Ergopeptine Alkaloids and Neotyphodium lolii-Mediated Resistance in Perennial Ryegrass Against Adult Heteronychus arator (Coleoptera: Scarabaeidae)

Abstract

Heteronychus arator F. adults are deterred from feeding on perennial ryegrass, Lolium perenne L., infected with the endophytic fungus Neotyphodium lolii, which produces many alkaloids and other mycotoxins in the host grass. This article examines the effects of a number of these compounds on adult H. arator feeding. Pure mycotoxins at several concentrations were incorporated into a carrot-based artificial diet developed specifically for this study. The mycotoxins tested were either compounds commonly found in N. lolii-infected perennial ryegrass (peramine, lolitrem B, paxilline, ergovaline, and ergovalinine), or compounds structurally similar to those occurring in N. lolii/perennial ryegrass associations (ergotamine, alpha-ergosine, alpha-ergocryptine, festuclavine, lysergol, lysergic acid amide, ergonovine, dihydroergotamine, alpha-bromoergocryptine, and dihydroergocrystine). Peramine, a Listronotus bonariensis (Kuschel) feeding deterrent, did not affect adult H. arator feeding. Lolitrem B, a mycotoxin involved in livestock health problems, and its structurally related precursor, paxilline, had no effect. The ergot alkaloids festuclavine, lysergol, and lysergic acid amide also did not deter adult H. arator feeding. Ergonovine was the only nonergopeptine ergot alkaloid to deter adult H. arator, though only moderately. The greatest antifeedant effects were observed with the ergopeptine alkaloids ergotamine, ergovaline, alpha-ergosine, and alpha-ergocryptine, all of which significantly reduced feeding at 5.0 micrograms/g. The ergopeptine epimer ergovalinine, and the ergopeptine alkaloid derivatives dihydroergotamine, dihydroergocrystine, and alpha-bromoergocryptine were also active, although less so than the parent ergopeptines. Thus ergopeptine alkaloids are likely to be a major factor in the N. lolii-mediated resistance to H. arator. It was further observed that perennial ryegrass seed containing an endophyte strain that did not produce ergot alkaloids, but did produce other mycotoxins normally associated with N. lolii infection, did not deter H. arator feeding, whereas an ergot alkaloid producing N. lolii/perennial ryegrass association did. The implications of these findings in relation to the toxicity of ergot alkaloids to mammals, and in relation to the definition of a desirable endophyte, are discussed.