The biological roles of pyrazines: evidence for a warning odour function

Recently it has been shown that pyrazines are associated with many aposematic, chemically defended insects. We have demonstrated that naive hatchling chicks, when offered drinking water to which 2-methoxy-3-isobutylpyrazine is added, develop a neophobic 'alerting' reaction. The birds are not only capable of forming a conditioned aversion to the pyrazine when it is paired with quinine sulphate but they can also detect it from a distance probably by olfaction. This suggests that birds, a major group of insect predators, can interpret pyrazines as alerting or warning signals. The relationship of pyrazines with other alerting signals, and their evocative qualities are discussed.