Signaling Who Does Which Chores

Abstract

Honey bees divvy up the labor of obtaining food and feeding the young by age: Young adult "nurse" bees feed the larvae, whereas older bees forage. The transition from nurse to forager, which can be accelerated or slowed in response to the needs of the hive, is accompanied by a decrease in nutrient stores. Noting that abundant nutrient stores typically promote synthesis of insulin [or insulin-like peptides (ILPs) in insects] and that insulin/insulin-like growth factor signaling (IIS) has been implicated in the central regulation of feeding-related behavior in Drosophila , Ament et al . investigated the role of IIS in honey-bee behavioral maturation. The abundance of mRNAs encoding the ILP AmIlp1 in brain and the ILP receptors AmInR1 and AmInR2 in abdomen was greater in foragers than in nurses (despite their decreased adiposity). This increase depended on nutritional status; immature bees fed on sugar (which led to forager-like lipid stores) expressed more brain ilp1 and brain and abdominal inR1 than their counterparts fed a more nutrient-rich diet of sugar and pollen. IIS stimulates TOR (target of rapamycin), and administration of the TOR inhibitor rapamycin elicited a seasonally dependent delay in the onset of foraging. Although insulin signaling is typically associated with increased energy metabolism, the expression of genes encoding proteins involved in energy metabolism--notably, five of six in the citrate cycle--was enhanced in the brains of nurse bees compared with foragers, although foragers have higher overall metabolic rates. The authors conclude that, in the honey bee, IIS--which is involved in regulation of metabolism and of feeding behavior in a solitary insect--is associated with regulation of social behavior. S. A. Ament, M. Corona, H. S. Pollock, G. E. Robinson, Insulin signaling is involved in the regulation of worker division of labor in honey bee colonies. Proc. Natl. Acad. Sci. U.S.A. 105 , 4226-4231 (2008). [Abstract] [Full Text]