AI Protein Models Predict a Moth’s Sex Pheromone Before Chemists Ever Extract It

In a striking demonstration of how computational biology is reshaping the study of chemical communication, researchers have predicted the sex pheromone of a moth species entirely from the structures of its odorant receptors, then confirmed the prediction in the laboratory. Writing in BMC Biology, a team led by Arthur Comte, Sébastien Fiorucci, Jin Zhang, and Emmanuelle Jacquin-Joly reports that three-dimensional modeling of two pheromone receptors correctly forecast the major female sex pheromone component of the lily moth, Spodoptera picta, a species whose chemical ecology had never previously been characterized. The work establishes a powerful reverse chemical ecology strategy that could dramatically accelerate pheromone discovery across the world’s largely unstudied insect species.

Sex pheromones are the linchpin of reproduction in most moths. Females synthesize and release species-specific blends of volatile molecules, usually during a defined window of the night, and males detect these blends over remarkable distances at astonishingly low concentrations. The precise composition of the blend, both its constituent molecules and their ratios, determines species identity and helps maintain reproductive isolation between closely related species that share habitat. Yet despite their central importance, pheromone compositions are well characterized almost exclusively for agricultural pest species, where the commercial incentive is clear: synthetic pheromones underpin population monitoring traps, mass trapping programs, and mating disruption strategies. Non-pest species, including the lily moth, whose caterpillars feed on ornamental Amaryllidaceae plants in gardens, have been largely overlooked.

Traditional pheromone identification is laborious and constrained. It typically requires access to living insects for gland extraction or headspace collection, careful determination of the females’ calling period, and painstaking analytical chemistry to pick out the behaviorally relevant compounds from complex extracts. The team sidestepped these hurdles by starting from a different vantage point altogether: the moth’s genome. Taking advantage of a recently assembled chromosome-level genome of S. picta, they searched for orthologs of OR5 and OR75, two pheromone receptors previously characterized in the sister species S. litura and S. littoralis, where OR5 is narrowly tuned to the major pheromone component (Z,E)-9,11-tetradecadienyl acetate, abbreviated (Z,E)-9,11-14:OAc.

The genomic search succeeded on both counts. The annotated S. picta genes, SpicOR5 and SpicOR75, encode proteins of 397 amino acids each, and quantitative PCR showed that SpicOR5 is strongly over-expressed relative to SpicOR75 in adult male antennae, a pattern mirroring the sister species and consistent with OR5’s established role as the principal receptor mediating male attraction in S. littoralis and S. litura. Expression levels were stable between one-day-old and three-day-old males, suggesting the receptors are not regulated by early adult sexual maturation. The sequence identities between S. picta receptors and their orthologs in the two sister species exceeded 94 percent, in sharp contrast to the roughly 67 to 72 percent identity they share with more distantly related Spodoptera species.

High sequence identity alone, however, is not a guarantee of conserved function. Research on other moths has shown that a single amino acid substitution can dramatically shift a pheromone receptor’s tuning. To address this uncertainty, the researchers built three-dimensional models of the receptors using the AlphaFold 3 web server and interrogated the physicochemical properties of their predicted ligand-binding pockets, including cavity volume and hydrophobicity, two parameters previously shown to correlate directly with odorant receptor tuning. The models of S. picta, S. litura, and S. littoralis receptors were nearly superimposable, with mean root-mean-square deviations of about 0.3 angstroms across the full-length proteins. Molecular docking then placed the candidate ligand (Z,E)-9,11-14:OAc in virtually the same binding pose within SpicOR5 as in its orthologs, engaging conserved residues across all three species.

Functional validation followed in a heterologous system. The S. picta receptors were expressed transgenically in Drosophila melanogaster olfactory neurons, replacing the fruit fly’s endogenous receptor in at1 sensilla, and tested against a panel of 26 moth pheromone compounds using single-sensillum recordings. As predicted, SpicOR5 responded to exactly one compound in the panel: (Z,E)-9,11-14:OAc, which elicited a median firing rate of 49 spikes per second and activated the receptor from doses as low as 10 micrograms. SpicOR75, true to its predicted broad tuning, responded significantly to seven of the 26 compounds, sharing most of its ligand repertoire with its orthologs in the sister species. The docking predictions and electrophysiology agreed almost perfectly.

