Availability and depletion of fat reserves in halictid foundress queens with a focus on solitary nest founding

Foundress queens of social Hymenoptera require considerable amounts of energy for survival, solitary nest founding, provisioning of the first brood, and egg production. Energy reserves in insects mostly consist of fat. We investigated how hibernation and the subsequent flight season, especially the solitary nest founding phase, influenced the abdominal fat content of gynes in the primitively eusocial sweat bee, Lasioglossum malachurum (Hymenoptera, Halictidae). In our study population, sexuals are produced in both the second and the third broods. Emerging gynes of the third brood had significantly more fat than those of the second brood, whereas there was no such difference in males. As expected, fat reserves in samples of female sexuals caught at emergence, after hibernation, during solitary nest founding, and at the end of the social phase of the nest cycle indicate a severe decrease of reserves that was highest during the 7 weeks of the solitary founding phase. Thus, the amount of fat reserves of foundress queens seems to be crucial, particularly for nest founding. However, investment of energy reserves in the solitary nest founding phase has probably to be balanced with the subsequent social phase in a way that maximizes the queen’s fitness. Possible consequences for the complexity and progress of the nest cycle are discussed.