UC Davis

In winter, honey bees undergo a transition to a diutinus state, during which time broodrearing declines or stops entirely, and worker bees live for up to 20 weeks. The mechanism, causes, and geographic prevalence of this transition are unknown, and can make managing honey bees in certain regions challenging. We hypothesized that the transition to overwintering is regulated by the forager pheromone, ethyl oleate, when forager bees are relegated to the hive for longer periods of time during poor weather conditions. We exposed bees of different ages and tasks to ethyl oleate in cage conditions and measured accepted markers of overwintering: hypopharyngeal gland size and protein content, fat body weight, longevity, pollen consumption, and vitellogenin gene expression. We also investigated a possible mechanism for the increased longevity seen in diutinus bees, by looking at gene expression of an immune gene, defensin. We found ethyl oleate only had a significant effect on fat body mass, and the ratio of fat body mass to hypopharyngeal gland protein synthesis in nurse bees. This indicates that ethyl oleate may affect the efficiency of metabolism of consumed protein into fat body stores, and an increased metabolic shift from hypopharyngeal gland protein synthesis to fat body production, allowing young bees to prepare for suboptimal conditions. While these findings indicate that ethyl oleate is likely not the sole cause of a transition to a diutinus state, it is possible that when concomitant with other factors such as gradual decline in brood pheromone, pollen dearth, cold temperatures, and photoperiod, ethyl oleate may contribute to the transition to overwintering, a notion worth investigating further.