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United States Department of Agriculture

Agricultural Research Service

Title: Intercontinental Differences in the Abundance of Solenopsis Fire Ants (Hymenoptera: Formicidae): An Escape from Natural Enemies?

Authors
item Porter, Sanford
item Williams, David
item Patterson, Richard - UNIV. OF FLORIDA
item Fowler, Harold - UNIV. ESTADUAL PAULISTA

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 1996
Publication Date: N/A

Interpretive Summary: The absence of natural enemies often allows exotic pests to reach densities that are much higher than normally occur in their native habitats. When Solenopsis fire ants were accidently introduced into the United States almost 60 years ago, numerous natural enemies were left behind in South America. In order to compare intercontinental fire ant densities, we selected 13 areas in South America and another 12 areas in North America. In each area, we measured fire ant densities at 5 preselected roadside sites that were at least 5 km apart. Fire ant populations in the United States were 4-7 times higher than fire ant populations in South America. Because this study was not experimental, we were unable to establish the cause of this intercontinental difference. However, we were able to largely exclude a number of possible explanations including sampling procedures, season, multiple-queen colonies, climate, and aspects of habitat. By a process of elimination, escape from natural enemies remains among the most likely explanations for the unusually high densities of fire ants found in the United States.

Technical Abstract: The absence of natural enemies often allows exotic pests to reach densities that are much higher than normally occur in their native habitats. When Solenopsis fire ants were introduced into the United States, numerous natural enemies were left behind in South America. In order to compare intercontinental fire ant densities, we selected 13 areas in South America and another 12 areas in North America. In each area, we measured fire ant densities at 5 preselected roadside sites that were at least 5 km apart. Fire ant populations along roadsides in North America were 4-7 times higher than fire ant populations in South America. These intercontinental differences in fire ant abundance were not associated with sampling conditions, seasonal variability, climate, habitat differences, or the frequency of polygyny. Cultural differences in roadside maintenance may explain some of the intercontinental differences in fire ant abundance, but they did not account for equivalent intercontinental differences in grazing land and mowed lawns. Because this study was correlational, we were unable to determine the cause(s) of the large intercontinental difference in fire ant abundance that we observed. However, we were able to largely exclude a number of possible explanations including sampling, season, polygyny, climate and aspects of habitat. By a process of elimination, escape from natural enemies remains among the most likely explanations for the unusually high densities of fire ants found in North America.

Last Modified: 9/10/2014
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