David C. Thompson and Alana L. Jacobson, New Mexico State University, Department of Entomology, Plant Pathology, and Weed Science, Box 30003, MSC 3BE, Skeen Hall #N220, Las Cruces, NM 88003

Doña Ana County, New Mexico was quarantined in 1999 for red imported fire ant, Solenopsis invicta. This very aggressive ant species displaces native ant populations, disrupts natural ecosystems, interferes with agricultural operations, and is a health hazard to livestock, wildlife and people. Despite regular surveys, S. invicta hasn’t become dominant in the county during the past seven years. In fact, only two populations of S. invicta have been confirmed since the initial quarantine. The predominant fire ant is the southern fire ant, S. xyloni. One speculation is that the native and predominant fire ant species, S. xyloni, was initially misidentified because variation of distinguishing characteristics is common within this species. Variability of these characteristics was quantified by conducting a morphological comparison using scanning electron microscopy (SEM). Despite the fact that statistical evidence suggests a positive identification can be achieved using the appropriate combination of characteristics, the separation of these two species using morphological characteristics is complicated. For situations requiring an absolute identification such as prior to quarantining a county or a portion of a county, a more accurate molecular technique should be used. This is especially important in locations with arid climates where S. invicta does not thrive, and eradication programs are likely to be successful. Under the current system, once a county is quarantined for Solenopsis invicta there are no established rules or guidelines which allow a county to be removed from this list.