A useful technique for synchronizing pollinators with the alfalfa, Medicago savita L. (Fabaceae), bloom is to interrupt the late spring incubation of developing bee pupae and pharate adults of Megachile rotundata (F.) (Hymenoptera: Megachilidae) with short-term low-temperature storage. However, low-temperature exposure can be stressful depending on the temperature, duration of exposure, and the developmental stage exposed. To evaluate the effect of low-temperature storage after development had already been initiated by exposure to 29°C, three developmental stages (eye pigment pupae, body pigment pupae, and pharate adults ready to emerge) were exposed to 6, 12, or 18°C for durations up to 28 d. The effect of delaying the termination of overwintering storage (6°C) from April to July (“April bees” and “July bees,” respectively) also was examined. The following observations were made: 1) All developmental stages of the April bees and July bees examined can be stored without harmful effects, as measured by percentage of survival, for 14 d at 12°C and above. 2) Postponing the termination of overwintering storage at 6°C from April until July significantly decreased the mean number of days to 95% adult emergence in the July ready-to-emerge bees across the three temperatures tested. 3) The increase of overwintering duration also caused a decrease in the postemergence longevity of the ready-to-emerge adults stored at 6°C for 14 d. 4) Of the three storage temperatures examined, 18°C seems to be the optimal storage temperature for short-term storage of developing bees because of their slow but continuing development without increased mortality either during storage or after emergence.
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Vol. 103 • No. 2