Beetle grazing reduces natural infection of Rumex obtusifolius by fungal pathogens

Abstract

In previously reported laboratory experiments, infection of Rumex obtusifolius by the rust fungus Uromyces rumicis was decreased on leaves which had prior herbivory by the beetle Gastrophysa viridula. In this paper we investigate whether this interaction is robust for natural infection by a variety of fungi in field experiments carried out in spring and autumn with plants given different levels of nitrogen fertilization. Grazing by G. viridula led to a decrease in lesion density of Ramularia rubella and Venturia rumicis in the spring and V. rumicis and U. rumicis in the autumn experiment. For V. rumicis and U. rumicis significant reductions in lesion density occurred on the undamaged leaves of damaged plants, compared with similar leaves on undamaged plants, suggesting systemic induced resistance. This induced resistance was usually independent of the amount of nitrogen fertilization, although the inhibitory effect of grazing on R. rubella in the spring and V. rumicis in the autumn experiment was enhanced by increasing nitrogen fertilization and was inhibited by increasing nitrogen fertilization for V. rumicis in the spring. In both experiments, the lesion density of V. rumicis was greater on leaves on which R. rubella was also present, and the presence of U. rumicis in the autumn experiment was linked to a similar but greater effect on V. rumicis lesion density. We found no evidence of induced resistance by fungi against fungi in these experiments. We highlight the complex interactions between inhibitory and facilitatory processes acting on leaf fungal infection. These results are compared with the proposed molecular mechanisms of induced resistance(s) and we consider the benefits of closer integration between molecular and ecological investigations of induced resistances that occur in the field.

Recruitment of predators and parasitoids by herbivore-injured plants

“…attacked by the leaf beetle Gastrophysa viridula and the biotrophic rust fungus Uromyces rumicis. Hatcher and co-workers (Hatcher et al, 1994a(Hatcher et al, ,b, 1995Hatcher and Paul, 2000) found that fungus infection made Rumex plants less preferred for oviposition and consumption by the beetle and, vice versa, that plants subjected to leaf beetle damage were less prone to rust infection. The studies reviewed by Rostàs et al (2003) showed a general tendency of adverse effects of plant antagonists on each other.…”

Gastrophysa viridula (Coleoptera: Chrysomelidae) and biocontrol of Rumex - a review

“…Both factors decrease leaf N content, increase leaf C and water content and additively raise leaf consumption by G. viridula (Hatcher 1995, 1997a. However, previous herbivory reduces the infection of Rumex leaves by U. rumicis (Hatcher et al 1994, Hatcher andPaul 2000). Air CO 2 content that is expected to increase may also influence leaf acceptability (Pearson andBrooks 1996, Brooks and.…”

Green Roofs and Urban Biodiversity: Their Role as Invertebrate Habitat and the Effect of Design on Beetle Community

“…A similar type of interaction could be important on roofs where herbivorous beetles could help reduce establishment of tree seedlings that can lead to waterproof membrane puncture and roof failure; yet, no granviores and a much lower percentage of herbivores in general were found on stormwater roofs. Another study found that grazing on an herbaceous plant by a specialist beetle limited the establishment of the plant's fungal pathogen (Hatcher and Paul 2000). If the increased functional diversity demonstrated in this study leads to similar interactions this could result in a desirable reduction in maintenance needs on green roofs.…”