The impact of selected Epichloë endophytes on invertebrate biodiversity in New Zealand ryegrass sheep pastures

Abstract

This study investigated the impact of six novel perennial ryegrass-Epichloë-associations in New Zealand sheep pasture on the above-ground and subterranean invertebrate fauna. The perennial ryegrass-endophyte treatments included cv. GA66 without endophyte, and infected with the selected Epichloë strains AR1, AR37 and the common-toxic endophyte. Additionally, two further perennial ryegrass lines, cv. GPD and cv. GPT, both infected with Epichloë strain AR37, were included to examine a cultivar effect. Invertebrates from above ground and subterranean environments were collected from pastures sown with each ryegrass-endophyte treatment at six intervals during 2021. Analysis of above-ground invertebrates found significant differences in density across ryegrass-endophyte treatments for Aranae and Opiliones, Acari, Psocoptera, Neuroptera, and Listronotus bonariensis (Argentine stem weevil), but overall differences for other taxa were not significant. Analysis of the Richness Index for all above-ground invertebrate taxa found significant differences amongst treatments, but not for Shannon’s diversity index H. Overall, all taxa showed a decline in density following sheep grazing, but the effect was taxa specific, with Acari, Coleoptera (beetles) and Hymenoptera (wasps, bees and ants) showing the most significant impact across all ryegrass-endophyte treatments.

The mostabundant soil invertebrates were Annelida (earthworms) and larvae of Costelytra giveni (New Zealand grass grub), with peak densities of both taxa observed in June (winter). Earthworm densities were significantly higher under all treatments following sheep grazing compared to pre-grazing densities, but the response varied for endogeic, epigeic and anecic earthworm taxa. Population fluctuations reflected grazing by sheep and the presence of dung introduced to the soil, soil moisture and season. There appearedto be minimal ryegrass-endophyte treatment effects on earthworm abundance or diversity, whereas for C. giveni larvae there were significant ryegrass-endophyte effects, attributed to colonisation flights in summer. Overall, large herbivore grazing had a significant impact on above-ground and subterranean invertebrate communities, irrespective of ryegrass-endophyte associations and invertebrates biology associated with seasonal changes, with the scale of impact being taxa dependent.