6.2.4. Selection and labelling of an appropriate precursor
Pheromonal signals, for example those produced by the mandibular gland often consist of multiple components (Blum, 1992). In addition, not all pheromonal components are necessarily derived from the same biosynthetic pathway. Thus precursors need to be selected according to the suspected biosynthetic pathway. For example, acetate is an appropriate precursor for evaluation of de novo biosynthesis in the case of pheromones that are derived from the fatty acid biosynthesis pathway such as Dufour's gland esters, hydrocarbons, 11- eicosanol and the acids of mandibular gland pheromone. However, for evaluation of other stages of synthesis, fatty acids or other compounds of appropriate length, saturated and unsaturated, should be used following the corresponding biosynthetic pathway (Blomquist et al., 1987; Martin and Jones, 2004; Plettner et al., 1995, 1996; Stanley-Samuelson, et al., 1988).
Precursors can be labelled with stable or radioactive isotopes. Selection of a type of labelling will determine the methods for analysis of the biosynthetic product and which may in turn affect the detection sensitivity. Using radioactive labelled precursors containing 14C/3H has advantages by providing fast evaluation and high sensitivity, but these demand authorization from appropriate agencies as they may pose environmental risks. Labelling precursors with stable isotopes (13C) is less hazardous but demands GC-MS analysis (see section 2.2.4). Precursors such as acetates/propionates/fatty acids are commercially available.