Hawai'i conservation alliance

2009 Best Student Oral Presentation

Effects of eradication and control of two species of invasive ants on offshore islets in the Hawaiian Archipelago

Sheldon Plentovich
University of Hawai‘i, United States

Invasive species eradication and control are vital components of the conservation and management of many native ecosystems.  Invasive ants, which are notoriously difficult to eradicate, have been largely overlooked despite the fact that many species have expanding ranges, can reach exceptionally high densities, and often cause catastrophic changes in ecosystems.  We experimentally tested the effects of hydramethylnon on two species of invasive ants (Pheidole megacephala and Solenopsis geminata) on two pairs of offshore islets.  In year one (i.e., 2002), P. megacephala was the most abundant arthropod on islets in pair 1 while S. geminata was the most abundant arthropod in pair 2.  Following treatments with hydramethylnon, P. megacephala was not detected on the treated islet in pair 1 from 2003-2008.  In pair 2, S. geminata numbers declined, but the species remained present on the treated islet from 2003-2005.  During these periods ant densities remained high on untreated islets.  Reduced densities resulted in increased weight and fledging success of wedge-tailed shearwater (Puffinus pacificus) chicks and increased leaf cover in the native plant Ilima (Sida fallax) on pair 2.  Substantial changes in the ant community were observed from 2003-2008 following the eradication of P. megacephala, including the appearance and spread of the yellow crazy ant (Anoplolepis gracilipes).  This invasion coincided with declines in number of seabird chicks.  We conclude that hydramethylnon can be used to effectively eradicate P. megacephala; however we recommend it be used cautiously, as part of an adaptive and integrated plan that includes continued monitoring and management.