Neotyphodium lolii, an endophytic fungus of perennial ryegrass, deters Argentine stem weevil, Listronotus bonariensis, an important insect pest of pastures in New Zealand. Deterrence is apparently due to several alkaloids the fungus produces. We asked if the fungus also affects the third trophic level. Specifically, we tested if several different isolates of the fungus altered the growth and survival of the parasitoid, Microctonus hyperodae. Adult weevils were collected from paddocks near Lincoln, New Zealand and maintained in an environmental chamber. Weevils were assorted into treatment groups and fed perennial ryegrass (cv. Nui) lacking endophyte infection (nil) or containing one of the following endophyte strains: ARW, AR1, AR6, AR37. All endophyte strains differed from one another with respect to the profile of alkaloids they produce. Following two weeks of acclimation, weevils were placed with M. hyperodae to allow for parasitization. Weevils were then placed into Petri dishes (10 per dish) and fed grass clippings from the appropriate treatment group. We collected weevils as they died and dissected them to assess the development of parasitoids. Emergence of prepupae from hosts and survival to adulthood were also recorded. Fungal isolates did not differ in their influence on weevil feeding or survival. In contrast, the effect of the endophyte on the parasitoid varied among isolates of the fungus. Isolates ARW and AR6 reduced parasitoid adult emergence relative to nil endophyte. In contrast, AR37 had no negative effect on survival of the parasitoid. Furthermore, an index of developmental rate showed that parasitoids developed more slowly when reared from hosts fed grass containing any of the strains of N. lolii, except AR37, compared to endophyte-free grass. Negative effects of the endophyte on parasitoid survival were associated with the presence of ergovaline while effects on parasitoid development rate were associated with the presence of any alkaloid. Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Trophic structure; Population dynamics; Land and freshwater zones; Australasian region Listronotus bonariensis (Curculionidae); Hymenopteran parasites; Microctonus hyperodae; Host deterrence by fungal endophyte of plant host, role of fungal isolate effect on parasite; Plant hosts; Lolium perenne; Parasite deterrence by endophytic fungus, role of fungal isolates effect on hymenopteran parasite; Food webs; New Zealand; South Island; Canterbury; Lincoln; Deterrence by fungal endophyte of plant host, role of fungal isolate effect on hymenopteran parasite Microctonus hyperodae (Braconidae); Growth; Coleopteran hosts; Listronotus bonariensis; Host deterrence by fungal endophyte of plant host, role of fungal isolate effect on parasite; Food webs; Survival; New Zealand; South Island; Canterbury; Lincoln; Coleopteran host deterrence by fungal endophyte of plant host, role of fungus effect on parasite none