title: Generalized plant defense: effects on multiple species.
abstract: Two species of lepidopteran herbivores, Manduca sexta (Sphingidae) and Trichoplusia ni (Noctuidae), were reared on synthetic diet containing either the alkaloid nicotine or the flavonoid rutin. Survival and pupal weight of the specialist M. sexta did not differ when larvae were reared on diet containing nicotine or rutin. In contrast, the generalist T. ni did not survive on diet containing 0.125% nicotine or greater, whereas larvae survived on all concentrations of rutin. These data demonstrate that the alkaloid nicotine is inhibitory toward generalist, but not specialist herbivores, whereas the flavonoid rutin has no effect on specialist herbivores and limited effects on generalist herbivores. Five species of Pseudomonas bacterial pathogens: P. syringae, P. syringae pv. angulata, P. syringae pv. tabaci, P. fluorescens, and P. solanacearum were grown on nutrient agar containing nicotine or rutin at concentrations ranging from 0.0 to 1.0% wet weight in 0.1% intervals. No species of Pseudomonas grew at concentrations greater than 0.5% nicotine when 106colony forming units (cfu) were used, but growth occurred at all concentrations of rutin when 102cfu were used. These data indicate that nicotine was inhibitory to growth of both herbivores and pathogens, suggesting that certain plant secondary chemicals with high toxicity are of a generalized nature and affect multiple species. Differences in the sensitivity of organisms to allelochemicals such as generalist or specialist can make it appear that specific allelochemicals affect specific organisms, when in fact it is the tolerance of the organism to the plant chemical that is responsible. In four separate studies, the growth of M. sexta, T. ni and Helicoverpa zea was significantly lower on plants inoculated with P. solanacearum. Alteration in leaf quality by P. solanacearum was due to either reductions in leaf nutrients or increases in allelochemicals. We speculate that localized or systemic induction by both herbivores and pathogens can cause changes in leaf quality, effecting each other's subsequent colonization. The generalized nature of plant secondary compounds and potential reciprocal effects on induction by both species suggests that herbivores and pathogens may affect plant quality through induction and diffuse interactions of disparate species can alter the community of organisms colonizing a plant.
authors.affiliation: Center for Agricultural Biotechnology and Department of Entomology, University of Maryland, 20742, College Park, MD, USA.
authors.forename: Vera A
authors.initials: VA
authors.lastname: Krischik
authors.affiliation: Vegetable Laboratory, U.S. Department of Agriculture, Agricultural Research Service, 20705, Beltsville, MD, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Goth
authors.affiliation: Department of Entomology, University of Maryland, 20742, College Park, MD, USA.
authors.forename: Pedro
authors.initials: P
authors.lastname: Barbosa
keywords: Community structure; Generalized plant defense; Manduca sexta; Pseudomonas sp.; Trichoplusia ni