PREFERENTIAL GRAZING BY MOLLUSKS OF PLANTS INFECTED BY RUST FUNGI

Infection by pathogenic rust fungi increased invertebrate herbivory of a number of plant species. This phenomenon was investigated in detail in Allium ursinum infected by Puccinia sessilis and Tussilago farfara infected by Puccinia poarum and Coleosporium tussilaginis. In the field, 57% of P. sessilis pustules on A. ursinum were grazed and the area consumed by herbivores was significantly greater in rusted than control leaves in 9 out of the 10 host populations studied. Examination of herbivores associated with rusted A. ursinum suggested that much of the observed grazing could be attributed to several species of mollusc. In a controlled preference test the slug Arion ater consumed 6-23 times more rusted tissue than controls. Aeciospores of P. sessilis were present in the faeces of 44 ± 4% of the snail Trichia striolata. Some 48% of P. poarum-infected T. farfara leaves showed some evidence of selective grazing. Such leaves had 29.25 ±3.52 rust pustules of which 4.57 ± 0.66 (c17%) were grazed. Arion hortensis and A. fasciatus consumed significantly greater amounts of P. poarum-infected T. farfara than uninfected tissues but another slug, Deroceras reticulatum, showed no significant preference. -from Authors