Yellow Crazy Ant (Anoplolepis gracilipes)
Compiled by the IUCN SSC Invasive Species Specialist Group (ISSG)
1.0 Preventative measures
Prevention, quarantine and rapid response are the best management strategies for preventing the establishment of invasive ants. To be successful they require active surveying, early detection and subsequent rapid treatment procedures often along with quarantines. This type of management approach remains the most practical strategy for dealing with invasive ants (Krushelnycky Loope and Reimer 2005).
The first step to solving any problem is to identify whether it exists and define what it is. Preparing risk assessments is a vital management tool for addressing the issue of invasive ants in a country or region.
In New Zealand an invasive ant risk assessment project (prepared for Biosecurity New Zealand by Landcare Research) identified ant species which pose the greatest potential threat to New Zealand. This project was divided into five sections: (i) gathering data on native and non-native New Zealand ants, (ii) producing a preliminary risk, (iii) producing information sheets on medium-risk and high-risk taxa, (iv) producing a detailed pest risk assessment for the eight highest-risk species, and (v) re-ranking these eight species. Of the 75 ant taxa which were ranked the following ants present the greatest potential risk to New Zealand: Anoplolepis gracilipes, Lasius neglectus, Monomorium destructor, Paratrechina longicornis, Solenopsis geminata, Solenopsis richteri, Tapinoma melanocephalum and Wasmannia auropunctata (Harris undated). An assessment of the current risk of A. gracilipes establishing itself in New Zealand (based on climate similarity of native and introduced ranges) lead to the prediction that it is lead to the prediction that it would be "unlikely to establish". This is because of the combined factors that New Zealand is too cold and the ant does not have a close enough association with humans and urban structures (R. Harris unpubl. data, in Stanley 2004).
1.2 Ant Prevention in the Pacific Region
The Pacific island region includes over 25 countries, most of which are served by two important regional international organizations, the Secretariat of the Pacific Community (SPC), which addresses agricultural issues, and the South Pacific Regional Environment Programme (SPREP), which addresses biodiversity issues. The biodiversity of the Pacific is particularly vulnerable to effects of invasive species (SPREP 2000).
Special concern regarding ant invasions has arisen now that the red imported fire ant occurs at or near the coast on both sides of the Pacific, and the little fire ant has arrived in Hawaii and is spreading in the western Pacific. These and other species threaten all Pacific islands, including Hawaii and the U.S. affiliated islands of Guam, Commonwealth of the Northern Marianas, Federated States of Micronesia, American Samoa, and Palau.
The SPC-Plant Protection Service (SPC-PPS) works in partnership with 22 Pacific members to maintain effective quarantine systems and to assist with regionally coordinated eradication/containment efforts. Priorities for emphasis are determined by member countries, which meet periodically as the Pacific Plant Protection Organization (PPPO).
A workshop sponsored by the Invasive Species Specialist Group (ISSG) of IUCN was held in Auckland, New Zealand, in September 2003, and resulted in the compilation of a draft Pacific Ant Prevention Plan (Pacific Invasive Ant Group 2004). The Pacific Ant Prevention Plan was presented to and embraced by 21 Pacific island countries and territories present at a PPPO meeting, the “Regional Biosecurity, Plant Protection and Animal Health” meeting held by SPC in Suva, Fiji, in March 2004 (Pacific Plant Protection Organization 2004). Like Hawaii’s Red Imported Fire Ant Prevention Plan, the Pacific Ant Prevention Plan is still a conceptual work, but ISSG and others are working toward obtaining the international funding needed to implement the plan with the assistance of SPC. The project presents an exceptional opportunity for agriculture and conservation interests to work together with international and bilateral aid entities at regional and country levels to build much needed quarantine capacity. Increased quarantine protection is desperately needed by PICT in order to address invasions that jeopardize both agriculture and biodiversity.
The information for this section was sourced directly from Krushelnycky Loope and Reimer (2005).
