Melatonergic Regulation of Polyethism and Circadian Foraging in Apis mellifera

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 (<i>Apis mellifera</i>). 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 (<i>AmMTR</i>/<i>AmMT2</i>; 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 <i>N</i>-acetyltransferase ortholog <i>AmNAT2</i> (≈10-fold increase near day 23), while <i>AmNAT1</i> remained unchanged; melatonin treatment was associated with a trend toward increased <i>Amα-glucosidase</i> 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 <i>AmMTR</i>. 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.