Impact of attack by gallmakers on their ancestral and novel plant hosts in a goldenrod-insect system
University of New Brunswick
Through coevolution reduced virulence and increased tolerance may evolve. Novel plant hosts may experience greater impact from herbivores compared to ancestral hosts. I tested this using Solidago altissima and Solidago gigantea as host plants and Eurosta solidaginis and Rhopalomyia solidaginis as gallmakers. In 4 out of 8 data sets, both gallmakers significantly reduced the aboveground biomass (by about 30%) in the novel host. (Overall, 7 out of 8 data sets showed a trend in the expected direction.). Coupled with previous data sets from Heard and Kitts 2012 on Gnorimoschema gallaesolidaginis, 6 out of 10 data show significant support for this coevolutionary hypothesis (9 out of 10 in the expected direction; sign test P = 0.011). In addition to herbivory, plants may also experience abiotic stressors. By inducing water stress and clipping on S. altissima and S. gigantea I found that S. altissima experiences synergistically greater damage when two stressors are present.