Impact of Epichloë endophytes on adult Argentine stem weevil damage of perennial ryegrass seedlings

In New Zealand, fungal endophytes (Epichloë festucae var. lolii (Latch, M.J. Chr & Samuels, formerly Neotyphodium lolii (Glen, Bacon & Hanlin)) are widely used to enhance productivity and survival of mature perennial ryegrass (Lolium perenne L.) by producing alkaloids that reduce damage by insect pests, such as Argentine stem weevil (Listronotus bonariensis, Coleoptera: Curculionidae (Kuschel), ASW) but knowledge of their effects in seedlings is limited. High concentrations of alkaloids occur in seed and can be translocated into seedlings to provide early protection from insect herbivory. A glasshouse experiment was conducted in which adult ASW were released onto perennial ryegrass seedlings without endophyte (Nil) or infected with endophyte strains AR1, AR37 and NZCT in ‘One50’, and NEA2 in ‘Trojan’ in three time periods; 7-22, 25 – 44 and 46 – 64 days post sowing. ASW feeding damage was scored and plant survival and dry matter production measured. In the first time period, endophyte infection with endophyte strains AR1, NZCT, and NEA2 that produce peramine, a strong deterrent to adult ASW, were less damaged than ryegrass without endophyte or infected with AR37 but became increasingly susceptible to ASW predation. Plant survival was reduced in all treatments with mortality highest in Nil and AR37 treatments. The same pattern of increasing damage occurred throughout the second time period although all endophyte strains had significantly less feeding than Nil. Strain NZCT was virtually undamaged in the third time period whereas damage initially increased in AR1 and NEA2 up until day 50-53 post planting and then declined. Nil and AR37 treatments were significantly more damaged than AR1, NZCT and NEA2. This research indicated there is a period of seedling vulnerability to adult ASW attack during germination, even for strains producing peramine. This possibly occurs at a stage when seed-storage of endophyte alkaloids have been diluted by expansion and the seedling endophyte is not yet producing its own alkaloids.