# Melatonergic Regulation of Polyethism and Circadian Foraging in Apis mellifera

## TL;DR

This study shows that melatonin influences task transitions and foraging behavior in honey bees, linking circadian rhythms to social behavior.

## Contribution

The study identifies melatonin as a modulator of task allocation and circadian foraging in honey bees, supported by behavioral, molecular, and computational evidence.

## Key findings

- Melatonin treatment advanced the age at first waggle dance by ≈9 days.
- RNAi knockdown of AmMTR suppressed foraging, indicating melatonin pathway dependence.
- AmNAT2 shows a forager-age peak in expression, suggesting a role in melatonin synthesis.

## Abstract

Melatonin is a conserved indolamine implicated in circadian and developmental timing, but its role in social-insect task allocation is unclear. Here, we show that melatonergic signaling modulates the nurse → forager transition in the honey bee (Apis mellifera). A single hemocoelic dose of melatonin (100 ng) markedly reduced hive retention and advanced the age at first waggle dance by ≈9 days (median 11.8 vs. 20.9 days; common-language effect size = 0.94). Complementary manipulations—pharmacological antagonism with luzindole and RNA interference (RNAi)-mediated knockdown of a candidate melatonin receptor (AmMTR/AmMT2; transcript reduction ≈65–79% at 24–72 h)—produced reciprocal suppression of foraging, indicating pathway dependence. Transcriptional profiling revealed a forager-age peak in the arylalkylamine N-acetyltransferase ortholog AmNAT2 (≈10-fold increase near day 23), while AmNAT1 remained unchanged; melatonin treatment was associated with a trend toward increased Amα-glucosidase expression. Computational analyses classify AmMTR as a class-A GPCR and identify plausible melatonin-compatible pockets; promoter scans reveal high-confidence circadian motif matches upstream of AmMTR. These in silico results are presented as hypothesis-generating. Together, the behavioral, molecular, pharmacological and computational lines of evidence support melatonin as a circadian-informed modulatory signal that helps align neuroendocrine and metabolic states with the timing of extranidal behavior. Confirmation via receptor functional assays and broader colony replication will be important.