Regulation of behavioral maturation by a primer pheromone produced by adult worker honey bees

Abstract

Previous research showed that the presence of older workers causes a delayed onset of foraging in younger individuals in honey bee colonies, but a specific worker inhibitory factor had not yet been identified. Here, we report on the identification of a substance produced by adult forager honey bees, ethyl oleate, that acts as a chemical inhibitory factor to delay age at onset of foraging. Ethyl oleate is synthesized de novo and is present in highest concentrations in the bee's crop. These results suggest that worker behavioral maturation is modulated via trophallaxis, a form of food exchange that also serves as a prominent communication channel in insect societies. Our findings provide critical validation for a model of self-organization explaining how bees are able to respond to fragmentary information with actions that are appropriate to the state of the whole colony.

Fig. 1.

Behaviorally related differences in quantity and localization of EO in honey bees. Shown are results of GC-MS analysis of tissue-specific analyses (n = 5 samples of nurses and foragers, each composed of 10 bees; n = 1 nurse and 1 forager sample for cuticle). The crop (specialized for storage of nectar and honey) was the only tissue that showed a significant difference between nurses and foragers (**, P < 0.05, Mann–Whitney U test).

Fig. 2.

Effect of EO on age at onset of foraging in honey bee colonies. In each trial (n = 14 trials) we calculated the mean age at which the first 50 bees from each focal cohort initiated foraging. Grand means depicted here ± SE. EO caused a significant delay in the mean age at onset of foraging (P < 0.0001, ANOVA). Significant trial and trial by treatment effects were also detected (P < 0.0001).

Fig. 3.

De novo biosynthesis of EO by honey bees. (A and B) Mass spectrum of EO extracted from the honey crop of foragers fed unlabeled glucose (A) or 1-¹³C glucose (B). Arrows denote EO. (A and B Insets) GC results that show similar quantities of EO in both samples. (C) Incorporation of ¹³C label from 1-¹³C glucose into EO over time, as measured by the isotope composition of the molecular ion (m/z 310 for unlabeled EO, 311 for a single ¹³C, 312 for two ¹³C, etc.). Percentages of incorporation were estimated by correcting for natural isotope abundance (see Materials and Methods). Foragers were fed for 24, 48, or 52 h (two replicates). (D) Mass spectrum of EO extracted from isolated honey crops perfused with 8% D₆ ethanol.