Analysis of the alarm pheromone components of the red imported fire ant,Solenopsis invicta Buren( Hymenoptera: Formicidae)

【Background】2-Ethyl-3,6-dimethylpyrazine is a main alarm pheromone component of the red imported fire ant,Solenopsis invicta Buren. This study aimed to isolate and identify the reported alarm pheromone component of fire ant workers and to analyze the electrophysiological response of fire ant workers to the synthetic alarm pheromone component mixture. 【Method】Hexane extract of 200 g of fire ant workers was subjected to a silica gel column chromatography and eluted with hexane-acetone solvent system. The alarm pheromone fraction was analyzed by gas chromatography( GC) and gas chromatography-mass spectrometry( GC-MS) analyses. The electrophysiological response of fire ant worker to synthetic 2-ethyl-3,5( 6)-dimethylpyrazine mixture was analyzed by gas chromatography-electroantennographic detection( GC-EAD). 【Result】A fraction containing 2-ethyl-3,6-dimethylpyrazine was obtained through the silica gel column chromatography of hexane extract of ant workers. The retention time of 2-ethyl-3,6-dimethylpyrazine in the alarm pheromone fraction in GC-MS analysis was 11.45 min. GC-EAD analysis demonstrated that fire ant worker showed significant electrophysiological response to 2-ethyl-3,5( 6)-dimethylpyrazine mixture. 【Conclusion and significance】Fire ant workers showed higher activity to 2-ethyl-3,6-dimethylpyrazine than to 2-ethy-3,5-dimethylpyrazine,which can be used in baits to attract workers.