Influence of endophytic perennial ryegrass, Lolium perenne L., on the population density of two insects and plant species composition in mixed turfgrass swards

The goal of this research was a practical strategy for using endophyte-mediated resistance to manage epigeal insects in turfgrass. Overseeding stands of Kentucky bluegrass, Poa pratensis L., (KB) with mixtures of endophytic and non-endophytic perennial ryegrass, Lolium perenne L., (PR+ and PR– respectively) altered turfgrass sward composition over time according to the seeding rate (kg/ha) and the cultivars used. Bluegrass billbug, Sphenophorus parvulus Gyllenhal, larval population density and damage were significantly reduced by overseeding, but damage varied between cultivars. In mixtures of PR+, PR–, and KB, S. parvulus larval populations decreased as the proportion of PR+ increased. No further decrease in S. parvulus populations was observed in swards containing >38.4 ± 3.8% PR+. When S. parvulus populations were higher, a lower proportion of PR+ was found in insecticide-treated plots. In swards containing only PR– and PR+, S. parvulus larval populations decreased as the proportion of PR+ increased. However, no further decrease in S. parvulus populations was observed in swards containing >68.0 ± 28.7% PR+.;In laboratory choice tests, adult male S. parvulus showed no preference between KB, PR and PR+. In non-choice assays more feeding punctures were observed on PR– and PR+ than KB. Feeding was strongly correlated with plant stem diameter. Longevity of adult male S. parvulus was reduced on PR+ compared with PR–, but was highly variable on KB. Bluegrass webworm, Parapediasia teterrella (Zincken), larvae showed no preference for KB or PR–, but both were preferred over PR+. P. teterrella survival to pupation and fresh pupal mass was the same on KB and PR–, but no larvae survived to pupation on PR+.;In pots containing mixtures of PR+, and KB, P. teterrella larval survival decreased as the proportion of PR+ increased to 40.3 ± 19.0%. No further reductions were observed in mixtures containing higher proportions of PR+. Emigration was only a significant determinant of larval population density in monocultures of PR+.