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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVE NUTRITION FOR HONEY BEE COLONIES TO STIMULATE POPULATION GROWTH, INCREASE QUEEN QUALITY, AND REDUCE THE IMPACT OF VARROA MITES Title: Differences Among Commonly Sprayed Orchard Fungicides in Targeting the Beneficial Fungi Associated with Honey Bee Colony and Bee Bread Provisions (In Vitro)

Authors
item Yoder, Jay -
item Hedges, Brian -
item Heydinger, Derrick -
item Sammataro, Diana
item Degrandi-Hoffman, Gloria

Submitted to: CRC Press
Publication Type: Book / Chapter
Publication Acceptance Date: May 30, 2011
Publication Date: January 2, 2012
Citation: Yoder, J.A., Hedges, B.Z., Heydinger, D.J., Sammataro, D., Hoffman, G.D. 2012. Differences among commonly sprayed orchard fungicides in targeting the beneficial fungi associated with honey bee colony and bee bread provisions (in vitro). In: Sammataro, D. and Yoder, J., editors. Honey Bee Colony Health: Challenges and Sustainable Solutions. Boca Raton, FL. CRC Press. p. 181-192.

Interpretive Summary: Our studies evaluated the effects of representative fungicides, boscalid and pryaclostrobin, propiconazole, and chlorothalonil, alone and in combination, on 12 fungi species isolated from bee bread. Chlorothalonil was fungistatic (slowed growth without killing) and was least effective on Aspergillus spp., Penicillium sp., Cloadosporium sp. and Ascosphaera apis. Boscalid and pryaclostrobin mixture was almost entirely fungicidal (9/12 fungi were killed), especially against Aspergfillus spp. and Penicillium sp. At lower concentrations, boscalid and pyraclostrobin showed an average 40% greater fungicistatic activity than chlorothalonil. Growth response of fungi exposed to propiconazole fell between these extremes. Adding the fungicides together did not improve effectiveness. Consistently, Rhizopus sp. was the most sensitive to the fungicides and A. apis was the most tolerant. Parallel studies with antibiotics, fumagillin, tylosin and oxytetracycline showed no effect on limiting growth of the 12 fungi. Thus, (1) antibiotics are not treatment for chalkbrood or stonebrood as some beekeepers believe; (2) effectiveness of test fungicides is boscalid and pyraclostrobin > propiconazole > chlorothalonil; and (3) bee colony fungi feature distinct growth rates that translate into differential responses to a fungicide. Our studies suggest that exposure to fungicides applied when plants are in bloom and collected with nectar and pollen by foraging bees could have a negative effect on colony health because they disrupt the mycoflora bees use to process and store their food. In this evaluation, chlorothalonil is the least damaging to Aspergillus spp. and Penicillium sp. that are inhibitory toward chalkbrood fungus (A. apis).

Technical Abstract: Our studies evaluated the effects of representative fungicides, boscalid and pyraclostrobin, propiconazole, and chlorothalonil, alone and in combination, on 12 fungi species isolated from bee bread. Chlorothalonil was fungicidal (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 (9/12 fungi were killed), especially against Aspergillus spp. and Penicillium sp. At lower concentrations, boscalid and pyraclostrobin showed an average 40% greater fungistatic activity than chlorothalonil. Growth response of fungi exposed to propiconazole fell between these extremes. Adding the fungicides together did not improve effectiveness. Consistently, Rhizopus sp. was the most sensitive to the fungicides and A. apis was the most tolerant. Parallel studies with antibiotics, fumagillin, tylosin, and oxytetracycline, showed no effect on limiting growth of the 12 fungi. Thus (1) antibiotics are not treatment for chalkbrood or stonebrood as some beekeepers believe; (2) effectiveness of test fungiciodes is boscalid and pyraclostrobin > propiconazole > chlorothalonil; and (3) bee colony fungi feature distinct growth rates that translate into differential responses to a fungicide. Our studies suggest that exposure to fungicides applied when plants are in bloom and collected with nectar and pollen by foraging bees could have a negative effect on colony health because they disrupt the mycoflora bees use to process and store their food. In this evaluation, chlorothalonil is the least damaging to Aspergillus spp. and Penicillium sp. that are inhibitory toward chalkbrood fungus (A. apis).

Last Modified: 10/26/2014
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