Testing for population-level impacts of introduced Pseudacteon tricuspis Xies, phorid parasitoids of Solenopsis invicta Wre ants

Parasitoid phorid Xies in the genus Pseudacteon are potential biocontrol agents of invasive Solenopsis Wre ants in the US. One Pseudacteon species, P. tricuspis Borgmeier, has been released and is now established over a large region of north central Florida. We conducted a multi-year, large-scale Weld experiment to investigate potential population-level impacts on host Solenopsis invicta Buren Wre ants and associated arthropods. We established and monitored 67 Weld sites over a 3.5 year period, documenting S. invicta density and activity by three complementary sampling methods: (1) mound counts and measurements, (2) attraction to baits, and (3) pitfall trap catches. P. tricuspis abundance was determined by censusing Xies at disturbed S. invicta mounds. P. tricuspis populations increased in abundance over the Wrst two years following colonization and then oscillated seasonally, reaching higher abundances in the fall than in the preceding spring. S. invicta populations varied greatly over time, and repeated-measures ANCOVA revealed no eVect of phorid parasitism pressure on S. invicta density or activity. P. tricuspis likely has a relatively small eVect on S. invicta populations, which may not be consistent over space and time and is diYcult to document against the background of high variability in Wre ant populations due to various environmental factors (i.e., rainfall, disturbance). P. tricuspis parasitism pressure (averaged over the course of the experiment) was positively associated with changes in S. invicta density. Additionally, P. tricuspis abundance was positively correlated with S. invicta density after P. tricuspis populations had been established for >1 year. Introduced phorid populations may require many years before a measurable impact is apparent. Alternatively, parasitism pressure of a single phorid species may not be a major factor regulating Wre ant populations. Published by Elsevier Inc.