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

Abstract

We measured winter survival, emergence time following incubation at 20°C, 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°C). For all temperatures, survival was highest at 90 d of wintering. Temperatures ≥10°C were unsuitable for wintering O. lignaria populations even for short periods. At 7°C, bees showed increased mortality, signs of excessive fat body depletion, and decreased longevity when wintered for >150 d. Wintering durations ≥210 d required temperatures ≤4°C for acceptable survival. Time to emerge following incubation at 20°C 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°C 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°C, and 210-270 d at 0 and 4°C), produced mean emergence times ≤5 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.