Even though almost all the larvae have now spun their cocoons, that doesn’t mean our work is finished! Indeed, Osmia bicornis larvae go through major life stages after cocoon completion, notably developing into adults inside their cocoons. This step is crucial because a larva that does not transform into an adult before winter will not be able to complete development. After metamorphosis, the fully developed adults spend the winter months in their cocoons (“overwintering”) and emerge the next spring.
To capture potential effects of the temperature treatments throughout development, we weighed cocoons at two important stages:
– pupal stage (i.e., before metamorphosis; 35 days after cocoon formation)
– adult stage (i.e., after metamorphosis; 65 days after cocoon formation)
Cocoons were taken out from their nest tubes, cleaned (Fig. 1a), and then weighed on a high precision scale (Fig. 1b).
Once weighed, we put the cocoons in individual foam nests, with all the details needed to identify them later (e.g., unique ID number, temperature treatment, nest of origin, position within the nest tube) (Fig. 2). The cocoons in their foam nests were then stored in a shed in Thwaite Botanic Gardens for the winter period. That way, the bees inside their cocoons will experience natural variations of temperature during the overwintering stage, whilst being protected from rain and frost.
Temperature, by modifying the quality and/or quality of pollen provisions or the timing of cocoon formation, could also affect adult body size after overwintering and at emergence, which are key life-history traits for bee survival and reproductive success. We therefore plan to weigh the cocoons again next spring, at the end of the overwintering period, and then the adult bees after emergence.
Fig. 3 shows Eliza, our team’s field and lab technician, in the middle of a weighing session. But it was all hands on deck to weigh all the cocoons (470 in total!) in time. A big thank you to everyone involved!
