To begin, sacrifice flies with ethyl acetate, and place the samples in three gas vials. Weigh the samples, and label them as fresh one, two, and three. Next, retrieve 2-year-old samples stored in alcohol filled centrifuge tubes, and absorb surface liquid with filter paper and weigh the samples.
Also, retrieve 2-year-old samples stored in centrifuge tubes and weigh them. Then, add a small amount of liquid nitrogen to a stainless steel container, and wait until all liquid nitrogen has evaporated. Place a fly sample in the container, and slowly pour liquid nitrogen.
Freeze the samples in liquid nitrogen, and remove them after the liquid nitrogen evaporates. Separate the thorax individually, followed by slicing each thorax. Place the slices in a two milliliter centrifuge tube.