Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2013
Publication Date: 6/1/2013
Publication URL: http://handle.nal.usda.gov/10113/56900
Citation: Rinehart, J.P., Yocum, G.D., Kemp, W.P., Greenlee, K.J. 2013. A fluctuating thermal regime improves long-term survival of quiescent prepupal Megachile rotundata (Hymenoptera: Megachilidae). Journal of Economic Entomology. 106(3):1081-1088. Interpretive Summary: Like many agricultural products, the production of alfalfa seed is heavily dependant on insects for pollination. Instead of using honeybees, much of this crop is pollinated by the alfalfa leafcutting bee Megachile rotundata. A critical element of the successful management of this species is winter storage, when bees are stored at approximately 40°F until the following spring, when they are removed from cold storage and their life cycle continues. In this paper, we investigated the effects of a fluctuating thermal regime during winter storage, during which bees were given a daily 1 hour pulse at 68°F, and compared their survival and quality to those stored at a constant temperature. Our results show that the daily pulse at 68°F dramatically increased the “shelf-life” of cold stored bees. This expansion of bee shelf-life extended into the next growing season, thereby giving users of this alternative pollinator greater flexibility while protecting them from yearly fluctuations in bee prices. Hence, we expect fluctuating thermal regime protocols to become a valuable tool for managers of this important alternative pollinator.
Technical Abstract: The alfalfa leafcutting bee Megachile rotundata (F.) is the primary pollinator for alfalfa seed production. Under standard management conditions, the alfalfa leafcutting bee develops to the prepupal stage under field conditions, after which they are cold-stored at a static temperature until the following spring, when temperatures are raised and development resumes. We have assessed the effects of a fluctuating thermal regime (FTR) during overwintering cold storage, where bees were exposed to a daily pulse of 20 °C, and compared viability and insect quality to bees stored under a static thermal regime (STR). Our results demonstrate that implementing an FTR protocol dramatically increases the survival of cold-stored alfalfa leafcutting bees, effectively extending their shelf-life into the subsequent growing season. These findings could substantially ameliorate significant obstacles that restrict the more widespread use of this important pollinator, such as the biological constraints that restrict its use in early blooming crops, and yearly fluctuations in bee prices that add significant financial uncertainty to end users. This study also strengthens a growing body of evidence that indicates FTR protocols are superior to STR protocols for insect cold storage.