|Tumlinson Iii, James|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2003
Publication Date: 10/20/2003
Citation: Cardoza, Y.J., Teal, P.E., Tumlinson III, J.H. 2003. Effect of peanut plant fungal infection on oviposition preference by Spodoptera Exigua and on host searching behavior by Cotesia Marginiventris. Environmental Entomology. 32(5):970-976. Interpretive Summary: Host plant selection by insect herbivores is influenced by a number of factors, including stimulants and deterrents within the plants. The amount of these compounds may vary from plant to plant and can be influenced by stress factors like as pathogen infection. Scientists at the Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS and University of Florida have been studying how stress on plants induced by fungal infection influences insect herbivore attack attraction of parasitoids of the insect herbivores. They found that more Beet armyworms were attracted to and laid eggs on peanut plants that were infected by the white mold fungus than on healthy ones. They also found that parasitoids of Beet armyworm larvae landed more frequently on infected than on healthy peanut plants. A possible reason attraction of more parasitoids to white mold infected peanut plants is that caterpillars feed more on infected plants, which may in turn be responsible for an increase in volatile emission causing the plant to be more attractive to the parasitoids.
Technical Abstract: (1.) In the present study we tested the effect of peanut, Arachis hypogaea L. (Leguminosae), 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 Cresson. (2.) 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 due to fungal infection. (3.) 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 to healthy ones, when plants were exposed to damage by BAW caterpillars. (4.) 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.