This page will be updated when the project starts generating data. Watch this space!
We conducted a field experiment during the summer of 2024 to answer the following question:
Do adult bees adjust larval pollen provisions to the nest temperature?
Nine wooden nests were heated at three temperatures (ambient, ambient + 4°C & ambient + 8°C) on our study site. From late June to mid-August, we monitored these nests in order to record information on the nesting process of Osmia bicornis females by collecting a variety of data: number of pollen provisions made, number of eggs laid, egg and larva mortality, success of cocoon completion. You will find more information on the experiment in the Project news & updates section of the website.
Osmia females provisioned twice as many pollen balls and laid twice as many eggs in the heated nests (Figure 1A) than in the ambient nest. Although a smaller proportion of eggs survived in the heated nests (Figure 1B), the number of eggs surviving to the larva stage remained higher in the heated nests (236 & 272 eggs) than in the ambient nest (143 eggs).
The eggs that survived then hatched to become larvae. We did not observe differences in mortality at the larva stage between heated and ambient nests. On average, 23% of the larvae died during the experiment across all three nest temperatures.
At the end of their development, the larvae spin cocoons inside which they develop into pupae and then adults. Successfully completing a cocoon is therefore an important step for the life cycle of Osmia bicornis.
We observed a similar success of cocoon completion between heated and ambient nests. In average, 89% of the cocoons were successfully completed across all three nest temperatures.
However, cocoons tend to be lighter in the heated nests (Figure 2). Smaller cocoons in the heated nests could lead to lower overwintering survival and emergence of smaller bees in the spring, which could then impact their survival and reproduction as adults.
Our initial results show that females seem to prefer to provision pollen and lay eggs in heated nests. However, this result needs to be refined by integrating temperature data measured inside the nests throughout the experiment.
Temperature affects survival at the egg stage, but doesn’t have a strong effect on life-history traits at the larval and cocoon stages. For a fuller picture of the effects of temperature on the nesting process of Osmia bicornis, we will measure life-history traits, such as overwintering survival and adult weight, when the bees emerge in spring 2025.