Author
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Morrison, Lloyd |
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KING, JOSHUA - UNIV. OF FLORIDA |
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Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/30/2004 Publication Date: 6/28/2004 Citation: Morrison, L.W., King, J.R. 2004. Host location behavior in a Parasitoid of Imported Fire Ants. Journal of Insect Behavior. 17(3):367-383. Interpretive Summary: Imported fire ants (Solenopsis invicta and S. richteri) are serious pests in the southeastern U.S. The release of natural enemies as biological control agents may reduce the abundance of these pests. Several species of parasitoid flies in the genus Pseudacteon (Diptera: Phoridae) are currently being released and evaluated at selected field sites. Scientists working at the USDA-ARS, Center for Medical, Agricultural, and Veterinary Entomology, and the Entomology and Nematology Department of the University of Florida, both in Gainesville, FL, studied the mechanisms by which one of these species, P. tricuspis, locates its host, S. invicta, in a series of field observations and experiments. P. tricuspis was commonly attracted to disturbed colonies, but was almost never attracted to foragers at baits. Addition of enemy S. invicta workers to S. invicta workers foraging at baits, however, resulted in the attraction of parasitoids to the majority of baits. Moreover, addition of greater numbers of enemy workers resulted in the attraction of greater numbers of flies. Addition of enemy S. invicta workers to disturbed mounds increased the numbers of flies attracted. Pseudacteon tricuspis is apparently attracted to the alarm pheromones released by the ants involved in aggressive interactions, and not to recruitment pheromones released when foraging. These results reveal the mechanisms by which P. tricuspis locates hosts, and the conditions under which P. tricuspis would be most effective in a biocontrol program. This study also indicates the need to release other Pseudacteon species with complementary host location behaviors. Technical Abstract: Female parasitoids use a hierarchy of cues to locate suitable hosts. We conducted a series of field observations and experiments to examine host location behavior in Pseudacteon tricuspis Borgmeier, a phorid fly parasitoid of Solenopsis invicta Buren worker ants. The parasitoids were frequently attracted to host workers at disturbed colonies, but were almost never attracted to host workers foraging at baits. When conspecific non-nestmate workers were introduced to baits, however, resulting in aggressive interactions, parasitoids appeared at the majority of baits. Moreover, larger numbers of parasitoids appeared at baits to which greater numbers of non-nestmate workers had been added. Addition of non-nestmate workers to disturbed colonies resulted in increased numbers of parasitoids attracted. Pseudacteon tricuspis did not display a pattern of uniform distribution at disturbed colonies, but often was very abundant at some colony locations while absent or rare at nearby colony locations. Taking into account variation in colony size did not explain this pattern. Solenopsis invicta workers release alarm pheromones in aggressive interactions with non-nestmates, and this substance is likely an important chemical cue that attracts P. tricuspis flies to host workers from a distance. Comparisons with other studies suggest that not all Pseudacteon ant parasitoids use the same host location cues, or at least not to the same degree. The use of alarm pheromones in host location may be adaptive if such cues emanate from richer host resources and confer a relative advantage to Pseudacteon species that utilize these pheromones. Pseudacteon phorids are biocontrol candidates for pest Solenopsis species, and the results of this study suggest conditions under which they would be most effective. |
