PATHOGENICITY OF ASCOSPHAERA-LARVIS TO LARVAE OF THE ALFALFA LEAFCUTTING BEE, MEGACHILE-ROTUNDATA

Laboratory assays and field surveys showed that Ascosphaera larvis (Bi ssett) is a pathogen of alfalfa leafcutting bee larvae, capable of cau sing high mortality in commercial populations. In one population over 21% of bees were found to be infected by A. larvis. However, overall l evels of the disease are low and it is unlikely that this pathogen pos es an immediate threat to commercial leafcutting bee populations in Ca nada. The LD50 was determined to be 1.9 x 10(5) spores/bee. Elevated l evels of CO2 are required for in vitro spore germination. The disease can easily be diagnosed within bee cells by X-ray radiography, thereby enabling disease levels to be monitored using conventional methods ut ilized by the industry to monitor leafcutting bee quality.