For the remaining species, the indicator compounds produced by a single male insect could not be detected in 1 kg of crushed grains. However, they could be detected with at least fifteen male beetles for C. ferrugineus (S/N 1⁄4 13 for ferrulactone 1 and S/N 1⁄4 21 for ferrulactone 2) and twenty C. pusillus (S/N > 3) respectively.
4.4. Development of streamlined method
Because the optimum extraction condition required a relatively long time and was operated at high temperature, a streamline method would be more practical to apply in the industrial situation.