Insecticidal, antifeedant and growth inhibitory activities of efrapeptins, metabolites of the fungus Tolypocladium

This study shows for the first time that efrapeptins secreted by Tolypocladium have antifeedant and growth inhibitory properties. In both choice and no-choice assays against Plutella xylostella and Phaedon cochleariae there were significant differences between consumption of treated and untreated leaf discs with DC50 values (concentration resulting,in a deterrency index 50%) of 25 and 69 ppm for P. xylostella and P. cochleariae, respectively. Reduced feeding resulted in significant,weight loss of larvae of both species exposed for 24 h to efrapeptin-trented leaves. The effect of the toxin persisted even after the larvae were transferred to fresh, untreated leaves reduced larval and pupal weights, retarded larval and pupal development and delayed adult emergence. The effects were mole pronounced in Phaedon than Plutella. This study shows that efrapeptins have direct contact toxicity but appear to be more efficacious against insects contacting treated leaves. Toxicity in both topical and leaf clip assays was dose-related with larvae of P. xylostella being more susceptible to the insecticidal activity of efrapeptins than P. cochleariae.