The Egyptian cotton leafworm, scientifically known as Spodoptera littoralis, is a troublesome pest in France, as well as in the Mediterranean Basin, Africa, and the Middle East. Its caterpillars, or moth larvae, have a wide-ranging diet and cause significant damage to various crops such as corn, legumes, cotton, tomatoes, and peppers.
In order to reduce the use of pesticides and develop more environmentally friendly methods of pest control, researchers are focusing on the development of effective biocontrol strategies. One common approach is to disrupt the reproduction of pests and trap them using sex pheromones. However, synthesizing these pheromones can be expensive, highlighting the need for alternative control methods. To address this, researchers are seeking a better understanding of the olfactory receptors in the Egyptian cotton leafworm.
In a study conducted in 2019, scientists identified a specific olfactory receptor called OR5 in the Egyptian cotton leafworm. This receptor recognizes the primary compound in the female sex pheromone blend. In a new study, the same researchers investigated the evolutionary trajectory of this receptor within the Spodoptera species to gain insights into its functionality and specificity.
The researchers took a combined approach, involving laboratory experiments to resurrect ancestral receptors with the aid of computer analysis. They also modeled the three-dimensional structure of the receptors. Through these methods, they determined that the OR5 receptor emerged approximately 7 million years ago. Additionally, they used site-directed mutagenesis, a technique to introduce specific genetic changes, to explore the fine-tuning of OR5. This allowed them to identify eight amino acids responsible for the receptor’s high degree of specificity.
The finding was unexpected because previous studies on receptor evolution suggested that one or two amino acid substitutions would be sufficient to alter the functionality of ecologically important receptors. The researchers believe that a deeper understanding of how olfactory receptors evolve and acquire specificity over time is crucial for predicting the development of resistance to pheromone-based plant protection products.
Furthermore, the study shed light on the function of OR5, a highly specific receptor that plays a vital role in the reproduction of two Spodoptera species—the Egyptian cotton leafworm and the tobacco cutworm (S. litura). The tobacco cutworm is mainly found in Asia and is also known for its varied diet. The insights gained from this research will contribute to the development of new biocontrol strategies using agonist and antagonist molecules. Agonists occupy the receptors, preventing the key pheromone compound from binding, while antagonists block the activation of the receptor by the key pheromone compound.
The research paper detailing these findings has been published in the journal Proceedings of the National Academy of Sciences.
Source: National Research Institute for Agriculture, Food and Environment