The phenology and dispersal abilities of Pseudacteon phorid ßies, parasitoids of Solenopsis Þre ants, were measured at multiple sites over several years. Four Pseudacteon species [P. browni Disney, P. spatulatus (Malloch), P. crawfordi Coquillett, and an undescribed species, P. sp. A.] were found in the vicinity of 5 S. geminata (F.) populations over a 3-yr period. P. browni was the most common at all sites and in all years, with a single exception. Pseudacteon species were observed hovering over disturbed S. geminata mounds from April through December of most years, although ßight activity was not observed on days when the air temperature fell below 20ЊC. Relative abundance patterns varied both temporally and spatially, although a rough positive correlation with rainfall was evident at some sites. Overall sex ratios were always highly male-biased at all sites and in all years, with 1 exception. Pseudacteon phorids were found at distances of up to 650 m from the nearest S. geminata colony, and appeared to disperse away from host colonies into areas without appropriate hosts in random directions. Although populations of host S. geminata in central Texas are fragmented, distances over which Pseudacteon dispersal frequently occurs may be relatively large compared with the interpatch distances separating host ant populations.

Summary 1. Solenopsis (Hymenoptera: Formicidae) fire ants are host to Pseudacteon (Diptera: Phoridae) parasitoids. The activity of S. geminata (F.) hosts and relative abundance of Pseudacteon phorids, along with five environmental variables, were measured at weekly intervals over an 8‐month period at two sites. 2. Pseudacteon relative abundances often varied greatly from week to week, and were only weakly positively correlated with S. geminata activity. 3. A quadratic function of soil temperature was the single best predictor of ant activity at both sites, explaining 32 and 73% of the variation in ant activity. A linear function of soil moisture was the single best predictor of phorid relative abundance at one site (r2 = 0.23) whereas no measured variables were significant predictors of phorid relative abundance at the other site. 4. Interspecific interactions at 600 baits were monitored at a third site to document dominance hierarchies and determine whether the presence of Pseudacteon phorids mediated interspecific interactions in their host, S. geminata. 5. Solenopsis geminata was near the top of dominance hierarchies, which did not diverge greatly from a linear pattern. Three species (S. geminata, S. invicta Buren, and Crematogaster laeviuscula Mayr) won the majority of their interspecific interactions and appear to be co‐dominants at this microhabitat‐rich site. 6. Overall, the presence of phorids had no significant effect on the outcome of interspecific contests involving S. geminata and all other ant species grouped together. Phorids may have contributed to some of the S. geminata losses against other co‐dominant species.

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