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

ABSTRACT.

• 1 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.
• 2 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.
• 3 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.
• 4 Lolitrem B extracted from A. lolii-infected perennial ryegrass reduced larval growth rates and survival.
• 5 Lolitrem B acted via the insect stomach rather than by absorption through the integument.
• 6 The potential role of endophytic fungi in plants is discussed briefly in relation to herbivory.