Evolution of insect pheromones and their role in reproductive isolation and speciation

The importance for reproductive isolation of a change in the pheromone biosynthetic pathway, resulting in a different pheromone blend, is discussed in Lepidoptera and Diptera. The different sites of pheromone production and the biosynthetic enzymes are briefly reviewed. Two examples of a modification in the pheromone blend leading to reproductive isolation in Lepidoptera are taken as examples: the first, in Ostrinia nubilalis, is involved in the formation of two different populations showing reproductive isolation; the second, in the genus Ostrinia, might be at the origin of the formation of two different species. In both examples, a modification in the function of a desaturase involved in pheromone biosynthesis brings about change in the pheromone blend. In the fruitfly, Drosophila melanogaster, a mutation at a desaturase locus leads to the formation of two populations which differ in their pheromone mixtures and have developed premating isolation. The closely related species, D. melanogaster and D. simulans, differ in their female pheromonal cuticular hydrocarbons. This pheromonal difference is due to two species- and female-specific genes, desatF and eloF. The activity of desatF could account for an effective barrier between these species. All these examples show that a birth and death process of desaturases is at the origin of major shifts in the pheromone blend leading to sexual isolation and speciation.