Detrimental and neutral effects of wild barley-Neotyphodium fungal endophyte associations on insect survival

Abstract

Neotyphodium (Clavicipitaceae: Balansieae) fungal endophyte infection does not always confer temperate grass resistance to insect herbivores, although reports indicate that over 40 species are adversely affected by its infection. Laboratory and glasshouse experiments were conducted to improve our knowledge of the anti-insect properties of Neotyphodium-infected (E+) non-commercial grasses, and E+ wild barley (Hordeum) specifically. Neotyphodium infection of four plant inventory (PI) lines of wild barley conferred resistance to Mayetiola destructor (Say) (Diptera: Cecidomyiidae), whereas none of the E+ wild barley accessions reduced the survival of Rhopalosiphum padi (L.) (Homoptera: Aphididae). Metopolophium dirhodum (Walker) (Homoptera: Aphididae) densities were significantly lower on the E+ clones of Hordeum brevisubulatum ssp. violaceum (Boissier and Hohenacker) (PI 440420), compared with densities on endophyte-free (E-) plants of this species in population growth experiments. Neotyphodium infection of three Hordeum bogdanii (Wilensky) PI lines did not confer resistance to M. dirhodum; however, one of these E+ lines (PI 314696) was resistant to this aphid in a second population growth experiment. Our results provide additional evidence that the outcome of a grass-endophyte-insect interaction is influenced by the host grass species or genotype, Neotyphodium species or genotype, and the insect species involved. They also reinforce this phenomenon for non-commercial grass-endophyte-insect interactions and underscore the potential role of endophytes in mediating wild barley-insect interactions and their potential to act as defensive mutualists.