Listronotus bonariensis; HYMENOPTERAN-PARASITES; Microctonus hyperodae; Susceptibility, plant host infection with fungal disease relations; PLANT-HOSTS; Lolium (ryegrass); Host infection with fungal disease; Susceptibility to hymenopteran parasite relationships Microctonus hyperodae; COLEOPTERAN-HOSTS; Listronotus bonariensis; Susceptibility, host plant host infection with fungal disease relations Laboratory experiments were done to examine the effect of ryegrass infection by the endophytic fungus Acremonium lolii Latch, Christensen & Samuels (Ascomycetes: Clavicipitaceae) on Microctonus hyperodae Loan, a parasitoid of Listronotus bonariensis (Kuschel). Infection of ryegrass did not influence the rate of parasitism in weevils confined with naive parasitoids to individual plants and to ryegrass swards in small plots. In contrast, M. hyperodae with prior experience of hosts feeding on endophyte infected grass subsequently were more efficient in parasitizing hosts on this diet. Feeding on individual plants and small plot swards by weevil for 3-4 d increased subsequent parasitoid attack rate. none