Argentine ants (Linepithema humile) are a highly invasive species that pose a serious threat to ecologically intact systems worldwide. Their aggressive interspecies interactions are linked to observed declines in the diversity and abundance a wide variety of invertebrate species. Pollination success and seed dispersal may be reduced as native invertebrate activity declines, with ensuing negative repercussions for native plant reproduction and community composition. Long distance dispersal is human-mediated, as these ants do not preform mating flights. In the last decade the number of exotic insect introductions in the U.S. has increased, and programs to prevent the spread of established pests have been largely unsuccessful. There is an urgent need to develop an effective field protocol to eliminate invasive ant colonies in ecologically sensitive areas before they become established and where they do the most harm to native biota. Argentine ants were first discovered on Santa Cruz Island, California in 1996 at two sites centered at decommissioned structures. Thereafter, Argentine ants established at two additional locations in the island’s central watershed.
Results/Conclusions
The island managers, The Nature Conservancy and National Park Service, began a treatment protocol in spring of 2012 targeting two of these infestations. We targeted one entire isolated infestation which encompasses seven acres of scrub and oak vegetation. This complete site treatment will eliminate the confounding variable present in most studies, of Argentine ant re-infestation from untreated edges, and will allow us to more precisely measure the efficacy of our protocol. The second infestation site is 37 acres, but due to current state and federal permitting, we are treating 10 acres in 2012 and plan to treat the entire infestation in 2013. Our treatment protocol consists of six applications of sucrose- attractant bait: two applications with S- Methoprene and four applications spaced one month apart with Thiamethoxam. Prior to each treatment we will conduct pitfall traps and bait monitors to detect ant activity at 300 points in paired treatment and control sites. Bait monitors consist of a carbohydrate, protein and carbohydrate-protein mix which will be used to evaluate seasonal bait preference and inform future baiting protocol. Island managers are also working with other landowners, such as the US Navy, to implement this protocol in other Channel Islands containing isolated Argentine ant infestations.