Endophyte fungus confers resistance to ryegrass: Argentine stem weevil larval studies

Abstract

ABSTRACT. Conferred insect resistance arises from a mutualistic relationship between claviciptaceous endophytic fungi and various grasses. A number of secondary compounds are responsible for the insect resistance. This paper describes studies of the relationship between the endophytic fungus Acremonium lolii Latch, Christensen & Samuels and the Argentine stem weevil Listronotus bonariensis (Kuschel) (Curculionidae); in particular, the effects on larval feeding behaviour, growth and survival. Larvae are stem borers. Tunnel length and distance bored into the basal sheath zone of ryegrass was reduced when the plants were infected by A. lolii. Lolitrem B, a potent mammalian neurotoxin, levels were highest in A. lolii infected grasses and ranged from 2.61 to 7.08 μg/g dry wt, the higher value being recorded in summer. Lolitrem B extracted from A. lolii‐infected perennial ryegrass reduced larval growth rates and survival. Lolitrem B acted via the insect stomach rather than by absorption through the integument. The potential role of endophytic fungi in plants is discussed briefly in relation to herbivory.