The Egyptian cotton leafworm (Spodoptera littoralis) is a pest species in France. It is found throughout the Mediterranean Basin as well as in Africa and the Middle East. Moth larvae are extremely polyphagous and cause damage to diverse crop species (e.g., corn, legumes, cotton, tomatoes, peppers).
As part of broader efforts to reduce pesticide levels, researchers must develop effective biocontrol methods. Such strategies often rely on disrupting reproduction and trapping moths using, most commonly, sex pheromones. However, pheromone synthesis is an expensive process, and it thus remains important to have other control strategies on hand. To this end, researchers need to improve their understanding of olfactory receptors in this moth.
In 2019, researchers identified OR5, an olfactory receptor in the Egyptian cotton leafworm that recognizes the main compound in the female sex pheromone blend. In this new study, the same scientists explored the receptor's evolutionary trajectory within Spodoptera to better characterize its functionality and specificity.
They used a combined approach in which they resurrected ancestral receptors in the laboratory, with the help of computer analysis, and they modeled the 3D structure of the receptors. They were thus able to determine that OR5 appeared around 7 million years ago. The researchers also employed site-directed mutagenesis to explore OR5's genetic fine-tuning, which allowed them to identify the eight amino acids (AAs) behind the receptor's high degree of specificity.
This finding is particularly unexpected, given that past research on receptor evolution has suggested just one or two AA substitutions suffice to change the functionality of ecologically important receptors.
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