Phorid flies in the genus Pseudacteon affect the foraging and defensive behaviors of their host, the red imported fire ant, Solenopsis invicta Buren. Field observations of Pseudacteon species indicated interspecific variation in attack behavior. Here, we assess whether differences in attack behavior and ant response might assist in prioritizing species for biocontrol. We studied the oviposition behavior of eight phorid fly species and determined how attack by each influenced the normal behavior of the red imported fire ant. The fly species tested were: Pseudacteon borgmeieri Schmitz, P. curvatus Borgmeier, P. nudicornis Borgmeier, P. obtusus Borgmeier, P. solenopsidis (Schmitz), P. tricuspis Borgmeier, P. litoralis Borgmeier, and P. wasmanni (Schmitz). Of these, P. borgmeieri attack interfered with normal red imported fire ant worker behavior the most, whereas P. curvatus had the least effect. Because the supposed effectiveness of phorids as biocontrol agents depend on their ability to interfere with normal fire and ant behavior, these results suggest that some species of phorids would be better candidates for biocontrol than others. Our results combined with results from other studies examining host specificity of phorids suggest that P. tricuspis and P. obtusus are excellent candidates for biocontrol of the red imported fire ant in geographical areas where polygyne colonies dominate, such as Texas. Conversely, where monogyne colonies dominate, such as Florida, P. litoralis should be considered.952257266Borgmeier, T., Zur Lebensweise von Pseudacteon borgmeieri Schmitz (in litt.) (Diptera ∼ Phoridae) (1922) Zs. Deutscher Verein Wissenschaft und Kunst São Paulo, 1, pp. 239-248. , 1921Cônsoli, F.L., Wuellner, C.T., Vinson, S.B., Gilbert, L.E., Immature development of Pseudacteon tricuspis (Diptera: Phoridae), an endoparasitoid of the red imported fire ant (Hymenoptera: Formicidae) (2001) Ann. Entomol. Soc. Am, 94, pp. 97-109Feener D.H., Jr., Competition between ant species: Competition controlled by parasitic flies (1981) Science, 214, pp. 815-817. , Wash., DCFeener D.H., Jr., Size-selective oviposition in Pseudacteon crawfordi (Diptera: Phoridae), a parasite of fire ants (1987) Ann. Entomol. Soc. Am, 80, pp. 148-151Feener D.H., Jr., Brown, B.V., Reduced foraging of Solenopsis geminata (Hymenoptera: Formicidae) in the presence of parasitic Pseudacteon spp. (Diptera: Phoridae) (1992) Ann. Entomol. Soc. Am, 85, pp. 80-84Folgarait, P.J., Gilbert, L.E., Phorid parasitoids affect foraging activity of Solenopsis richteri under different availability of food in Argentina (1999) Ecol. Entomol, 24, pp. 1-11Fowler, H.G., Pesquero, M.A., Campiolo, S., Porter, S.D., Seasonal activity of species of Pseudacteon (Diptera: Phoridae) parasitoids of fire ants (Solenopsis saevissima) (Hymenoptera: Formicidae) in Brazil (1995) Cientifica, 23, pp. 367-371Gilbert, L.E., Morrison, L.W., Patterns of host specificity in Pseudacteon parasitoid flies (Diptera: Phoridae) that attack Solenopsis fire ants (Hymenoptera: Formicidae) (1997) Environ. Entomol, 26, pp. 1149-1154Godfray, H.C.J., (1994) Parasitoids: Behavioral and Evolutionary Ecology, , Princeton University Press, Princeton, NJGoodisman, M.A.D., Ross, K.G., Relationship of queen number and worker size in polygyne colonies of the fire ant Solenopsis invicta (1996) Insect. Soc, 43, pp. 303-307Greenberg, L., Fletcher, D.J.C., Vinson, S.B., Differences in worker size and mound distribution in monogynous and polygynous colonies of the fire ant Solenopsis invicta Buren (1985) J. Kans. Entomol. Soc, 58, pp. 9-18Grodowtiz, M.J., Center, T.D., Cofrancesco, A.F., Freedman, J.E., Release and establishment of Hydrellia balciunasi (Diptera: Ephydridae) for the biological control of the submersed aquatic plant Hydrilla verticillata (Hydrocharitaceae) in the United States (1997) Biol. Control, 9, pp. 15-23Hawkins, B.A., Sheehan, W., (1994) Parasitoid Community Ecology, , eds. Oxford University Press, Oxford, New YorkHölldobler, B., Wilson, E.O., The multiple recruitment systems of the African