Half a century of pheromone science in the quest for green pest control

Abstract: Chemical ecology is the science of species interaction via secondary chemical substances. Depending on their function as sex attractants, trail and territorial determinators, defensive secretions, group cohesion and caste determination substances, lures for food plant and oviposition site recognition, different terms have been invented. While contemporary biologists now take the term as well as the concept of “pheromones” for granted, it was a sensational event when the January 1959 issue of the British Nature magazine published a two pagecommunication by Karlson and Lüscher on “Pheromones, a new term for a class of biologically active substances”. This seminal paper appeared simultaneously with the first identification of the chemical structure of any pheromone. Bombykol, (E,Z)-10,12-hexadecadien-1-ol, was isolated and identified from domesticated female silk moths, Bombyx mori L. (Lepidoptera: Bombycidae). It induces very specifically and in most minute concentrations the males of this species to perform a mating dance. This response test served as a behavioural indicator for both the presence and also the concentration of this sex pheromone. Two years later, the total synthesis of bombykol via several independent routes by Butenandt, Hecker and co-workers in 1961 concluded more than twenty years of pioneering work into uncharted territory. Immediately, the impact of this discovery for chemical communication, sensory physiology and practical plant protection was recognized. It paved the way for establishing chemical ecology as an academic but also as a practical discipline and as an important component in the pursuit of integrated pest management (IPM). Thus, bombykol served as a prototype for an entirely new class of exogenously active natural signal compounds. It spearheaded subsequent developments in chemical ecology. Therefore it did not come as a surprise when the enterprise of analytically inclined chemical ecologists boomed. It produced, within a few decades, thousands of new pheromones described within a body of twenty thousand original research articles and at least 4 dozen monographs. Today, pheromones are known from pest insects in all major food and fiber crops and from stored products. Most prominent are still insect sex attractants because of their spectacular function. Meanwhile, crop protection via pheromones is a worldwide endeavour. In IPM, pheromones and the related kairomones play a key role as lures in traps for monitoring and mass trapping, and (without traps) for mating disruption. In favourable cases like in cotton, in fruit, in vegetable pest management or in glass house cultures, pheromones can also economically compete with the non sustainable toxic pesticides which invariably provoke eco-toxicity and resistance (Georghiou & Saito, 1983).