Behavioural, morphological, and metabolic maturation of newly emerged adult workers of the bumblebee, Bombus impatiens

Newly emerged adult holometabolous insects must still complete considerable morphological, metabolic, and neural maturation. Despite this, adults have frequently been documented to fly prior to finishing maturation and attaining peak physiological capacity. In some species, flight is limited by the unfurling of the wing, while in other species it may be limited by biochemical capacity. We charted maturation trajectories of adult bumblebee workers (Bombus impatiens) for both morphological and flight muscle metabolic capacities, and compared these to the first age at flight. Workers began regular flights as soon as two days after emergence. The unfurling of the wings was completed well before first flights and before any other studied factor, suggesting this did not initially limit flight. Wing beat frequencies, measured as a struggling response to grasping the hindlegs, were about 90% mature by two days old, and did not significantly change after three days. Conversely, by the initiation of flight, the mean enzyme maturation was only 63% completed relative to adult enzyme capacity, though specific enzyme profiles ranged from 42% to 73%. Maximum ADP-stimulated mitochondrial respiratory activity on pyruvate and proline matured along a similar time frame to glycolytic capacity, reaching its maximum three days after emergence. Bumblebees, as other adult insects, thus begin flights prior to fully maturing.