The Control of Yellow Crazy Ants (Anoplolepis gracilipes). An Empirical Study

Abstract

It is acknowledged in the scientific community that Yellow Crazy Ants (Anoplolepis gracilipes) are a key threatening process to Christmas Island’s biodiversity, threatening the islands native species and detrivore land crab populations, especially the Red Crab (Gecarcoidea natalis). Since their introduction to the island between 1915 and 1935 these tramp ants have increased in number and density forming super-colonies resulting in substantial Red Crab and other native invertebrate mortalities. To try to control and contain this invasive specie the Australian Commonwealth Government has financially and physically exerted substantial effort to control impacts of this specie using fipronil by hand and aerial baiting. Despite this intensive baiting campaign, the distribution of YCA’s has continued to increase with super-colonies now occurring throughout the island. Present management and baiting regimes of YCA follow the rationale that when YCA reach super-colony density they will have displaced all other invertebrates and therefore no none-target native species will be impacted by the use of fipronil. This results in the management of super-colonies only once they have developed or reactive management. An independent trial was undertaken between 2009 and 2012 using Disodium Octaborate Tetrahydrate (DOT) to trial an alternative bait and baiting method to control YCA that is more environmentally friendly and a more proactive management strategy than is presently in use on Christmas Island. From the results of this trial it is very clear that the bait has had a significant impact on Yellow Crazy Ants, which is supported by follow-up monitoring post DOT trial in 2012 showing evidence of the effectiveness of the bait and baiting method in controlling YCA by preventing super-colony development.