Behavioral and Electroantennogram Responses of Phorid fly Pseudacteon tricuspis (Diptera: Phoridae) to Red Imported Fire Ant Solenopsis invicta Odor and Trail Pheromone

Abstract

The phorid fly, Pseudacteon tricuspis is an introduced parasitoid of the red imported fire ant, Solenopsis invicta in the United States. Previous studies show that phorid flies are attracted to host ant workers at disturbed colonies, to colonies exhibiting aggressive interspecific interactions, and to fire ant mating flights. In a series of behavioral and electroantennogram (EAG) experiments, we confirm the possible use of fire ant odor as cues for host location by P. tricuspis. We tested the response of P. tricuspis of different sex and mating status to several host-related odor stimuli including live fire ant workers, extracts of worker whole body, head, thorax, and abdomen, and (E,E)-α-farnesene, a trail pheromone component of Solenopsis fire ants. Results from Y-tube olfactometer bioassays demonstrated the attraction of mated female P. tricuspis to live S. invicta workers. In addition, extracts of S. invicta worker whole body and thorax elicited strong olfactometer response in female flies (mated and unmated) and mated males, but not in unmated males. Pseudacteon tricuspis did not show significant attraction to extracts of S. invicta worker head and abdomen, or to (E,E)-α-farnesene, irrespective of sex and mating status. In EAG experiments, female and male P. tricuspis showed significant EAG response to extracts of worker whole body, head, and abdomen, and to a less extent, thorax extract, but not to (E,E)-α-farnesene. Females showed slightly greater EAG response than males, but EAG response was not affected by mating status. These results suggest that fire ant thorax is likely the source of kairomones used as host location cues by P. tricuspis, and support the hypothesis that fire ant worker trail pheromones are not likely used by P. tricuspis for host location.