African big-headed ant case studies

Kakadu National Park, Australia : Cousine Island, Seychelles : Mokuauia and Popoia, Hawaii : Lord Howe Island, Australia

Location: Kakadu National Park, Australia

Justification: Conservation

Goal: Eradication

Size: <1 ha-10 ha (30 ha total)

Products: Amdro (hydramethylnon; 9 g/kg; 2.5 kg/ha); Gourmet Ant Bait Gel (boric acid; 2.6 g/bait station; unknown application rate) 

Time of year: October/November; April

Outcome: Eradication achieved

Programme cost: approximately 56 000 AUD

Manager: Ben Hoffmann (ben.hoffmann@csiro.au), CSIRO

The big-headed ant was discovered in Kakadu National Park in 2001. One application of Amdro was broadcast first by hand, then later using hand spreaders in the infested area (with a 5 m buffer zone). The bait was applied more generously at the bases of trees, logs, rocks and thick vegetation where African big-headed were more likely to be collecting food.

Eight infestations, all in and beside buildings, were not killed outright by the first treatment. These infestations were re-treated with hydramethylnon around the outside of the buildings and bait stations containing Gourmet Ant Bait Gel (boric acid; 2.6 g/bait station; unknown application rate) were placed inside the buildings. As hydramethylnon is soluble in water, treatment was done when conditions were dry.

Infestations outside the township were done in October/November prior to wet season rains. Infestations within the township were done in April at the beginning of the dry season. Eradication was successfully achieved.

Information source

Further information was provided by Ben Hoffmann, CSIRO Land and Water Flagship

Hoffmann, O’Connor. 2004. Eradication of two exotic ants from Kakadu National Park. Ecological Management & Restoration 5(2): 98-105

case study reviewed by Ben Hoffmann, CSIRO Australia, September 2016

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Location: Cousine Island, Seychelles

Manager: collaboration between Rene Gaigher (reneg@sun.ac.za) and Michael Samways, Stellenbosch University; Kevin Jolliffe, San-Marie Jolliffe and Jock Henwood, Cousine Island

Cousine Island, Seychelles is a nature preserve that contains many endemic and endangered species. This control programme for African big-headed ants was designed to limit non-target effects of baiting as much as possible while reducing the ant population to levels that were not harmful to the native wildlife.

Bait stations with Seige were distributed thoroughly (bait stations are only effective over 5 m) throughout the infested area, mostly at the base of trees. Due to the extremely high abundances of African big-headed ants, 4 kg/ha was distributed instead of 2.5 kg/ha as per the manufacturer’s instructions. Bait stations were left out for one week, then removed. In areas where African big-headed ant nests remained another bait station was put out.

Eleven months after baiting the local invertebrate community had increased significantly in invaded areas. Within one week of baiting, there was a 99.4% reduction in African big-headed ant numbers. This reduction in numbers continued throughout the entire subsequent 11-month monitoring period.

The cost of this programme was approximately 350 USD for materials and 41 hours worked per hectare. This programme successfully achieved its aims, but the methods used (bait stations) are probably most appropriate for localized infestations in very sensitive areas where impact from non-target effects are not acceptable.

Information source

Gaigher, Samways, Jolliffe, Jolliffe. 2012. Precision control of an invasive ant on an ecologically sensitive tropical island: a principle with wide applicability. Ecological Applications 22(5): 1405: 14-12

case study reviewed by René Gaigher, Stellenbosch University, August 2016

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Location: Mokuauia and Popoia, Hawai'i

Justification: Conservation/experiment

Goal: Eradication

Size: 3.85 ha (Mokuauia); 1.6 ha (Popoia)

Products: Amdro (hydramethylnon; 7.3 g/kg; corn grit/soybean oil granular matrix; 1.1 kg/ha) on Mokuauia, while using Popoia as an experimental control (untreated) site

Time of year: between December and March

Outcome: Eradication achieved on Mokuaia, while ant numbers remained relatively consistent on the untreated islet, Popoia.  

Programme cost: not available

Manager: Sheldon Plentovich (sheldon_plentovich@fws.gov), U.S. Fish and Wildlife Service

Mokuauia and Popoia are tiny islets off the coast of Oahu, Hawai'i that are used by nesting seabirds. It was suspected that the big-headed ants which covered these islets were hurting the seabird chicks and threatening their survival.

Amdro was manually applied twice over the infestation on Mokuaia between December and March 2003 (these are the months there are no seabirds on the islets), and reapplied in February 2004. The 3.85 ha infestation on Mokuauia was eradicated after a single treatment. Unfortunately, the islet was subsequently invaded by the yellow crazy ant following the eradiation of the African big-headed ant.

The 1.6 ha infestation on Popoia remained untreated, thus providing an experimental control. Ant numbers remained relatively consistent.

Information source

Plentovich, Hebshi, Conant. 2009. Detrimental effects of two widespread invasive ant species on weight and survival of colonial nesting seabirds in the Hawai'ian Islands. Biological Invasions 11: 289-298

Plentovich, Eijzenga, Eijzenga, Smith. 2011. Indirect effects of ant eradicaton efforts on offshore islets in the Hawai'ian Archipelago. Biological Invasions 13: 545-557

case study reviewed by Sheldon Plentovich, US Fish and Wildlife Service, July 2016

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Location: Lord Howe Island, Australia

Justification: Conservation

Goal: Eradication

Size: 200 ha

Products: Amdro (hydramethylnon; 7.3 g/kg; corn grit/soybean oil granular matrix; 2.5 kg/ha); Distance Plus (pyriproxyfen; 5 g/kg; corn grit/soybean oil granular matrix; 2.5 kg/ha); Advion (indoxacarb; 0.5 g/kg)

Time of year: spring or summer

Outcome: mostly eradicated

Programme cost: 500 000 AUD as of end of 2015

Manager: Ben Hoffmann (ben.hoffmann@csiro.au), CSIRO

The African big-headed ant is considered one of the greatest threats to Australia’s Lord Howe Island’s ecosystem. Infested areas were also treated between 2006-2010, however this did not result in eradication, likely due to a lack of expert advice, identification and application skills and bad weather that delayed treatments to the next season.

Initial confusion of a native ant species with the African big-headed ant, resulted in the infested area being greatly overestimated.

Expert training was provided in 2012, and the actual infested area was recognized to be about 200 ha and confined to the human settlement. In March 2012, the infestation, along with a 20 m buffer zone, was treated with Amdro using hand-spreaders. Distance® Plus was applied on areas with crops.

Buildings within the infested zone were treated with Advion inside Ant Café bait stations. Nests that persisted after 3-4 months were retreated. Treatment was only done in spring and summer and not done up to 24 hours before rain and during temperatures higher than 30ºC (ideal temperatures for treatment were between 24-30ºC).

Two years post-treatment, most of the infestation has been eradicated with only a few persistent nests left that will be re-treated.

Information sources

Further information was provided by Ben Hoffmann, CSIRO Land and Water Flagship

Lach, Barker. 2013. Assessing the effectiveness of tramp ant projects to reduce impacts on biodiversity. A report prepared for the Australian Government Department of Sustainability, Environment, Water, Population, and Communities

Lord Howe Island Board. 2013. Work plan to guide the eradication of the African big-headed ant (Pheidole megacephala) from Lord Howe Island. Lord Howe Island Board (please note that this report is updated yearly, go to the Lord Howe Island Board website to check for updated versions)

case study reviewed by Ben Hoffmann, CSIRO Australia, September 2016

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