|Rinehart, Joseph - Joe|
|Kemp, William - Bill|
|Bowsher, Julia - North Dakota State University|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2016
Publication Date: 6/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63015
Citation: Rinehart, J.P., Yocum, G.D., Kemp, W.P., Bowsher, J.H. 2016. Optimizing fluctuating thermal regime storage of developing Megachile rotundata (Hymenoptera: Megachilidae). Journal of Economic Entomology. 109(3):993-1000.
Interpretive Summary: Many agricultural practices, including the production of alfalfa seed, is heavily dependent on insects for pollination. This crop is unique in that it is heavily pollinated by the alfalfa leafcutting bee Megachile rotundata instead of honeybees. An important part of the protocols for successful management of this species is an approximately one month warming period in the spring which much be timed so that adult emergence coincides with crop bloom. This timing can be further complicated by weather patterns that can delay crop bloom after the warming period has already been started. Previously, our group showed that when cold-storing developing bees in the spring to delay their emergence, a short, daily warm pulse greatly improves the survival and the quality of bees. This study expands on this discovery by testing daily warm pulses of varying temperatures and durations. We found that the benefits of a warm pulse can be achieved by a considerable range of temperatures and durations, making the application of FTR protocols a less cumbersome process. Additionally, the higher temperature and longer pulses resulted some bee emergence during storage, giving bee managers who want to release some bees early an additional tool to do so. Taken with our previous studies, it is becoming increasingly evident that fluctuating thermal regime protocols could become a valuable tool for managers of this important alternative pollinator.
Technical Abstract: The alfalfa leafcutting bee, Megachile rotundata, is the primary pollinator for alfalfa seed production in North America. Under current management practice developing pupae are incubated at 29ºC until the adults emerge for pollination. If unfavorable spring weather delays peak alfalfa bloom, bee managers will cool pupae to slow development. Although cooling allows synchronization of emergence with peak bloom, exposure to constant low temperature (6ºC) increases mortality and causes sub-lethal effects. However, we have demonstrated previously that exposure to a daily warm pulse, called a fluctuating thermal regime (FTR), increases survival and extends the viable storage period. To determine the optimal conditions for FTR during M. rotundata pupal storage, we manipulated four variables: the temperature of the daily warm pulse, the length of the warm pulse, the number of weeks exposed to the FTR treatment, and the developmental stage of the pupae. Survival was measured by successful eclosion to the adult stage. Under all conditions, exposure to FTR increased survival compared to exposure to a constant 6ºC. When the temperature of the daily warm pulse was 20-25ºC from a base temperature of 6ºC, and the pulse length was extended to three hours, survival rates were as high as those observed under standard storage conditions (29ºC). Under this FTR storage protocol, bee managers can delay emergence for approximately eight weeks without significant decreases in survival. However, pharate adults exposed to warm pulses of 20-25ºC tend to emerge while still in the temperature treatments, thus potentially emerging prior to being placed in the field. Red-eye pupal stage exposed to FTR did not emerge early, demonstrating that the red-eye pupal stage has greater potential for synchronizing emergence of bees with bloom of the target crop. Our findings have significant economic implications for bee management and alfalfa seed production by increasing the flexibility and efficiency of M. rotundata adult emergence.