ABSTRACT
The red and black imported fire ants, Solenopsis invicta Buren and Solenopsis richteri Forel, have been extremely successful immigrants to the United States. Since the first infestation was noted at Mobile, Alabama in 1929, they have spread to ca 108 ha in 11 southeastern states and Puerto Rico (Lofgren, 1986). In recent years their rate of spread has slowed, for they are approaching their ecological limits in the Southeast (Francke and Cokendolpher 1986). Recently they have been accidentally moved by man across the arid southwest to Arizona (Frank 1988) and California (C.S. Lofgren, Personal communication). Should they become established in the west, their range will increase substantially. In addition, a polygynous form with denser populations, and which is sometimes more difficult to control, is spreading. However, the diminished territorial behavior of polygynous colonies may render them more vulnerable to biotic agents.
