Differences among fungicides targeting beneficial fungi associated with honey bee Colonies

Abstract

This chapter draws attention to individual fungi commonly found in stored pollen (bee bread) and how they may respond to different fungicides. We evaluated the effects of boscalid and pyraclostrobin (PristineR BASF), propiconazole (OrbitTMTiltR Syngenta), and chlorothalonil (BravoR Syngenta), on 12 fungi species isolated from bee bread. A key observation was that no two fungi cultured from bee bread respond the same with regard to percentage reduction in radial growth rate, mortality, and lowest effective concentration. Chlorothalonil was fungistatic (slowed growth without killing) and was least effective on Aspergillus spp., Penicillium sp., Cladosporium sp., and Ascosphaera apis. Boscalid and pyraclostrobin mixture was almost entirely fungicidal, especially against Aspergillus spp. and Penicillium sp. Consistently, Rhizopus sp. was the most sensitive to the fungicides and A. apis was the most tolerant. Parallel studies with antibiotics showed no effect on limiting growth of the 12 fungi. Thus, effectiveness of test fungicides is boscalid and pyraclostrobin > propiconazole > chlorothalonil. Our studies suggest that exposure to fungicides applied when plants are in bloom and collected by foraging bees could have a negative effect on colony health because they disrupt the mycoflora bees use to process and store their food.