Apidologie 23 (1992) 119-132
DOI: 10.1051/apido:19920204

Analysis of alfalfa leafcutter bee (Megachile rotundata) provisions pre-and post-sterilization with propylene oxide

G.D. Inglis^a, M.S. Goettel^b and L. Sigler<sup>a

a</sup>  University of Alberta Microfungus Collection and Herbarium, Devonian Botanic Garden, Edmonton, Alberta T6G 2E1, Canada
^b  Agriculture Canada Research Station, Lethbridge, Alberta T1J 4B1, Canada

Abstract - Provisions of Megachile rotundata were analyzed for their physical, chemical and microbial properties prior to and following fumigation with propylene oxide. The effects of treated and untreated provisions on larval development and susceptibility to Ascosphaera aggregata were also studied. Bacteria, yeasts and filamentous fungi averaged 1.3 x 10³, 1.5 x 10 ² and 7.5 x 10³ colony-forming-units g^-1, respectively. Fumigation with propylene oxide for 24 h at concentrations of 0.6 and 1.2%, but not 0.1%, effectively sterilized provisions. Untreated provisions consisted of 18.1% water, 56.8% nectar and 25.1 % pollen with a pH of 4.1. The sugar content was 65.9% and was comprised of fructose (48.1%), glucose (43.6%), sucrose (1.4%) and turanose/palatinose (1.8%). Pollen contained 6% protein. Pollen was not stratified within provisions and Medicago sativa was the most prevalent taxon (66.2%). Propylene oxide treatment had no effect on the protein content or distribution of pollen within provisions but increased the pH by 0.2-0.5. Total sugars and quantities of fructose and glucose were reduced by 3.2, 10.4 and 8.7%, respectively, whereas the caloric content of treated provisions was 1.6% greater than the control treatment. Detoxification under vacuum for 120 h reduced the water content of provisions by 40.3%. Eggs of M rotundata did not survive when placed on provisions detoxified under vacuum for 24 h post-fumigation. On provisions detoxified for 120 h, there were no differences in mortality between larvae reared on sterilized, artificial and non-sterilized provisions, but time to prepupation was delayed relative to the non-sterilized treatment. The mean mortalities of larvae inoculated with A aggregata were 98.0, 97.8 and 27.4%, respectively on artificial, sterilized and non-sterilized provisions.

Key words: Megachile rotundata / provisions / sterilization / chalkbrood / Ascosphaera aggregata