Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 10, 1998
Publication Date: N/A
Interpretive Summary: Health and environmental concerns have led to the withdrawal of a number of commercial pesticides, leaving some crops vulnerable to diseases. Increasing demand for new, more environmentally friendly toxicants for Medfly and other exotic fruit fly pests has renewed interest in the use of food dyes as potential replacements for malathion as the insecticidal principle in aerially applied toxic baits for adult flies. The use of thes xanthene dyes, however, raises concerns about possible deleterious effects on non-target organisms, such as beneficial fungi, that control the target pest or other pests in nature and those already in use or in development as biological control agents. In this study, we found that several of these dyes, at very low concentrations, inhibit growth of insect-pathogenic fungi in the light. This is the first demonstration of such effects on both germination and growth of filamentous fungi.
We studied effects of the xanthene dyes, eosin B, erthrosin B, and phloxine B on three species of entomopathogenic hyphomycetous fungi, Beauveria bassiana, Metarhizium anispoliae, and Paecilomyces farinosus. In a test of inhibition of fungal colony development on agar by treated filter paper disks, erythrosin B and phloxine B, but not eosin B, were active againist all three species at 100 g/disk under continuous exposure to light, but none of the dyes inhibited fungal colony development in the absence of light. In an assay measuring effects of erythrosin B on colony diameter over 9 days, growth of all three fungi varied inversely with dosage among colonies exposed to light but not among those held in the dark. Inhibition of condial samples exposed to light but not for those held in the dark. At a fixed dosage of erythrosin B, conidial germination of B. bassiana varied inversely with length of exposure to light. These results are consistent with reports of light-dependent toxic effects of xanthene dyes on other organisms. However, this is the first demonstration of such effects on germination and growth of filamentous fungi.