Final report | Monitoring of the 2009 aerial baiting of yellow crazy ants (Anoplolepis gracilipes) on non-target invertebrate fauna on Christmas Island


Prepared for the Director of National Parks by Dr Andrew Weeks and Stuart McColl CESAR Consultants | 17 June 2011

Executive summary

The highly invasive yellow crazy ant, Anoplolepis gracilipes, has caused widespread destruction and ecosystem changes on Christmas Island in the Indian Ocean over the last 20 years. This small ant, which forms highly aggressive supercolonies, has caused major changes in the islands rainforest, as they have displaced and killed many of the islands unique fauna such as the islands keystone species, the endemic red crabs, Gecaroidea natalis. Fipronil baits have been used extensively on the island to control the yellow crazy ant since 2000 with over 4500 hectares baited in the last ten years. An aerial baiting program was undertaken in 2002, with over 2500 hectares and 11000 kg of bait distributed on Christmas Island. This effectively depressed the yellow crazy ant colony for many years, but in 2009 over 800 hectares of the island was again covered by super colonies. A new fipronil aerial baiting program was again undertaken in September/October 2009. Relatively little information is known about fipronil, and especially the potential impacts that the bait formulation may have on non-target organisms. The potential for bioaccumulation of the pesticide in the environment of Christmas Island is also unknown. CESAR Consultants were commissioned by National Parks Australia to undertake an assessment of the effects of the 2009 fipronil aerial baiting on non-target fauna and potential bioaccumulation of fipronil in the environment on Christmas Island. Invertebrate surveys were undertaken on three separate occasions to assess the affects of the aerial fipronil baiting program. The first survey was immediately prior to the aerial baiting in August 2009, the second immediately after the aerial baiting was completed in October 2009 and the final survey was approximately 6 months later in May 2010. Invertebrate communities were surveyed in three different environments:

  • pitfall traps were used intensively to assess fipronil baiting impacts on ground-dwelling invertebrates
  • yellow sticky traps were used to assess the potential effects on canopy invertebrates
  • and freshwater/sediments were surveyed for macroinvertebrates to determine whether the fipronil had entered the freshwater springs on the island.

In addition, to determine whether fipronil is bioaccumulating in the environment on Christmas Island, soil, water and sediment samples were analysed using liquid chromatography tandem mass spectrometry (LC-MS/MS) for the presence of fipronil and three key toxic degradates (fipronil sulfide, fipronil sulfone and fipronil desulfinyl). The key findings of the surveys were:

  1. Strong seasonal (collection) effects on invertebrates communities were found for ground-dwelling, canopy-dwelling and freshwater arthropods.
  2. The fipronil aerial baiting undertaken in September/October 2009 had significantly negative impacts on A. gracipiles, with over a 98% reduction at sites that were baited.
  3. The LC-MS/MS analyses provided no evidence that fipronil or three toxic degradation by-products, fipronil sulfide, fipronil sulfone and fipronil desulfinyl, are accumulating in the environment on Christmas Island.
  4. No evidence was found that the fipronil aerial baiting undertaken in September/October 2009 caused significantly negative impacts on arthropod communities.