ISHS Acta Horticulturae 288: VI International Symposium on Pollination
BIOLOGY AND CONTROL OF CHALKBROOD, A FUNGAL DISEASE OF THE ALFALFA LEAFCUTTER BEE, MEGACHILE ROTUNDATA |
| Authors: | Mark S. Goettel, K. W. Richards |
| Abstract:
The alfalfa leafcutter bee, Megachile rotundata (F.), is used to pollinate alfalfa for seed production in North America. Chalkbrood is a disease of bees caused by several species of fungi in the genus Ascosphaera. The principle causative agent in leafcutter bees is Ascosphaera aggregata. The disease was first reported from the United States in 1973 and remains most severe in the western states where losses of more than 65% of bees are not uncommon. Chalkbrood was first detected in Canada in 1982. Losses of up to 26% of bees have been recorded; however, overall infection rates remain below 1%. Bee larvae become infected after consuming pollen provisions contaminated with A. aggregata spores. The spores germinate in the midgut and penetrate into the hemocoel. Larvae soon die and turn a chalk white color as the mycelium fills the body. Sporogenesis occurs beneath the host cuticle resulting in the formation of ascospores which are bound in "spore balls" within ascomata. At this stage, the cadaver turns black. Present practices for chalkbrood control center around the decontamination of bee cells and nesting material. Although these practices have provided some control, they have not achieved the level of control needed to stem the spread of the disease. Studies on the pathology, epizootiology and distribution of Ascosphaera spp. in North America and evaluation of fungicides and other methods for chalkbrood control are underway. | |
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