Conserving biodiversity on Christmas Island

Project name: Indirect biological control for an invasive ant; conserving biodiversity values and restoring ecological function in protected areas on Christmas Island.

The introduced yellow crazy ant (YCA; Anoplolepis gracilipes) forms super-colonies in protected rainforest on Christmas Island. These super-colonies that have myriad negative impacts on native biodiversity and ecosystem function. Super-colony formation depends on carbohydrates from introduced, honeydew-producing scale insects.

We developed a program to mitigate the impacts of YCA by introducing a parasitic wasp Tachardiephagus somevilli to reduce the abundance of the lac scale insect Tachardina aurantiaca, the most important source of honeydew in super-colonies.

Our aim is to indirectly control YCA by using classical biological control to reduce its carbohydrate supply.

Several hundred individuals were introduced to Christmas Island from Malaysia in December 2016, and following captive breeding, several thousand were released at each of four monitoring sites between January-April 2017.

The wasp has established at all sites and dispersed unaided more than 1.5 km.

Parasitism rates on lac scales are increasing, and intensive monitoring is continuing to measure the indirect impact on YCA abundance and ecosystem recovery.

Project partners

  • Federal Department of Environment and Energy (Director of National Parks)
  • Christmas Island National Park
  • Forest Research Institute of Malaysia
  • Christmas Island National Park - Crazy ant biocontrol
  • O'Dowd, D. J., Green, P. T., & Lake, P. S. (2003). Invasional ‘meltdown’ on an oceanic island. Ecology Letters, 6, 812-817.
  • Neumann, G., O'Dowd, D. J., & Green, P. T. (2018). Host specificity of an encyrtid parasitoid: Historical records and field-based tests in the native region to predict introduction risk. Biological Control, 121, 66-73.