Entomopathogenic fungi being developed as biological control agents (BCAs) may have the potential to spread and become established in the environment. For registration purposes, the risks concerning their persistence have to be evaluated according to EU legislation which requires the decline of BCAs to acceptable background levels unless related risks are acceptable. In order to deal with this requirement, applicants of a BCA need to give information on its persistence and natural background levels. For risk assessors and registration authorities guidance on how to evaluate data on natural background levels of indigenously occurring species (0same species as the introduced BCA) is needed. For this purpose, an overview is presented on background levels of some indigenous fungi as well as persistence data of some applied fungal BCAs. Data were restricted to commerical species. It was found that for the species Metarhizium anisopliae, Beauveria bassiana and Beauveria brongniartii natural densities were relatively low and introduced strains of these fungi decreased gradually in time. Many factors were found in the literature, such as intrinsic, edaphic, biotic, climatic, and cultural factors, that could explain this decline.

The nematode Steinemema feltiae (Nematoda: Steinernematidae) was tested for its ability to control two main mushroom pests i.e. the sciarid Lycoriella auripila (Diptera: Sciaridae) and the phorid Megaselia halterata (Diptera: Phoridae) in growing-rooms filled with spawned compost. A clear difference between female and male sciarid control was observed. A nematode application 1 day after casing preceded by an application 1 day before casing on the compost caused an almost complete control (97%) of the F1-generation of female sciarids. The FZgeneration of females was similarly controlled (95%) by an application 7 days after casing. A dosage of 1 x lo6 nematodes mP2 was found to be equally effective as higher dosages. Diflubenzuron remained active throughout entire the cropping period with high sciarid mortality rates varying from 72% to 99%.Phorid control was variable and seemed to depend on the presence of sciarids. In one occasion the control rate of F2-generation phorid larvae was 75% and was possibly caused by the presence of new infective juvenile nematodes recycled in FZgeneration sciarid larvae. Diflubenzuron did not significantly reduce phorid numbers.

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