Consequently, time and temperature were adjusted. Rhyzopertha dominica produced a higher amount of volatile pheromone than the other species, thus detection of a single male in 1 kg of grain was still possible in a short time and at a low temperature. In contrast, the other species produced relatively smaller amounts than R. dominica and therefore the sensitivities determined in previous section were changed.
S/N decreased with shorter extraction time and lower temper- ature. However, detection of volatile pheromone produced from R. dominica was still achieved at 30 C for 1 h. Extraction for 30 min gave acceptable S/N, but there was a significant variation of volatile pheromone produced by individual beetles that could not be detected in some of the triplicate samples. Therefore, 1 h extraction time was selected to be used in practice. The quantified amount of Dom 1 and Dom 2 was approximately 1.93 and 1.48 mg respectively.
Tbl released by T. castaneum extracted at 30 C for 4 h was detected only when the population reached twelve beetles. How- ever, the extraction time still did not meet the practical purpose (fast method) so it was further adjusted to a shorter time of maximum 2 h. Within 2 h, detection of volatile pheromone released from six beetles could not be achieved, so more insects were added until the volatile pheromone was detected. The final population was thirteen male beetles in 1 kg of flour and the amount of volatile pheromone released was found to be approximately 0.43 mg (n 1⁄4 3).
Ferlc I and II were detected when there was a total of twenty four beetles at 30 C for 4 h and they produced approximately 1.22 and 1.35 mg for Ferlc I and Ferlc II respectively (n 1⁄4 3). The extrac- tion time was not further adjusted because volatile pheromone may not be detected in a shorter time and hence addition of more beetles was not considered as meaningful. Such large insect pop- ulation could easily be detected by visual inspection.
A population of 50 beetles were the minimum number of C. pusillus that were needed for detection at 30 C for 4 h and compound I released was about 0.22 mg (n 1⁄4 3). Like C. ferrugineus, the extraction time was not further adjusted as adding more beetles was not meaningful, as stated above.