Import Risk Analyses (IRA) : Pest Risk Analyses (PRA) :  Threat assessment  : Risk management

Risk analyses

Forewarned is forearmed!

Before allowing something to be imported it is important to ask:

  • Which (if any) invasive ant species are known to be present in the exporting country?
  • Are any of the invasive ant species from the exporting country already present in your country? If so, is it under management?
  • Is the commodity that is being imported a known pathway for invasive ant species?
  • Is the invasive ant species capable of surviving the journey between the exporting country and your own?
  • Does the invasive ant species occur in climates similar to your own? Is the exporting country’s climate similar to your own?
  • Is the species capable of establishing in your country?
  • Does the invasive ant species form associations with other organisms, such as mealybugs or aphids, and are those organisms already present in your country?
  • Is the invasive ant species already named in your countries unwanted organism register?
  • Are your existing border inspection and quarantine protocols likely to detect the invasive ant species?

Import Risk Analyses (IRA)

Import Risk Analyses (IRA) may focus on a particular species, but in this case that species is a commodity (e.g. fresh breadfruit fruit) rather than the pest itself. Import Risk analyses may also focus on pathways (e.g. the passenger pathway or the cargo pathways), or a type of transport (e.g. ants on sawn timber arriving by sea freight)

An IRA should focus on:

  • The risks associated with the commodity (diseases carried, associated pests etc.), pathway (known hitchhikers and associations) or type of transport (pest species known to have been detected)
  • The likelihood of risk species establishing (climate matching, known hosts or associates present or absent in importing country etc.)
  • The effectiveness of current biosecurity measures and border systems at detecting the risk
  • Additional biosecurity measures that may be required.

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Pest Risk Analyses (PRA)

Pest Risk Analysis (PRA) is species specific and focuses on the means and likelihood of entry, the likelihood of establishment and potential damage caused. The PRA also examines current biosecurity and border systems and suggests improvements that may be necessary to prevent the pest species from entering the country. A PRA should be conducted for all high risk invasive ant species.

Key information that is required in a PRA includes:

*Many pathways are common to all ant species. These potential entry pathways for ants include commodities such as:

  • Sea containers
  • Fresh produce
  • Cut flowers
  • Furniture
  • Machinery
  • Appliances
  • Vehicles
  • Timber
  • Personal effects
  • Ships in dock, private yachts, cruise ships
  • Gravels, sands and soils (these are usually prohibited imports as the risk of invasion is so high)

The risk factors around the establishment of these ants include:

Identifying these risks early means that priority can be given to examination of goods arriving from areas where invasive ants are known to be abundant.

New Zealand Landcare and NZ MPI has risk assessments for African big-headed ant (Pheidole megacephala) (as part of multi-ant summary), Argentine ant (Linepithema humile), little fire ant (Wasmannia auropunctata), red imported fire ant (Solenopsis invicta), yellow crazy ant (Anoplolepis gracilipes), black crazy ant (Paratrechina longicornis), ghost ant (Tapinoma melanocephalum), Singapore ant (Trichomyrmex destructor) and tropical fire ant (Solenopsis geminata). 

Extensive guidelines for the preparation Pest Risk Analyses are provided by the FAO.

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Vectors1 and pathways1 for the Pacific's 18 worst threat ants

The following tables are derived from the CABI Invasive Species Compendium profiles for each of the species listed, and gives a general indication of the major pathways. Additional sources are indicated in the key.

1 Vectors and pathways are terms used to describe how pests and diseases get from place to place (or person to person). The terms are used frequently in a biosecurity context, but sometimes with different meanings to different people. Here, we've used both terms in the tables as some of the ways described are considered to be vectors, and some are pathways (although people might define them differently).


A.gra=Anoplolepis gracilipes L.fra=Lepisiota frauenfeldi L.hum=Linepithema humile M.pha=Monomorium floricola M.pha=Monomorium pharaonis N.ful=Nylanderia fulva P.lon=Paratrechina longicornis P.meg=Pheidole megacephala S.gem=Solenopsis geminata S.inv=Solenopsis invicta T.mel=Tapinoma melanocephalum T.dif=Technomyrmex albipes T.dif=Technomyrmex difficilis T.vit=Technomyrmex vitiensis T.bic=Tetramorium bicarinatum T.sim=Tetramorium simillimum T.des=Trichomyrmex destructor W.aur=Wasmannia auropunctata

* inferred from Landcare Research factsheet and information sheet.

