Evolutionarily entrenched odorant receptors for (E)-β-farnesene signaling in Aphidinae aphids

Alarm pheromones are crucial for the survival of social insects, enabling coordinated escape from predators. Their evolution has co-evolved with the development of olfactory recognition systems, suggesting specific molecular mechanisms underlie this adaptive relationship. We analyzed alarm pheromone compositions across 36 aphid species and found that EBF serves as the sole or primary alarm signal in the Aphidinae subfamily. Genomic annotation of 13 aphid species identified eight conserved, Aphidinae-specific odorant receptor (OR) clades under strong purifying selection. Three receptors-OR5, OR40, and OR43-were EBF-selective in Aphidinae species. Their individual or collective knockdown suppressed EBF-induced repellency in Acyrthosiphon pisum, indicating non-redundant roles in receptor combinational coding. Phylogenetic analyses demonstrated variation in gene age among these receptors, with losses confined to species that do not use EBF as an alarm signal. This study demonstrates a multi-receptor system for EBF detection in Aphidinae aphids and advances the understanding of olfactory system evolution.