ARS | Publication request: Microscopic evaluation of the fate of Conidia of two entomogenous fungi in soil

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2007
Publication Date: August 20, 2007
Citation: Scocco, E.A., Gardner, W.A., Shapiro Ilan, D.I. 2007. Microscopic evaluation of the fate of Conidia of two entomogenous fungi in soil. Journal of Entomological Science. 42:413-414.

Interpretive Summary: Due to problems associated with certain chemical insecticides such as destruction of beneficial insects and harm to humans and the environment, development of safe and natural alternative pest control measures is needed. Two natural insecticides that have been developed are fungi called Beauveria bassiana and Metarhizium anisopliae. When studying these fungi and how to use them most effectively for pest control, we need to have accurate measurement techniques. When the fungus is applied to the soil, we must be able to accurately measure its persistence. In this study we demonstrated that the fungi can germinate upon contact with the soil. Therefore, when the soil is plated onto an artificial medium to determine fungal spore counts, the density may be overestimated due to growth of fungal hyphae fragments (vegetative pieces from the germinated spores).

Technical Abstract: Accurate measurement techniques are required for development of microbial control agents such as entomopathogenic fungi. Using artificial media and CFU plating, some researchers have found that the numbers of fungal propagules recovered from soils apparently increased within 2 to 3 days of application. This has caused some to postulate that the increased fungal biomass detected is noninfective hyphal fragments resulting from the germination of the fungal conidia in soil. We tested this hypothesis. We detected germination of both Beauveria bassiana and Metarhizium anisopliae conidia in soil 36-48 h after placement in soil, and mycelial growth was evident thereafter. These results support the premise that increases in the numbers of CFUs of entomogenous deuteromycetes after application to soils is due to the mycelial fragments that are recovered from soils and enumerated on selective media.