With the receptor tuning established, the team flipped the logic of pheromone discovery. If SpicOR5, the dominant receptor in male antennae, is exquisitely tuned to (Z,E)-9,11-14:OAc, then this compound should be the major component of the female pheromone blend. Behavioral observations first pinpointed the optimal extraction window: female calling behavior peaked on the first two days after adult emergence, six and a half to nine hours into the dark phase, when up to 60 percent of females were calling. Gas chromatography coupled to electroantennographic detection of extracts from females collected during this window revealed a single compound that activated male antennae, and it was also the most prominent peak in the chromatogram. Subsequent mass spectrometry confirmed its identity as (Z,E)-9,11-14:OAc, alongside three minor components, (Z)-9-14:OAc, (E)-11-14:OAc, and (Z)-11-14:OAc, in a relative ratio of 100:45:34:3.

The behavioral assays sealed the conclusion. At 10 micrograms on filter paper, (Z,E)-9,11-14:OAc alone triggered wing-fanning in 56.3 percent of tested males, with additional males performing hair-pencil displays and contacting the odor source. A synthetic four-component blend matching the gland extract ratio elicited even more sexual behaviors, though still fewer than a natural female gland extract, which provoked the full behavioral sequence in every male tested. That shortfall echoes a pattern documented in the fall armyworm, S. frugiperda, where a trace pheromone component present at only about 0.2 percent of the major component’s abundance significantly enhances male attraction. The authors suggest that additional, still-unidentified trace compounds likely contribute to the complete S. picta pheromone signal.

Beyond its practical implications, the study illuminates a fascinating evolutionary story. OR75 exists only as a duplicated copy of OR5 in S. picta, S. litura, and S. littoralis; related species such as S. frugiperda and S. exigua, which do not produce (Z,E)-9,11-14:OAc, carry only a single, broadly tuned OR5 ortholog. The duplication apparently freed one copy to specialize. Multiple amino acid substitutions in the OR5 binding pocket shifted its specificity toward narrow recognition of the major pheromone component, while OR75 largely retained the ancestral broad tuning, though with modified specificity. Both copies thus represent cases of neofunctionalization relative to the ancestral receptor, and the functional divergence is mirrored by structural divergence in their binding sites, which cluster into two distinct groups that exclude the more distant Spodoptera orthologs.

The shared major pheromone component also raises ecological questions. S. picta and S. litura overlap geographically across large regions of South Asia and Oceania, and both call during the second half of the night, creating a potential risk of interspecific sexual signal interference. The two species’ minor components differ qualitatively, however, and these species-specific minor compounds may serve as critical discrimination cues for males, a mechanism documented in other Spodoptera species where heterospecific pheromone components act as behavioral antagonists. Host plant volatiles may further refine mate finding, since S. picta specializes on certain Amaryllidaceae plants, while its polyphagous sister species does not.

For applied entomology, the payoff is immediate. Identifying (Z,E)-9,11-14:OAc as a sufficient male attractant in S. picta opens the door to pheromone-based monitoring and trapping in gardens and nurseries where synthetic pesticides are restricted. More broadly, the study demonstrates a generalizable workflow: mine a genome for candidate pheromone receptors, model their structures, dock candidate ligands, verify with electrophysiology, and only then commit to chemical analysis. As genomic resources proliferate and AI-driven structure prediction matures, this receptor-guided strategy promises to bring chemical ecology within reach for the vast majority of insect species that will never enjoy the attention devoted to a handful of crop pests.

Subject of Research: Structure-based prediction of moth sex pheromone components from odorant receptor models in Spodoptera picta

Article Title: Odorant receptor structures predict the major female sex pheromone component in a moth

Article References: Comte, A., Wei, Z., Li, H., Xing, W.-Z., Moracci, R., Zhang, J., Fiorucci, S., & Jacquin-Joly, E. (2026). Odorant receptor structures predict the major female sex pheromone component in a moth. BMC Biology, 24(1), Article 193. https://doi.org/10.1186/s12915-026-02717-1

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02717-1

Keywords: Spodoptera picta, sex pheromone, pheromone receptors, odorant receptors, AlphaFold 3, molecular docking, reverse chemical ecology, GC-MS, electrophysiology, gene duplication, reproductive isolation, pest management