PARENT SESSION
Contributed Oral Session 80: Mutualism / Parasitism: Pollination, Dispersal, Ants, Aphids, and Fungi
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal
Food web responses to the presence of fungal endophytes.
Krauss, Jochen*,1, Müller, Christine B.1, 1 Institute of Environmental Sciences, Zürich, Switzerland
ABSTRACT- Neotyphodium lolii is a symbiotic endophyte of the grass Lolium perenne that produces herbivore toxic alkaloids. The associations between fungal endophytes and grass species are generally assumed to be mutualistic. However, different grass cultivars and nutrient availability may change the nature of the association. Apart from negative effects of the endophyte-produced alkaloids on herbivores it is not known how endophyte effects cascade up to higher trophic levels. In a garden experiment, we used four different cultivars of the grass Lolium perenne, each either infected with the endophyte Neotyphodium lolii or not, and added NPK fertiliser at a concentration of 200 kg/ha/year to 96 plots as a split-plot design (E+/E-; N+/N- for four cultivars). In 2004 every second week all colonizing aphids and their parasitoids were counted to assess endophyte and fertiliser effects at higher trophic levels. At the end of the growing season, we destructively harvested the total plant biomass and analysed alkaloid concentrations in a subsample of above ground tissue. The fertilizer additions and grass cultivars significantly affected plant biomass but no effect of the endophyte was detected on plant biomass. The total number of aphids and mummies was significantly higher on fertilized plots, while effects of grass cultivar and endophyte infection showed no significant effects. Even though endophyte infection is known to decrease herbivore abundance and might affect higher trophic levels, the results of our experiment suggest that fertilization of grass has a much stronger impact on densities of aphids and parasitoids, particularly when agricultural amounts of NPK are applied.
Key words: aphids, Neotyphodium, Lolium perenne, parasitoids