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United States Department of Agriculture

Agricultural Research Service

Title: Phenology and Parasitism Rates in Introduced Populations of Pseudacteon Tricuspis, a Parasitoid of Solenopsis Invicta.

Authors
item Morrison, Lloyd
item Porter, Sanford

Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2004
Publication Date: May 4, 2005
Citation: Morrison, L.W., Porter, S.D. 2005. Phenology and parasitism rates in introduced populations of Pseudacteon tricuspis, a parasitoid of Solenopsis invicta.. Biocontrol. 50: 127-141.

Interpretive Summary: Imported fire ants are serious pests in the southeastern U.S. The release of natural enemies such as parasitoid Pseudacteon species (Diptera: Phoridae) may reduce the abundance of these pests. Scientists working at the USDA-ARS, Center for Medical, Agricultural, and Veterinary Entomology, in Gainesville, FL, studied patterns of seasonal abundance and rates of parasitism in introduced populations of Pseudacteon tricuspis Borgmeier, a phorid parasitoid of the red imported fire ant, Solenopsis invicta Buren. Adult P. tricuspis populations were censused at monthly intervals for one year at three sites in northern Florida. Censuses were conducted by collecting phorids attracted to disturbed S. invicta mounds. Pseudacteon tricuspis adults were present in every month at all sites, although abundances varied greatly among sites and over time. The highest densities of flies were observed in November, and changes in abundance over time were positively correlated among sites. Parasitism rates were evaluated by collecting workers from field colonies and monitoring them in the laboratory for evidence of parasitism. Parasitism rates were low-always less than 1%. These low parasitism rates can be reconciled with relatively high adult phorid densities by considering the large number of host ants present at the study sites. These results indicate this introduced phorid parasitoid will survive over the long term and be active year-round in Florida, yet parasitize relatively few host ants. Although the direct effect of mortality of this potential biocontrol agent appears to be small, its efficacy will be increased if it also exerts strong indirect effects.

Technical Abstract: We documented patterns of seasonal abundance and rates of parasitism in introduced populations of Pseudacteon tricuspis Borgmeier, a phorid parasitoid of the red imported fire ant, Solenopsis invicta Buren. Adult P. tricuspis populations were censused at monthly intervals for one year at three sites in northern Florida. Censuses were conducted by aspirating phorids attracted to disturbed S. invicta mounds. Pseudacteon tricuspis adults were present in every month at all sites, although abundances varied greatly among sites and over time. The highest densities of flies (up to 453 censused at 10 disturbed S. invicta mounds in 30 min) were observed in November, and changes in abundance over time were positively correlated among sites. Sex ratios were usually male biased. Parasitism rates were evaluated by collecting workers from field colonies and monitoring them in the laboratory for evidence of parasitism. Parasitism rates were very low-always less than 1%. The average parasitism rate per colony over 16 colonies and 2 years was 0.058%. No pupariation occurred within the first 8 days of collection, suggesting parasitism by P. tricuspis induced behavioral changes in parasitized workers that precluded such workers from our collections. If so, true field parasitism rates may be several times higher than measured here, yet still low in an absolute sense. These low parasitism rates can be reconciled with observed adult phorid densities by considering the large number of host ants present at the study sites.

Last Modified: 9/20/2014
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