Semiochemical mediated interactions in insects: A case study of fire ants and parasitic phorid flies

Decapitating phorid flies, Pseudacteon spp are introduced parasitoids of imported fire ants, Solenopsis spp. in the United States. However, little is known about their host location cues. Previous studies by our group demonstrated attraction of Pseudacteon tricuspis to live and body extracts of the red imported fire ant, Solenopis invicta workers, suggesting that the response of the parasitoid to fire ant hosts is odor-mediated. In this paper, we present the results of follow-up studies to determine the identity of the chemicals mediating fire ant-phorid fly interactions. First, we demonstrated response of P. tricuspis to extracts of the venom gland of S. invicta workers. Next, using bioassay-guided analytical techniques such as silica gel column chromatography and coupled gas chromatography mass spectrometry (GC-MS), we identified several novel alkaloids from the venom of S. invicta workers. Further studies with electrophysiological techniques (i.e., electroantennogram (EAG) and GC-EAD) and behavioral bioassays demonstrated response of P. tricuspis to some fractions/components of the venom alkaloids of S. invicta workers. The results suggest that fire ant venom alkaloids may play a role in mediating fire ant-phorid fly interactions.