Effect of Ethyl Oleate Pheromone on Honey Bee (Apis mellifera) Overwintering Physiology

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 honeybees in certain regions challenging. We hypothesized that the transition to overwintering isregulated by the forager pheromone, ethyl oleate, when forager bees are relegated to the hive forlonger periods of time during poor weather conditions. We exposed bees of different ages andtasks 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 increasedlongevity seen in diutinus bees, by looking at gene expression of an immune gene, defensin. Wefound ethyl oleate only had a significant effect on fat body mass, and the ratio of fat body massto hypopharyngeal gland protein synthesis in nurse bees. This indicates that ethyl oleate mayaffect the efficiency of metabolism of consumed protein into fat body stores, and an increasedmetabolic shift from hypopharyngeal gland protein synthesis to fat body production, allowingyoung bees to prepare for suboptimal conditions. While these findings indicate that ethyl oleateis likely not the sole cause of a transition to a diutinus state, it is possible that when concomitantwith 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 worthinvestigating further.