Assessing the Impacts of Metarhizium and Beauveria on Bumblebees

Abstract

In this chapter we present as an example a specific case study from the ecological safety evaluation of the Hyphomycete fungi Metarhizium anisopliae (Metsch.) Sorokin and Beauveria bassiana (Bals.) Vuill., carried out in Finland during the ERBIC-research project. Only the part concerning the safety to bumblebees is presented here (for a full report see Hokkanen et al., 2003). Metarhizium anisopliae and Beauveria bassiana are two well-studied, commercialised, and commonly used entomopathogenic fungi (EPF), also occurring naturally in Finland. We decided to focus on bumblebees because they are the most important group of natural pollinators of crop plants and wild flowers in the temperate zone. While possible impacts of Metarhizium and Beauveria on the honeybee have been addressed by several authors in many publications, to our knowledge no earlier information exists on the possible impact of these fungal pathogens on bumblebees. These pollinators are also abundant in our model agroecosystem, turnip oilseed rape, which was chosen because both the key pest, the pollen beetle (Meligethes aeneus), and its natural enemy complex have been well studied under Scandinavian conditions. Background information was already available on the occurrence of deuteromycetous EPF in the model system (Vä nninen et al. 1989), on the persistence of augmented fungal propagules in cultivated soils of the study area in question (southern Finland) (Vänninen et al. 2000), and on the impact of entomopathogenic fungi on the pollen beetle (Hokkanen 1993). In addition, entomopathogenic fungi and nematodes are a possible future option for managing the soil-dwelling stages of the pollen beetle and other pests in this system via incorporation in the soil (Butt et al. 1994). Fungi can also be used against foliage-dwelling stages of the pest either by spraying, or when vectored by honeybees (Butt et al. 1998). Different application strategies for entomopathogens could therefore be considered, linked to differing non-target risk scenarios based on the impact of the application strategies on key components of the ecosystem.