Introduction

This research was undertaken in response to growing concerns about the health and environmental risks posed by conventional chemical pesticides and the urgent need for guidelines for the risk assessment of fungal BCAs which were being developed as environmentally friendly alternatives to chemical pesticides.

Underpinning research

The underpinning research "Monitoring the spatial-temporal distribution of secondary metabolites produced by the entomogenous fungus Beauveria brongniartii with particular reference to oosporein" was undertaken by Butt in 1999.  It was clear, following publication of the paper in 2000, that although guidelines existed for risk assessment of conventional chemical pesticides, no such guidelines existed for fungal BCAs or their metabolites. This was problematic for the registration and commercial development of fungal BCAs. Regulators and industry needed reassurance that the metabolites did not enter the food chain posing a risk to humans and the environment.

The EU-funded projects BIPESCO (1999-2001) and RAFBCA (2001-2004), within which Butt played a pivotal role, created the framework and understanding of the health and environmental risks associated with EPF being developed as BCAs.  Within BIPESCO, Butt identified key EPF metabolites, demonstrating inter- and intra-specific variation in metabolite production. The BIPESCO-RAFBCA teams showed that EPF produce many metabolites, often in extremely small quantities, making risk assessment extremely expensive and deterring industry from developing these products. This was compounded by the very few commercially available standards.

Butt co-ordinated development of methods and tools to isolate, characterise and quantify metabolites from disparate substrates (fungal culture media, crops and insect hosts).  Different toxicity testing systems were evaluated as an alternative to the murine model. The Ames and new Vitotox assay systems were compared and confirmed that EPF did not secrete genotoxic compounds. Destruxins, major metabolites of Metarhizium, and the cuticle degrading protease Pr1 were shown to be useful quality control markers with attenuated/degenerate cultures producing little or no destruxin/Pr1.

Detailed meta-analysis

These markers were later validated in subsequent NERC- funded projects. Molecular markers were developed to monitor fungal BCAs in the environment. Butt’s group was the first to monitor in vivo production and subsequent degradation of destruxins in the soil.  The RAFBCA team proposed a risk assessment strategy focusing on crude extracts (concentrated mixtures of metabolites from culture filtrates), a strategy automatically accounting for differences in metabolite profiles linked with strain, culture conditions and extraction method and potential synergies between compounds. This strategy was endorsed by the Regulation of Biological Control Agents, an EU policy support action reviewing risks of BCAs.

Overall, RAFBCA showed that the metabolites of Metarhizium and other fungal BCAs did not enter the food chain and pose a risk to human health.

Another major concern to regulators is the fate of inoculum in the environment. Butt and Scheepmaker, Rijksinstituut voor Volksgezondheid en Milieu (RIVM, = the Netherlands National Institute for Public Health and the Environment), conducted a detailed meta-analysis that showed that EPF do not accumulate in the environment but decline over time. The work was published in a peer reviewed journal (Scheepmaker & Butt, 2010) and adopted by the OECD BioPesticide Steering Group which decided to “refer directly to your work that is contributing to further international harmonization in the assessment of microbial biological control agents” Sylvie Poret, Head of OECD Pesticides Programme.

The OECD also proposed that the study could be referred to in a waiver/statement to fill the data requirement for EPF for persistence in soil (OECD 2011); which will help accelerate the registration process in the future.