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

## TL;DR

Aphidinae aphids use specific odorant receptors to detect an alarm pheromone, and these receptors are evolutionarily conserved.

## Contribution

The study identifies three conserved odorant receptors that selectively detect the alarm pheromone (E)-β-farnesene in Aphidinae aphids.

## Key findings

- Three odorant receptors (OR5, OR40, OR43) are selective detectors for the alarm pheromone (E)-β-farnesene in Aphidinae aphids.
- Knockdown of these receptors suppressed EBF-induced repellency in Acyrthosiphon pisum.
- OR gene loss occurred only in lineages that no longer use EBF as an alarm signal.

## Abstract

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.

•Identified three conserved ORs as selective detectors for the alarm pheromone EBF•Silencing OR5, OR40, or OR43, singly or together, blocked EBF-induced repellency in aphids•Phylogenetics reveals that OR gene loss occurred exclusively in lineages losing EBF usage

Identified three conserved ORs as selective detectors for the alarm pheromone EBF

Silencing OR5, OR40, or OR43, singly or together, blocked EBF-induced repellency in aphids

Phylogenetics reveals that OR gene loss occurred exclusively in lineages losing EBF usage

Evolutionary Biology; Molecular Biology and Genetics; Neurobiology and Sensory Systems; Chemical Ecology; Entomology and Insect Physiology