Argentine ant case studies

 Tiritiri Matangi, New Zealand : Channel Islands, USA : Haleakala National Park, Maui, Hawaii

Location: Tiritiri Matangi, New Zealand

Justification: Conservation

Goal:Eradication

Size:  11 ha

Product: Xstinguish (0.1 g/kg fipronil; lipid and protein-based paste; ~10 kg/ha) was applied using caulking guns on the ground in a 2 m ´ 3 m grid pattern over the entire area (10 – 15 kg/ha) the first year, and reapplied in a 1 m ´ 3 m pattern (6.7 – 10 kg/ha) one year later. To prevent the bait from drying out it was placed under vegetation where possible. After the first two whole area applications, the remnant infestations were treated twice a year, four-eight weeks apart.  How applied (rates in kg/ha, methods, frequency etc.)

Time of year: Summer, when conditions were warm (20-25°C) and dry (no rain forecast for 24 hours)

Outcome: Eradication was successfully declared in 2016

Programme cost: not available

Manager: Chris Green (cgreen@doc.govt.nz), New Zealand Department of Conservation

Tiritiri Matangi is a conservation sanctuary in the Hauraki Gulf islands of northern New Zealand.

Argentine ants were first detected in 2000. The ants were initially found at two locations which initiated a five year eradication programme. Ten years after beginning the campaign on Tiritiri Matangi, a few small colonies of ants were still being detected, but it was unclear whether these were survivors of the original infestation or subsequent new incursions to the island. However, the ongoing control on Tiritiri Matangi was successful in completely minimising the spread and impacts of the ants on the island. 

The difficulty in eradication was detecting and eradicating the very few last nests. The last detection of ants was in 2013 and intensive monitoring continued until eradication was finally declared in 2016. Visual surveys were not able to detect small remnant Argentine ant colonies, so lures of non-toxic Xstinguish Argentine ant monitoring paste were used for all monitoring. Lure paste was placed in vials, which were then placed every 2-5 m in a grid pattern over the target area. Due to budget constraints the entire formerly infested area was only intensively monitored twice over the 16 year programme, otherwise the areas with detections of remnant Argentine ant colonies were intensively monitored, and certain sites with formerly high densities were monitored every year. As detection was difficult, 3 years of monitoring was allowed for after the first year of no detections, which is a year longer than the typical monitoring period.

Information sources

Further information was provided by Chris Green, Technical Advisor, New Zealand Department of Conservation

Green. 2019. Effort required to confirm eradication of an Argentine ant invasion: Tiritiri Matangi Island, New Zealand. In: Island invasives: scaling up to meet the challenge, (eds Veitch, Clout, Martin, Russell, West) pp 370–374. Gland, IUCN

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Location: Channel Islands, USA

Hygrogel crystals awaiting application (© Christina Boser, The Nature Conservancy)

Santa Cruz Island (part of the Channel Islands), off the coast of California, is a very important conservation area, with several endemic species. Thus, when the decision to try to eradicate Argentine ants on the island was made, it was necessary to find a treatment method that limited non-target impacts as much as possible.

Hydrogel beads consist of polyacrylamide, which easily absorbs water and chemicals that dissolve in water (such as toxins and sugar), making them ideal bait carriers.

Four infestations were treated, ranging in size from 16 ha to 336 ha.

Infestations were treated between June and October, when higher temperatures mean that Argentine ants are at their most active. Optigard in hydrogel beads were aerially or manually broadcast throughout the infested area 12 times every 1-2 weeks between June and October. Two additional applications were done one year later, one in early September, and one in early October, for a total of 14 applications.

On very steep slopes, hydrogel shards were mixed with hydrogel beads, because the shards are less likely to roll down the steep terrain, so remain accessible to the ants.

At two of three sites no remnant nests have been detected two and a half years after treatment (the fourth site is still being monitored).

One year after the final application, a single 0.5 ha remnant population of Argentine ants was discovered at one site. This was retreated 3 times using the same methods as above in late summer. No further Argentine ants have been seen at this site since this treatment, one and a half years ago.

At this point successful eradication seems likely, as no Argentine ants have been found in the latest monitoring efforts. However, monitoring will continue for the next 3 years to ensure success.

