Grass cultivar diversity and endophyte infection affect abundance of herbivores and their natural enemies

Abstract

How does diversity in plant cultivars and endophyte infection affect higher trophic levels? We manipulated the number of cultivars (1 or 4) and the endophyte infection (-E, +E, and both, -E and +E) of potted Lolium perenne plants and left aphids and their parasitoids to assemble naturally. Aphid number and plant biomass were not influenced by our treatments, while the number of parasitised aphids (mummies) was significantly higher on mixed plant stands than on monocultures. The effect of endophytes was stronger in mixed plant stands than in monocultures with the most mummies found in endophyte-free mixed plant stands. Although number of mummies did not differ among cultivars, the rate of parasitism varied with cultivar and showed an endophyte x cultivar interaction. The number of successfully emerging parasitoids was also higher on high diversity treatments than on monocultures, indicating that increased diversity at resource levels translates to increased abundance at consumer levels. Key words: fungal endosymbionts, biodiversity, genetic diversity, multitrophic interactions, insect food webs, insect density, Neotyphodium lolii