weaver ant Oecophylla longinoda (Latrielle) (Hymenoptera: Formicidae) (1978) Behav. Ecol. Sociobiol, 3, pp. 19-60Jander, R., Macroevolution of a fixed action pattern for learning: The exploration flights of bees and wasps (1997) Comparative Psychology of Invertebrates: The Field and Laboratory Study of Insect Behavior, pp. 79-99. , G. Greenberg and E. Tobach [eds.], Garland Publishing, Inc., New YorkKaya, H.K., Koppenhofer, A.M., Effects of microbial and other antagonistic organisms and competition on entomopathogenic nematodes (1996) Biocontrol Sci. Technol, 6, pp. 357-371Krombein, K.V., Hurd P.D., Jr., Smith, D.R., (1979) Catalog of Hymenoptera in America North of Mexico, 3. , Smithsonian Institution Press, Washington, D.CMills, J.J., Getz, W.M., Modelling the biological control of insect pests: A review of host-parasitoid models (1996) Ecol. Model, 92, pp. 121-143Monnin, T., Peeters, C., Dominance hierarchy and reproductive conflict among subordinates in a monogynous queenless ant (1999) Behav. Ecol, 10, pp. 323-332Morrison, L.W., Indirect effects of phorid fly parasitoids on the mechanisms of interspecific competition among ants (1999) Oecologia, 121, pp. 113-122Morrison, L.W., Gilbert, L.E., Host specificity in two additional Pseudacteon spp. (Diptera: Phoridae), parasitoids of Solenopsis fire ants (Hymenoptera: Formicidae) (1999) Fla. Entomol, 82, pp. 1-6Morrison, L.W., Dall'Aglio-Holvercem, C.G., Gilbert, L.E., Oviposition behavior and development of Pseudacteon flies (Diptera: Phoridae), parasitoids of Solenopsis fire ants (Hymenoptera: Formicidae) (1997) Environ. Entomol, 26, pp. 716-724Nicholson, A.J., Bailey, V.A., The balance of animal populations. I (1935) Proc. Zool. Soc. Lond, 3, pp. 551-598Obin, M.S., Vander Meer, R.K., Gaster flagging by fire ants (Solenopsis spp.): Functional significance of venom dispersal behavior (1985) J. Chem. Ecol, 2, pp. 1757-1768Orr, M.R., Seike, S.H., Benson, W.W., Gilbert, L.E., Flies suppress fire ants (1995) Nature, 373, pp. 292-293. , LondOrr, M.R., Seike, S.H., Gilbert, L.E., Foraging ecology and patterns of diversification in dipteran parasitoids of fire ants in South Brazil, genus Pseudacteon (Phoridae) (1997) Ecol. Entomol, 22, pp. 305-314Pesquero, M.A., Campiolo, S., Fowler, H.G., Phorids (Diptera: Phoridae) associated with mating swarms of Solenopsis saevissima (Hymenoptera: Formicidae) (1993) Fla. Entomol, 76, pp. 179-181Pesquero, M.A., Campiolo, S., Fowler, H.G., Porter, S.D., Diurnal patterns of ovipositional activity in two Pseudacteon fly parasitoids (Diptera: Phoridae) of Solenopsis fire ants (Hymenoptera: Formicidae) (1996) Fla. Entomol, 79, pp. 455-457Porter, S.D., Biology and behavior of Pseudacteon decapitating flies (Diptera: Phoridae) that parasitize Solenopsis fire ants (Hymenoptera: Formicidae) (1998) Fla. Entomol, 88, pp. 1-18Porter, S.D., Pesquero, M.A., Illustrated key to Pseudacteon decapitating flies (Diptera: Phoridae) that attack Solenopsis saevissima complex fire ants in South America (2001) Fla. Entomol, , in pressPorter, S.D., Fowler, H.G., Campiolo, S., Pesquero, M.A., Host specificity of several Pseudacteon (Diptera: Phoridae) parasites of fire ants (Hymenoptera: Formicidae) (1995) Fla. Entomol, 78, pp. 70-75Porter, S.D., Vander Meer, R.K., Pesquero, M.A., Campiolo, S., Fowler, H.G., Solenopsis (Hymenoptera: Formicidae) fire ant reactions to attacks of Pseudacteon flies (Diptera: Phoridae) in Southeastern Brazil (1995) Ann. Entomol. Soc. Am, 88, pp. 570-575Porter, S.D., Williams, D.F., Patterson, R.S., Fowler, H.G., Intercontinental differences in the abundance of Solenopsis fire ants (Hymenoptera: Formicidae): Escape from natural enemies? (1997) Environ. Entomol, 26, pp. 373-384Vander Meer, R.K., Slowik, T.J., Thorvilson, H.G., Semiochemicals released by electrically-shocked red imported fire ants (1999) Proceedings of the Imported Fire Ant Res. Conference, p. 92. , Imported Fire Ant Res. Conference, 6-8 April 1998, Charleston, SC. University of Arkansas, Division of Agriculture, Cooperative Extension Service, Little Rock, AR