Safety Of Entomopathogenic Fungi

Biopesticides based on entomopathogenic fungi are now available, with a range of different species and strains used.

The growing use of these insect pathogens has raised interest in the safety of microbial pesticides, above the level previously required for registration purposes. This increased scrutiny of environmental and mammalian safety of entomopathogenic fungi is part of a worldwide move to more awareness of potential negative impacts of biotechnology. Few of the entomopathogenic fungi are thought to pose a direct threat to human health. There are exceptions, such as the entomophthoralean fungus, Conidiobolus coronatus, but it is unlikely any development of the potentially hazardous strains would be contemplated. Many products have required mammalian toxicology packages to be submitted during the registration process to demonstrate safety. Generally, the entomopathogenic Deuteromycetes are considered to have low risk of mammalian toxicity [e.g., Donovan-Peluso et al. (1980) and Shadduck et al. (1982)]. Recent papers on Metarhizium and Beauveria have raised some issues regarding mammalian safety of immunocom-prised individuals (Burgner et al. 1998; Henke et al. 2002).

In addition to viewing bioactives from entomopathogenic fungi as potentially useful, there has been consideration of their effect as potential hazards in registering entomopatho-genic fungi. There are some results showing activity against human cell lines, such as tumor cell lines for P. tenuipes cytotoxic components (Nam et al. 2001). Production of toxic secondary metabolites has caused problems in the registration of some fungi in Europe. Strasser et al. (2000) summarizes data on specific secondary metabolites (destruxins, efra-peptins, oosporein, beauvericin, and beauveriolides) produced by the genera Beauveria, Metarhizium, and Tolypocladium. They found that fungal bioactives posed no obvious risk to humans, although the number of detailed studies is limited. Some studies have indicated low-level activity against animals of selected bioactives such as destruxins of Metarhizium have an intraperitoneal injection LD50 of 1-16mg/kg in mice. However, the levels of metabolites produced during insect infection were much lower than in culture.

There is a growing body of research on nontarget impacts of fungal-based insecticides [e.g., Goettel et al. (2001) and Hokkanen and Hajek (2002)], which have not found increased environmental risk from their use. The present evidence is that mycoinsecticides are very safe in production and use from both an environmental and mammalian toxicity viewpoint (Goettel et al. 2001). However, the formulations being developed require stringent testing to ensure their superior safety compared with comparable chemical pesticides (Moore and Prior 1993). While the fungi themselves have generally not been found to be a risk through testing and natural exposure, the development of novel formulations and strain combinations will require careful evaluation to ensure no unexpected effects occur. This could be especially true of nontarget impacts. Similarly, any development of genetically modified strains will have to be carefully studied for environmental and mammalian safety. Regulations in all countries are becoming more stringent on these issues, especially for genetically modified organisms.

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