Argentine ants on a baited hydrogel bead (© Cause Hanna, Cal State University)

Helicopter distributing baited hydrogel beads over Santa Cruz Island, USA (© Christina Boser, The Nature Conservancy)

In an initial study on the Channel Islands, nests that remained after treatment were spot treated with a mixture of cooked egg, 25% sugar and 0.0006% Optigard (this treatment was either spread or sprayed directly onto nests).

Initial trials showed that the mixture of sugar and protein (egg) is preferred by Argentine ants to the pure sugar solution between July and September.

The sugar / protein is too costly a method to use for broadcast baiting, but ideal for spot treatments of remnant nests or for use in very small incursions. It is particularly useful because it sticks to vegetation, allowing treatment of a 3-dimensional space, such as areas with dense vegetation.

Information sources

Further information was provided by Christina Boser, California Islands Ecologist, The Nature Conservancy

Boser, Hanna, Faulkner, Cory, Randall, Morrison. 2014. Argentine ant management in conservation areas: results of a pilot study (download 2 MB). Monographs of the Western North American Naturalist 7: 518-530

Boser, Hanna, Holway, Faulkner, Naughton, Merrill, Randall, Cory, Choe, Morrison. 2017. Protocols for Argentine ant eradication in conservation areas. Journal of Applied Entomology DOI: 10.1111/jen.12372

case study reviewed by Christine Boser, The Nature Conservancy, March 2017

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Location: Haleakala National Park, Maui, Hawai'i

Extensive research has been done on Argentine ant control in Haleakala National Park. Between 1994 and 2009, 30 commercial or experimental ant bait products were tested for their attractiveness to Argentine ants, and 10 of the most attractive were were then tested in field plots for their efficacy against Argentine ants. Many of these field tests are detailed in our invasive ant management database, and all of them can be found in greater detail in the excellent review by Krushelnycky et al. 2011: The Haleakala Argentine ant project: a synthesis of past research and prospects for the future.

Here we detail one of the most successful field tests using Synergy Pro.

Justification: Conservation

Goal: Eradication

Size: Three 1 ha infestations

Products: 0.5 HP Ant Bait (now known as Synergy Pro) which consists of both fish meal matrix and corn grit/soybean oil granules, both containing hydramethylnon (3.5 g/kg) and pyriproxyfen (2.5 g/kg)

Time of year: August and September (summer-early autumn)

Outcome: More than 90% of Argentine ant workers killed, but eradication was not achieved

Programme cost: not available

Manager: Paul Krushelnycky (pauldk@hawaii.edu), University of Hawai'i

Argentine ants infest 625 ha of Haleakala National Park (an international biosphere reserve) in Hawai'i.

Three 1 ha areas were treated to test if different toxins were able to kill all Argentine ants in the treatment area. 0.5 HP Ant Bait which consists of both fish meal matrix and corn grit/soybean oil granules, both containing hydramethylnon (3.5 g/kg) and pyriproxyfen (2.5 g/kg) was used.

To determine if one of these granule matrices worked better than the other, one infestation was treated with only the fishmeal granules, one only with the corn grit/soybean oil granules, and one with a 50:50 mixture of both (as the product is meant to be used). All plots were treated twice at a rate of 2.24 kg/ha using hand spreaders.

After the first treatment ant numbers were reduced by more than 90% in all treatment plots but increased again after 3-5 weeks. After the second treatment there was again a greater than 90% reduction in numbers, which remained low after 5 weeks; however, eradication was not achieved as many nests remained.

The type of granule used did not seem to make a difference.

Field tests of Maxforce Granular Insect Bait (hydramethylon) and Maxforce FC Granular Bait (fipronil) also yielded good results in other trials, though, as with Synergy Pro®, eradication was not achieved. However, the formulation and granule size of Maxforce Granular Insect Bait seemed to change in 2004 to one that was much less effective against Argentine ants. The use of this bait at Haleakala is currently being phased out and replaced with another granular bait, Maxforce Complete Granular Bait. Development and production of Maxforce FC was discontinued, so though this bait showed very promising results, further investigations with it were not possible after 1998.   

Information source

Krushelnycky. 2008. Developing techniques for invasive ant control: a test of 0.5 HP granular ant bait on Argentine ants at Haleakala National Park. Hawai'i Invasive Species Council PCSU contract 438221

Krushelnycky, Haines, Loope, Van Gelder. 2011. The Haleakala Argentine ant project: a synthesis of past research and prospects for the future. Pacific Cooperative Studies Unit Technical Report 173

case study reviewed by Paul Krushelnycky, University of Hawai'i, September 2016