Despite intensive attempts at pesticide-based eradication, the red imported fire ant, Solenopsis invicta Buren, continues to infest almost the entire southeastern United States. Consequently, researchers have begun to explore other options for control of this pest, including biological control. Phorid flies in the genus Pseudacteon are among the most promising biological control agents for use against S. invicta. Pseudacteon tricuspis Borgmeier is the one phorid fly currently available and approved for release. Consequently, P. tricuspis was the phorid used in this study.
Though phorids parasitize only a small percentage of fire ant workers in a colony (~1-2%), they are thought to decrease the fitness of a colony by disrupting foraging behavior. This idea presumes that the presence of phorids results in a decrease in the foraging rate and hence the reproductive rate of S. invicta. Furthermore, attack by phorids on S. invicta may allow native ants to gather resources that would otherwise have been collected by S. invicta. This may shift the competitive balance in favor of native ants.
We directly tested this idea by allowing colonies of S. invicta to compete for a protein resource with colonies of Forelius pruinosus, a native ant species. Treatments were competition arenas that included phorids and phorid-free controls. The experiment was replicated under conditions of high and low protein availability. The ability of phorids to mediate competition between the two ant species was determined by quantifying the reproductive rates and foraging rates of all ant colonies.
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