** based on information in BugGuide: "Todd Staples, Texas Commissioner of Agriculture, suspects this to be a potentially serious agricultural pest. These ants show likelihood of being transported through movement of almost any infested container or material. Thus, movement of garbage, yard debris, bags or loads of compost, potted plants, bales of hay, can transport these ant colonies by truck, railroad, and airplane"

*** based on AntWeb descriptions of the species’ biology

**** based on findings by Flybusters Antiants Consulting, who have treated multiple private yachts, arriving in New Zealand, carrying red imported fire ants from the Caribbean through the Pacific

Vector/Pathway A.gra L.fra L.hum M.flo M.pha N.ful P.lon P.meg S.gem
Aircraft Yes       Yes Yes**      
Bulk freight/cargo Yes         Yes** Yes    
Containers and packaging (non-wood) Yes                
Containers and packaging (wood) Yes   Yes            
Land vehicles Yes   Yes     Yes**   Yes  
Machinery/equipment Yes                
Plants or plant parts Yes   Yes Yes Yes Yes** Yes Yes Yes
Ship/boat structures above waterline/holds Yes****                
Soil, compost, mulch, sand, gravel etc. Yes Yes*** Yes     Yes**   Yes Yes
Debris and waste associated with human activities Yes   Yes     Yes**      
Luggage             Yes    
Clothing, footwear, possessions               Yes  
Post               Yes  
Floating vegetation/debris Yes                
Hides, trophies, feathers                  

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Vector/Pathway S.inv T.mel T.alb T.dif T.vit T.bic T.sim T.des W.aur
Aircraft   Yes              
Bulk freight/cargo   Yes             Yes  
Containers and packaging (non-wood)   Yes               
Containers and packaging (wood) Yes           Yes*    
Land vehicles Yes                
Machinery/equipment Yes                
Plants or plant parts    Yes Yes*** Yes*** Yes*** Yes* Yes* Yes Yes
Ship/boat structures above waterline/holds  Yes                
Soil, compost, mulch, sand, gravel etc. Yes   Yes***  Yes***  Yes*** Yes* Yes*   Yes
Debris and waste associated with human activities Yes   Yes*** Yes***   Yes***   Yes*    
Luggage   Yes              Yes 
Clothing, footwear, possessions   Yes               
Floating vegetation/debris Yes           Yes*    Yes 
Hides, trophies, feathers   Yes               

The Invasive Species Compendium at is a useful resource that provides much of this information for significant invasive ant species in the Pacific such as the little fire ant (Wasmannia auropunctata), yellow crazy ant (Anoplolepis gracilipes), African big headed ant (Pheidole megacephala), red imported fire ant (Solenopsis invicta) and Argentine ant (Linepithema humile).

The Secretariat of the International Plant Protection Convention (IPPC) produced a detailed Framework for Pest Risk Analysis that lays out the stages involved in invasive pest species identification, analysis and management.

In addition, a detailed outline of the procedures and framework for the preparation risk analysis documents that support Import Health Standards developed by Biosecurity New Zealand is provided in the MPI publication Risk Analysis Procedures and its subsequent amendments document.

A paper by Tana and Daldry at the 10th International Symposium on Veterinary Epidemiology and Economics (2003) illustrates how the OIE risk analysis may be directly applied to invasive ant species.

Landcare New Zealand produced this risk assessment scorecard as part of the invasive ants section of their website. The scorecard is a useful tool for quantifying the relative threat posed by each invasive ant species based on the likelihood and severity of establishment given parameters of invasiveness, climate matching. proximity and detectability. The scorecard was developed specifically to produce a risk summary of various ant species establishing in New Zealand, but the methods are wholly transferable for use in the Pacific. Information sheets were produced for ant species that fell into the medium or high risk categories. Several of the species in the summary are also a threat in the Pacific, including the black crazy ant (Paratrechina longicornis), bicoloured trailing ant (Monomorium floricola), ghost ant (Tapinoma melanocephalum), little fire ant (Wasmannia auropunctata), similar groove headed ant (Tetramorium simillimum), Singapore ant, (Trichomyrmex destructor) tropical fire ant (Solenopsis geminata) and yellow crazy ant (Anoplolepis gracilipes).

Based on the answers to these questions, a  border inspection protocol document should be drafted, held and applied at any port or airport. Example documents from the USA and New Zealand, and a review of Australian pre- and post-border protocols are available.  All incoming goods should be inspected before release and items identified as high risk (such as machinery, vehicles, building materials, soil, produce etc.) should be prioritised for inspection.

These protocols should be revised as new information comes to light. If the current protocols are not likely to detect invasive ant species are there ways to improve them so that they do (e.g. surveillance)? What additional resources are required? 

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Threat assessment

The introduction of an invasive ant species may result in negative impacts on agriculture, the environment and human wellbeing. The ants may form associations with sap sucking bugs that damage crops and spread plant diseases. Ants are efficient predators and, at high abundance, can interfere with the breeding success of birds, kill chicks, crabs and reptiles as well as other beneficial insects.  Many invasive ants bite, spray acid or sting and can reach high numbers in new environments making it difficult for people to eat, sleep or work without ants crawling on them.

It only takes one mated queen ant to start an invasion! Nearly a quarter (24.1%) of all ant interceptions at the New Zealand border between December 2004 and June 2005 contained reproductive castes (queens, males, winged queens, or some combination of these with workers).

A less obvious hazard involves introducing an organism that allows ants that are already present in the country at low abundance to rapidly increase their numbers. Such organisms include aphids, scale insects and mealy bugs, which produce honeydew that ants use for food. These pests can carry viruses and other plant diseases and are protected and farmed by some ant species resulting in the bugs' numbers increasing, which in turn leads to significant crop damage and/ or loss of yield.

