Submitted to: American Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2007
Publication Date: 2/14/2008
Citation: Oi, D.H., Williams, D.F., Pereira, R.M., Horton, P.M., Davis, T., Hyder, A.H., Bolton, H.T., Zeichner, B.C., Porter, S.D., Hoch, A.L., Boswell, M.L., Williams, G. 2008. Combining biological and chemical controls for the management of red imported fire ants (Hymenoptera: Formicidae). American Entomologist. 54:46-55. Interpretive Summary: The red imported fire ant is an aggressive, stinging ant that infests over 333 million acres in 14 states and causes an estimated $6.5 billion annually in damage, control, and medical expenditures. In an effort to suppress this invasive pest, biological control agents from South America are being established in the United States. In a cooperative project with the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology, Clemson University, South Carolina Army/Air National Guard, Department of Defense and the U.S. Environmental Protection Agency, the effect of combining both biological controls and insecticides against fire ants was documented. In the study site where a fire ant specific pathogen (Thelohania solenopsae) and a parasitic fly (Pseudacteon tricuspis) were introduced and insecticide applied, 95% control was maintained for 3 years. In contrast, in an area where only insecticide was applied, suppression lasted half that time. Other ants besides fire ants also increased in the areas receiving the combination of biological and chemical controls. Integrating both chemical and biological control methods against fire ants represents the potential benefit of establishing biological control agents for this exotic pest.
Technical Abstract: Two South American natural enemies of imported fire ants were first detected or released in the United States approximately 10 years ago. The fire ant pathogen, Thelohania solenopsae Knell, Allen, and Hazard, was found in the U.S. in 1996 and a parasitic phorid fly from Brazil, Pseudacteon tricuspis Borgmeier, was released in 1997 and both are well established in fire ant infested areas. As biological control agents of the red imported fire ant, Solenopsis invicta Buren, their colony level impact in the field are often indirect and subtle as they work slowly by debilitating queens and impeding foraging by workers. Their effect on colony densities may be inadequate in sensitive sites, where there is a low tolerance for fire ants stings, and may require faster-acting insecticide treatments. Comparisons of S. invicta populations and the presence of other ants were made among field sites that 1) the biocontrol agents T. solenopsae and P. tricuspis were released and established, and also were treated with insecticide containing fipronil (integrated site); 2) were treated only with the fipronil insecticide (chemical site); and, 3) was not treated. S. invicta populations were suppressed by '95 % for 3 years at the integrated site. In the chemical site, S. invicta control was '85 % after 1.4 years, while the untreated site had an average 32% increase in population. Average prevalence of T. solenopsae among nests per plot peaked at 72% and P. tricuspis was observed at the release site and up to 0.7 km away. The average percentage of ants other than S. invicta collected in pitfall traps in the insecticide treated area of the integrated site increased from 13% before treatment to 70% for the last 2 years of the study. In the chemical site, the percentage of non-S. invicta ants was 0.4% before insecticide application and averaged 9% for the final 2 years. Non-S. invicta ants averaged 9.6% (range, 2.7-17.3%) in the untreated site for the entire study. The extended reduction in S. invicta populations in the integrated site demonstrated the potential impact of the establishment of biological control agents for imported fire ants.