Effect of Peanut Plant Fungal Infection on Oviposition Preference by Spodoptera exigua and on Host-Searching Behavior by Cotesia marginiventris

In the current study, we tested the effect of peanut, Arachis hypogaea L. (Leguminoseae), stem infection by the white mold fungus, Sclerotium rolfsii Saccodes (Basidiomycetes), on the oviposition preference of beet armyworms (BAW), Spodoptera exigua Hübner (Lepidoptera: Noctuidae) and on the host-searching behavior by a BAW larval parasitoid Cotesia marginiventris. We found that, in choice tests, adult BAW oviposited more on white mold-infected plants than on healthy plants. We also found evidence that this preference is mediated by plant volatiles and other biochemical changes in plant chemistry caused by fungal infection. When plants were exposed to BAW feeding, the parasitoid C. marginiventris landed more frequently on infected than on healthy plants. We conducted wind tunnel choice experiments to determine whether the more frequent landing by the wasps was mediated by the volatiles emitted by healthy and white mold-infected plants in response to BAW damage. In these wind tunnel experiments, wasps were more responsive to volatiles from plants infected with the white mold compared with healthy ones, when both types of plants were exposed to damaged by BAW caterpillars. Thus, white mold-infected peanut plants were preferred by BAW for oviposition, but, when damaged by BAW larvae, infected plants were also more attractive to one of the BAW natural enemies. To our knowledge, this is the first time that the effect of pathogen-induced biochemical changes in plants on parasitoid behavior has been evaluated.