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

Abstract

Provisions of Megachile rotundata were analyzed for their physical, chemical and mi- crobial 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 ,3 10 1.5 x 102 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 con- tained 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 distribu- tion of pollen within provisions but increased the pH by 0.2-0.5. Total sugars and quantities of fruc- tose 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.