Posted by Darren Ward @nzhymenoptera

Effective detection plays an important role in the surveillance and eradication of invasive species. Invasive ants are regarded as very difficult to eradicate and are prone to imperfect detection because of their small size and cryptic nature.

One species, the Argentine ant, Linepithema humile, is highly invasive and has been accidentally introduced by human trade to many countries throughout the world. It has invaded numerous habitats, including coastal sage scrub in southern California, riparian woodland in California, matorral in Chile, fynbos in South Africa, subalpine shrubland in Hawaii, and oak and pine woodland in Portugal. In New Zealand, Argentine ants are known to occupy a range of open-canopy ecosystems, including native habitats and anthropogenic environments.

One of the key goals of Argentine ant management in New Zealand is the eradication, and prevention of re-establishment, of Argentine ant populations from offshore islands. A major part of this goal is developing surveillance and analytical methods to increase confidence that offshore islands are free of Argentine ants, or that a population has been successfully eradicated.

Our recent research demonstrates the use of two very different science tools to help achieve an outcome. First the use of a detection dog, trained to detect Argentine ant colonies, and secondly the use of spatially explicit surveillance models. Both tools are used to estimate the probability that Argentine ants have been eradicated from an offshore island site, given their absence across four survey periods and three surveillance methods, conducted since ant control was applied.

Rhys-Jones, the world’s first detection dog for Argentine ants. Trained by Brian Shields at the Auckland Council.

We found the probability of eradication increased sharply as each survey was conducted. Using all surveys and surveillance methods combined, the overall median probability of eradication of Argentine ants was 0.96. Our results demonstrate the value of spatially explicit surveillance models for the likelihood of eradication of Argentine ants. We argue that such models are vital to give confidence in eradication programs, especially from highly valued conservation areas such as offshore islands. The concept is also applicable to other species of invasive ants, and indeed other invasive taxa.

Ward DF, Anderson DP, Barron MC. 2016. Using spatially explicit surveillance models to provide confidence in the eradication of an invasive ant. Scientific Reports. 6:34953. DOI: 10.1038/srep34953

Darren Ward is an entomologist in the New Zealand Arthropod Collection at Landcare Research, and a senior lecturer at the School of Biological Sciences, University of Auckland.