Eradication of the little fire ant; Wasmannia auropunctata (Hymenoptera: Formicidae), from Marchena Island, Galápagos: on the edge of success?

The development of effective techniques to eradicate populations of invasive ant species is crucial to the conservation of native biodiversity. An intensive program was initiated in 2001 to eradicate the invasive little fire ant, Wasmannia auropunctata (Roger) from ~21 ha on Marchena Island in the Galápagos Archipelago. Linear transects, approximately 10 m apart, were cut through the vegetation of the infested area and a buffer zone of 6 ha. Amdro® (Hydramethylnon) was applied manually up to three times in the treatment area at three-month intervals between March and October 2001. To date, five follow-up monitoring surveys have placed sticks painted with peanut butter in a grid 3-4 m apart. Two small populations (0.1% of the area originally occupied by W. auropunctata) were detected in April and October 2002 and were subsequently treated with Amdro®. No W. auropunctata ants were found in May 2003 and April 2004. Five nocturnal surveys carried out in the immediate area of introduction of W. auropunctata did not detect any individuals. Monitoring surveys will continue for an additional two years to ensure eradication of any remaining populations and verify the success of this program. This paper discusses the procedures used to kill W. auropunctata and monitor the efficacy of the eradication methods, the program's costs, and its applicability to other island ecosystems.