2.1 General Considerations
Most if not all ant eradications have employed the use of baits and toxicants, many of which are developed for agriculture or urban settings. However, indiscriminate pesticide use in natural areas and fragile island ecosystems is not advocated. While some toxins such as hydramethylnon break down quickly in the environment, any and all pesticide use is likely to be accompanied by at least some undesirable non-target effects. These include increased runoff or drift outside the intended area, adverse affects on beneficial insects and non-target impacts on native species (Krushelnycky Loope and Reimer 2005).
Non-target impacts must be weighed up carefully against the benefits of ant eradication. Cleary, treating whole ecosystems or islands is too risky as entire populations of rare invertebrates may be at risk of extinction. On the other hand, eradicating populations of exotic ants before they become established in a natural ecosystem or island has the potential to prevent the potentially disastrous consequences of ant invasions (Krushelnycky Loope and Reimer 2005).
Baits should be designed with the specific foraging strategies of the target ant in mind. The preferred size, type and dispersal of bait and the nesting, foraging and behavioural traits of the ant should be considered in the planning stages of the operation. The use of appropriately designed and chosen baits and toxins will help reduce the impact of toxins on native ants and non-target fauna (McGlynn 1999).
3.2 Ant Toxins
Ant toxins can be classed into three categories: “stomach” poisons (or metabolic inhibitors), Insect Growth Regulators (IGRs) and neurotoxins. Stomach toxins include hydramethylnon (eg: Maxforce® or Amdro®), sulfuramid and sodium tetraborate decahydrate (eg: Borax). IGRs include compounds such as methoprene, fenoxycarb or pyriproxyfen. Neurotoxins include fipronil (eg: Xstinguish®). Stomach poison kills all workers and reproductives it comes into contact with. IGRs work by disrupting development of the queens ovarian tissues, effectively sterilising the colony. Neurological inhibitors disrupt insect central nervous systems by blocking neuron receptors. The onset of mortality is contingent upon the type of active ingredient. In general, ant baits that contain active ingredients that are metabolic inhibitors have a two to three day delay before extensive mortality occurs in the colony (Oi Vail and Williams 2000). Baits containing IGRs take several weeks before colony populations are reduced substantially (Oi Vail and Williams 2000). The latter (IGRs) provide gradual long-term control, while metabolic inhibitors provide short-term, localised and rapid control (Oi Vail and Williams 2000). This is because while stomach poisons are faster than IGRs, they sometimes eliminate workers before the toxin can be effectively distributed throughout the colony (O’Dowd Green and Lake 1999).
In the Seychelles in the 1970s, toxic baits based on chlorinated hydrocarbons were developed for the control of Anoplolepis. Bait use proved to be more effective than chemical spray treatments. On Mahé in the Seychelles the toxic baits were used to effectively control ants in agriculture areas and near homes, killing more than 90% of the population in the first few days. However, within a year ant populations had recovered (partly through re-invasion from untreated areas). A two hectare area required 85 days for 50% of the population to recover, while a 50 hectare area required up to 300 days for 50% of the population to recover. Baiting was more effective in built-up areas free from vegetation (Haines and Haines 1979, in O’Dowd Green and Lake 1999). Toxins such as these are no longer considered safe for use and many are deregistered.
Presto® (fipronil in fish meal bait matrix) is well known for its effectiveness in controlling A. gracilipes on Christmas Island (Green et al. 2004, in Stanley 2004) and is currently being used in an attempted large-scale (combined total infestation: 400ha) eradication of A. gracilipes in Arnhem land in Australia (B. Hoffmann, pers. comm. , in Stanley 2004). Presto® (fipronil) appears to be highly effective at controlling A. gracilipes. In an incursion event in New Zealand it is recommended that Xstinguish® (fipronil) or Presto® (fipronil) should be used on P. longicornis, T. melanocephalum, and A. gracilipes, but research is required to determine the most effective baits for incursion management. Current research is aimed at trialling the effectiveness of Presto 001® in comparison to Presto 01® (Stanley 2004).
