Doctor of Philosophy (PhD)



Document Type



Aspects of the population ecology of a parasitoid (Pseudacteon tricuspis) of the red imported fire ant (Solenopsis invicta) in Louisiana were studied. The spatio-temporal abundance patterns, dispersal, population spread, aggregation, direct mutual interference and functional response characteristics of this parasitoid were studied to address deficiencies in our knowledge about phorid flies, particularly Pseudacteon parasitoids. This endoparasitoid was discovered to manipulate host ant behavior in ways that benefit its own survival. Laboratory experiments to gain insights into behavioral and functional responses revealed that fly aggregations were density-dependent and interference was not significant when 1-3 females were simultaneously confined with hosts, although per capita oviposition success appeared to decline. Searching efficiency of 2-3 simultaneously ovipositing females was not significantly different than solitary females. Solitary females parasitized a constant proportion of hosts according to a Type 1 functional response. Modelling of the local spatial population structure of P. tricuspis, and relationship of abundances to host social form and pathogen-infected colonies, revealed no significant spatial associations between fly counts and infected host colonies. When fly populations peaked, significant count clusters were associated with polygyne colonies. Fly counts reflected a random spatial and temporal distribution, as count patterns were not stable. Dispersal experiments were conducted to quantify local fly movement. Diffusion rates tended to decline over time after release and most dispersal density-distributions did not conform to a simple diffusion model, implying heterogeneous population dispersal. Long-term population spread was monitored for two expanding populations of P. tricuspis. Range expansion accelerated the first four years post release, contrasting with a linear pattern expected with simple diffusion. Annual rates of spread were low in the first two years, increased rapidly years 3-4, and leveled off years 5-6, peaking at 15-25 km/yr. Finally, daily and seasonal dynamics of P. tricuspis were studied. Findings resulted in a protocol for sampling P. tricuspis populations in Louisiana. In addition to providing essential information about P. tricuspis population ecology, results of this study will be useful in conservation, augmentation, sampling and management of P. tricuspis and other species of Pseudacteon that have been released in the United States.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Seth Johnson

Included in

Entomology Commons