A biological assay for detection of toxins associated with Acremonium-infected tall fescue

The effects of toxic compounds in endophyte-infected (E+) tall fescue on the development of Drosophila melanogaster Meigen, the laboratory fruit fly/ were evaluated. Drosophila melanogaster was useful as a model insect for bioassays of insecticidal compounds in E+ tall fescue plant tissues and individual compounds found in these tissues.

Toxins in diets prepared with E+ tall fescue leaf, root, and tiller base powders reduced larval survival significantly. The response induced by these toxins varied with different plant tissues because the concentration of toxins is higher where the endophyte grows (i.e. seed and tiller base).

Ergonovine retarded the growth of Drosophila only slightly; however, two of the ergopeptide alkaloids tested, ergotamine and ergocryptine, reduced larval survival significantly. N-formylloline but not N-acetylloline or loline alkaloid, caused significant larval mortality at the highest concentration assayed.

These studies with Drosophila revealed that the roots of E+ tall fescue contain insecticidal compounds. N-formylloline, which was previously identified in E+ tall fescue roots, is probably a major contributor to toxicity of these plant organs.