Electrically Stimulated Fire Ants (Solenopsis invicta, Hymenoptera: Formicidae) Release Chemical Cues That Attract Parasitic Pseudacteon Decapitating Flies (Diptera: Phoridae)

We previously determined that electrically stimulated fire ants release exocrine gland products, e.g., venom, recruitment and alarm pheromones. We hypothesized that exocrine gland emissions from electrically stimulated fire ant workers might attract phorid fly parasitoids of fire ants. Bioassays demonstrated that electrically stimulated worker ants did attract phorid fly parasitoids in the field. Phorid fly (Pseudacteon tricuspis) mass rearing boxes were then used for lab bioassays to determine the glandular source and active components from electrically stimulated fire ants that elicited phorid fly attraction. The crude extract of fire ant poison sacs showed a significant increase in attacking phorid flies at the 10 min evaluation time, whereas purified venom alkaloids had no effect on phorid flies. Dufour's glands (the source of recruitment pheromones) elicited no fly activation/attraction. However, mandibular gland extracts, the source of alarm pheromones, were found to activate and attract phorid flies. Moreover, a previously identified pyrazine alarm pheromone from mandibular glands was found to be the active component. This was confirmed by specific alarm pheromone bioassays showing the expected ephemeral characteristic of the attraction and by directly using synthetic fire ant alarm pheromone. Use of the fire ant alarm pheromone may aid in detecting the presence of phorid flies in the field and in increasing attack/parasitism rates during mass production.