Influence of clavicipitaceous endophyte infection in ryegrass on development of the parasitoid Microctonus hyperodae loan (Hymenoptera: Braconidae) in Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae)

Laboratory experiments were conducted to examine the effect of ryegrass infection by the endophytic fungus Acremonium lolii Latch, Christensen and Samuels on Microctonus hyperodae Loan, a parasitoid of Listronotus bonariensis (Kuschel). Progression of parasitoids through the larval instar stages was shown to depend on adequate nutrition of the weevil host. Compared to confinement on endophyte-free ryegrass, parasitized weevils held on nonpreferred diets comprising leaf segments from endophyte-infected ryegrass and switchgrass contained parasitoid larvae with retarded development. Similarly, development of parasitoid larvae was retarded in hosts feeding on artificial diet containing diterpenes and alkaloids of A. lolii origin. Several diterpenes incorporated into the diet reduced survival of the parasitoid larvae. Attack rate of parasitoids was reduced when the quality of potential host weevils was compromised by confinement on nonpreferred A. lolii-infected ryegrass or without food for 14 days. (C) 1996 Academic Press, Inc.