AN ON-FARM LOOK AT CHALKBROOD

Authors: James, Rosalind; Huntzinger, Craig

Submitted to: Proceedings of the Northwest Alfalfa Seed Growers Association
Publication Type: Other
Publication Acceptance Date: 1/19/2003
Publication Date: N/A
Citation: N/A

Interpretive Summary: The alfalfa leafcutting bee (Megachile rotundata) is used extensively in the U.S. and Canada as a pollinator for alfalfa seed production. Chalkbrood is fungal disease in the larvae of this bee, a disease that can be quite devastating. Currently, growers disinfect the nesting boards every year or two to help control the disease. We found that some of the current practices for disinfection do not adequately kill spores of the chalkbrood fungus. However, we found that even the use of new boards that should be free of chalkbrood, have little impact on disease control. Thus, the boards may not be the most important source of contamination. To find alternatives for disease control, agricultural fungicides were tested in the laboratory to determine which have the potential to prevent or cure the disease in the bee larvae. Rovral® was found to be the most effective fungicide and it was also of low toxicity to the bee larvae. Fungicides may prove to be an effective means for controlling the disease if a good application method can be developed because the fungicide needs to be delivered to larvae that are enclosed within individual cells in nesting blocks. In addition, more information is needed on the means by which the disease persists from one year to the next and on how it spreads.

Technical Abstract: The alfalfa leafcutting bee (Megachile rotundata) is used extensively in the U.S. and Canada as a pollinator for alfalfa seed production. Chalkbrood is fungal disease in the larvae of this bee, a disease that can be quite devastating. Currently, growers disinfect the nesting boards every year or two to help control the disease. We found that some of the current practices for disinfection do not adequately kill spores of the chalkbrood fungus. However, we found that even the use of new boards that should be free of chalkbrood, have little impact on disease control. Thus, the boards may not be the most important source of contamination. To find alternatives for disease control, agricultural fungicides were tested in the laboratory to determine which have the potential to prevent or cure the disease in the bee larvae. Rovral® was found to be the most effective fungicide and it was also of low toxicity to the bee larvae. Fungicides may prove to be an effective means for controlling the disease if a good application method can be developed because the fungicide needs to be delivered to larvae that are enclosed within individual cells in nesting blocks. In addition, more information is needed on the means by which the disease persists from one year to the next and on how it spreads.