Areawide Suppression of Fire Ants

The imported fire ants, Solenopsis invicta and S. richteri, were inadvertently introduced into the USA in the early 1900s and currently inhabit over 129 million ha in Puerto Rico and 12 southern states, from Texas to Virginia (Callcott and Collins, 1996; USDA-APHIS map). Imported fire ants have also become established in isolated sites in California, Arizona, New Mexico and Maryland. Strict quarantine procedures have limited the spread of this pest (Lockley and Collins, 1990), but eventually populations will expand westward in increasing numbers in New Mexico, Arizona and California. They will also move upward along the Pacific coast, southward into Mexico and the Caribbean and northward in Oklahoma, Arkansas and Tennessee and along the eastern seaboard into Maryland and possibly Delaware (Korzukhin et al., 2001). Mature monogyne (single queen) fire ant colonies contain 100,000 to 250,000 workers (Tschinkel, 1988, 1993) and reach infestation rates of over 130 mounds/ha. In the last few decades, polygyne fire ant colonies (multi-queen colonies) appear to be proliferating in the southern states. With polygyne populations, the number of mounds may reach over 500/ha (Porter et al., 1991; Porter, 1992), resulting in interconnected super-colonies because of the lack of territoriality among polygyne colonies (Morel et al., 1990; Vinson, 1997). Control is difficult because more queens must be killed. Imported fire ants destroy many ground-inhabiting arthropods and other small animals (Vinson and Greenberg, 1986; Porter and Savignano, 1990;Jusino-Atresino and Phillips, 1994; Wojcik, 1994; Forys et al., 1997; Allen et al., 1998; Williams et al., 2003). Because fire ants are highly aggressive when their nests are disturbed, this often results in painful stings to humans and their pets. Between 30 and 60% of the people in the infested areas are stung each year, with hypersensitivity occurring in 1% or more of those people (deShazo et al., 1990, 1999; deShazo and Williams, 1995), suggesting that over 200,000 persons per year may require medical treatment