Sixty unmated 3-d-old cosmopolitan and Zimbabwe females (n = 9 and n = 10, respectively) were transferred to standard glass rearing vials (24.5 × 95 mm, borosilicate glass; Fisher Scientific, Sweden), which had been baked at 350°C overnight. After 24 h, the flies were removed and the vial was rinsed with 200 μL of hexane, containing 100 ng decanal as internal standard, in an ultrasonic water bath for 3 min. The solvent was transferred to 1.5 mL GC-MS vials with insert and condensed to ca. 5 μL in a fume hood.
Two μL of the solvent rinses were analyzed by gas chromatography-mass spectrometry (GC-MS) (6890 GC and 5975 MS, Agilent, Santa Clara, CA, USA) on a fused silica capillary column (60 m × 0.25 mm), coated with HP-5MS UI (df = 0.25 μm; Agilent). Injections were made in splitless mode (30 s), at 275°C injector temperature. The GC oven was programmed from 50 to 250 °C at 8 °C/min (2 and 10 min hold, respectively) and a final temperature of 275°C, the mobile phase was helium (34 cm/s). The MS operated in scanning mode. Aldehydes were identified by direct comparison of mass spectra and retention data with synthetic standards.
Two μL of the solvent rinses were analyzed by gas chromatography-mass spectrometry (GC-MS) (6890 GC and 5975 MS, Agilent, Santa Clara, CA, USA) on a fused silica capillary column (60 m × 0.25 mm), coated with HP-5MS UI (df = 0.25 μm; Agilent). Injections were made in splitless mode (30 s), at 275°C injector temperature. The GC oven was programmed from 50 to 250 °C at 8 °C/min (2 and 10 min hold, respectively) and a final temperature of 275°C, the mobile phase was helium (34 cm/s). The MS operated in scanning mode. Aldehydes were identified by direct comparison of mass spectra and retention data with synthetic standards.