Effect of pH on the volatiles of hydrolyzed protein insect baits

Four volatile concentrates were prepared from acidic corn protein hydrolysate and from basified hydrolysate, under atmospheric and vacuum conditions. Examination by capillary gas chromatography/mass spectrometry revealed that both the atmospheric and vacuum concentrates prepared from acidic hydrolysate were qualitatively very similar, with phenylacetaldehyde and several other aromatic oxygenated compounds predominating. In contrast, nitrogenous compounds were the major components of the two basic concentrates. Some attraction was shown for all four concentrates in field bioassays with Dacus dorsalis, Ceratitis capitata , and Dacus cucurbitae , but with one exception (basified atmospheric concentrate vs D. dorsalis ), none were as attractive as basified protein hydrolysate itself. No attractancy could be demonstrated for the four major imines.