INTERACTIONS BETWEEN RUMEX SPP, HERBIVORES AND A RUST FUNGUS - GASTROPHYSA-VIRIDULA GRAZING REDUCES SUBSEQUENT INFECTION BY UROMYCES-RUMICIS

1. The chrysomelid beetle Gastrophysa viridula and the rust fungus Uromyces rumicis both occur on leaves of Rumex crispus or Rumex obtusifolius. We investigated reciprocal interactions between herbivory and infection. 2. In both Rumex species the amount of leaf eaten by Gastrophysa viridula was not affected by prior rust infection of the same leaf, whereas there was a significant reduction in infection when the same leaves had been previously grazed by Gastrophysa viridula. 3. Herbivory induced an 80% reduction in pustule density within and immediately around the feeding site within 1 day of feeding damage; it also induced resistance throughout the undamaged portion of the leaf, and a less effective, and slower, resistance in undamaged leaves. 4. Cutting discs from the entire leaf surface, to mimic the natural damage caused by Gastrophysa viridula, induced resistance to Uromyces rumicis throughout the leaf, although we found no systemic effect. Artificially holed leaves also developed significantly less natural Uromyces rumicis infection over a 1-month period in the field. 5. In the UK Gastrophysa viridula is commonly present in the field for several months before Uromyces rumicis infection takes place, so the pattern and degree of leaf damage by the beetle may have significant effects on subsequent rust infection.