Red imported fire ant - Response update (Whirinaki 2006)

The red imported fire ant (RIFA) eradication programme is entering the busy season. Spring surveillance started in late October using protein and sugar attractant baits. Insecticidal ant baits will be applied in December 2006. Another round of surveillance and bait application is scheduled for March and April 2007.

Biosecurity New Zealand (BNZ) initiated a response following the discovery of a red imported fire ant nest (Solenopsis invicta) at Pan Pac Forest Products, Whirinaki, in early June 2006 (Biosecurity 69:9).

Investigation and Diagnostic Centre (IDC) staff and contractors conducted a nest extraction as part of this response. An assessment of the size and age of the nest showed that the population was about 30,000 workers and was around two to two-and-a-half years old. Based on these features, IDC staff determined that there could have been reproductive flights during each of the previous two summers, and that queens could have established new nests up to 2 km from the nest site.

Ants not linked to 2004 Napier find

The nest was found in a junkyard area of the forest products plant. Where it came from is uncertain. To determine whether this find was related to the 2004 Port of Napier incursion, United States Department of Agriculture (USDA) experts conducted Gp-9 allele testing, GC mass spectroscopy and venom alkaloids analysis. These results showed the Whirinaki nest was the polygyne social form (multiple reproductive queens per nest) and that it was not related to the monogyne (single queen) form found in 2004.

Work to trace risk imports and goods into the nest area and analyse imported products from RIFA-infested countries to determine the introduction pathway is nearing completion. However, at least a partial answer lies in further genetic analysis to be conducted by the USDA in a large-scale research project aimed at identifying the global invasion pathway of this species. RIFA, a native of South America, has been introduced to a number of countries, including the United States, Australia, China and Taiwan.

Surveillance recommences for spring

Surveillance around the nest site at Whirinaki, using non-toxic attractant baits, was conducted in June. These activities were halted during winter, due to temperatures falling below reliable limits for detecting ant foraging behaviour, but re-commenced in spring. Intensive pitfall trapping out to 200 metres from the nest has been in operation since July. No further S. invicta have been detected since the treatment of the original nest.

A Controlled Area out to a 2 km radius from the nest site was declared on 23 June. Two important trace forward sites, the Omarunui Land Fill and the Redclyffe Waste Transfer Station were placed under Biosecurity Act section 122 Directions to contain and reduce the inadvertent spread of potential S. invicta colonies via contaminated material. More than 170 permits to safely move risk items have been issued to date. A project to trace movements of risk goods in to and out of the Controlled Area since 1 January 2003 was initiated to help identify where the nest may have arisen from and where it may have since dispersed to within New Zealand.

High-risk sites identified

IDC incursion investigators and entomologists developed the operational response strategy after considering expert advice from the RIFA Technical Advisory Group (TAG), overseas RIFA experts, and experience gained in eradicating two earlier RIFA incursions. NIWA wind plume modelling analysis was used to determine further high-risk sites in the Whirinaki area for surveillance or treatment.

Two ground-based surveys of high-risk areas are planned for the 2006–2007 summer, while single surveys will be conducted in late summer of the following two seasons (2008 and 2009). Insecticidal ant baits will be applied to inaccessible areas and sites where surveillance detection probabilities are low, using either ground-based or aerial application methods. A combination of slow-acting (insect growth regulators) and fast-acting (hydramethylnon-based) ant baits will be used to achieve maximum ant kill rates.

Due to predicted slow colony growth rates in New Zealand, it may take up to three years of surveillance to ensure any incipient colony is detected if present.

Effective and robust initial response actions are vital to ensure this highly invasive species does not establish in New Zealand. Efforts to eradicate RIFA are continuing in Australia and Taiwan, while control measures are ongoing in heavily infested areas of the United States.

  • Dr Disna Gunawardana, Scientist (Entomology), Plant Health and Environment Laboratory, Investigation and Diagnostic Centre, Biosecurity New Zealand, disna.gunawardana@maf.govt.nz
  • Incursion Investigation Plants and Environment Team, Investigation and Diagnostic Centre, Biosecurity New Zealand
  • Megan Sarty, Senior Adviser Environmental and Marine Response, Biosecurity New Zealand, phone 04 894 0665, megan.sarty@maf.govt.nz

Page last updated: 30 April 2008