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Risk management evaluates the economic, environmental and social consequences of the potential introduction of an invasive species and weighs them against the financial and political costs associated with keeping the pest out (such as potential trade restrictions and screening and management costs).

If a country with an established population of an invasive ant species is seeking to export commodities that are known pathways for those ants, an importing country is within their rights to refuse entry to those commodities. 

Before refusing entry based on the presence of an invasive species, it is important to understand what safeguards the exporter has put in place to prevent the pest being accidentally exported and to ask whether the pest is:

  • a known pest or associated with known pests of crops grown in your country
  • known to cause harm to species or close relatives of species naturally occurring or deliberately cultivated in your environment
  • a known risk to human health or well-being
  • likely to survive the journey from the exporting country to your own
  • capable of establishing (based on climate, dietary and other environmental needs)
  • likely to interfere with potential trade with outside partners if it became established

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Risk Management

Unwanted Organisms Register

The criteria defining what is meant by an Unwanted Organism should be laid out in a country's Biosecurity Act (or equivalent). Typically, an Unwanted Organism is one that is deemed "capable of causing unwanted harm to any natural and physical resources or human health" by the Chief technical Officer (CTO), or equivalent of a country's Biosecurity Department or Ministry.

If the answer to any of the first three questions above is yes, then the species should be considered for addition to your country’s Unwanted Organism Register by the Biosecurity Department or Ministry's Chief Technical Officer (or equivalent).

Holding a register of Unwanted Organisms allows the powers available under the Biosecurity Act (or Equivalent) to be exercised against that organism. Unwanted ant species may be further categorised into:

Notifiable Organisms

Ants that are either not established, are currently established but under management or that have previously been established but are now eradicated and a “Country Free” declaration made by the country issuing the Act. These ants are likely to have an adverse impact on either the economic viability of animal or plant production or market access and would either require some investigation into control if they were detected or are likely to have a serious impact on international trade.

Other Exotic Organisms

Organisms that are not established in the country issuing the Act, which would potentially have an economically significant impact on the viability of animal or plant production or market access, and some form of investigation or control might be undertaken if they were detected in New Zealand or are capable of inflicting harm on natural and physical resources.

Reportable Organisms

Organisms that are reportable to a specified authority by rule of a National or Regional Pest Management strategy

Small-Scale Management Programme Organisms

Ants that have been declared unwanted in response to a regional request to commence a management programme.

Regulated Pests

Ants specified as unwanted in an import risk analysis or Import Health Standard.

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Import Health Standards

Risk management results in an Import Health Standard document tailored to mitigate the risks associated with a particular pest species or pathway for pest species. These pathways may be either commodities (fresh produce, building materials, tyres etc.) or means of entry such as sea containers or passengers.

An Import Health Standard (IHS) is issued under the Biosecurity Act (or equivalent) of a country. The document outlines the safety measures and treatments that are needed before goods can be imported. These safety measures and treatments are based on an Import Risk Analysis.  Example: the New Zealand Import Health Standard for Sawn Wood is informed by the Pest Risk Analysis for Ants on Sawn Timber

The IHS typically requires exports to be clean and states that the commodity should be free of any animals, insects (or other invertebrates), organic material of animal origin, plant material or soil. In some countries (such as New Zealand), items that are not covered by an import health standard cannot be imported under any circumstances.

The exporter must have a documented procedure that ensures the requirements of the IHS are met and the procedure must be approved by the country that issued the IHS. These procedures may include fumigation, heat treatment and storage in a special clean area. The importer must monitor the exporter to make sure that this procedure is followed.  How often this monitoring occurs depends on how well the exporter follows the IHS. If they are found to follow the guidelines well, they may need to be monitored less often.

Depending on the agreements between the exporting country’s National Plant Protection Organization (NPPO) and the issuer of the IHS, a certificate from an Official Assurance Programme (OAP) may be accepted. The certificate indicates that the area the export left from is clear of a particular invasive pest species. Knowing there is a good surveillance programme in place helps importers feel confident about issuing an OAP.

Any item that does not comply with the cleanliness or other requirements of the IHS should be decontaminated (at the exporter’s cost), reshipped or destroyed.  

The New Zealand IHS for Vehicles Machinery and Tyres, simply stipulates that all incoming goods must be clean. This cleanliness is assured by pre-border heat treatment and fumigation.   The processes for ensuring cleanliness in line with New Zealand’s definition are stipulated by the New Zealand Chief Technical Officer (CTO).  The importer provides a guidance document indicating how the conditions of import may be met.

Further examples of New Zealand Import Health Standards may be found at the MPI website. More examples of New Zealand Import Health Standards can be found here.

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Further information

Ward, Beggs, Clout, Harris, O'Connor. 2006. The diversity and origin of exotic ants arriving in New Zealand via human-mediated dispersal. Diversity and Distributions. 12: 601-609

content reviewed by Souad Boudjelas, Pacific Invasives Initiative, November 2016

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