The Neuropeptide Corazonin Promotes Higher Rates of Foraging in Apis mellifera Workers

Abstract

Honey bee workers take on specific roles within the colony. Young adult workers (~1 week old) perform in-hive tasks such as cleaning or brood care (“nursing”), while older workers forage for pollen, nectar, and water. This behavioral shift is regulated by hormones such as juvenile hormone (JH) and vitellogenin (vg), however the role of other hormones in this process is less-well understood. Additionally, stressors like poor nutrition and infection can accelerate this behavioral transition leading to precocious foraging and may result in reduced forager performance and accelerated colony decline. The neurohormone corazonin (crz), an 11 amino acid peptide with structural similarity to vertebrate gonadotropin-releasing hormone (GnRH) and invertebrate adipokinetic hormone (AKH), plays a part in determining caste identity in ants and other Hymenopterans. Harpegnathos ants performing nest-associated tasks have higher levels of vg and low levels of crz, while ants performing tasks outside of the nest have low vg and higher crz expression. Crz is a proposed stress hormone demonstrating a variety of functions across several groups of insects, however, the exact purpose of this hormone has yet to be identified in honey bees. In this study, I explore the molecular mechanism underlying the nutritional stress response that leads to precocious foraging, and whether crz is involved in this response. Additionally, I examine whether crz plays a role in the behavioral transition of honey bee nurses to foragers by injecting honey bee workers in the head with crz peptide. I found that although age did not have a significant effect on crz expression, starvation altered crz expression. Finally, I found that bees injected with crz take greater amounts of foraging trips than bees injected with a control and bees that were left un-injected.