Italian ryegrass (Lolium multiflorum) and short-term hybrid ryegrass (L. boucheanum) have reliable establishment and high cool season growth, but varying persistence after the first summer. In Northland, there is increased stress on ryegrass from invertebrate insect attack. Selected strains of endophyte (Neotyphodium lolii) have been identified that protect perennial ryegrass from invertebrate attack. Two of these endophyte strains (AR1 and AR37) were inoculated into two Italian ryegrass cultivars (Status and Corvette) and compared in a small plot agronomic trial with the same cultivars free or low in the naturally-occurring endophyte N. occultans. From April 2004 to June 2005, ryegrass plots with these endophyte-cultivar combinations were measured for dry matter yields and plant survival under summer/autumn insect pressure in Northland. In autumn/winter 2005, novel endophytes resulted in greater plant survival and yield advantages (82%) than the same cultivars with no/low N. occultans endophyte. These effects were consistent across cultivars. Increased agronomic performance corresponded with lower damage from African black beetle larvae (Heteronychus arator). This result has implications for extending the persistence and potential yields of Italian/hybrid ryegrass pastures subject to pest attack.