Crop protection: a new method for understanding insect sexual communication

Although insects are essential for the services they provide to ecosystems, they are also known for the damage they cause to crops. Some approaches known as “biocontrol” make use of insect sexual communication, which relies on odorant molecules called pheromones, to address this problem. Knowing a species’ sex pheromone can help control its populations, for example by releasing large quantities of these molecules into the air to disrupt mating, or by using insect traps to estimate or control population density. However, identifying pheromones is not so simple: it requires access to live insects, knowing the exact time when the insect produces them and analysing numerous chemical compounds and assessing their attractiveness.

Starting from receptors to identify sex pheromones

The scientists have developed an innovative method to identify the sex pheromone of the lily moth, whose sexual communication was previously unknown. Their approach works in reverse: instead of starting with the signal emitter, as is traditionally the case, they started with the receiver and its olfactory receptors, identified by analysing the insect’s genes. The receptors were modelled using computer software and tested with different odorant molecules to predict which ones were likely to interact with them. This analysis identified a potential pheromone and its associated receptors, which was then confirmed through a series of electrophysiological, analytical and behavioural tests.

To identify both the pheromone and its associated olfactory receptors, the research team combined several complementary approaches. Based on the species’ genes and comparisons with related species, they first selected two candidate receptors. The researchers then used artificial intelligence to predict their three-dimensional structures and molecular docking² to test volatile molecules and identify those likely to interact with the receptors.

Next, the researchers experimentally tested the selected olfactory receptors with the predicted volatile molecules, confirming that they could detect these compounds. They then combined physicochemical and electrophysiological methods to confirm that females actually secrete this sex pheromone and that males can detect the volatile molecule³. Finally, behavioural tests confirmed the pheromone’s ability to attract male lily moths and elicit sexual behaviour.

Identifying pheromones to better understand the world around us

The experiments are currently being carried out on the lily moth, a “non-model” species that is not found in mainland France and is therefore not considered a pest of concern there. However, it is a significant pest in many parts of the world, particularly in private gardens, public parks and botanical gardens, where regulations on the use of pest-control products are particularly strict. This work thus opens up the possibility of using pheromone-based methods to control this moth.

The main significance of this study is that it provides proof of concept for an innovative approach to identifying receptor–pheromone pairs in insects. This approach could considerably speed up the characterisation of previously unknown sex pheromones in many species, particularly current, emerging and invasive crop pests. Identifying the molecules that make up the pheromones of insects such as moths also offers new insights into the evolutionary history of these species: pheromones act as chemical signatures of a species and participate in species isolation.

1. Spodoptera picta.
2. A computational method used to predict how two molecules can bind and interact with each other. 
3. In this case, the molecule is (Z,E)-9,11-tetradecadienyl acetate.