Methods for identifying and studying semiochemicals

Abstract

Progress in science depends on new techniques, new discoveries and new ideas, probably in that order. Sydney Brenner (2002) Since Butenandt’s landmark identification in 1959 of the silk moth sex pheromone bombykol, there have been spectacular developments in our ability to identify semiochemicals (Meinwald 2009). In their work over some two decades, Butenandt’s team needed more than 10 metric tonnes of female moths, providing 500,000 pheromone glands from which they extracted ~12 mg of the pheromone to identify (Billen 2006; Butenandt et al . 1959). The identification of the first ant trail pheromone in 1971 still required 3.7 kg of Atta texana ants (Tumlinson et al . 1971). Today, it is possible to work with far, far less than a single moth’s pheromone gland. The revolution has come from chromatographic techniques in particular and the direct coupling of these with mass spectrometers, and other detection devices including animals’ own sensors. The ever-increasing power of nuclear magnetic resonance (NMR) spectroscopy has made complete structure determination (though perhaps not complete stereochemistry) possible on a microgram scale (Meinwald 2009). Insect pheromone identifications can be made from picogram to femtogram quantities, using gas chromatography–electroantennogram detector (GC-EAD, with the insect’s antenna) to get retention indices, and microchemical reactions to determine presence/absence of functional groups (e.g., with a gall midge sex pheromone, Gries et al . 2002).