Insect sex pheromones (SPs) are central to mate‐finding behaviour, and play an essential role in the survival and reproduction of organisms. Understanding the roles, biosynthetic pathways and evolution of insect chemical communication systems has been an exciting challenge for biologists. Compared with Lepidoptera, little is known about the mechanisms underlying pheromone biosynthesis in Hemiptera. In this study, we isolated and characterized two new desaturase‐like genes, termed Asutdes1 and Asutdes2, from Adelphocoris suturalis, an important agricultural pest in China. Although the two genes encode an identical protein, Southern blot analysis revealed that they are duplicated genes. The Asutdes2 transcript is more abundant than Asutdes1 in the tissues tested, in particular the metathoracic scent gland and fat body. Silencing Asutdes expression in females by injecting double‐stranded RNA (dsAsutdes) against a portion of the coding sequence shared by the two genes enhanced the production of (E)‐4‐oxo‐2‐hexenal, a component of the A. suturalis SP blend, and dramatically suppressed the sexual attractiveness of A. suturalis females. We conclude that dsAsutdes is associated with the SP biosynthetic pathway in A. suturalis.