AEROBIC MICROORGANISMS ASSOCIATED WITH ALFALFA LEAFCUTTER BEES (MEGACHILE-ROTUNDATA)

Characterization of microorganisms associated with alfalfa leafcutter bee (Megachile rotundata) nectar, pollen, provisions, larval guts, and frass (excreta) in Alberta demonstrated a varied aerobic microflora. Yeasts were isolated frequently from nectar, pollen, and provisions bu t rarely from guts or frass. The most prevalent yeast taxa were: Candi da bombicola, Cryptococcus albidus, Metschnikowia reukaufii, and Rhodo torula glutinis. Although few filamentous fungi were found in nectar, they were frequently isolated from pollen and provisions; the predomin ant taxa were Alternaria alternata, Cladosporium cladosporioides, C. h erbarum, Epicoccum nigrum, and Penicillium chrysogenum. Bacteria, incl uding species of Bacillus, Corynebacterium, Micrococcus, and the actin omycete Streptomyces, also were prevalent in provisions and/or on poll en. In general, the diversity of microorganisms isolated from alimenta ry canals and frass was lower than from nectar, pollen, and provisions . Bacillus firmus, B. licheniformis, B. megaterium, B. pumilus, and St reptomyces spp. were the most frequently isolated bacteria, whereas Tr ichosporonoides megachiliensis was the most common filamentous fungus isolated from larval guts and/or frass. These taxa may be part of the resident microflora of the alimentary canal. Populations of bacteria a nd filamentous fungi, but not yeasts, were larger from Ascosphaera agg regata-infected larvae than from healthy larvae. However, with the exc eption of Aspergillus niger and T. megachiliensis in frass from health y larvae, no taxon of filamentous fungi was conspicuously present or a bsent in infected larvae, healthy larvae, or their frass.