Identification of chemicals emitted by calling males of the Sapote fruit fly, Anastrepha serpentina.

Emissions from sexually active Anastrepha serpentina males were collected by solid-phase microextraction. Calling behavior of wild-type males showed no clear peak during the day, except that it was evident less frequently immediately after daybreak and just before dark. Calling by laboratory males was highest between 8 and 11 h after onset of the photophase, and mating by wild flies occurred mostly between 6 and 10 h after onset of the photophase. Two major components of male emissions were identified as 2,5-dimethylpyrazine (DMP) and 3,6-dihydro-2,5-dimethylpyrazine (DHDMP). DHDMP was synthesized, and the identity of the natural product confirmed by comparison of gas chromatographic retention times and mass spectrum. Emissions of DMP and DHMP were greatest during peak calling behavior, with males emitting up to 1.8 and 3.3 microg/h of DMP and DHDMP, respectively. A minor component, which did not vary with time of day, was identified as 2,3,5-trimethylpyrazine. To our knowledge, this is the first report of 3,6-dihydro-2,5-dimethylpyrazine in nature.