Comparison of Total Lipid Content of FTR and STR Treated Megachile rotundata

Megachile rotundata,, the alfalfa leafcutting bee, is an agriculturally and ecologically important crop pollinator. After being collected from the field in late summer, offspring in brood cells are overwintered at 6° C. Farmers initiate bee development in the following summer by placing brood cells in warmer temperatures, typically 29° C. This move is timed so that adult bees will emerge when the alfalfa crops reach approximately 50% bloom. Bloom may not occur when predicted, meaning that bee development must be delayed. Brood cells are often placed back into constant 6° C (static thermal regime, STR), halting development, but surviving bees often have deformities, and mortality may increase with the length of interruption. To reduce mortality and deformities, brood cells can be stored in a fluctuating thermal regime (FTR), consisting of 21 hours at 6° C and a one-hour pulse of heat at 20° C with one-hour ramping periods. The exact mechanism behind the improvement in bee condition with FTR is unknown. Increased survival could be attributed to molecules responsible for membrane fluidity and energy. Fatty acids in membranes are damaged during cold stress, but can be produced from sugars, commonly used natural cryoprotectants. To test the hypothesis that FTR treatment reduces lipid energy stores, total lipid levels of untreated and FTR- and STR-treated pupae were measured. Understanding the role of thermal stress on lipid concentrations will enable farmers and researchers to better rear and care for alfalfa leafcutting bees and pinpoint the mechanisms behind increased survival of cold storage.