Effect of wintering duration and temperature on survival and emergence time in males of the orchard pollinator Osmia lignaria (Hymenoptera: Megachilidae)

We measured winter survival, emergence time following incubation at 20 degreesC, and postemergence longevity in males of the orchard pollinator Osmia lignaria Say exposed to 25 artificial wintering treatments differing in duration (30, 90, 150, 210, and 270 d) and temperature (0, 4, 7, 10, and 13 degreesC). For all temperatures, survival was highest at 90 d of wintering. Temperatures greater than or equal to 10 degreesC were unsuitable for wintering O. lignaria populations even for short periods. At VC, bees showed increased mortality, signs of excessive fat body depletion, and decreased longevity when wintered for >150 d. Wintering durations greater than or equal to 210 d required temperatures : 4 degreesC for acceptable survival. Time to emerge following incubation at 20 degreesC decreased with increasing wintering duration and wintering temperature. Many bees emerged before incubation when wintered for long periods at the warmest temperatures. Postemergence longevity was highest when bees were wintered at 0 degreesC for 210 d. Managing the activity of O. lignaria to coincide with fruit tree bloom initiation is much more easily accomplished with the use of populations exhibiting short emergence times. Several wintering treatments that resulted in acceptable survival and longevity (150 d at 0, 4 and 7 degreesC, and 210 -270 d at 0 and 4 degreesC), produced mean emergence times greater than or equal to5 d. Our results can be used to establish appropriate wintering regimes for O. lignaria populations managed to pollinate orchard crops differing in bloom time (from almonds in February to apples in May), and therefore, allowing for shorter or longer wintering durations.