Fipronil has been used in the Christmas Island programme to control A. gracilipes, which has also involved island-wide surveys, the broadcasting of bait by helicopter and post-treatment monitoring (CBD 2003).
One promising approach is to use pheromones (compounds produced by a species that regulate their own behaviour) as “biopesticides” to disrupt the reproduction by the queen. However, this would first require development of a large research base for the ecology and chemical bases for the behaviour of Anoplolepis (O’Dowd Green and Lake 1999).
5.2 Bait and Toxin Research
Stanley (2004) suggests that future research on A. gracilipes focus on:
Determining the most effective baits for incursion management
Following the progress made and results of trials testing the efficacy of Presto 001® to control A. gracilipes in Tokelau (K. Abbott, pers. comm)
Following the progress made and results of eradication trials using Presto 001® in Northern Territory, Australia (B. Hoffmann, pers. comm.)
Following the trials testing the attractiveness of various formulations of the IGR, Distance® (pyriproxyfen) to A. gracilipes, in order to determine if Presto® remains the best option for control of A. gracilipes
5.3 Biosecurity New Zealand
Biosecurity New Zealand, the branch of government responsible for managing invasive species, has responded to a series of incursions of exotic invasive ant species by relying heavily on a small number of baits and toxins. The absence of a wide variety of effective baits may compromise the success of incursion responses. As a first step to ensuring effective incursion response, Biosecurity New Zealand commissioned Landcare Research to research and review international literature about the baits and toxins used for ant control (see Stanley 2004). The next step will be testing the most promising of these against a selected group of high-risk invasive ant species.
Convention on Biological Diversity (CBD). 2003. Pilot Assessments: The Ecological and Socio-Economic Impact of Invasive Alien Species on Island Ecosystems. Subsidiary Body on Scientific, Technical and Technological Advice (Ninth meeting: Item 7.1 of the provisional agenda, Montreal, 10-14 November 2003). [Accessed 18 April 2005, from: http://www.biodiv.org/doc/meetings/sbstta/sbstta-09/information/sbstta-09-inf-33-en.pdf]
Harris, R. Undated. Invasive Ant Pest Risk Assessment Project. [Accessed 29 March 2007, from: http://issg.appfa.auckland.ac.nz/database/species/reference_files/Ant_RA/overview.pdf] This document describes an ant risk assessment and ranking project.
Krushelnycky, P.D., Loope, L.L. and Reimer, N.J. 2005. The Ecology, Policy, and Management of Ants in Hawaii, Proc. Hawaiian Entomol. Soc. 37. Accessed 2 April 2007, from http://www.ctahr.hawaii.edu/peps/museum/ant_website/Krushelnycky_et_al_Ant_review2005.pdf]
O’Dowd, D.J., Green, P.T. and Lake, P.S. 1999. Status, Impact, and Recommendations for Research and Management of Exotic Invasive Ants in Christmas Island National Park. Centre for the Analysis and Management of Biological Invasions: Clayton (Victoria, Australia). [Accessed 4 April 2007, from: http://www.issg.org/database/species/reference_files/Christmas_Island_Report.pdf]
Oi, D.H., Vail, K.M. and Williams, D.F. 2000. Bait distribution among multiple colonies of Pharaoh ants (Hymenoptera: Formicidae), Journal of Economic Entomology 93 (4): 1247 - 1255. [Accessed 13 Friday 2007, from: http://www.bioone.org.ezproxy.auckland.ac.nz/archive/0022-0493/93/4/pdf/i0022-0493-93-4-1247.pdf]
Stanley, M.C. 2004. Review of the Efficacy of Baits Used for Ant Control and Eradication (Landcare Research Contract Report: LC0405/044). [Accessed 29 March 2007, from: http://www.landcareresearch.co.nz/research/biocons/invertebrates/ants/BaitEfficacyReport.pdf]