Determination of indicator compounds
Two kilograms of feed were equally divided into two portions: the first portion was infested with adult insects and the second portion contained feed only.
For infested sample, five hundred of each insect species were added to 1 kg of feed and stored for twenty five days at 30 C and 70% RH. Five replicate samples were collected from the top, middle and bottom of the jar containing the infested sample. The volatile components were sampled from the headspace by SPME according to condition developed in Section 3.1.
The volatile compounds from sample B were also extracted by SPME using the same conditions. The volatile components from both samples were identified by GSeMS method as described in Section 3.2. The chromatograms were compared and the volatile components that appeared in sample A, but not in sample B were identified as “indicator compounds”.
The volatile components from live insects alone were also extracted and identified. These were then compared with the in- dicator volatile components in order to confirm that they were insect metabolites.