato, and was reversible and relatively long-term (i.e., lasted $>$ 2 days). Furthermore, plant learning affected plant finding and plant examining differently. Unlike its effect on searching time on potato, adult experience with potato did not increase orientation to potato odor in a wind tunnel. Adult experience with collard, on the other hand, did not increase searching time on collard but did result in a trend (nonsignificant) of increased likelihood of flying to collard odor.;Responses of natural enemies to vegetation texture are reviewed, with special emphasis on response to diversification of agricultural systems. Evidence is presented to support the hypothesis that specialist enemies may respond differently from generalists to the concentration of food plants of herbivorous victims. |
