Influence of Japanese Beetle Popillia japonica Larvae and Fungal Endophytes on Competition between Turfgrasses and Dandelion

In a series of greenhouse experiments, we examined the influence of below‐ground herbivory by larvae of the Japanese beetle, Popillia japonica Newman, on performance and competitive interactions between dandelion, Taraxacum officinale Weber, and two turfgrass species, Lolium perenne L. (perennial ryegrass) and Festuca arundinacea Schreb. (tall fescue) infected or uninfected by Neotyphodium endophytes. In doing so, we aimed to determine how below‐ground insect feeding and endophyte infection might influence the ability of dandelion to act as a turfgrass weed. In monocultures of perennial ryegrass or tall fescue, herbivory significantly reduced the number of tillers per plant and above‐ and below‐ground biomass. Endophyte infection significantly reduced perennial ryegrass tillers but significantly increased the number of tall fescue tillers and above‐ and below‐ground biomass. Herbivory had no significant influence on dandelion growth parameters in monocultures. In mixtures of dandelion and either grass species, herbivory significantly reduced the number of grass tillers and above‐ and below‐ground biomass, whereas endophyte infection significantly reduced the number of perennial ryegrass tillers but had little influence on tall fescue. Herbivory significantly increased the number of dandelion leaves and above‐ and below‐ground biomass in mixtures with perennial ryegrass or tall fescue. Endophyte infection had no significant influence on Japanese beetle larval survival or biomass in monocultures or mixtures. Findings indicate that below‐ground herbivory by Japanese beetle larvae alters competitive interactions between grasses and dandelion in a way that favors dandelion. Data support the view that endophyte‐related effects on interactions between plants may not always be predictable and that below‐ground herbivory may not affect endophyte‐infected and uninfected plants differentially.