Interspecific variation of Δ1,6-piperideines in imported fire ants

Δ1,6-Piperideines have been recently reported in the venom of the red imported fire ants, Solenopsis invicta Buren and the black imported fire ants, Solenopsis richteri Forel. However, they have never been quantified in either species. Furthermore, there is no information available about those piperideines in the hybrid imported fire ants (S. invicta × S. richteri). The abundance of six Δ1,6-piperideines was investigated in both species and their hybrid using gas chromatography–mass spectrometer (GC–MS). They include 2-methyl-6-tridecenyl-6-piperideine, 2-methyl-6-pentadecenyl-6-piperideine, 2-methyl-6-heptadecenyl-6-piperideine, 2-methyl-6-tridecyl-6-piperideine, 2-methyl-6-pentadecyl-6-piperideine, and 2-methyl-6-heptadecyl-6-piperideine. S. invicta produced all six Δ1,6-piperideines, whereas, S. richteri did not produce 2-methyl-6-heptadecenyl-6-piperideine and 2-methyl-6-heptadecyl-6-piperideine. The Δ1,6-piperideine profiles of the hybrid was similar to that of S. richteri, except trace amounts of 2-methyl-6-heptadecenyl-6-piperideine and 2-methyl-6-heptadecyl-6-piperideine were found in some of the samples. The ratio of 2-methyl-6-pentadecenyl-6-piperideine to 2-methyl-6-pentadecyl-6-piperideine (C15:1/C15:0) was significantly different among two species and their hybrid. In addition to Δ1,6-piperideines, hybrid workers also contained significantly more piperidines than their parent species. This is the first evidence of heterosis of imported fire ants in venom production.