D3119: Oogenesis-flight syndrome in bumble bees: effects of reproductive state on energy stores

The oogenesis-flight syndrome has been characterized as a continuum from a reluctance to fly to, in the extreme, a massive loss of flight muscle that occurs with ovarian maturity in many insect species. The bumble bee life cycle suggests an oogenesis-flight trade-off. As workers emerge, they take over foraging and much of the brood incubation, drastically decreasing the demands on the flight muscles of the colony queen, which focuses almost entirely on egg laying. Thus, diversion of resources away from the flight muscles could allow queens to maximize reproduction. But, to our knowledge, this potential trade-off has not been explored in bumble bees. To measure effects of reproduction on flight muscle and thoracic energy stores in bumble bees (Bombus huntii), we measured thoracic protein, free-sugar, lipid, and glycogen in fall queens that were either newly caught, held in the lab, or treated with CO2 to stimulate ovary development (simulated spring queens). Egg length was then measured as a marker of reproductive investment. Simulated spring queens experienced a marked loss of weight that correlated with ovary development and had lower protein, lipid, and sugar levels than both control groups. Per unit body weight, queens investing in reproduction prioritized maintenance of thoracic protein over thoracic lipid and free-sugar stores. These data suggest that trade-offs between flight and ovary development may operate at the level of local energy stores that power flight muscle rather than atrophy of flight muscle, as would be indicated by loss of protein.