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Optimizing Fluctuating Thermal Regime Storage of Developing Megachile rotundata (Hymenoptera: Megachilidae)

Joseph P. Rinehart, George D. Yocum, William P. Kemp, Julia H. Bowsher
Journal of economic entomology 2016 v.109 no.3 pp. 993-1000
Megachile rotundata, adults, alfalfa, eclosion, managers, pollination, pollinators, pupae, spring, storage time, sublethal effects, survival rate, temperature, weather, North America
The alfalfa leafcutting bee, Megachile rotundata (F.), is the primary pollinator for alfalfa seed production in North America. Under current management practice, developing pupae are incubated at 29–30C until the adults emerge for pollination. If unfavorable spring weather delays peak alfalfa bloom, managers will cool pupae to slow development, which can increase mortality and causes sublethal effects. Previously, we demonstrated that exposure to a fluctuating thermal regime (FTR) increases survival and extends the viable storage period. To determine the optimal conditions for FTR during storage of developing M. rotundata, we examined four variables: temperature of the daily warm pulse, duration of the warm pulse, number of weeks exposed to the FTR treatment, and developmental stage of the bee. Survival was measured by successful eclosion to the adult stage. Under all conditions, exposure to FTR increased survival compared with exposure to a constant 6C. When the temperature of the daily warm pulse was 20–25C from a base temperature of 6C, and the pulse duration was extended to 3 h, survival rates were as high as those observed under standard storage conditions (29C). Under this FTR storage protocol, bee managers can delay emergence for 8 wk without significant decreases in survival. Our findings have substantial economic implications for bee management and alfalfa seed production by increasing the flexibility and efficiency of M. rotundata adult emergence.