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.